JP2006324690A - Semiconductor laser, semiconductor light emitting element, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a threshold current density in a short wavelength semiconductor laser using a nitride compound semiconductor, relating to a semiconductor laser, a semiconductor light emitting element, and a method for manufacturing it. <P>SOLUTION: A multiple quantum well structure is used as an active layer 4, and further a maximum position of an intensity distribution of emitted light is shifted from the center position of the active layer 4 to a p-type cladding layer 6 side. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a semiconductor laser, a semiconductor light emitting element, and a manufacturing method thereof, and is particularly characterized in a configuration for reducing a threshold current density _Jth in a semiconductor laser using a nitride compound semiconductor. The present invention relates to a short wavelength semiconductor laser and a manufacturing method thereof.

  Conventionally, short-wavelength semiconductor lasers have been used as light sources for optical disks, DVDs, etc., but since the recording density of optical disks is inversely proportional to the square of the wavelength of the laser light, shorter-wavelength semiconductor lasers have been demanded. The shortest-wavelength semiconductor laser that has been commercialized is a red semiconductor laser having a wavelength in the vicinity of 630 to 650 nm, and is used in the DVD released last year.

  However, in order to further increase the recording density, it is necessary to further shorten the wavelength. For example, in order to record a moving image on an optical disk for 2 hours, a blue semiconductor laser having a wavelength of around 400 nm is indispensable. As a light source for an optical disk, a short wavelength semiconductor laser having a wavelength in a blue region has been actively developed.

  As such blue semiconductor laser materials, IISe-VI group compound semiconductor ZnSe series and III-V group compound semiconductor GaN series have been studied. Of these, ZnSe series has been proven as a high-quality substrate. It is considered that the ZnSe system is more advantageous for a long time because it is lattice-matched to GaAs, which has a high level of GaAs. Most of the researchers all over the world have been engaged in research on this ZnSe system. Regarding the research, the ZnSe system is ahead.

  As for this ZnSe system, room temperature continuous oscillation by injection excitation has already been reported, but since it is a material that is inherently easily deteriorated, reliability is a problem, and it has not yet been put into practical use.

  On the other hand, in the case of the GaN system, GaN with excellent environmental resistance has been reconsidered with respect to the reliability that has become a bottleneck in the ZnSe system after the announcement of GaN high-brightness LED by Nichia Chemical at the end of 1993. We are seeing a large increase in researchers.

  Next, in early December 1995, Nichia also reported the success of pulsed laser oscillation, and research has progressed rapidly. In room temperature continuous oscillation (CW oscillation), a 35-hour oscillation duration was reported. Since then, an oscillation duration of an estimated 10,000 hours has been reported in an accelerated test.

Here, a conventional short wavelength semiconductor light emitting device will be described with reference to FIGS. 31 and 32. FIG. 31A is a schematic sectional view perpendicular to the optical axis of the conventional short wavelength semiconductor laser. 31 (b) is a schematic sectional view of a short wavelength light emitting diode, and FIG. 32 is a schematic sectional view perpendicular to the optical axis of a short wavelength semiconductor laser having a different buffer layer structure.
31A. First, an n-type GaN buffer layer 813, an n-type In _0.1 Ga _0.9 N layer 814, and an n-type are disposed on a sapphire substrate 811 having a (0001) plane as a main surface via a GaN buffer layer 812. Al _0.15 Ga _0.85 N clad layer 815, n-type GaN light guide layer 816, InGaN MQW active layer 817, p-type Al _0.2 Ga _0.8 N layer 818, p-type GaN light guide layer 819, p-type Al _0.15 Ga _0.85 N clad layer 820 Then, the p-type GaN contact layer 821 is epitaxially grown by the MOVPE method (metal organic vapor phase epitaxy).

  Next, a part of the n-type GaN buffer layer 813 is exposed by dry etching, an n-side electrode 822 made of Ti / Au is provided, and a p-side electrode made of Ni / Au is formed on the p-type GaN contact layer 821. After providing 823, dry etching is further performed to form a pair of parallel end faces, and this end face is used as a resonator face to succeed in pulsed laser oscillation (see, for example, Non-Patent Document 1). .

In the case of a light emitting diode, an n-type GaN layer 824, an n-type or p-type In _0.15 Ga _0.85 N active layer 825 is provided on a sapphire substrate 811 via a GaN buffer layer 812. Then, the p-type GaN layer 826 is epitaxially grown by the MOVPE method.

In this case, in order to obtain light emission luminance practical as a light emitting diode operating with low injection, the Si concentration or Zn concentration of the In _0.15 Ga _0.85 N active layer 825 is set to 1 × 10 ¹⁷ to 1 × 10 ²¹ cm ⁻³ . In addition, the layer thickness of the In _0.15 Ga _0.85 N active layer 825 needs to be 1 to 500 nm, and more preferably 10 to 100 nm (see, for example, Patent Document 1 or Patent Document 2).

32 is a cross-sectional view perpendicular to the optical axis of another conventional short wavelength semiconductor laser. First, on a sapphire substrate 831 having a (0001) plane as a main surface, a GaN buffer layer 832 is interposed. n-type GaN intermediate layer 833, n-type Al _0.09 Ga _0.91 N cladding layer 834, n-type GaN light guide layer 835, MQW active layer 836, p-type Al _0.18 Ga _0.82 N overflow prevention layer 837, p-type GaN light guide layer 838 Then, the p-type Al _0.09 Ga _0.91 N clad layer 839 and the p-type GaN contact layer 840 are sequentially epitaxially grown by the MOVPE method.

Next, as in the case of FIG. 31A, the p-type GaN contact layer 840 and the p-type Al _0.09 Ga _0.91 N cladding layer 839 are mesa-etched by dry etching, and a part of the n-type GaN intermediate layer 833 is removed. An n-side electrode 841 made of Ti / Au is provided on the exposed portion of the n-type GaN intermediate layer 833 so as to be exposed, and a Ni / Ni electrode 841 is formed on the p-type GaN contact layer 840 via a SiO ₂ film 842 having a stripe-shaped opening. A p-side electrode 843 made of Au is provided, and then dry etching is performed to form a pair of parallel end faces serving as a resonator surface.

It has also been proposed to provide an overflow prevention layer, that is, a carrier stopper layer on the n-type layer side (see, for example, Patent Document 3). In this case, the n-type impurity concentration is 1 × 10 ¹⁸ cm ^{−. 3} Si-doped n-type Al _0.15 Ga _0.85 N layer as a hole stopper layer, and Mg-doped p-type Al _0.15 Ga _0.85 N layer with a p-type impurity concentration of 5 × 10 ¹⁹ cm ⁻³ as an electron stopper layer The growth temperature is 1100 ° C., which is a normal growth temperature for growing GaN or AlGaN.
Japanese Patent Laid-Open No. 06-260682 Japanese Patent Laid-Open No. 06-260683 Japanese Patent Laid-Open No. 10-056236 S. Nakamura et al. , Japan Journal of Applied Physics, vol. 35, p. L74, 1996

However, in the case of the conventional short wavelength semiconductor laser, there is a problem that the threshold current density is about 3.6 kA / cm ² , which is very large. This is because a material such as a nitride compound semiconductor, that is, a nitride compound semiconductor, essentially requires a large carrier density in order to generate an optical gain.

  In other words, the semiconductor lasers that have been put into practical use use III-V group compound semiconductors with zinc blende type crystal structures such as AlGaAs and AlGaInP, whereas nitride compound semiconductors are extremely This is because it has a hexagonal wurtzite structure with a large forbidden band width, and has completely different physical properties from the zinc blende type crystal material.

  The major physical properties of such nitride compound semiconductors are hexagonal crystals and the presence of anisotropy in crystals, large forbidden band width and large effective mass, small spin-orbit interaction, and valence electrons. There are three bands in which three bands of HH (Heavy Hole), LH (Light Hole), and CH are close to each other.

More specifically, first, as a feature due to the large effective mass of holes, first,
a. The effective mass of the hole is large, so that the quasi-Fermi level E _{Fp of} the valence band is difficult to increase; Since the effective mass of the hole is large and LO (longitudinal optical) phonon scattering is large, the mobility of the hole is small,
c. Since the effective mass m of the hole is large, the average hole velocity at the temperature T, that is, the heat velocity v _{p of the} hole is
From (m / 2) v _p ² = (3/2) kT,
v _p ∝m ^-1/2
It is mentioned that the heat velocity v _{p of the} hole is small.

Second, there are three bands of HH, LH, and CH close to the valence band, and the two effective masses of them are large, so that the quasi-Fermi level E _Fp for the hole is difficult to increase. Cause
d. Increase in quasi-Fermi level E _Fn of the conduction band required to achieve the population inversion is larger than the conventional material, and the barrier layer and the well layer, or, GaN constituting the active layer and the optical guide layer / The ratio between the energy discontinuity ΔE _V in the valence band and the difference ΔE _g of the forbidden band width in the heterojunction of InGaN or In _x Ga _1-x N / In _y Ga _1-y N, that is, ΔE _V / ΔE _g is as large as about 0.7 compared to about 0.4 in the conventional material system, and the band offset at the interface is 3: 7 and is biased toward the valence band side.

For these reasons, holes are not efficiently injected from the p-type layer side into the active layer. In particular, when the active layer has a multiple quantum well (MQW) structure, the poor hole injection efficiency is The hole density is uneven between the well layers (well layers), and electrons that are not effectively consumed in the active layer overflow to the p-side and overflow current to the p-side light guide layer or p-type cladding layer. Since the present inventors have found through simulation, this situation will be described with reference to FIGS.
The simulations shown in FIGS. 33 to 37 are performed with a configuration in which an electron block layer, that is, an overflow prevention layer is not provided.

FIG. 33 shows the change of the Fermi level in the vicinity of the active layer. As shown in the enlarged circle in the figure, the pseudo Fermi level E _Fp for the hole in the valence band is expressed in the active layer. It can be seen that it is on the lower energy side than the p-side light guide layer.

That is, in a normal material system, a pseudo-equilibrium state is reached by hole injection, and the quasi-Fermi level E _Fp of the active layer and the p-side light guide layer substantially coincide with each other. The mismatch between the quasi-Fermi level E _Fp between the active layer and the p-side light guide layer is very large, indicating that holes are not effectively injected from the p-side light guide layer into the active layer.

FIG. 34 is a diagram showing the layer position dependency of the hole current in the MQW structure short wavelength semiconductor laser having five well layers. The simulation result of where the injected holes disappear due to recombination is shown. As is apparent from the figure, the hole current injected from the p-type cladding layer is consumed by 4 kA / cm ² in the p-side light guide layer before reaching the active layer.

This consumed current is a reactive current that does not contribute to laser oscillation and leads to an increase in the threshold current density _Jth . Thus, the reason why recombination in the p-side light guide layer is large is as follows. This is probably because the efficiency of hole injection from the p-type cladding layer to the active layer is poor.

In addition, when the active layer has an MQW structure, the poor hole injection efficiency results in non-uniform hole density between the quantum well layers (well layers), which makes laser oscillation inefficient. This will be described with reference to FIGS. 35 and 36. FIG.
FIG. 35 is a diagram showing a simulation result of the hole density distribution in the element thickness direction in the state of FIG. 33. As is clear from the figure, the hole density in the MQW active layer is close to the p-side light guide layer. It is understood that it is so large and non-uniform.

36. FIG. 36 is a diagram showing a simulation result of the electron density distribution in the element film thickness direction in the state of FIG. 33. As is apparent from FIG. 36, the MQW active layer injected from the n-side light guide layer side. It is understood that the electron density in the region also becomes large and non-uniform as it goes toward the p-side light guide layer. This is due to the above-described non-uniform injection of holes, and the electrons are attracted to the holes to satisfy the charge neutrality condition. It is a result.

In this way, it is expected that the generation of optical gain in the multiple quantum well structure will be remarkably non-uniform due to the occurrence of the same non-uniformity in both holes and electrons. I will explain.
FIG. 37 is an explanatory diagram of the optical gain distribution in the multiple quantum well of the MQW semiconductor laser using the above-mentioned nitride compound semiconductor. In the first quantum well from the p-type cladding layer side, p is shown. Since the supply of holes from the type cladding layer is large, it has a large optical gain. However, the optical gain decreases toward the n-type cladding layer side, and the two quantum wells on the n-type cladding layer side are optical. This is different from the conventional laser using a zincblende crystal structure semiconductor that not only generates gain but also causes light loss.

  That is, in conventional semiconductor lasers using a zincblende crystal structure semiconductor, it is common knowledge that carriers are uniformly injected when the MQW structure is composed of about five quantum well layers. The long wavelength laser for optical communication uses about 5 to 10 layers, and the red laser for DVD uses about 5 layers, but the optical gain is uniformly generated.

  The generation of the light absorption layer due to the non-uniformity between the quantum well layers having such an optical gain has two adverse effects. First, even in the two quantum well layers on the n side serving as the light absorption layer, As apparent from FIGS. 35 and 36, carriers exist at a high density, which means that the recombination current is large, and the three quantum well layers on the p side reach the threshold Fermi level of laser oscillation. As a result, the two quantum well layers on the n side increase the amount of current.

Second, since the two quantum well layers on the n side are light absorption layers, the internal loss to be overcome for laser oscillation increases, and the threshold Fermi level E ^F _th itself increases. This will cause an adverse effect.

FIG. 38 is a diagram showing optical output-current characteristics of an MQW semiconductor laser actually manufactured by changing the number of quantum well layers in the multiple quantum well active layer. In this case, the entire optical confinement is constant. However, the MQW semiconductor laser provided with the active layer consisting of the five quantum well layers is different from the MQW semiconductor laser provided with the active layer consisting of the three quantum well layers. It can be seen that the threshold current density _Jth is high and the efficiency after laser oscillation is also poor.

  This is because the efficiency of the semiconductor laser is determined by the internal quantum efficiency and the internal loss, and both the internal quantum efficiency and the internal loss are degraded by the fact that the two quantum well layers on the n side are light absorption layers. This is considered to be the cause.

  Further, in the conventional MQW structure semiconductor laser, the intensity distribution (radiation intensity distribution) of the radiated photoelectric magnetic field has a symmetric structure so that the maximum intensity position comes to the center position of the active layer as shown in FIG. There is a problem that optical confinement is not effectively performed because the quantum well of the first layer that generates optical gain and the maximum intensity position do not match.

  That is, the substantial gain that contributes to laser oscillation is the optical gain multiplied by the radiated light intensity distribution. Even if the optical gain is large, the radiated light intensity distribution must be present at the position where the optical gain is generated. It cannot contribute to oscillation.

  Actually, the distribution of the radiated light to the active layer is about 3% of the total light intensity even if all the layers are summed, so that even a small light distribution is maximum as shown in FIG. It is a big problem that the layer that generates the optical gain does not become large.

In addition, in the case of MQW lasers with 10 to 20 quantum well layers, which are currently reported, even if the entire quantum well structure has sufficient optical confinement, an optical gain is substantially generated. There is a problem that the optical confinement in the first quantum well from the p-type cladding layer side becomes considerably small and the threshold current density _Jth increases.

Furthermore, for the reason of d described above, about 70% of the influence of the forbidden band width difference ΔE _g appears on the valence band side, the energy discontinuity ΔE _C on the conduction band side becomes small, and electron overflow becomes a problem. Therefore, in the conventional short wavelength semiconductor laser, an overflow prevention layer or a carrier stopper layer is provided, but this results in an asymmetric structure in which the emitted light intensity distribution is further shifted to the n side, and a p-type cladding layer having a large optical gain. There is a problem that light confinement in the first quantum well from the side is further reduced and the threshold current density _Jth is increased.

Therefore, in order to improve the characteristics of an MQW semiconductor laser using a nitride compound semiconductor, it is necessary to reduce the threshold current density _Jth . For this purpose, the above-described non-uniform carrier injection is performed. It is effective to improve.

  However, in the case of MQW semiconductor lasers using nitride compound semiconductors as described above, there are problems peculiar to nitride compound semiconductors, and simply applying the common sense of conventional zincblende crystal structure semiconductors. An excellent solution cannot be found, and it is necessary to examine whether the nitride compound semiconductor has a non-essential configuration in the MQW semiconductor laser using the nitride compound semiconductor. become.

Therefore, in general, in order to improve the hole injection efficiency, it is conceivable to increase the hole concentration by making the p-side light guide layer a p-type layer. In this case, however, There exists a problem that injection | pouring efficiency falls.
That is, the main cause of the low hole injection efficiency is that the mobility of holes in the p-side light guide layer is small, but the scattering increases due to p-type doping, which further reduces the mobility of holes.
Furthermore, even if the doping concentration of the p-type impurity is increased, since the activation rate of the impurity is small, the hole concentration does not increase easily.

  In general, in order to improve the non-uniform injection of carriers in the MQW semiconductor laser, the thickness of the well layer in the multiple quantum well structure, the thickness of the barrier layer, and the barrier layer It is considered effective to reduce the height, that is, to reduce the forbidden bandwidth.

  Among these, the film thickness of the well layer greatly affects the optical gain characteristics of the laser and is the most important item in laser design, so there is a problem that it is difficult to change it independently, and the nitride MQW blue semiconductor In the laser, reducing the forbidden band width of the barrier layer means increasing the In composition in the barrier layer, which leads to an increase in strain and deteriorates the crystallinity. Since this is not preferable, this situation will be described with reference to FIG.

See FIG. 39. FIG. 39 is a diagram showing an experimental result on the dependence of the luminous efficiency on the In composition ratio x when In _x Ga _1-x N used as the barrier layer is used. As the In composition ratio x increases, FIG. Since the strain applied to the active layer is increased and the light emission efficiency is decreased, the In composition ratio x of the barrier layer cannot be increased. Therefore, the barrier of the quantum well structure cannot be decreased to increase the injection efficiency.

  On the other hand, with regard to the film thickness of the barrier layer, in the conventional laser using a zinc blende type crystal structure semiconductor, if the film thickness is thin, the interaction due to the oozing of the wave function between the quantum well layers cannot be ignored, and the stepped shape The optical gain distribution that should have been reduced and the generation of the optical gain per fixed carrier density is reduced, so the thickness is set to 5 nm or more. This structure is also applied to an MQW semiconductor laser using a nitride compound semiconductor as it is. Adopted.

  However, in the MQW semiconductor laser using a nitride compound semiconductor, since the effective mass of the carrier is large as described above, the wave function oozes out from the quantum well and the band gap is not uniform. For this reason, the stepwise optical gain distribution has been slightly reduced from the beginning, and therefore, it has been concluded that a film thickness of 5 nm or more is not an essential requirement.

  In addition, as described above, electrons that are not effectively consumed in the active layer overflow to the p-side and become an overflow current to the p-side light guide layer or the p-type cladding layer, and holes from the p-side light guide layer to the active layer. Due to the poor injection efficiency, the holes accumulated in the p-side light guide layer attract electrons to the p-side layer, thereby increasing the overflow.

Furthermore, because of the above-mentioned d, since the band offset at the heterojunction interface is 3: 7, the band is biased toward the valence band side, and the energy discontinuity ΔE _C on the conduction band side becomes small. has become a problem, in the semiconductor laser of conventional short wavelength, is provided with the overflow preventing layer or the carrier stopper layer, nevertheless, there is a problem that the overflow easily occurs because the threshold carrier density N _th is high, Thus, in a nitride-based semiconductor, an overflow of electrons becomes an essential problem as compared with other semiconductors.

That is, the threshold current density J _th of the semiconductor laser is as follows: τ _s is the electron lifetime, d is the thickness of the active layer, e is the elementary charge, and N _th is the threshold carrier density.
J _th = N _th · d · e / τ _s
The threshold Fermi level E ^F _th is a value at the threshold carrier density N _th of the Fermi level E _F depending on the carrier density N, that is,
E ^F _th = E _F (N _th )
It is represented by

The threshold carrier density N _th is a carrier density at which G _m (modal gain), which is a function of the carrier density N, exceeds the cavity loss to start laser oscillation, and the threshold carrier density N _th In order to reduce the value, it is necessary to increase G _m .

This G _m has Γ as an optical confinement factor, and G as a gain determined by the composition of the active layer, carrier density, etc.
G _m = Γ · G
Therefore, if the thickness of the active layer is thin and the optical confinement is insufficient, G _m becomes small, and accordingly, the threshold carrier density N _th also becomes large. The Fermi level E ^F _th is likely to rise.
If this threshold Fermi level E ^F _th is also increased, the number of electrons in a high energy state is increased, so that the overflow of electrons becomes a problem also from this point.

In addition, the present inventors have found through simulation that the leakage current due to the overflow of electrons to the p-type cladding layer is very large when the overflow prevention layer is not provided mainly due to the large effective mass. The circumstances will be described with reference to FIG.
FIG. 40 shows a simulation of the dependence of the overflow current of electrons on the total current amount in an MQW structure short wavelength semiconductor laser in which five well layers of In _0.15 Ga _0.85 N are sandwiched between In _0.05 Ga _0.95 N barrier layers. The results are shown by changing the Al composition of the AlGaN cladding layer. When the Al composition ratio of the cladding layer is 0.05, that is, when an Al _0.05 Ga _0.95 N layer is used, the low current region is shown. Thus, it can be seen that the leakage current starts to increase, and at 20 kA / cm ² , more than half of the total current leaks.

Such a leakage current is a reactive current that does not contribute to laser oscillation, which itself leads to an increase in the threshold current density _Jth and also causes heat generation, which further makes laser oscillation more difficult. .

When an Al _0.05 Ga _0.95 N layer having an Al composition ratio of 0.05 is used as the cladding layer, the difference in the forbidden band width from the active layer is 500 meV, which is a sufficient difference in the conventional material system. In the nitride system, since the overflow current is not negligible, an Al _0.15 Ga _0.85 N layer or the like having a large Al composition ratio in the cladding layer is used to reduce the leakage current due to overflow. .

The inventor has found through simulation that the overflow current also depends on the element temperature. This situation will be described with reference to FIG.
FIG. 41 shows the simulation result of the total current amount dependence of the electron overflow current when the Al _0.1 Ga _0.9 N clad layer is used, with the element temperature changed, which is apparent from the figure. Thus, it can be seen that the overflow increases in the high current region as the element temperature rises.

  In an actual device, the overflowed current reaches the p-side electrode and heat is generated to raise the device temperature. This rise in device temperature creates a vicious circle in which the overflow current further increases, impeding laser oscillation. It is thought to do.

On the other hand, when an overflow prevention layer such as a p-type Al _0.15 Ga _0.85 N layer or an Al _0.18 Ga _0.82 N layer is provided to prevent an overflow of electrons, this Al _0.15 Ga _0.85 N layer or Al _0.18 Ga _0.82 N layer is provided. Has a lower refractive index than that of the p-side light guide layer, so that there is a problem that the optical confinement necessary for obtaining laser oscillation is greatly reduced, and an energy spike is formed at the heterojunction interface to prevent hole injection. There is a problem that becomes a barrier.

Further, as shown in FIG. 32 described above, in a conventional MQW semiconductor laser using a nitride compound semiconductor, a p-type having a large forbidden band between the MQW active layer 836 and the p-type GaN light guide layer 838. In the case where the Al _0.18 Ga _0.82 N overflow prevention layer 837 is provided, there is a problem that the increase of internal loss is increased and the potential barrier against holes is increased to increase the driving voltage, and also due to the difference in electron affinity. Since there is a problem that the drive voltage rises due to the potential barrier, this situation will be described with reference to FIG.

FIG. 42 (a) is a band diagram of a conventional short wavelength semiconductor laser. As is apparent from the figure, the forbidden band width of the p-type Al _0.18 Ga _0.82 N overflow prevention layer 837 is large. A barrier formed between the p-type GaN light guide layer 838, that is, between the band edge of the valence band when no voltage is applied as indicated by a solid line and the band edge 844 of the valence band when a voltage is applied as indicated by a broken line. Therefore, the applied voltage V for injecting holes into the MQW active layer 836 is increased.

FIG. 42 (b) is a diagram schematically showing a band diagram on the valence band side in the vicinity of the p-type Al _0.18 Ga _0.82 N overflow prevention layer 837. As shown in FIG. Due to the difference in electron affinity at the interface between the active layer 836 and the p-type Al _0.18 Ga _0.82 N overflow prevention layer 837 and at the interface between the p-type Al _0.18 Ga _0.82 N overflow prevention layer 837 and the p-type GaN light guide layer 838 Thus, notches 845 and 846 are formed, and the notches 845 and 846 serve as a potential barrier against hole injection, and the hole injection efficiency is lowered.

  In addition, other factors that promote this overflow include a high specific resistance of the p-type cladding layer and a short non-emission lifetime in the p-type cladding layer. These factors are not essential. Therefore, it is conceivable to reduce overflow by improving them.

  However, a p-type cladding layer having sufficient crystal quality has not been obtained at present. For example, regarding the specific resistance, doping to the p-type cladding layer is difficult and insufficient, but the Al composition ratio is low. As doping increases, doping becomes more difficult. Therefore, when a p-type cladding layer having a large Al composition ratio is used to reduce overflow, it is not easy to reduce the specific resistance.

  Further, regarding the non-emission lifetime, even in an undoped crystal, the non-emission lifetime is about 1 ns (nanosecond), which is shorter than that of the conventional material. There is a problem.

That is, the crystal quality characteristics of the nitride-based compound semiconductor include a very high dislocation density. In particular, when a sapphire substrate is used as the growth substrate, it does not sufficiently lattice match with the growth layer. The crystallinity of the growth layer is poor. For example, it has been reported that the normal dislocation density reaches 10 ¹⁰ cm ⁻² , and there is a problem that the non-emission lifetime is as fast as about 1 ns (nanosecond).

In addition, the p-type impurity doping deteriorates the crystallinity of the p-side light guide layer, the non-emission lifetime is further shortened to about 0.1 ns (= 100 ps), and the amount of non-emission recombination increases. As a result, the threshold current density J _th for laser oscillation further increases.

  For this reason, in a nitride-based semiconductor where it is not easy to increase the hole concentration even if Mg is doped, the effect of increasing the hole concentration of the p-side light guide layer is due to a decrease in mobility associated with p-type doping, It is considered that the deterioration of crystallinity becomes a problem.

On the other hand, regarding the dislocation density, the value of 10 ¹⁰ cm ⁻² is about 1 million times that of the conventional zinc blende type crystal structure semiconductor whose dislocation density is 10 ⁴ cm ⁻² or less. In compound semiconductors, it is said that dislocations do not form non-luminescent centers and thus do not affect device characteristics.Therefore, it is not necessary to reduce the dislocation density in order to reduce non-luminescent centers. Semiconductor lasers have been realized in the presence of a high density of dislocation density.

InGaN, which is usually used as an active layer of a nitride semiconductor laser, has properties that are completely different from those of conventional materials, in addition to the physical characteristics common to the nitride compound semiconductor.
That is, InGaN is a mixed crystal of InN and GaN, while the forbidden band width of InN is 1.9 eV, whereas the forbidden band width of GaN is very different from 3.4 eV. Also, while InN is around 600 ° C., GaN is significantly different from around 1000 ° C.

  For these reasons, it is known that this InGaN mixed crystal is very difficult to mix, and even in a region where the non-mixed crystal region is large and the In composition ratio is as small as 0.2 or less, the In composition ratio is low. There is a problem that the proportion of composition separation increases with the increase.

  As a result, in the InGaN layer with an In composition ratio of about 0.15, the half-value width of the photoluminescence (PL) spectrum seen in a macro region of about 200 μm is very large, reflecting in-crystal nonuniformity due to composition separation. Even a good crystal is 150 meV.

  This is because the half-width of the PL spectrum, which should increase when the semiconductor is thinned with a conventional zinc blende crystal structure, becomes smaller with an InGaN mixed crystal. This phenomenon is reduced even when cooled to a very low temperature. This is due to a property that is completely different from the conventional material, that is, there is almost no change in the value range.

  The characteristics of these InGaN do not depend on the type of substrate used as a growth substrate such as a sapphire substrate, SiC substrate, or spinel substrate, and also include a reduced pressure MOVPE method (a reduced pressure metal organic vapor phase growth method), a normal pressure MOVPE method. Or, it does not depend on the growth method such as MBE method (molecular beam epitaxial growth method), and also appears without depending on the crystal structure such as hexagonal crystal or cubic crystal. Features are considered to be inevitable specialities that should be tolerated to some extent.

  In this way, conventional short-wavelength semiconductor lasers and light-emitting diodes (LEDs) that use InGaN as an active layer have been developed with such in-crystal composition non-uniformity intact. It is thought that commercialization is carried out with a large compositional non-uniformity.

  Even in short-wavelength semiconductor lasers, although laser oscillation has been successful as described above, there has been no appropriate evaluation means so far. It is not known whether the compositional nonuniformity is occurring, and it is not known how the compositional nonuniformity affects the device characteristics. Therefore, how much crystal quality is necessary for laser oscillation. It was completely unknown whether the crystal of such quality can be obtained with good reproducibility when grown.

  Therefore, the present inventors recently performed photoluminescence (PL) measurement with a small spot diameter of 1 μm on an InGaN mixed crystal serving as an active layer of a short-wavelength semiconductor laser, thereby achieving non-uniform composition in the InGaN mixed crystal. A method to quantitatively evaluate the degree was developed.

As a result of such an evaluation, it has been found that the PL peak wavelength of the InGaN MQW (multiple quantum well) active layer has a very large distribution in the crystal, which will be described with reference to FIGS. 43 and 44.
The details of the conventional short-wavelength semiconductor laser that performed this measurement have not been published.

See FIG. 43A. FIG. 43A shows the PL peak wavelength and the PL light at each measurement point when the PL spectrum was measured at 2500 points every 2 μm within the region of 10,000 μm ^{2 in} the element that did not oscillate. It shows the correlation of intensity, and both PL peak wavelength and PL light intensity are widely distributed over a range of 396 nm (≈3.11 eV) to 416 nm (≈2.980 eV), and the PL peak wavelength distribution range is 151 meV, That is, it was about 150 meV.

  Incidentally, as a result of the same evaluation of the InGaAs-based active layer used as a semiconductor laser for optical communication, the PL peak wavelength distribution is about 5 meV, that is, about 1/30 of the InGaN mixed crystal. From this result, it was found that the InGaN system is a very special material system, and conventional common sense is not applicable.

In this InGaN-based semiconductor laser, the threshold current density J _th is essentially high for reasons of physical properties, and the nonuniform composition of the active layer is fatal in achieving laser oscillation. This is a drawback. From the above evaluation, it is obtained that the laser oscillation does not occur when the PL peak wavelength distribution is 150 meV or more.

See FIG. 43 (b). FIG. 43 (b) shows the PL peak wavelength and the PL light intensity at each measurement point when the PL spectrum is measured at 2500 points every 2 μm within the region of 10,000 μm ² in the laser-oscillated device. The PL peak wavelength distribution range is 91 meV, that is, about 90 meV over the range from 400 nm (≈3.100 eV) to 412 nm (≈3.009 eV), and the PL light intensity distribution is also It was a small one.

44A. FIG. 44A is a diagram showing current-light output characteristics (IL characteristics) of an InGaN-based semiconductor laser having the PL peak wavelength distribution as described above, and has a wavelength of 414.3 nm. At room temperature, pulse oscillation was achieved, but kink clearly appears as the current is increased.
Note that the PL wavelength and the laser oscillation wavelength are slightly different from each other.

FIG. 44B shows the same InGaN-based semiconductor laser as FIG. _44A , which is 1.1 times, 1.2 times, or 1.3 times the threshold current density J _th. The multi-wavelength oscillation occurs as the current increases, and this multi-wavelength oscillation causes a kink in the IL characteristic in FIG. 44 (a). I understand that.

Conventionally, in InGaN-based semiconductor lasers, it is known that the oscillation wavelength is multi-wavelength or changes greatly depending on the injection current, which reflects the formation of quantum dots (quantum boxes) in the active layer. It was thought that.
That is, in the past, it has been considered that multiwavelength oscillation is caused by the quantum effect (see Japan Journal of Applied Physics, vol. 35, 1996, p. 217, if necessary). It has been reported that dots are present (if necessary, see Applied Physics Letters, vol. 70, 1997, p. 981).

  However, as a result of the inventor's research, the spatial distribution of the PL peak wavelength caused by the compositional non-uniformity in the active layer as described above has been considered to be the cause of multiwavelength oscillation. Will be described with reference to FIG.

45 is a histogram of the PL peak wavelength in the measurement result shown in FIG. 43 (b), while the line graph is a result of optical excitation of the semiconductor laser actually oscillated as shown in FIG. This shows the intensity distribution of the oscillation spectrum, and when they are overlapped, a very good agreement is obtained. From this, the multiwavelength oscillation is caused by the PL peak wavelength distribution, that is, the compositional non-uniformity in the active layer. It is believed that there is.

Then, such a multi-wavelength oscillation is only or kink in the I-L characteristic, because it leads to deterioration of the optical properties of the deterioration of the near-field pattern and the far field pattern to increase the threshold current density J _th, In an InGaN-based semiconductor laser as an optical device light source, it is important to suppress the composition distribution of the active layer.

  As described above, as a result of experiments by the present inventors, it is necessary to set the PL peak wavelength distribution of 150 meV or less, that is, within the distribution range of ± 0.03 in the In composition ratio for laser oscillation. It was also found that the PL peak wavelength distribution must be 90 meV or less, that is, the In composition ratio must be ± 0.018 or less in order to suppress multiwavelength oscillation. , Preferably 50 meV or less, more preferably 20 meV or less.

  Furthermore, since the short wavelength semiconductor light emitting device of FIG. 31 (b) is essentially a light emitting diode, there are descriptions on the impurity concentration or the layer thickness, but under any conditions when a semiconductor laser is used. There is no suggestion about whether laser oscillation occurs at a low threshold current density with high efficiency.

  Accordingly, an object of the present invention is to reduce the threshold current density of a short wavelength semiconductor laser using a nitride compound semiconductor.

Here, means for solving the problem will be described. FIG. 1 is an explanatory diagram of the principle configuration relating to claims 1 to 7, and FIG. 2 is a graph showing the current density of the mode gain in the quantum well structure semiconductor laser. It is a figure which shows the layer number dependence of a well layer.
See FIG. 1. (1) In the present invention, in a semiconductor laser using a nitride compound semiconductor, a multiple quantum well structure is used as the active layer 4 and the maximum position of the emitted light intensity distribution is set to p from the center position of the active layer 4. It is shifted to the mold clad layer (6) side.

Thus, by shifting the maximum position of the radiated light intensity distribution from the center position of the active layer 4 to the p-type cladding layer (6) side, the maximum optical gain position and the maximum position of the radiated light intensity distribution coincide with each other. Since the confinement effect is enhanced, the threshold current density _Jth can be reduced.

  (2) Further, according to the present invention, in the above (1), the maximum position of the emitted light intensity distribution coincides with the position of the first quantum well from the p-type cladding layer (6) side of the multiple quantum well structure. It is characterized by that.

  In the MQW structure semiconductor laser using a nitride compound semiconductor, the maximum optical gain position is the first quantum well from the p-type cladding layer (6) side. It is desirable to match the maximum position of.

  (3) Further, in the above (1) or (2), the present invention provides an n-side light guide layer (between the active layer 4 and the n-type cladding layer (2) and the p-type cladding (6) layer). 3) and a p-side light guide layer (5) are provided, and the forbidden band width of the n-side light guide layer (3) is made larger than the forbidden band width of the p-side light guide layer (5).

  In a nitride compound semiconductor, the larger the forbidden band width, the smaller the refractive index, so that the forbidden band width of the n-side light guide layer (3) is made larger than the forbidden band width of the p-side light guide layer (5). The emitted light intensity distribution moves to the p side.

  (4) Further, according to any of the above (1) to (3), the present invention provides an n-side light between the active layer 4 and the n-type cladding layer (2) and the p-type cladding layer (6). A guide layer (3) and a p-side light guide layer (5) are provided, and the p-side light guide layer (5) is thicker than the n-side light guide layer (3).

  Such asymmetry of the light guide structure can also be formed by making the thickness of the light guide layer, that is, the SCH layer asymmetric, and the thickness of the p-side light guide layer (5) can be changed to the n-side light guide. The radiated light intensity distribution also moves to the p side by making it thicker than the layer (3).

  (5) Further, according to the present invention, in any one of the above (1) to (4), the forbidden band width of the n-type cladding layer (2) is made larger than the forbidden band width of the p-type cladding layer (6). Features.

In this way, the emitted light intensity distribution can also be moved to the p side by making the forbidden band width of the n-type cladding layer (2) larger than the forbidden band width of the p-type cladding layer (6).
In this case, the forbidden band width of the n-side light guide layer (3) may be larger than the forbidden band width of the p-side light guide layer (5), or the thickness of the light guide layer may be asymmetric. .

  (6) In addition, the present invention uses a nitride compound in which a single quantum well structure is used as the active layer 4 and a wide forbidden bandwidth layer is provided between the active layer 4 and the p-side light guide layer (5). In a semiconductor laser using a semiconductor, the n-side layer compensates for a shift between the maximum position of the emitted light intensity distribution caused by the wide forbidden bandwidth layer and the center position of the active layer 4.

  When a wide forbidden bandwidth layer is provided between the active layer 4 and the p-side light guide layer (5) to prevent electron overflow, the radiation intensity distribution of the wide forbidden bandwidth layer is reduced. Although the maximum position shifts from the center position of the active layer 4 to the n side, the shift can be compensated by increasing the forbidden band width of the n side layer, whereby the maximum position of the synchrotron radiation intensity distribution and the activity The center position of the layer 4 can be substantially matched.

  (7) Further, according to the present invention, in the above (6), the n-side layer is at least the n-side light guide layer (3), and the forbidden bandwidth of the n-side light guide layer (3) is set to the p-side light guide layer. It is characterized by being larger than the forbidden bandwidth of (5).

  Thus, by making the forbidden band width of the n-side light guide layer (3) larger than the forbidden band width of the p-side light guide layer (5), the emitted light intensity distribution can be moved to the p side, Thus, the maximum position of the synchrotron radiation intensity distribution and the center position of the active layer 4 can be made substantially coincident.

  (8) In the present invention, in the above (6) or (7), the n-side layer is at least the n-side light guide layer (3), and the layer thickness of the n-side light guide layer (3) is set to the p-side. It is characterized by being made thinner than the thickness of the light guide layer (5).

  In this way, asymmetry may be introduced by making the layer thickness of the n-side light guide layer (3) thinner than the layer thickness of the p-side light guide layer (5), thereby reducing the emitted light intensity distribution to p. The maximum position of the emitted light intensity distribution and the center position of the active layer 4 can be made to substantially coincide with each other.

  (9) Further, according to the present invention, in any one of the above (6) to (8), the n-side layer is at least an n-type cladding layer (2), and the forbidden band width of the n-type cladding layer (2) is increased. It is characterized by being larger than the forbidden band width of the p-type cladding layer (6).

In this way, even if the forbidden band width of the n-type cladding layer (2) is made larger than the forbidden band width of the p-type cladding layer (6), the emitted light intensity distribution can be moved to the p side, thereby The maximum position of the radiant light intensity distribution and the center position of the active layer 4 can be substantially matched.
Also in this case, the forbidden band width of the n-side light guide layer (3) may be larger than the forbidden band width of the p-side light guide layer (5), or the layer thickness of the light guide layers 3 and 5 may be increased. May be asymmetric.

(10) Further, according to the present invention, in any one of the above (1) to (9), the well layer constituting the active layer 4 having the quantum well structure is Al _x Ga _y In _1-xy N (provided that 0 ≦ x <1, 0 <y ≦ 1).

As the well layer constituting the active layer 4 of the quantum well structure in such a short wavelength semiconductor laser, a nitride compound semiconductor such as GaN, InGaN, AlGaN, or AlInGaN, that is, Al _x Ga _y In _{1− xy} N (where 0 ≦ x <1, 0 <y ≦ 1) is preferable.

  (11) Further, the present invention is characterized in that, in a semiconductor laser using a nitride compound semiconductor, the active layer 4 is constituted by a multiple quantum well structure having two gain layers.

When the laser cavity loss (threshold gain) is large, as is apparent from FIG. 2 and FIG. 36 described above, the threshold current density _Jth is further increased when the gain layer is made two layers. Can be lowered.

  (12) In the semiconductor laser using a nitride compound semiconductor according to the present invention, the active layer 4 has a multiple quantum well structure having two or three gain layers each having a thickness of 6 nm or more. It is characterized by doing.

For example, when the cavity loss is as small as 100 cm ⁻¹ , the threshold current density J _{th at which} the mode gain G _m exceeds the cavity loss and starts laser oscillation is expressed as follows:
J _th (1 layer) <J _th (2 layers) <J _th (3 layers) <J _th (4 layers) <J _th (5 layers) When the total thickness of the gain layers is the same, the active layer 4 is The threshold current density _Jth can be lowered by the single gain layer.

On the other hand, when the cavity loss is as large as 200 cm ⁻¹ , the threshold current density J _{th at which} the mode gain G _m exceeds the cavity loss and laser oscillation starts is
When J _th (2 layers) <J _th (3 layers) ≈J _th (1 layer) <J _th (4 layers) <J _th (5 layers) and the total thickness of the gain layers is the same, the gain layer is 2 The threshold current density _Jth can be lowered by configuring a multi-quantum well structure consisting of three layers or three layers.

  (13) Further, the present invention is characterized in that, in the above (11) or (12), the gain layer is composed of an undoped layer.

  As described above, even when an active layer having a multiple quantum well structure is used, it is desirable that the gain layer be an undoped layer to reduce impurity scattering and increase the mobility of holes, thereby making the holes more uniform. Can be injected into.

(14) Further, according to the present invention, in any one of the above (11) to (13), the gain layer 4 may be Al _x Ga _y In _1-xy N (where 0 ≦ x <1, 0 <y ≦ 1 ).

Such as the gain layer constituting the short wavelength semiconductor laser, GaN, InGaN, AlGaN, or nitride compound semiconductor such as AlInGaN, _{namely, Al x Ga y In 1-} xy N ( where, 0 ≦ x <1, 0 <y ≦ 1) is preferred.

(15) In the semiconductor laser using a nitride compound semiconductor according to the present invention, the p-side light guide layer is made of either InGaN or GaN, and the impurity concentration of the p-side light guide layer is 1 × 10 ¹⁷ cm. It is less than ^-3 .

Thus, by using a p-side light guide layer made of InGaN or GaN having an impurity concentration of less than 1 × 10 ¹⁷ cm ⁻³ , the mobility of holes in the p-side light guide layer can be increased, thereby Since the hole injection efficiency can be increased and the crystallinity can be improved, non-luminous recombination can be reduced, and thereby the threshold current density _Jth can be lowered.

  (16) Further, in the above (15), the present invention is characterized in that the p-side light guide layer is an undoped layer.

  Such a low impurity concentration layer is preferably composed of an undoped layer.

(17) Further, the present invention is characterized in that, in the above (15) or (16), the mobility of holes in the p-side light guide layer is 2 cm ² / V · s or more.

The hole mobility in such a low impurity concentration layer is required to be 2 cm ² / V · s or more, which is considered to enable laser oscillation at the present time point where necessary hole injection is obtained. It is.

  (18) Further, the present invention is characterized in that in the semiconductor laser using the nitride compound semiconductor, the layer thickness of the p-side light guide layer is made thinner than the layer thickness of the n-side light guide layer.

In this way, non-radiative recombination in the p-side light guide layer can be reduced by making the thickness of the p-side light guide layer thinner than that of the n-side light guide layer. A semiconductor laser having a threshold current density _Jth can be configured.

  (19) Further, the present invention is characterized in that, in a semiconductor laser using a nitride compound semiconductor, the thickness of the p-side light guide layer is less than 0.1 μm.

  In this way, non-radiative recombination in the p-side light guide layer is effectively achieved by setting the thickness of the p-side light guide layer to less than 0.1 μm, and more preferably 0.08 μm (80 nm) or less. Can be reduced.

  (20) Further, in the above (18) or (19), the present invention is characterized in that the forbidden band width of the p-side light guide layer is larger than the forbidden band width of the n-side light guide layer.

  Thus, by making the forbidden band width of the p-side light guide layer larger than the forbidden band width of the n-side light guide layer, it is possible to prevent electrons from overflowing to the p-side light guide layer side.

  (21) Further, according to the present invention, in a semiconductor laser using a nitride compound semiconductor, the forbidden band width of the p-side light guide layer is small in a portion adjacent to the active layer and a portion adjacent to the p-type cladding layer. It is characterized by being larger.

  Thus, by using the p-side light guide layer whose forbidden band width is small in the portion adjacent to the active layer and large in the portion adjacent to the p-type cladding layer, sufficient light confinement is ensured. Electron overflow into the p-type cladding layer can be prevented, and hole injection efficiency into the active layer can be improved.

  (22) Further, the present invention is characterized in that, in the above (21), the forbidden band width of the p-side light guide layer changes stepwise.

  The change in the forbidden band width in the p-side light guide layer as described in (21) above may be a step change, that is, a step-like change, and may be composed of two layers or a multilayer structure of two or more layers. It ’s fine.

  (23) Further, in the above (21), the present invention is characterized in that the forbidden bandwidth of the p-side light guide layer is continuously changed.

  Further, the change in the forbidden bandwidth in the p-side light guide layer as in (21) may be a continuous change, that is, a graded change.

  (24) Further, according to the present invention, in the semiconductor laser using a nitride compound semiconductor, the forbidden bandwidth of the p-side light guide layer is from the side adjacent to the active layer toward the side adjacent to the p-type cladding layer 3. It is characterized by being continuously reduced.

  Thus, the p-side light guide layer whose forbidden band width continuously decreases from the side adjacent to the active layer toward the side adjacent to the p-type cladding layer, that is, the p-side light guide having an inverse graded shape. By using the layer, energy spikes that hinder hole injection do not occur, and electron overflow can be prevented while securing sufficient hole injection.

  (25) Further, according to the present invention, in any one of the above (21) to (24), the layer having a small forbidden band width constituting the p-side light guide layer is made of InGaN or GaN and has a large forbidden band width. The layer is made of AlGaN.

As described above, in order to effectively prevent the overflow of electrons, ΔE _C / ΔE _{g at} the GaN / AlGaN or InGaN / AlGaN interface is large, so that it is desirable to employ AlGaN as a layer having a large forbidden bandwidth.

  (26) The semiconductor light emitting device using a nitride compound semiconductor according to the present invention is characterized in that the photoluminescence wavelength distribution of the active layer in the resonator is 90 meV or less.

  (27) Further, in the above (26), the present invention is characterized in that the distribution of the photoluminescence wavelength of the active layer in the resonator is 50 meV or less.

  Thus, in order to suppress multiwavelength oscillation in a short wavelength semiconductor laser, the photoluminescence wavelength distribution of the active layer in the resonator needs to be 90 meV or less, and more preferably 50 meV or less. It is desirable to make it.

(28) The semiconductor light-emitting device using a nitride compound semiconductor according to the present invention is characterized in that the dislocation density of the active layer in the resonator is 10 ⁹ cm ⁻² or less.

(29) Further, in the above (28), the present invention is characterized in that the dislocation density of the active layer in the resonator is 10 ⁸ cm ⁻² or less.

The dislocation density in the conventional short wavelength semiconductor laser is on the order of 10 ⁹ cm ⁻² , that is, 10 ⁹ to 10 ¹⁰ cm ⁻² , and the non-uniform magnitude of the PL peak wavelength coincides with the distance between dislocations. The distribution of the PL peak wavelength can be reduced by reducing the dislocation density of the active layer in the resonator, and for this purpose, the dislocation density of the active layer in the resonator needs to be 10 ⁹ cm ^-2 or less. Preferably, it is 10 ⁸ cm ⁻² or less, more preferably 10 ⁷ cm ⁻² or less.

That is, in the conventional short wavelength semiconductor laser, sapphire having an extremely large lattice mismatch of about 13% with a nitride compound semiconductor is used as a growth substrate, and therefore the dislocation density of the active layer in the resonator is 10 ^10. Although it is about cm ^-2 , in nitride compound semiconductors, dislocations do not form non-emissive centers, so it is said that they do not affect the characteristics of the device. Although device development has been promoted, as described above, the dislocation density and the compositional non-uniformity are correlated, and as the dislocation density decreases, the compositional non-uniformity also decreases, so the lattice mismatch is greatly reduced to 3%. By using a SiC substrate, the dislocation density can be reduced to 10 ⁹ cm ^-2 or less, at least to about 10 ⁷ cm ^-2 , thereby suppressing multiwavelength oscillation. A short wavelength semiconductor light emitting device can be realized.

  (30) Further, the present invention is characterized in that in any one of the above (26) to (29), the active layer contains In as a constituent element.

  As described above, when a semiconductor containing In as a constituent element is used as an active layer, particularly when InGaN having a relatively large In composition ratio is used, the above conditions (26) to (29) are satisfied. Thus, an active layer having good crystallinity suitable as a blue light emitting element, particularly, a blue semiconductor laser can be obtained.

  (31) The present invention is characterized in that, in the method for producing a semiconductor light emitting device using a nitride compound semiconductor, the growth rate when growing the active layer is 0.1 μm / hour or more.

In the nitride compound semiconductor, when the growth rate when growing the active layer is 0.1 μm / hour (0.1 μm / h) or less, the PL wavelength distribution, that is, the standard deviation of the PL wavelength is large. will, in particular, when the growth rate r _g is 0.075 .mu.m / h, the standard deviation of the larger the PL wavelength the in composition ratio of the InGaN mixed crystal is increased, it becomes impossible to laser oscillation.

  Therefore, by adopting a growth rate of 0.1 μm / h or more, the PL peak wavelength distribution can be made 90 meV or less, so that a semiconductor laser in which multiwavelength oscillation is suppressed can be manufactured with good reproducibility, In addition, a high-purity blue light-emitting element with a narrow half-width of wavelength can be realized as an LED.

  (32) Further, the present invention is characterized in that, in the above (31), the growth rate is 0.2 μm / hour or more.

  In this way, by increasing the growth rate, the PL peak wavelength distribution can be made narrower, and multi-wavelength oscillation can be easily suppressed.

  (33) Further, the present invention is characterized in that, in the above (31), the growth rate is set to 0.3 μm / hour or more.

  As described above, when the growth rate is 0.3 μm / hour or more, the PL wavelength standard deviation does not increase even when growing a relatively large InGaN having a suitable In composition ratio as a blue light emitting element. An active layer having a narrow PL peak wavelength distribution, for example, 90 meV or less can be grown with good reproducibility, and an active layer having a high PL light intensity and good crystallinity can be grown.

  (34) Further, the present invention is characterized in that, in any of the above (31) to (33), an SiC substrate is used as a substrate and the surface of the SiC substrate is etched.

  Since the dislocation density of the active layer, and hence the distribution of the photoluminescence wavelength due to the compositional inhomogeneity, depends on the surface defect density of the substrate, even when using a SiC substrate with a small lattice mismatch, the surface is etched, especially dry. -By removing surface defects by etching, an active layer having a low dislocation density can be grown with good reproducibility.

  (35) Further, the present invention is characterized in that, in any one of the above (31) to (34), the active layer contains In as a constituent element.

  As described in (33) above, the manufacturing method of the present invention is particularly effective for a semiconductor light emitting device having an active layer containing In as a constituent element.

  (36) According to the present invention, in a semiconductor laser using a nitride compound semiconductor, a p-type cladding layer is sandwiched between two wide-bandwidth p-type semiconductor layers with a narrow forbidden band width intermediate layer. It is characterized by comprising a multilayer structure.

In this way, by sandwiching an intermediate layer having a narrow forbidden band width in the middle of the p-type cladding layer, electrons overflowing in the intermediate layer are recombined and emitted as light, thereby generating heat due to the overflow current. Thus, the vicious circle in which the overflow current increases can be interrupted, and the threshold current density _Jth can be reduced.

  (37) Further, in the above (36), the present invention is characterized in that the intermediate layer 6 is formed of a single narrow band gap layer.

  Such an intermediate layer may be composed of a single narrow forbidden bandwidth layer. In this case, in order to reduce the resistance of the p-type cladding layer, p-type doping is desirable.

  (38) Further, in the above (36), the present invention provides the forbidden band width so that the intermediate layer has the minimum forbidden band width at any position between the two wide forbidden band p-type semiconductor layers. Is characterized by continuously changing.

  In this way, by configuring the intermediate layer with a layer having a U-shaped forbidden bandwidth distribution, holes can be smoothly injected into the p-side light guide layer.

  (39) Further, the present invention is characterized in that, in the above (36), the intermediate layer has a multilayer structure in which a plurality of layers having a wide forbidden band width and a layer having a narrow forbidden band width are alternately laminated.

In this way, the intermediate layer may be formed in a multilayer structure. In this case, the crystallinity is improved by undoping the layer having the narrow forbidden band width, and the light emission characteristics in the layer having the narrow forbidden band width are improved. The coupling probability can be increased.

  (40) In the present invention, in the above (39), the forbidden bandwidth between the wide forbidden bandwidth layer and the narrow forbidden bandwidth layer constituting the intermediate layer is continuously changed. Features.

  In this way, by continuously changing the forbidden bandwidth between the wide forbidden bandwidth layer and the narrow forbidden bandwidth layer constituting the intermediate layer, holes are smoothly injected into the p-side light guide layer. Can be done.

  (41) Further, the present invention is characterized in that in any one of the above (36) to (40), at least a part of the narrow band gap side layer in the intermediate layer is an undoped layer.

  In this way, by making at least a part of the layer on the narrow band gap side of the intermediate layer an undoped layer, the crystallinity can be improved and the luminescent recombination probability can be increased.

  (42) Further, in the present invention, in any of the above (36) to (41), the wide forbidden band layer is made of AlGaN, and the narrow forbidden band layer is made of InGaN, GaN, or AlGaN. It is characterized by comprising either.

  In this way, the wide forbidden band layer, that is, the wide forbidden band portion constituting the p-type semiconductor layer and the intermediate layer is made of AlGaN, and the narrow forbidden band layer is made of InGaN, GaN, or AlGaN. It is suitable to comprise either.

  (43) The present invention is characterized in that in a multiple quantum well structure semiconductor laser using a nitride compound semiconductor, the thickness of the barrier layer constituting the multiple quantum well active layer is less than 5 nm.

  As described above, in the nitride-based compound semiconductor, since the wave function oozes out from the well layer, the optical gain is not generated even if the thickness of the barrier layer constituting the multiple quantum well active layer is reduced. Since the degradation problem does not become so large, the characteristics of the multiple quantum well structure semiconductor laser can be improved by improving the nonuniform injection of carriers by setting the thickness of the barrier layer to less than 5 nm.

  (44) Further, in the above (43), the present invention is characterized in that the barrier layer constituting the multiple quantum well active layer is made of InGaN having an In composition ratio of 0.04 or more.

  In this way, when the thickness of the barrier layer constituting the multi-quantum well active layer is reduced, the effect of reducing strain is produced and the deterioration of crystallinity is reduced. Therefore, the In composition ratio of the barrier layer made of InGaN is reduced. Since the height of the barrier layer can be lowered by 0.04 or more, thereby making it possible to further improve non-uniform carrier injection.

(45) Further, according to the present invention, in the semiconductor laser using the nitride compound semiconductor, the impurity concentration of the electron block layer provided on the p side of the active layer is less than 1.0 × 10 ¹⁷ cm ^−3. Features.

  (46) Further, in the above (45), the present invention is characterized in that the electron block layer provided on the p side of the active layer is an undoped layer.

As described in the above (45) or (46), the electron block layer provided on the p side of the active layer is formed of a layer having an impurity concentration of less than 1.0 × 10 ¹⁷ cm ⁻³ , in particular, an undoped layer. Is not scattered by impurities, the effective mobility of holes is improved, the efficiency of hole injection is improved, and the applied voltage V can be reduced.

  (47) Further, according to the present invention, in the semiconductor laser using a nitride compound semiconductor, the forbidden band width gradually changes in the p-side region of the electron block layer provided on the p-side of the active layer. Features.

  In this way, in the region on the p side of the electron block layer provided on the p side of the active layer, the forbidden band width is gradually changed, that is, changed continuously or stepwise to change the electron block. The electron affinity between the layer and the p-side layer, that is, the p-side light guide layer or the p-type cladding layer, can be gradually changed, thereby suppressing the occurrence of a notch serving as a potential barrier at the interface. Therefore, the hole injection efficiency is improved and the applied voltage V can be reduced.

  (48) Further, according to the present invention, in the semiconductor laser using the nitride compound semiconductor, the forbidden band width is gradually changed in the n-side region of the electron block layer provided on the p-side of the active layer. Features.

  In this way, in the region on the n side of the electron block layer provided on the p side of the active layer, the forbidden band width is gradually changed, that is, continuously changed, or changed stepwise. The electron affinity between the active layer and the active layer can be gradually changed, thereby suppressing the occurrence of notches serving as potential barriers at the interface, so that the hole injection efficiency is improved and the applied voltage V is reduced. Can be small.

  (49) Further, according to the present invention, in the semiconductor laser using a nitride compound semiconductor, the forbidden band width gradually changes in the n side and p side regions of the electron block layer provided on the p side of the active layer. It is characterized by being.

  In this manner, by changing the forbidden band width gradually, that is, continuously or stepwise in the n-side and p-side regions of the electron block layer provided on the p-side of the active layer. The electron affinity between the electron block layer and the active layer and between the electron block layer and the p-side layer can be gradually changed, thereby suppressing the generation of notches that become potential barriers at both interfaces. Therefore, the hole injection efficiency is improved, and the applied voltage V can be reduced.

(50) The present invention is characterized in that, in a semiconductor laser using a nitride compound semiconductor, the Mg concentration of the electron block layer provided on the p side of the active layer is 7 × 10 ¹⁹ cm ⁻³ or more.

Thus, by setting the Mg concentration of the electron block layer provided on the p side of the active layer to 7 × 10 ¹⁹ cm ⁻³ or more, carrier overflow can be effectively suppressed from the evaluation of the emission spectrum.

  The reason for this is not necessarily clear, but deep impurity levels are formed at a high density on the valence band side of the electron block layer. Impurity conduction or hopping conduction or tunnel conduction through this impurity level. This is because holes are injected into the active layer due to the above, and the hole injection efficiency is improved.

  (51) Further, the present invention is characterized in that, in the method of manufacturing a semiconductor laser using a nitride compound semiconductor, the growth temperature of the electron block layer provided on the p side of the active layer is 600 ° C. to 900 ° C. .

  (52) Further, in the above (51), the present invention is characterized in that the growth temperature of the electron block layer is the same as the growth temperature of the active layer.

  Thus, the emission temperature in the active layer is increased by setting the growth temperature of the electron block layer to 600 ° C. to 900 ° C., which is the same as the growth temperature of the active layer, lower than the conventional growth temperature of about 1100 ° C. In addition, light emission in the p-type light guide layer can be reduced.

(53) Further, the present invention is characterized in that, in the above (51) or (52), Mg is doped so that the Mg concentration of the electron block layer is 7 × 10 ¹⁹ cm ⁻³ or more.

Thus, by doping Mg so that the Mg concentration of the electron block layer provided on the p side of the active layer is 7 × 10 ¹⁹ cm ⁻³ or more, it is possible to effectively prevent carrier overflow from the evaluation of the emission spectrum. Can be suppressed.

According to the inventions of the above (1) to (10), the light guide layer and the light guide layer and the maximum position of the radiated light intensity distribution in the short wavelength semiconductor laser made of a nitride compound semiconductor coincide with each other. By selecting the forbidden band width and thickness of the cladding layer, it is possible to increase the optical confinement effect and reduce the threshold current density J _th , thereby enabling low power consumption. Since the generation of heat can be suppressed to the minimum, the reliability is improved, and it greatly contributes to the higher density as a light source for an optical information recording apparatus or the like.

According to the above inventions (11) to (14), the active layer of the short wavelength semiconductor laser made of a nitride compound semiconductor is constituted by a single gain layer having a thickness of 3 nm or more, and the light guide layer Or the gain layer is an undoped layer, and the threshold current density J _th can be reduced. If the cavity loss is large, the well layer has a multi-quantum of 3 layers or less having a thickness of 6 nm or more. The structure can also reduce the threshold current density _Jth, thereby reducing power consumption and minimizing heat generation, thereby improving reliability. As a light source for an optical information recording apparatus or the like, it greatly contributes to increasing the density.

Further, according to the inventions of (15) to (25), the hole mobility in the p-side light guide layer of the short wavelength semiconductor laser made of a nitride compound semiconductor is increased, or the re-measurement in the p-side light guide layer is performed. Since the coupling probability is reduced, the threshold current density J _th can be reduced, thereby enabling low power consumption and minimizing the generation of heat, thereby improving reliability. As a light source for an optical information recording apparatus or the like, it greatly contributes to increasing the density.

Further, according to the inventions of (26) to (35), when growing an active layer of a semiconductor light emitting device made of a nitride compound semiconductor, the growth rate is more preferably 0.1 μm / h or more. Is 0.3 μm / h or more, so that the dislocation density is 10 ⁹ cm ⁻³ or less, the standard deviation of PL wavelength is small, and the PL peak wavelength distribution is 90 meV or less, more preferably 50 meV or less. Since the layer can be manufactured with good reproducibility, it is possible to reduce the threshold current density of the blue semiconductor laser, thereby greatly contributing to the high density as a light source for an optical information recording apparatus or the like.

  According to the inventions (36) to (42), a narrow band gap portion is provided in the p-type cladding layer of the short wavelength semiconductor laser made of a nitride compound semiconductor, and the narrow band gap portion. Since the electrons that overflowed in the light are recombined with light emission, the heat generation due to the overflow current can be greatly reduced, thereby breaking the vicious circle of the increase in overflow current due to the heat generation. The current density can be increased, and the element deterioration due to the electrode deterioration is suppressed, so that the reliability is improved and the light source for the optical information recording apparatus or the like contributes to the higher density.

According to the inventions of (43) and (44), the thickness of the barrier layer constituting the multiple quantum well active layer of the multiple quantum well structure semiconductor laser made of a nitride compound semiconductor is set to less than 5 nm. Therefore, it is possible to improve the non-uniform injection of carriers and improve the non-uniform generation of optical gain, thereby reducing the threshold current density J _{th and} enabling low power consumption. Since reliability is improved, it contributes greatly to increasing the density as a light source for an optical information recording apparatus or the like.

According to the above inventions (45) to (49), the electron block layer to be inserted into the semiconductor laser made of a nitride compound semiconductor is constituted by an undoped layer or a layer having a graded layer. Therefore, the hole injection efficiency can be improved, thereby reducing the threshold current density _{Jth and} reducing the power consumption, contributing to the higher density as a light source for an optical information recording apparatus or the like. However, it is big.

Furthermore, according to the inventions of (50) to (53), the p-type electron block layer inserted into the semiconductor laser made of a nitride compound semiconductor is a high-concentration layer having an Mg concentration of 7 × 10 ¹⁹ cm ⁻³ or more. Therefore, the overflow of electrons can be suppressed almost completely, thereby reducing the threshold current density _{Jth and} reducing the power consumption. As a light source for an optical information recording apparatus or the like The place that contributes to the higher density is great.

Here, the first and second embodiments of the present invention in which the threshold current density _Jth is reduced by selecting the thickness of the active layer or the well layer will be described with reference to FIGS. To do.
First, before describing the specific configuration of the short-wavelength semiconductor laser according to the first embodiment of the present invention with reference to FIG. 4, the threshold in the first embodiment of the present invention with reference to FIG. The dependence of the value current density _Jth on the layer thickness of the active layer will be described.

See FIG. 3. In FIG. 3, an In _0.15 Ga _0.85 N layer is used as an active layer, a GaN light guide layer having a thickness of 0.1 μm is provided on both sides of the active layer, and an Al _0.15 Ga _0.85 N cladding layer is provided on both sides thereof. The calculation result of the layer thickness dependence of the threshold current density _{Jth in} the case of the active layer is shown, and is an ideal case calculation result when there is no overflow of electrons.

As apparent from the figure, when the thickness of the active layer is 3 nm or less, the optical confinement is not sufficient and the optical confinement coefficient Γ is small, so that the threshold Fermi level E ^F _th is increased and the threshold current density is increased. _Jth rises.
G _th is a threshold gain.

On the other hand, when the film thickness is 6 nm or more, the threshold current density J _th increases due to the relationship of J _th = N _th · d · e / τ _s , but actually, in this material system, the overflow of electrons is large. Therefore, by increasing the film thickness and increasing the optical confinement, the threshold Fermi level E ^F _th can be lowered, and thereby the overflow of electrons can be reduced, so that the threshold current density J _th can be reduced. Therefore, it is possible to effectively use the injection current up to 30 nm or less, and it is more preferable to make the thickness less than 10 nm.

Next, the manufacturing process of the semiconductor laser according to the first embodiment of the present invention will be briefly described with reference to FIG. 4. First, the (0001) plane, that is, the c plane is the main plane. On the n-type SiC substrate 11 made of hexagonal 6H—SiC, the growth pressure is increased by the MOVPE method using TMGa (trimethylgallium), TMAl (trimethylaluminum), ammonia, and hydrogen as the carrier gas as the growth gas. The AlGaN buffer layer 12 having a thickness of 50 to 300 nm, for example, 100 nm is grown in a state where the thickness is 70 to 760 Torr, for example, 100 Torr, and the growth temperature is 800 to 1200 ° C., for example, 950 ° C.

  Subsequently, using TMGa, ammonia and a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 920 ° C. A GaN intermediate layer 13 having a thickness of 2.0 μm, for example, 0.5 μm is grown.

Subsequently, TMAl, TMGa, ammonia, SiH ₄ as the dopant, and hydrogen as the carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 950 ° C. In this state, the thickness is 0.1 to 2.0 μm, for example, 0.5 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ²⁰ cm ⁻³ , for example, 1.0 × 10 ^18. An n-type Al _0.15 Ga _0.85 N clad layer 14 of cm ⁻³ is grown.

  Subsequently, using TMGa, ammonia, and hydrogen as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 930 ° C. An undoped GaN light guide layer 15 having a thickness of ˜300 nm, for example, 100 nm is grown.

Subsequently, using TEGa (triethylgallium), TMIn (trimethylindium), ammonia, and nitrogen as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 550 to 900 ° C., for example, SQW comprising an undoped In _0.15 Ga _0.85 N well layer having a thickness of 3 to 30 nm, for example, 8 nm, sandwiched between undoped In _0.05 Ga _0.95 N barrier layers having a thickness of 1 to 10 nm, for example, 5 nm, at 700 ° C. An active layer 16 is grown.

Subsequently, using TMGa, ammonia, biscyclopentadienyl magnesium and nitrogen as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 930 ° C. In this state, p-type GaN having a thickness of 10 to 300 nm, for example, 100 nm, and an impurity concentration of 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 5.0 × 10 ¹⁷ cm ^−3. The light guide layer 17 is grown.

Subsequently, using TMAl, TMGa, ammonia, biscyclopentadienylmagnesium, and nitrogen as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 950. At a temperature of 0.1 ° C., the thickness is 0.1 to 2.0 μm, for example, 0.5 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 5.0 × 10 ^{A 17} cm ⁻³ p-type Al _0.15 Ga _0.85 N cladding layer 18 is grown.

Subsequently, using TMGa, ammonia, biscyclopentadienyl magnesium and nitrogen as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 930 ° C. In this state, the thickness is 0.1 to 2.0 μm, for example, 0.5 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 1.0 × 10 ¹⁸ cm. ^-3 p-type GaN contact layer 19 is grown.

  Next, a Ni electrode 20 having a thickness of 100 nm is provided on the back surface of the n-type SiC substrate 11 as an n-side electrode, and an Ni electrode having a thickness of 100 nm and a width W of 10 μm is provided on the p-type GaN contact layer 19 as a p-side electrode. 21 and by dividing the element so that the resonator length L becomes 700 μm, a SQW structure short wavelength semiconductor laser is completed.

As described above, in the first embodiment of the present invention, the injection current can be effectively utilized by making the active layer a single SQW structure contrary to the conventional common sense, and the well layer, That is, the threshold current density _Jth can be reduced by setting the thickness of the gain layer to 8 nm and increasing the light confinement efficiency by using the light guide layer.

That is, when the gain layer thickness is 8 nm and the cavity loss is small, the SQW structure with the 8 nm well layer has a threshold value rather than the MQW structure with the two 4 nm well layers. The current density J _th can be reduced, and without the light guide layer, the light confinement coefficient Γ is reduced, and light oozes out to the cladding layer side, so that the threshold current density J _th becomes too high.

  In the description of the first embodiment, the thickness of the well layer, that is, the gain layer is 8 nm. However, as described with reference to FIG. 3, it may be 3 nm or more, and preferably 6 nm or more. On the other hand, in order to effectively use the injection current, 30 nm or less is preferable, and a range of less than 10 nm is more preferable.

Next, an MQW structure semiconductor laser according to a second embodiment of the present invention will be described with reference to FIG.
As shown in FIG. 5, first, similarly to the first embodiment, TMGa, TMAl are formed on an n-type SiC substrate 11 made of hexagonal 6H—SiC having a (0001) plane, that is, a c-plane as a main surface. In a state where the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 950 ° C., by MOVPE using ammonia and hydrogen as a carrier gas as a growth gas. An AlGaN buffer layer 12 having a thickness of 50 to 300 nm, for example, 100 nm is grown.

  Subsequently, using TMGa, ammonia and a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 920 ° C. A GaN intermediate layer 13 having a thickness of 2.0 μm, for example, 0.5 μm is grown.

Subsequently, using TMAl, TMGa, ammonia, SiH ₄ as a dopant, and H ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 950. At a temperature of 0.1 ° C., the thickness is 0.1 to 2.0 μm, for example, 0.5 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ²⁰ cm ⁻³ , for example, 1.0 × 10 ^{An 18} cm ⁻³ n-type Al _0.15 Ga _0.85 N cladding layer 14 is grown.

  Subsequently, using TMGa, ammonia, and hydrogen as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 930 ° C. An undoped GaN light guide layer 15 having a thickness of ˜300 nm, for example, 100 nm is grown.

Subsequently, TEGa, TMIn, ammonia, nitrogen as a carrier gas, a growth pressure of 70 to 760 Torr, for example, 100 Torr, and a growth temperature of 550 to 900 ° C., for example, 700 ° C. 10 nm, for example, undoped in _0.05 Ga _0.95 N barrier layers and a thickness of 5 nm 3 to 10 nm, for example, undoped in _0.15 Ga _0.85 N well layers is 2 or 3 layers alternately undoped in _0.15 Ga _0.85 N well layers of 8 nm, For example, the MQW active layer 22 is formed by growing to be two layers.

Subsequently, again as in the first embodiment, using TMGa, ammonia, biscyclopentadienylmagnesium, and nitrogen as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is increased. Is 800 to 1200 ° C., for example, 930 ° C., thickness is 10 to 300 nm, for example, 100 nm, and impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 5. A p-type GaN optical guide layer 17 having a size of 0 × 10 ¹⁷ cm ⁻³ is grown.

Subsequently, using TMAl, TMGa, ammonia, biscyclopentadienylmagnesium, and nitrogen as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 950. At a temperature of 0.1 ° C., the thickness is 0.1 to 2.0 μm, for example, 0.5 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 5.0 × 10 ^{A 17} cm ⁻³ p-type Al _0.15 Ga _0.85 N cladding layer 18 is grown.

Subsequently, using TMGa, ammonia, biscyclopentadienyl magnesium and nitrogen as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 930 ° C. In this state, the thickness is 0.1 to 2.0 μm, for example, 0.5 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 1.0 × 10 ¹⁸ cm. ^-3 p-type GaN contact layer 19 is grown.

  Next, a Ni electrode 20 having a thickness of 100 nm is provided on the back surface of the n-type SiC substrate 11 as an n-side electrode, and an Ni electrode having a thickness of 100 nm and a width W of 10 μm is provided on the p-type GaN contact layer 19 as a p-side electrode. 21 and by dividing the element so that the resonator length L becomes 700 μm, a SQW structure short wavelength semiconductor laser is completed.

As described above, in the second embodiment of the present invention, the active layer is composed of an MQW structure having two well layers. However, as is apparent from FIG. 2, the cavity loss is large. If the total thickness of the gain layer is the same, the threshold current density _Jth can be reduced by using a plurality of gain layers, and, as is clear from FIG. 30, the well layer By setting 2 to 3, the injection current can be used effectively, and the threshold current density _Jth can also be reduced.

  For example, in the second embodiment of the present invention, since the SiC is used as the growth substrate, the formation of the resonator surface is easy, but the sapphire substrate is used as in the conventional example shown in FIG. In this case, the cavity surface is increased by dry etching, so that the cavity loss increases. In such a case, it is effective to use the MQW structure as in the second embodiment. Become.

  In the description of the second embodiment, the thickness of the well layer, that is, the gain layer is 8 nm. However, as described with reference to FIG. 3, it is preferably 6 nm or more. Therefore, a range of 6 to 10 nm is desirable.

Although the first and second embodiments of the present invention have been described above, the present invention is not limited to the configurations described in the embodiments, and various modifications can be made within the scope of the technical idea. For example, in the first and second embodiments described above, In _0.15 Ga _0.85 N is adopted as the gain layer, but the mixed crystal ratio is changed to Al _x Ga _y In ₁₋ according to the required wavelength. _xy N (0 ≦ x <1, 0 <y ≦ 1) may be changed, and accordingly, the mixed crystal ratio of the light guide layer and the clad layer is changed to Al _a Ga _b In _{1. You} may change within the range of _-ab N (0 <= a <= 1, 0 <= b <= 1).

In the first and second embodiments, an undoped layer is used as a gain layer in order to increase the mobility of holes. In the case of an undoped layer, impurities are inevitably auto-doped. Therefore, the resulting impurity concentration may be less than 1.0 × 10 ¹⁷ cm ⁻³ .

In the first embodiment, the SQW structure using the In _0.05 Ga _0.95 N barrier layer is used. However, the light guide layer may be used as the barrier layer without using the barrier layer. .

  In the first and second embodiments, the light guide layer has a single-layer structure. However, a multi-layer structure may be used by using semiconductor layers having different compositions, and a graded band gap layer may be used. It may be used.

Next, referring to FIGS. 6 to 8, third to fifth embodiments of the present invention in which the threshold current density J _th is reduced by matching the maximum light emission gain position with the maximum position of the radiation intensity distribution. Will be described.
First, an MQW structure short wavelength semiconductor laser according to a third embodiment of the present invention will be described with reference to FIG.
See FIG. 6. First, TMGa, TMAl, ammonia, and hydrogen as a carrier gas are grown on an n-type SiC substrate 111 made of hexagonal 6H—SiC having a (0001) plane, that is, a c-plane as a main surface. An AlGaN buffer layer having a thickness of 50 to 300 nm, for example, 100 nm, with a growth pressure of 70 to 760 Torr, for example, 100 Torr, and a growth temperature of 800 to 1200 ° C., for example, 950 ° C., by the MOVPE method used as the gas. Grow 112.

  Subsequently, using TMGa, ammonia and a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 920 ° C. A GaN intermediate layer 113 having a thickness of 2.0 μm, for example, 0.5 μm is grown.

Subsequently, using TMAl, TMGa, ammonia, SiH ₄ as a dopant, and H ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 950. At a temperature of 0.1 ° C., the thickness is 0.1 to 2.0 μm, for example, 0.5 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ²⁰ cm ⁻³ , for example, 1.0 × 10 ^{An 18} cm ⁻³ n-type Al _0.15 Ga _0.85 N cladding layer 114 is grown.

Subsequently, using TMAl, TMGa, ammonia, and hydrogen as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 930 ° C. An undoped Al _0.05 Ga _0.95 N light guide layer 115 having a thickness of 10 to 300 nm, for example, 100 nm is grown.

Subsequently, using TMGa, TMIn, ammonia, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 550 to 900 ° C., for example, 700 ° C. thickness 1 to 10 nm, for example, 5 nm of undoped in _0.05 Ga _0.95 N barrier layers and thickness 3 to 10 nm, for example, undoped in _0.15 Ga _0.85 N well layers alternately undoped in _0.15 Ga _0.85 N well layers of 8nm 2 The MQW active layer 116 is formed by growing to 10 layers, for example, 5 layers.

Subsequently, using TMGa, ammonia, biscyclopentadienylmagnesium, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 930 ° C. P-type having a thickness of 10 to 300 nm, for example, 100 nm, and an impurity concentration of 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 5.0 × 10 ¹⁷ cm ⁻³ . A GaN light guide layer 117 is grown.

Subsequently, using TMAl, TMGa, ammonia, biscyclopentadienylmagnesium, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, In a state of 950 ° C., the thickness is 0.1 to 2.0 μm, for example, 0.5 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 5.0 × A p-type Al _0.15 Ga _0.85 N cladding layer 118 of 10 ¹⁷ cm ⁻³ is grown.

Subsequently, using TMGa, ammonia, biscyclopentadienylmagnesium, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 930 ° C. In this state, the thickness is 0.1 to 2.0 μm, for example, 0.5 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 1.0 × 10 ^18. A cm ⁻³ p-type GaN contact layer 119 is grown.

  Next, an Ni electrode 120 having a thickness of 100 nm is provided on the back surface of the n-type SiC substrate 111 as an n-side electrode, and an Ni electrode having a thickness of 100 nm and a width W of 10 μm is provided on the p-type GaN contact layer 119 as a p-side electrode. 121, and dividing the element so that the resonator length L is 700 μm, the MQW structure short wavelength semiconductor laser is completed.

Thus, in the third embodiment of the present invention, an undoped Al _0.05 Ga _0.95 N optical guide layer 115 having a larger forbidden bandwidth than the p-type GaN optical guide layer 117 is used as the n-side optical guide layer. Therefore, the refractive index on the n side becomes small, the radiated light intensity distribution shifts to the p side, and the maximum position of the radiated light intensity distribution matches the maximum gain position in the MQW active layer 116.
In this case, it is not always necessary to match exactly.

Therefore, the maximum position of the radiated light intensity distribution is located at the position where the maximum optical gain is generated, so that the light confinement efficiency is increased and the threshold current density _Jth can be reduced.

In the third embodiment, the undoped Al _0.05 Ga _0.95 N light guide layer 115 is used as the n-side light guide layer. However, the composition is not limited to this, and the composition can be changed as appropriate. In this case, the layer thickness may be adjusted as appropriate so that the maximum position of the radiated light intensity distribution comes to the position where the maximum optical gain is generated as the composition is changed.

Next, an MQW structure semiconductor laser according to a fourth embodiment of the present invention will be described with reference to FIG. 7, except for the composition of the third embodiment except for the composition of the n-type cladding layer and the n-side light guide layer. It is the same as the form.
Refer to FIG. 7. First, as in the third embodiment, a thickness of 50 is formed on an n-type SiC substrate 111 made of hexagonal 6H—SiC having a (0001) plane, that is, a c-plane as a principal plane. An AlGaN buffer layer 112 having a thickness of ˜300 nm, for example, 100 nm, and a GaN intermediate layer 113 having a thickness of 0.1 to 2.0 μm, for example, 0.5 μm are grown.

Subsequently, the flow rate ratio of TMAl is increased from that of the third embodiment, the thickness is 0.1 to 2.0 μm, for example, 0.5 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10. After growing the n-type Al _0.2 Ga _0.8 N cladding layer 122 of ²⁰ cm ⁻³ , for example, 1.0 × 10 ¹⁸ cm ⁻³ , the supply of TMAl and SiH ₄ is stopped, and the thickness is 10 to 300 nm. For example, a 100 nm undoped GaN light guide layer 123 is grown.

Thereafter, similarly to the third embodiment, the undoped In _0.05 Ga _0.95 N barrier layer having a thickness of 1 to 10 nm, for example, 5 nm, and the undoped In _0.15 Ga _0.85 N having a thickness of 3 to 10 nm, for example, 8 nm. The well layers are alternately grown so that there are 2 to 10 undoped In _0.15 Ga _0.85 N well layers, for example, 5 layers, thereby forming the MQW active layer 116.

Next, a p-type GaN light guide having a thickness of 10 to 300 nm, for example, 100 nm, and an impurity concentration of 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 5.0 × 10 ¹⁷ cm ^−3. The layer 117 has a thickness of 0.1 to 2.0 μm, for example, 0.5 μm, and an impurity concentration of 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 5.0 × 10 ¹⁷ cm ^{−. 3} p-type Al _0.15 Ga _0.85 N cladding layer 118 and a thickness of 0.1 to 2.0 μm, for example, 0.5 μm, and an impurity concentration of 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ^{−. 3.} For example, a p-type GaN contact layer 119 of 1.0 × 10 ¹⁸ cm ⁻³ is grown.

  Next, an Ni electrode 120 having a thickness of 100 nm is provided on the back surface of the n-type SiC substrate 111 as an n-side electrode, and an Ni electrode having a thickness of 100 nm and a width W of 10 μm is provided on the p-type GaN contact layer 119 as a p-side electrode. 121, and dividing the element so that the resonator length L is 700 μm, the MQW structure short wavelength semiconductor laser is completed.

As described above, in the fourth embodiment of the present invention, the light guide layer has a symmetric structure, but the n-type clad layer has a larger forbidden band than the p-type Al _0.15 Ga _0.85 N clad layer 118. Since the Al _0.2 Ga _0.8 N clad layer 122 is used, the refractive index on the n side becomes small, the radiated light intensity distribution shifts to the p side, and the maximum position of the radiated light intensity distribution and the maximum gain position in the MQW active layer 116 Matches.
In this case also, it is not always necessary to exactly match.

In the fourth embodiment, the n-type Al _0.2 Ga _0.8 N clad layer 122 is used as the n-type clad layer. However, the present invention is not limited to such a composition, and the composition may be changed as appropriate. In this case, the layer thickness and the like may be adjusted as appropriate so that the maximum position of the emitted light intensity distribution comes to the position where the maximum optical gain is generated with the change of the composition.

  In this case, the light guide layer does not necessarily have a symmetric structure, and the forbidden band width of the n-side light guide layer is larger than the forbidden band width of the p-side light guide layer as in the third embodiment. Alternatively, the maximum position of the emitted light intensity distribution may be moved to the p side by a synergistic effect of the n-side light guide layer and the n-type cladding layer.

Next, the SQW structure semiconductor laser according to the fifth embodiment of the present invention will be described with reference to FIG. 8, except for the composition of the n-side light guide layer, the structure of the active layer, and the overflow prevention layer. This is the same as the third embodiment.
First, as in the third embodiment, a thickness of 50 is formed on an n-type SiC substrate 111 made of hexagonal 6H—SiC having a (0001) plane, that is, a c-plane as a main surface. ˜300 nm, for example 100 nm, AlGaN buffer layer 112, thickness 0.1-2.0 μm, for example 0.5 μm GaN intermediate layer 113, and thickness 0.1-2.0 μm, for example 0.5 μm Then, an n-type Al _0.15 Ga _0.85 N cladding layer 114 having an impurity concentration of 1.0 × 10 ^{17 to} 1.0 × 10 ²⁰ cm ⁻³ , for example, 1.0 × 10 ¹⁸ cm ⁻³ is grown.

Subsequently, an undoped Al _0.05 Ga _0.95 N light guide layer 124 having a thickness of 10 to 300 nm, for example, 100 nm, is grown, and then sandwiched by an undoped In _0.05 Ga _0.95 N barrier layer having a thickness of 1 to 10 nm, for example, 5 nm. An SQW active layer 125 is formed by growing an undoped In _0.15 Ga _0.85 N well layer having a thickness of 3 to 10 nm, for example, 8 nm.

Next, p-type Al _0.2 Ga having a thickness of 5 to 50 nm, for example, 20 nm, and an impurity concentration of 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 5.0 × 10 ¹⁷ cm ^−3. _{A 0.8} N overflow prevention layer 126 is grown.

Thereafter, as in the third embodiment, the thickness is 10 to 300 nm, for example, 100 nm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 5. A p-type GaN light guide layer 117 of 0 × 10 ¹⁷ cm ⁻³ , a thickness of 0.1 to 2.0 μm, for example, 0.5 μm, and an impurity concentration of 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 5.0 × 10 ¹⁷ cm ⁻³ p-type Al _0.15 Ga _0.85 N cladding layer 118, a thickness of 0.1 to 2.0 μm, for example, 0.5 μm, and an impurity concentration of 1. A p-type GaN contact layer 119 having a size of 0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 1.0 × 10 ¹⁸ cm ⁻³ is grown.

  Next, an Ni electrode 120 having a thickness of 100 nm is provided on the back surface of the n-type SiC substrate 111 as an n-side electrode, and an Ni electrode having a thickness of 100 nm and a width W of 10 μm is provided on the p-type GaN contact layer 119 as a p-side electrode. The SQW structure short wavelength semiconductor laser is completed by providing 121 and dividing the element so that the resonator length L becomes 700 μm.

In this SQW semiconductor laser, the maximum position of the synchrotron radiation intensity distribution shifts to the n side due to the presence of the wide forbidden band-type p-type Al _0.2 Ga _0.8 N overflow prevention layer 126 provided to prevent the overflow of electrons. However, as described above, since the undoped Al _0.05 Ga _0.95 N light guide layer 124 having a larger forbidden band than the p-type GaN light guide layer 117 is used as the n-side light guide layer, the p-type Al _0.2 Ga is used. The influence of the _0.8 N overflow prevention layer 126 is offset and the radiated light intensity distribution is shifted to the p side, so that the maximum position of the radiated light intensity distribution and the center position of the SQW active layer 125 substantially coincide.
In this case also, it is not always necessary to exactly match.

In the fifth embodiment, the undoped Al _0.05 Ga _0.95 N light guide layer 124 is used as the n-side light guide layer. However, the composition is not limited to such a composition. According to the composition and the layer thickness, the composition and the layer thickness may be adjusted as appropriate so that the maximum position of the emitted light intensity distribution comes to the center position of the SQW active layer 125.

In the above fifth embodiment, the influence of the p-type Al _0.2 Ga _0.8 N overflow prevention layer 126 is offset by the n-side light guide layer, but the forbidden band width of the n-side cladding layer is set to the p-type. It may be offset by making it larger than the forbidden band width of the cladding layer.

In this case, the light guide layer does not necessarily have a symmetric structure. The forbidden band width of the n-side light guide layer is made larger than the forbidden band width of the p-side light guide layer, so that The influence of the p-type Al _0.2 Ga _0.8 N overflow prevention layer 126 may be offset by the synergistic effect of the cladding layer.

The third to fifth embodiments of the present invention have been described above. However, the present invention is not limited to the conditions described in the embodiments. For example, the above third to fifth embodiments are described. In the description of the embodiment, the MQW structure or SQW structure made of In _0.15 Ga _0.85 N / In _0.05 Ga _0.95 N is adopted as the active layer, but the mixed crystal ratio is changed to Al _x Ga _y according to the required wavelength. In _1-xy N (0 ≦ x <1, 0 <y ≦ 1) may be changed, and accordingly, the mixed crystal ratio of the light guide layer and the cladding layer is changed to Al _a Ga. _You may change within the range of bIn1 _-abN (0 <= a <= 1, 0 <= b <= 1).

  In the third to fifth embodiments, the p-side light guide layer and the n-side light guide layer have the same layer thickness, but the p-side light guide layer is thicker than the n-side light guide layer. For example, it may be formed to be 10 to 100 nm, for example, 50 nm thicker than the n-side guide layer to form an asymmetric light guide structure. In this case, the composition of the p-side light guide layer is changed to the n-side light guide. It may be the same as the composition of the layer.

In the above third to fifth embodiments, the light guide layer has a single layer structure, but it may have a multilayer structure or a graded band gap structure using semiconductor layers having different compositions. For example, in the case of the fifth embodiment, the n-side light guide layer is divided into two parts, an undoped GaN light guide layer having a thickness of 100 nm and an undoped Al _0.2 Ga _0.8 N light guide layer having a thickness of 20 nm from the n-type cladding layer side. A layer structure may be used.

Next, referring to FIGS. 9 to 14, the threshold current density J _th is reduced by increasing the hole mobility in the p-side light guide layer or by reducing the recombination probability in the p-side light guide layer. Sixth to eleventh embodiments of the present invention will be described.
First, an SQW structure short wavelength semiconductor laser according to a sixth embodiment of the present invention will be described with reference to FIG.
See FIG. 9. First, TMGa, TMAl, ammonia, and hydrogen as a carrier gas are grown on an n-type SiC substrate 211 made of hexagonal 6H—SiC having a (0001) plane, that is, a c-plane as a main surface. An AlGaN buffer layer having a thickness of 50 to 300 nm, for example 50 nm, with a growth pressure of 70 to 760 Torr, for example, 100 Torr and a growth temperature of 800 to 1200 ° C., for example, 950 ° C., by the MOVPE method used as the gas. Grow 212.

Subsequently, using TMGa, ammonia, SiH ₄ as the dopant source, and hydrogen as the carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 920 ° C. And an n-type GaN intermediate layer having a thickness of 0.1 to 2.0 μm, for example, 0.5 μm, and an impurity concentration of 5 × 10 ¹⁷ to 1 × 10 ¹⁹ cm ⁻³ , for example, 2 × 10 ¹⁸ cm ^−3. Grow 213.

Subsequently, using TMAl, TMGa, ammonia, SiH ₄ as a dopant, and hydrogen as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 950 ° C. In this state, the thickness is 0.1 to 2.0 μm, for example, 0.5 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ²⁰ cm ⁻³ , for example, 1.0 × 10 ¹⁸ cm. ^-3 n-type Al _0.15 Ga _0.85 N cladding layer 214 is grown.

  Subsequently, using TMGa, ammonia, and hydrogen as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 930 ° C. An undoped GaN light guide layer 215 of ˜300 nm, for example, 100 nm is grown.

Subsequently, using TMGa, TMIn, ammonia, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 550 to 900 ° C., for example, 700 ° C. An SQW active layer 216 is formed by growing an undoped In _0.15 Ga _0.85 N well layer having a thickness of 3 to 30 nm, for example, 5 nm, sandwiched between undoped In _0.05 Ga _0.95 N barrier layers having a thickness of 1 to 10 nm, for example, 5 nm. To do.

Subsequently, using TMGa, ammonia, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 1130 ° C. An undoped GaN light guide layer 217 having a thickness of 10 to 300 nm, for example, 100 nm is grown.

Subsequently, using TMAl, TMGa, ammonia, biscyclopentadienylmagnesium, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, In a state of 950 ° C., the thickness is 0.1 to 2.0 μm, for example, 0.5 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 2.0 × A 10 ¹⁷ cm ⁻³ p-type Al _0.15 Ga _0.85 N cladding layer 218 is grown.

Subsequently, using TMGa, ammonia, biscyclopentadienylmagnesium, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 930 ° C. In this state, the thickness is 0.1 to 2.0 μm, for example, 0.5 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 1.0 × 10 ^18. A cm ⁻³ p-type GaN contact layer 219 is grown.

  Next, a Ni electrode 220 having a thickness of 100 nm is provided as an n-side electrode on the back surface of the n-type SiC substrate 211, and a Ni electrode having a thickness of 100 nm and a width W of 3 μm is provided as a p-side electrode on the p-type GaN contact layer 219. The SQW structure short wavelength semiconductor laser is completed by providing elements 221 and dividing the element so that the resonator length L becomes 700 μm.

  In the sixth embodiment of the present invention, the p-side light guide layer is composed of an undoped layer contrary to conventional common sense, and there is no carrier scattering due to impurities, so that the hole mobility is improved. Thereby, improvement of hole injection efficiency is expected.

  In addition, when the p-side light guide layer is an undoped layer, there is no deterioration of the crystal due to impurity doping, and therefore recombination that does not contribute to laser oscillation in the p-side light guide layer can be greatly reduced. .

  As a result, since the reactive current in the p-side light guide layer is reduced, a short wavelength semiconductor laser with a low threshold current density can be manufactured, and the generation of heat due to the reactive current is suppressed. The reliability of the short wavelength semiconductor laser can be improved.

The undoped in this case does not have to be pure undoped, and may be a mixture of some impurities during the growth process. For example, 2 cm considered to be necessary for laser oscillation as the hole mobility. ² / V · s or more is sufficient, and for example, an impurity concentration of 1 × 10 ¹⁷ cm ⁻³ or less is sufficient.

Next, a seventh embodiment of the present invention will be described with reference to FIG.
The seventh embodiment is the same as the sixth embodiment except for the thickness of the p-side light guide layer, and thus the description of the manufacturing method is omitted.
First, as in the sixth embodiment, a thickness of 50 is formed on an n-type SiC substrate 211 made of hexagonal 6H—SiC having a (0001) plane, that is, a c-plane as a main surface. AlGaN buffer layer 212 of ~ 300 nm, for example 50 nm, thickness of 0.1 to 2.0 μm, for example 0.5 μm, and impurity concentration of 5 × 10 ¹⁷ to 1 × 10 ¹⁹ cm ⁻³ , for example 2 × 10 ¹⁸ cm ⁻³ Si-doped n-type GaN intermediate layer 213 and a thickness of 0.1 to 2.0 μm, for example, 0.5 μm, and an impurity concentration of 1.0 × 10 ^{17 to} 1.0 × 10 ²⁰ A Si-doped n-type Al _0.15 Ga _0.85 N cladding layer 214 having a thickness of cm ⁻³ , for example, 1.0 × 10 ¹⁸ cm ⁻³ is grown.

Subsequently, after growing an undoped GaN light guide layer 215 having a thickness t _{n of 10} to 300 nm, for example, 100 nm, it was sandwiched by an undoped In _0.05 Ga _0.95 N barrier layer having a thickness of 1 to 10 nm, for example, 5 nm. An SQW active layer 216 is formed by growing an undoped In _0.15 Ga _0.85 N well layer having a thickness of 3 to 30 nm, for example, 5 nm.

Next, an undoped GaN light guide layer 217 having a thickness t _p of 100 nm or less, for example, 80 nm, a thickness of 0.1 to 2.0 μm, for example, 0.5 μm, and an impurity concentration of 1.0 × 10 ¹⁷ to 1. Mg doped p-type Al _0.15 Ga _0.85 N clad layer 218 with a thickness of 0 × 10 ¹⁹ cm ⁻³ , for example, 2.0 × 10 ¹⁷ cm ⁻³ , and a thickness of 0.1 to 2.0 μm, for example, An Mg-doped p-type GaN contact layer 219 having an impurity concentration of 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 1.0 × 10 ¹⁸ cm ⁻³ is grown at 5 μm.

  Next, a Ni electrode 220 having a thickness of 100 nm is provided as an n-side electrode on the back surface of the n-type SiC substrate 211, and a Ni electrode having a thickness of 100 nm and a width W of 3 μm is provided as a p-side electrode on the p-type GaN contact layer 219. The SQW structure short wavelength semiconductor laser is completed by providing elements 221 and dividing the element so that the resonator length L becomes 700 μm.

In the seventh embodiment, since the layer thickness t _p of the p-side light guide layer is smaller than the layer thickness t _n of the n-side light guide layer, that is, t _p <t _n , the p-side light guide layer Since the recombination current at is reduced, and the reactive current can be reduced, the threshold current density J _th can be reduced.

In particular, the recombination in the p-side light guide layer is achieved by reducing the thickness t _p of the p-side light guide layer to less than 100 nm (less than 0.1 μm), more preferably 0.08 μm or less (80 nm or less). Since the current decreases, and thereby the reactive current can be decreased, the threshold current density _Jth can be decreased.
When the layer thickness t _p of the p-side light guide layer is less than 100 nm, t _p = t _n may be set, thereby correcting the asymmetry of the light guide structure.

  In this case, the composition of the p-side light guide layer and the n-side light guide layer is not necessarily the same, and the forbidden band width of the p-side light guide layer is larger than the forbidden band width of the n-side light guide layer. By setting the composition, the overflow of electrons can be prevented, while the composition is set so that the forbidden band width of the n-side light guide layer is larger than the forbidden band width of the p-side light guide layer. The asymmetry of the light guide structure accompanying the thinning of the p-side light guide layer can be corrected.

  In the seventh embodiment, since the p-side light guide layer is undoped, the same effect of improving the hole mobility as in the sixth embodiment can be obtained. The p-side light guide layer may be doped p-type.

Next, an eighth embodiment of the present invention will be described with reference to FIG.
FIG. 11A is a perspective view of the SQW semiconductor laser according to the eighth embodiment of the present invention, and FIG. 14B is a band gap structure in the vicinity of the active layer, that is, the conduction band side. It shows the energy level.
Also in the eighth embodiment, since the structure is substantially the same as that of the sixth embodiment except for the structure of the n-side light guide layer and the p-side light guide layer, the description of the manufacturing method is omitted.
First, as in the sixth embodiment, on the n-type SiC substrate 211 made of hexagonal 6H—SiC having the (0001) plane, that is, the c-plane as the principal plane, AlGaN buffer layer 212 having a thickness of 50 to 300 nm, for example, 50 nm, a thickness of 0.1 to 2.0 μm, for example, 0.5 μm, and an impurity concentration of 5 × 10 ¹⁷ to 1 × 10 ¹⁹ cm ⁻³ , for example, 2 × 10 ¹⁸ cm ⁻³ Si-doped n-type GaN intermediate layer 213 and a thickness of 0.1 to 2.0 μm, for example, 0.5 μm, and an impurity concentration of 1.0 × 10 ^{17 to} 1.0 A Si-doped n-type Al _0.15 Ga _0.85 N cladding layer 214 of × 10 ²⁰ cm ⁻³ , for example, 1.0 × 10 ¹⁸ cm ⁻³ is grown.

Subsequently, an undoped Al _0.05 Ga _0.95 N optical guide layer 222 having a thickness of 10 to 100 nm, for example, 50 nm, and an undoped In _0.03 Ga _0.97 N optical guide layer 223 having a thickness of 10 to 100 nm, for example, 50 nm, are sequentially grown. Subsequently, an SQW activity is obtained by growing an undoped In _0.15 Ga _0.85 N well layer having a thickness of 3 to 30 nm, for example, 5 nm, sandwiched between undoped In _0.05 Ga _0.95 N barrier layers having a thickness of 1 to 10 nm, for example, 5 nm. Layer 216 is formed.

Next, an undoped In _0.03 Ga _0.97 N light guide layer 224 having a thickness of 10 to 100 nm, for example, 50 nm, and an impurity concentration of 1 × 10 ¹⁷ to 1 × 10 ¹⁹ cm ^{− with} a thickness of 10 to 100 nm, for example, 50 nm. ^3. For example, a 5 × 10 ¹⁷ cm ⁻³ Mg-doped p-type Al _0.05 Ga _0.95 N light guide layer 225, a thickness of 0.1 to 2.0 μm, for example, 0.5 μm, and an impurity concentration of 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ^-3 , for example, 1.0 × 10 ¹⁷ cm ^-3 Mg-doped p-type Al _0.15 Ga _0.85 N cladding layer 218 and a thickness of 0.1 to 2. Mg-doped p-type GaN contact layer 219 having an impurity concentration of 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 1.0 × 10 ¹⁸ cm ⁻³ at 0 μm, for example, 0.5 μm. Grow.

  Next, a Ni electrode 220 having a thickness of 100 nm is provided as an n-side electrode on the back surface of the n-type SiC substrate 211, and a Ni electrode having a thickness of 100 nm and a width W of 3 μm is provided as a p-side electrode on the p-type GaN contact layer 219. The SQW structure short wavelength semiconductor laser is completed by providing elements 221 and dividing the element so that the resonator length L becomes 700 μm.

In FIG. 11B, in the eighth embodiment, the n-side light guide layer and the p-side light guide layer have a two-layer structure with different forbidden band widths, and the forbidden side on the side adjacent to the clad layer. Since the band width is increased, the p-type Al _0.05 Ga _0.95 N light guide layer 225 constituting the p-side light guide layer also functions as an overflow prevention layer for electrons, while ensuring light confinement necessary for laser oscillation. , p-type Al _0.05 Ga _0.95 N optical guiding layer 225, or it is possible to reduce the electron leakage to the p-type cladding layer, whereby it is possible to reduce the reactive current, the threshold current density J _th It becomes possible to reduce.

  In the eighth embodiment, the p-side light guide layer having a larger forbidden bandwidth is formed of a p-type layer. However, similarly to the sixth embodiment, the p-side light guide layer is formed of an undoped layer. In this case, the mobility of holes can be increased, and the p-side light guide layer or the n-side light guide layer may be composed of a multilayer structure of three or more layers. The number of layers of the p-side light guide layer and the n-side light guide layer may not be the same.

Next, a ninth embodiment of the present invention will be described with reference to FIG.
FIG. 12A is a perspective view of the SQW semiconductor laser according to the ninth embodiment of the present invention, and FIG. 12B is a band gap structure in the vicinity of the active layer, that is, the conduction band side. It shows the energy level.
The ninth embodiment is the same as the third embodiment except for the structure of the n-side light guide layer, and a description of the manufacturing method is omitted.
First, as in the first embodiment, on the n-type SiC substrate 211 made of hexagonal 6H—SiC having the (0001) plane, that is, the c-plane as the principal plane, AlGaN buffer layer 212 having a thickness of 50 to 300 nm, for example, 50 nm, a thickness of 0.1 to 2.0 μm, for example, 0.5 μm, and an impurity concentration of 5 × 10 ¹⁷ to 1 × 10 ¹⁹ cm ⁻³ , for example, 2 × 10 ¹⁸ cm ⁻³ Si-doped n-type GaN intermediate layer 213 and a thickness of 0.1 to 2.0 μm, for example, 0.5 μm, and an impurity concentration of 1.0 × 10 ^{17 to} 1.0 A Si-doped n-type Al _0.15 Ga _0.85 N cladding layer 214 of × 10 ²⁰ cm ⁻³ , for example, 1.0 × 10 ¹⁸ cm ⁻³ is grown.

Subsequently, after growing a GaN light guide layer 226 having a thickness of 10 to 300 nm, for example, 100 nm, a thickness of 3 to 10 sandwiched between undoped In _0.05 Ga _0.95 N barrier layers having a thickness of 1 to 10 nm, for example, 5 nm. An SQW active layer 216 is formed by growing an undoped In _0.15 Ga _0.85 N well layer of 30 nm, for example, 5 nm.

Next, an undoped In _0.03 Ga _0.97 N light guide layer 224 having a thickness of 10 to 100 nm, for example, 50 nm, and an impurity concentration of 1 × 10 ¹⁷ to 1 × 10 ¹⁹ cm ^{− with} a thickness of 10 to 100 nm, for example, 50 nm. ³ , for example, 2 × 10 ¹⁷ cm ⁻³ Mg-doped p-type Al _0.05 Ga _0.95 N light guide layer 225, thickness 0.1-2.0 μm, for example 0.5 μm, impurity concentration 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ^-3 , for example, 1.0 × 10 ¹⁷ cm ^-3 Mg-doped p-type Al _0.15 Ga _0.85 N cladding layer 218 and a thickness of 0.1 to 2. Mg-doped p-type GaN contact layer 219 having an impurity concentration of 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 1.0 × 10 ¹⁸ cm ⁻³ at 0 μm, for example, 0.5 μm. Grow.

  Next, a Ni electrode 220 having a thickness of 100 nm is provided as an n-side electrode on the back surface of the n-type SiC substrate 211, and a Ni electrode having a thickness of 100 nm and a width W of 3 μm is provided as a p-side electrode on the p-type GaN contact layer 219. The SQW structure short wavelength semiconductor laser is completed by providing elements 221 and dividing the element so that the resonator length L becomes 700 μm.

In FIG. 12B, in the ninth embodiment, since the n-side light guide layer is composed of a single layer, the film forming process can be shortened, and the composition of the n-side light guide layer can be shortened. Since the composition is such that a forbidden band width in the middle of the p-side light guide layer can be obtained, the asymmetry of the light guide structure can be corrected even if a single layer is used, so that the maximum optical gain is generated. Since the maximum position of the emitted light intensity distribution is located, the threshold current density J _th can be reduced.

Also in this case, the p-type Al _0.05 Ga _0.95 N light guide layer 225 constituting the p-side light guide layer also functions as an overflow prevention layer for electrons, so that the p-type is ensured while ensuring the optical confinement necessary for laser oscillation. Electron leakage to the Al _0.05 Ga _0.95 N light guide layer 225 or the p-type cladding layer can be reduced, thereby reducing the reactive current, thereby reducing the threshold current density J _th. Is possible.

  In the ninth embodiment as well, the p-side light guide layer having a larger forbidden bandwidth is formed of a p-type layer. However, similarly to the sixth embodiment, it is formed of an undoped layer. As a result, the hole mobility can be increased, and the p-side light guide layer may be composed of a multilayer structure of three or more layers.

Next, a tenth embodiment of the present invention will be described with reference to FIG.
FIG. 13A is a perspective view of the SQW semiconductor laser according to the tenth embodiment of the present invention, and FIG. 13B shows a band gap structure in the vicinity of the active layer.
The tenth embodiment is the same as the sixth embodiment except for the structure of the n-side light guide layer and the p-side light guide layer.
First, as in the sixth embodiment, on the n-type SiC substrate 211 made of hexagonal 6H—SiC having the (0001) plane, that is, the c-plane as the principal plane, AlGaN buffer layer 212 having a thickness of 50 to 300 nm, for example, 50 nm, a thickness of 0.1 to 2.0 μm, for example, 0.5 μm, and an impurity concentration of 5 × 10 ¹⁷ to 1 × 10 ¹⁹ cm ⁻³ , for example, 2 × 10 ¹⁸ cm ⁻³ Si-doped n-type GaN intermediate layer 213 and a thickness of 0.1 to 2.0 μm, for example, 0.5 μm, and an impurity concentration of 1.0 × 10 ^{17 to} 1.0 A Si-doped n-type Al _0.15 Ga _0.85 N cladding layer 214 of × 10 ²⁰ cm ⁻³ , for example, 1.0 × 10 ¹⁸ cm ⁻³ is grown.

Subsequently, using TMGa, TMIn, TMAl, ammonia, and hydrogen as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 1130 ° C. First, supply TMAl in a state where TMIn is not supplied and gradually decrease TMAl. When TMAl supply is reduced to 0, the temperature is lowered to 800 ° C. and TMIn supply is started, and the supply amount is gradually increased. Therefore, the composition of the portion in contact with the n-type Al _0.15 Ga _0.85 N cladding layer 214 becomes Al _0.05 Ga _0.95 N, and the final composition becomes In _0.03 Ga _0.97 N. The undoped gray with a thickness of 10 to 300 nm, for example, 100 nm A dead light guide layer 227 is grown.

Subsequently, an SQW activity is obtained by growing an undoped In _0.15 Ga _0.85 N well layer having a thickness of 3 to 10 nm, for example, 5 nm, sandwiched by an undoped In _0.05 Ga _0.95 N barrier layer having a thickness of 1 to 10 nm, for example, 5 nm. Layer 216 is formed.

Subsequently, using TMGa, TMIn, TMAl, ammonia, biscyclopentadienylmagnesium, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C. For example, in a state where the temperature is set to 800 ° C., TMAl is first supplied in a state where TMAl is not supplied and TMIn is gradually decreased. When the TMIn supply is set to 0, the temperature is raised to 1130 ° C. and the supply of TMAl is started. By gradually increasing the supply amount, the composition of the portion in contact with the SQW active layer 216 becomes In _0.03 Ga _0.97 N, and the final composition becomes Al _0.05 Ga _0.95 N. The thickness is 10 to 300 nm, for example, 100 nm. A Mg-doped p-type graded light guide layer 228 is grown.

Subsequently, the thickness is 0.1 to 2.0 μm, for example, 0.5 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 1.0 × 10 ¹⁷ cm ^{−. 3} Mg-doped p-type Al _0.15 Ga _0.85 N clad layer 218 and a thickness of 0.1 to 2.0 μm, for example, 0.5 μm, and an impurity concentration of 1.0 × 10 ^{17 to} 1.0 × 10 An Mg-doped p-type GaN contact layer 219 of ¹⁹ cm ⁻³ , for example, 1.0 × 10 ¹⁸ cm ⁻³ is grown.

  Next, a Ni electrode 220 having a thickness of 100 nm is provided as an n-side electrode on the back surface of the n-type SiC substrate 211, and a Ni electrode having a thickness of 100 nm and a width W of 3 μm is provided as a p-side electrode on the p-type GaN contact layer 219. The SQW structure short wavelength semiconductor laser is completed by providing elements 221 and dividing the element so that the resonator length L becomes 700 μm.

See FIG. 13B. In the tenth embodiment, the p-side light guide layer is composed of a graded band gap layer whose composition changes continuously, and the p-type cladding layer side is forbidden. The region having a large bandwidth acts as an overflow prevention layer for electrons, and the hole injection efficiency into the active layer is improved.

  Also in this case, the p-type graded light guide layer 228 that constitutes the p-side light guide layer is composed of the p-type layer, but it is composed of an undoped layer as in the sixth embodiment. Accordingly, the mobility of holes can be increased, and the active layer side can be undoped by continuously changing the supply amount of biscyclopentadienylmagnesium.

In the tenth embodiment, the Al ratio of the portions of the undoped graded light guide layer 227 and the p-type graded light guide layer 228 in contact with the cladding layer is Al _0.05 Ga _0.95 N of _0.05 . However, the Al _0.15 Ga _0.85 N of 0.15, which is the same as the Al ratio of the clad layer, or an AlGaN layer having a mixed crystal ratio in the vicinity thereof may be used. In this way, the Al ratio of the portion in contact with the clad layer is increased. As a result, the hole injection efficiency can be further improved.

Next, an eleventh embodiment of the present invention will be described with reference to FIG.
14A is a perspective view of the SQW semiconductor laser according to the eleventh embodiment of the present invention, and FIG. 14B is a band gap structure in the vicinity of the active layer, that is, the conduction band side. It shows the energy level.
The eleventh embodiment is substantially the same as the ninth embodiment except for the structure of the p-side light guide layer.
14A. First, similarly to the sixth embodiment, on the n-type SiC substrate 211 made of hexagonal 6H—SiC having the (0001) plane, that is, the c-plane as a main surface, AlGaN buffer layer 212 having a thickness of 50 to 300 nm, for example, 50 nm, a thickness of 0.1 to 2.0 μm, for example, 0.5 μm, and an impurity concentration of 5 × 10 ¹⁷ to 1 × 10 ¹⁹ cm ⁻³ , for example, 2 × 10 ¹⁸ cm ⁻³ Si-doped n-type GaN intermediate layer 213 and a thickness of 0.1 to 2.0 μm, for example, 0.5 μm, and an impurity concentration of 1.0 × 10 ^{17 to} 1.0 A Si-doped n-type Al _0.15 Ga _0.85 N cladding layer 214 of × 10 ²⁰ cm ⁻³ , for example, 1.0 × 10 ¹⁸ cm ⁻³ is grown.

Subsequently, an undoped Al _0.05 Ga _0.95 N light guide layer 229 having a thickness of 10 to 300 nm, for example, 100 nm is grown, and then sandwiched by an undoped In _0.05 Ga _0.95 N barrier layer having a thickness of 1 to 10 nm, for example, 5 nm. An SQW active layer 216 is formed by growing an undoped In _0.15 Ga _0.85 N well layer having a thickness of 3 to 30 nm, for example, 5 nm.

Subsequently, using TMGa, TMIn, TMAl, ammonia, biscyclopentadienylmagnesium, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C. For example, in a state where the temperature is 1130 ° C., TMAl is supplied so as to gradually decrease, the composition of the portion in contact with the SQW active layer 216 becomes Al _0.20 Ga _0.8O N, and the final composition becomes GaN. A 300 nm, for example, 100 nm Mg-doped p-type reverse graded light guide layer 230 is grown.
The composition on the side in contact with the p-type cladding layer may be InGaN.

Then, the thickness is 0.1 to 2.0 μm, for example, 0.5 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 1.0 × 10 ¹⁷ cm ^−3. Mg-doped p-type Al _0.15 Ga _0.85 N cladding layer 218 and a thickness of 0.1 to 2.0 μm, for example, 0.5 μm, and an impurity concentration of 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ An Mg-doped p-type GaN contact layer 219 of cm ⁻³ , for example, 1.0 × 10 ¹⁸ cm ⁻³ is grown.

  Next, a Ni electrode 220 having a thickness of 100 nm is provided as an n-side electrode on the back surface of the n-type SiC substrate 211, and a Ni electrode having a thickness of 100 nm and a width W of 3 μm is provided as a p-side electrode on the p-type GaN contact layer 219. The SQW structure short wavelength semiconductor laser is completed by providing elements 221 and dividing the element so that the resonator length L becomes 700 μm.

See FIG. 14B. In the eleventh embodiment, the p-side light guide layer is constituted by an inverse graded layer having a large forbidden bandwidth on the active layer side. Since the region having a large forbidden band width functions as an overflow prevention layer for electrons, leakage of electrons to the p-side light guide layer can be reduced, thereby reducing recombination in the p-side light guide layer. Can do.

  In addition, since the p-side light guide layer has an inverse graded band gap structure, energy spikes for holes are not formed. Therefore, the p-side light guide layer is less likely to be a barrier to holes compared to conventional overflow prevention layers, and hole injection efficiency. Is not reduced.

  Also in this case, since the n-side light guide layer is composed of a single layer, in order to correct the asymmetry of the light guide structure, the composition of the n-side light guide layer is set to the middle of the p-side light guide layer. It is desirable that the composition has a forbidden bandwidth.

  Also in this case, the p-side light guide layer is composed of a p-type layer, but it may be composed of an undoped layer in the same manner as in the sixth embodiment, thereby increasing the hole mobility. Can be bigger.

Although the sixth to eleventh embodiments of the present invention have been described above, the present invention is not limited to the configuration of the embodiment. For example, in the sixth to eleventh embodiments, the active adopts a SQW structure consisting of _{in 0.15 Ga 0.85 N / in 0.05} Ga 0.95 N as a layer, requires a mixed crystal ratio according to the wavelength of the _{Al x Ga y in 1-xy} N (0 ≦ x <1 , 0 <y ≦ 1), and accordingly, the mixed crystal ratio of the light guide layer and the cladding layer is changed to Al _a Ga _b In _1-ab N (0 ≦ a ≦ It may be changed within the range of 1, 0 ≦ b ≦ 1).

In the sixth to eleventh embodiments described above, the active layer has an SQW structure, but may have an MQW structure. In this case, for example, the thickness is 1 to 10 nm. For example, 5 nm of undoped In _0.05 Ga _0.95 N barrier layer and a thickness of 3 to 10 nm, for example, 5 nm of undoped In _0.15 Ga _0.85 N well layer alternately with 2 to 10 undoped In _0.15 Ga _0.85 N well layers, for example, The MQW active layer may be formed by growing it to have 5 layers.

Next, referring to FIGS. 15 and 16, the twelfth embodiment of the present invention that reduces the dislocation density and the PL wavelength distribution by controlling the growth rate, thereby reducing the threshold current density J _th. A method of manufacturing a short wavelength semiconductor laser of the form will be described.
Refer to FIG. 15. First, the surface of an n-type SiC substrate 311 made of hexagonal 6H—SiC having a (0001) plane, that is, a c-plane as a principal plane is 0.1 to 2 μm by dry etching using CF ₄ . For example, after removing 0.2 μm to reduce the surface defect density, the growth pressure is set to 70 to 760 Torr, for example, by MOVPE using TMGa, TMAl, ammonia, and hydrogen as a carrier gas as a growth gas. The AlGaN buffer layer 312 having a thickness of 50 to 300 nm, for example, 50 nm is grown at 100 Torr and a growth temperature of 800 to 1200 ° C., for example, 950 ° C.

Subsequently, using TMGa, ammonia, SiH ₄ as a dopant, and a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 920 ° C. Si having a thickness of 0.1 to 2.0 μm, for example, 0.5 μm, and an impurity concentration of 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 2.0 × 10 ¹⁸ cm ⁻³ A doped n-type GaN intermediate layer 313 is grown.

Subsequently, TMAl, TMGa, ammonia, SiH ₄ as the dopant, and hydrogen as the carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 950 ° C. In this state, the thickness is 0.1 to 2.0 μm, for example, 0.5 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ²⁰ cm ⁻³ , for example, 1.0 × 10 ^18. A cm ⁻³ n-type Al _0.15 Ga _0.85 N cladding layer 314 is grown.

  Subsequently, using TMGa, ammonia, and hydrogen as a carrier gas, a growth pressure of 70 to 760 Torr, for example, 100 Torr, a growth temperature of 800 to 1200 ° C., for example, 930 ° C., and a thickness of 10 An undoped GaN light guide layer 315 of ˜300 nm, for example, 100 nm is grown.

Subsequently, using TEGa, TMIn, ammonia, and nitrogen as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 550 to 900 ° C., for example, 700 ° C. the rate r _g 0.1 [mu] m / h or more, for example, under the above conditions 0.3 [mu] m / h, thickness of 1 to 10 nm, for example, 5 nm of undoped in _0.03 Ga _0.97 N barrier layer and the thickness of 3 to 10 nm, for example, An 8 nm undoped In _0.15 Ga _0.85 N well layer is alternately grown so that there are two or three undoped In _0.15 Ga _0.85 N well layers, for example, two layers to form an MQW active layer 316.

  Subsequently, using TMGa, ammonia, and nitrogen as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 930 ° C. An undoped GaN light guide layer 317 of ˜300 nm, for example, 100 nm is grown.

Subsequently, using TMAl, TMGa, ammonia, biscyclopentadienylmagnesium, and nitrogen as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 950. At a temperature of 0.1 ° C., the thickness is 0.1 to 2.0 μm, for example, 0.5 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 2.0 × 10 ^{A 17} cm ⁻³ p-type Al _0.15 Ga _0.85 N cladding layer 318 is grown.

Subsequently, using TMGa, ammonia, biscyclopentadienyl magnesium and nitrogen as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 930 ° C. In this state, the thickness is 0.1 to 2.0 μm, for example, 0.5 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 1.0 × 10 ¹⁸ cm. ^-3 p-type GaN contact layer 319 is grown.

  Next, an Ni electrode 320 having a thickness of 100 nm is provided on the back surface of the n-type SiC substrate 311 as an n-side electrode, and an Ni electrode having a thickness of 100 nm and a width W of 3 μm is provided on the p-type GaN contact layer 319 as a p-side electrode. The MQW structure short wavelength semiconductor laser is completed by providing the element 321 and dividing the element so that the resonator length L becomes 700 μm.

In the above twelfth embodiment, the growth rate of the active layer is 0.1 μm / h or more, particularly 0.3 μm / h. Here, referring to FIG. Explain the causal relationship between crystallinity and growth rate.
Figure 16 (a) see Figure 16 (a) is a diagram showing the growth rate dependence of the standard deviation of the PL wavelengths of the InGaN active layer, as is apparent from the figure, the growth rate r _g is 0.1 [mu] m / h In the following case of 0.075 μm / h, as the flow rate of TMI (trimethylindium) increases, the standard deviation of the PL wavelength increases and the inhomogeneous composition of InGaN increases, and the average PL wavelength composition of 400 nm or more However, it is clear that a high quality InGaN mixed crystal cannot be obtained.

On the other hand, if the growth rate r _g is 0.1 [mu] m / h or more 0.3 [mu] m / h, the standard deviation of the PL wavelengths even flow of TMI is increased to increase the average PL wavelength remain small, i.e., The In composition ratio increases, and the standard deviation of the PL wavelength decreases near 420 nm.

  From this, it can be seen that the compositional nonuniformity can be suppressed by increasing the growth rate, and at least in the case of a growth rate in the vicinity of 0.3 μm / h, an InGaN active having a composition in a wavelength range suitable as a blue semiconductor laser. It can be seen that the layer can be grown with good crystallinity.

FIG. 16B is a diagram showing the dependence of the PL light intensity on the growth rate. As is clear from the figure, the PL light intensity increases as the growth rate increases. A relatively large PL light intensity is obtained on the long wavelength side suitable as a blue semiconductor laser. From this fact, it can be seen that a crystal having a more uniform composition can be obtained with a higher growth rate.

According to the twelfth embodiment of the present invention, a dislocation density of 10 ⁹ is obtained by using a SiC substrate with good quality and removing the surface by dry etching to reduce the surface defect density. An InGaN active layer having a cm ⁻³ or less and a PL peak wavelength of 90 meV or less is obtained, thereby obtaining an IL characteristic without kink.

Then, based on the experience to date, the growth rate r _g is compared with results for 0.075 .mu.m / h, it is estimated to very good active layer is obtained in the case of more than 0.3 [mu] m / h Also, it is considered that a good active layer can be obtained at least up to 0.2 μm / h, and an active layer that can withstand practical use even at 0.1 μm / h.

  This is contrary to the conventional common sense that it is believed that the slower the growth rate, the more homogeneous crystals can be obtained. Also from this point, the peculiarities of nitride compound semiconductors containing In as a constituent element are clear. .

The twelfth embodiment of the present invention has been described above. However, the present invention is not limited to the conditions of the twelfth embodiment, and various modifications are possible within the scope of the technical idea. in the twelfth embodiment adopts the in _0.15 Ga _0.85 N as the well layer, the Al _x mixed crystal ratio according to a wavelength in need _{Ga y in 1-xy N (} 0 ≦ x <1 , 0 <y ≦ 1), and accordingly, the mixed crystal ratio of the light guide layer and the cladding layer is changed to Al _a Ga _b In _1-ab N (0 ≦ a ≦ It may be changed within the range of 1, 0 ≦ b ≦ 1).

In the description of the twelfth embodiment, the active layer is composed of the MQW active layer 16, but the SQW active layer may be used. In this case as well, the growth rate is 0.1 μm. / H or more, for example, 0.3 μm / h, under a growth condition of 3 to 30 nm, for example, 8 nm, sandwiched between undoped In _0.03 Ga _0.97 N barrier layers having a thickness of 1 to 10 nm, for example, 5 nm. An SQW active layer composed of an undoped In _0.15 Ga _0.85 N well layer may be grown.

In the twelfth embodiment, an undoped layer is used as an active layer in order to increase hole mobility. However, in the case of an undoped layer, impurities may inevitably be autodoped. Therefore, the resulting impurity concentration may be less than 1.0 × 10 ¹⁷ cm ⁻³ .

Next, referring to FIG. 17 and FIG. 18, by providing a narrow forbidden band width region in the p-type cladding layer and performing luminescent recombination in this narrow forbidden band width region to prevent heat generation due to overflow current. Thirteenth to fifteenth embodiments of the present invention that reduce the threshold current density _Jth will be described.
First, a thirteenth embodiment of the present invention will be described with reference to FIG.
FIG. 17A is a perspective view of the SQW semiconductor laser according to the thirteenth embodiment of the present invention, and FIG. 17B is a diagram showing the energy level on the conduction band side in the vicinity of the active layer. is there.
Refer to FIG. 17A. First, TMGa, TMAl, ammonia, and carrier gas as n-type SiC substrate 411 made of hexagonal 6H—SiC having a (0001) plane, that is, c-plane as a main surface. By a MOVPE method using hydrogen as a growth gas, a growth pressure is set to 70 to 760 Torr, for example, 100 Torr, a growth temperature is set to 800 to 1200 ° C., for example, 950 ° C., and a thickness of 50 to 300 nm, for example, 50 nm. An AlGaN buffer layer 412 is grown.

Subsequently, using TMGa, ammonia, SiH ₄ as the dopant source, and hydrogen as the carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 920 ° C. And an n-type GaN intermediate layer having a thickness of 0.1 to 2.0 μm, for example, 0.5 μm, and an impurity concentration of 5 × 10 ¹⁷ to 1 × 10 ¹⁹ cm ⁻³ , for example, 2 × 10 ¹⁸ cm ^−3. Grow 413.

Subsequently, using TMAl, TMGa, ammonia, SiH ₄ as a dopant, and hydrogen as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 950 ° C. In this state, the thickness is 0.1 to 2.0 μm, for example, 0.5 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ²⁰ cm ⁻³ , for example, 1.0 × 10 ¹⁸ cm. ^-3 n-type Al _0.15 Ga _0.85 N cladding layer 414 is grown.

  Subsequently, using TMGa, ammonia, and hydrogen as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 930 ° C. An undoped GaN light guide layer 415 of ˜300 nm, eg, 100 nm is grown.

Subsequently, using TMGa, TMIn, ammonia, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 550 to 900 ° C., for example, 700 ° C. An SQW active layer 416 is formed by growing an undoped In _0.15 Ga _0.85 N well layer having a thickness of 3 to 30 nm, for example, 5 nm sandwiched between undoped In _0.05 Ga _0.95 N barrier layers having a thickness of 1 to 10 nm, for example, 5 nm. To do.

Subsequently, using TMGa, ammonia, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 1130 ° C. An undoped GaN light guide layer 417 of 10 to 300 nm, for example, 100 nm is grown.

Subsequently, using TMAl, TMGa, ammonia, biscyclopentadienylmagnesium, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, In a state of 950 ° C., the thickness is 0.05 to 0.50 μm, for example, 0.2 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 2.0 × A 10 ¹⁷ cm ⁻³ p-type Al _0.15 Ga _0.85 N cladding layer 418 is grown.

Subsequently, using TMGa, ammonia, biscyclopentadienylmagnesium, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 950 ° C. The thickness T is 1 to 500 nm, for example, 100 nm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 1.0 × 10 ¹⁸ cm ⁻³ . A p-type GaN intermediate layer 419 is grown.

Subsequently, again using TMAl, TMGa, ammonia, biscyclopentadienylmagnesium, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C. For example, at a temperature of 950 ° C., the thickness is 0.05 to 0.50 μm, for example, 0.2 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ . A p-type Al _0.15 Ga _0.85 N clad layer 420 of 0 × 10 ¹⁷ cm ⁻³ is grown.

Subsequently, using TMGa, ammonia, biscyclopentadienylmagnesium, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 930 ° C. In this state, the thickness is 0.1 to 2.0 μm, for example, 0.5 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 1.0 × 10 ^18. A cm ⁻³ p-type GaN contact layer 421 is grown.

  Next, an Ni electrode 422 having a thickness of 100 nm is provided as an n-side electrode on the back surface of the n-type SiC substrate 411, and an Ni electrode having a thickness of 100 nm and a width W of 3 μm is provided on the p-type GaN contact layer 421 as a p-side electrode. The SQW structure short wavelength semiconductor laser is completed by providing 423 and dividing the element so that the resonator length L becomes 700 μm.

In the thirteenth embodiment of the present invention, a p-type GaN intermediate layer having better crystallinity and a narrow forbidden band width than the Al _0.15 Ga _0.85 N layer between the p-type Al _0.15 Ga _0.85 N cladding layers 418 and 420. Since the layer 419 is sandwiched, the overflowing electrons effectively stay in the p-type GaN intermediate layer 419 and recombine with light emission, so that the electrons reach the p-side electrode and cause heat generation. Never become.

  Therefore, since the element temperature does not rise, the overflow current remains almost constant, and the vicious circle of the increase in overflow current due to heat generation can be interrupted. As a result, a short wavelength semiconductor laser with a low threshold current density is manufactured. In addition, device deterioration due to deterioration of the p-side electrode is also suppressed, so that reliability can be improved.

In this case, since the p-type GaN intermediate layer is doped to about 1.0 × 10 ¹⁸ cm ⁻³ , compared to the case where the p-type cladding layer having the same thickness is made of Al _0.15 Ga _0.85 N, The resistance of the p-type cladding layer can be further reduced.

Next, a fourteenth embodiment of the present invention will be described with reference to FIG. 18 (a) showing the energy level on the conduction band side.
Note that the fourteenth embodiment is the same as the thirteenth embodiment except for the structure of the intermediate layer, and a description of the manufacturing method will be omitted.
First, as in the thirteenth embodiment, a thickness of an n-type SiC substrate made of hexagonal 6H—SiC having a (0001) plane, that is, a c-plane as a principal plane is as shown in FIG. 50-300 nm, for example 50 nm AlGaN buffer layer, thickness 0.1-2.0 μm, for example 0.5 μm, impurity concentration 5 × 10 ¹⁷ to 1 × 10 ¹⁹ cm ⁻³ , for example 2 × A 10 ¹⁸ cm ⁻³ Si-doped n-type GaN intermediate layer and a thickness of 0.1 to 2.0 μm, for example, 0.5 μm, and an impurity concentration of 1.0 × 10 ^{17 to} 1.0 × 10 ²⁰ A Si-doped n-type Al _0.15 Ga _0.85 N clad layer 414 having a thickness of cm ⁻³ , for example, 1.0 × 10 ¹⁸ cm ⁻³ is grown.

Subsequently, after growing an undoped GaN optical guide layer 415 having a thickness of 10 to 300 nm, for example, 100 nm, the thickness sandwiched by an undoped In _0.05 Ga _0.95 N barrier layer having a thickness of 1 to 10 nm, for example, 5 nm. An SQW active layer 416 is formed by growing an undoped In _0.15 Ga _0.85 N well layer of 3 to 30 nm, for example, 5 nm.

Next, an undoped GaN light guide layer 417 having a thickness of 10 to 300 nm, for example, 100 nm, a thickness of 0.05 to 0.50 μm, for example, 0.2 μm, and an impurity concentration of 1.0 × 10 ^{17 to} 1.0 × An Mg-doped p-type Al _0.15 Ga _0.85 N cladding layer 418 of 10 ¹⁹ cm ⁻³ , for example, 2.0 × 10 ¹⁷ cm ⁻³ is grown.

Next, by continuously changing the flow rate ratio of TMAl and TMGa, the thickness T continuously changed so that the Al composition ratio becomes the lowest GaN in the intermediate portion is 1 to 500 nm, for example, 100 nm, and the impurity concentration A graded intermediate layer 324 having a thickness of 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 1.0 × 10 ¹⁸ cm ⁻³ is grown.

Next, the thickness is 0.05 to 0.50 μm, for example, 0.2 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 2.0 × 10 ¹⁷ cm ^−3. Mg-doped p-type Al _0.15 Ga _0.85 N cladding layer 420 and a thickness of 0.1 to 2.0 μm, for example, 0.5 μm, and an impurity concentration of 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ A p-type GaN contact layer of cm ⁻³ , for example, 1.0 × 10 ¹⁸ cm ⁻³ is grown.

  Next, a Ni electrode having a thickness of 100 nm is provided as an n-side electrode on the back surface of the n-type SiC substrate, and a Ni electrode having a thickness of 100 nm and a width W of 3 μm is provided as a p-side electrode on the p-type GaN contact layer. The SQW structure short wavelength semiconductor laser is completed by dividing the element so that the resonator length L becomes 700 μm.

  In the fourteenth embodiment, since the intermediate layer is composed of the graded intermediate layer 424 having a U-shaped forbidden band width distribution, holes can be smoothly injected into the p-side light guide layer. Can do.

  In this case, the narrow forbidden band width portion at the center of the graded intermediate layer 424 may be non-doped. By improving the crystallinity of this portion, the probability of luminescent recombination can be increased. .

Next, a fifteenth embodiment of the present invention will be described with reference to FIG. 18B showing the energy level on the conduction band side.
Note that the fifteenth embodiment is the same as the thirteenth embodiment except for the structure of the intermediate layer, and a description of the manufacturing method will be omitted.
As shown in FIG. 18B, first, as in the thirteenth embodiment described above, a thickness is formed on an n-type SiC substrate made of hexagonal 6H—SiC having a (0001) plane, that is, a c-plane as a principal plane. 50-300 nm, for example 50 nm AlGaN buffer layer, thickness 0.1-2.0 μm, for example 0.5 μm, impurity concentration 5 × 10 ¹⁷ to 1 × 10 ¹⁹ cm ⁻³ , for example 2 × A 10 ¹⁸ cm ⁻³ Si-doped n-type GaN intermediate layer and a thickness of 0.1 to 2.0 μm, for example, 0.5 μm, and an impurity concentration of 1.0 × 10 ^{17 to} 1.0 × 10 ²⁰ A Si-doped n-type Al _0.15 Ga _0.85 N clad layer 414 having a thickness of cm ⁻³ , for example, 1.0 × 10 ¹⁸ cm ⁻³ is grown.

Subsequently, after growing an undoped GaN optical guide layer 415 having a thickness of 10 to 300 nm, for example, 100 nm, the thickness sandwiched by an undoped In _0.05 Ga _0.95 N barrier layer having a thickness of 1 to 10 nm, for example, 5 nm. An SQW active layer 416 is formed by growing an undoped In _0.15 Ga _0.85 N well layer of 3 to 30 nm, for example, 5 nm.

Next, an undoped GaN light guide layer 417 having a thickness of 10 to 300 nm, for example, 100 nm, a thickness of 0.05 to 0.50 μm, for example, 0.2 μm, and an impurity concentration of 1.0 × 10 ^{17 to} 1.0 × An Mg-doped p-type Al _0.15 Ga _0.85 N cladding layer 418 of 10 ¹⁹ cm ⁻³ , for example, 2.0 × 10 ¹⁷ cm ⁻³ is grown.

Next, by increasing or decreasing the flow rate ratio of TMAl and TMGa alternately and continuously, the thickness of 1 to 500 nm consisting of a multilayer structure in which the Al composition ratio continuously changes from Al _0.15 Ga _0.85 N to GaN, more preferably , A multilayer structure intermediate layer 425 having a thickness of 10 to 500 nm, for example, 100 nm is formed.
In this case, the thickness t of one cycle is 0.3 to 50 nm, more preferably 1 to 50 nm, for example, 20 nm, and the composition has a narrow forbidden band width of about 3 nm (= 30 mm) close to GaN. The part is undoped.

Next, the thickness is 0.05 to 0.50 μm, for example, 0.2 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 2.0 × 10 ¹⁷ cm ^−3. Mg-doped p-type Al _0.15 Ga _0.85 N cladding layer 420 and a thickness of 0.1 to 2.0 μm, for example, 0.5 μm, and an impurity concentration of 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ A p-type GaN contact layer of cm ⁻³ , for example, 1.0 × 10 ¹⁸ cm ⁻³ is grown.

  Next, a Ni electrode having a thickness of 100 nm is provided as an n-side electrode on the back surface of the n-type SiC substrate, and a Ni electrode having a thickness of 100 nm and a width W of 3 μm is provided as a p-side electrode on the p-type GaN contact layer. The SQW structure short wavelength semiconductor laser is completed by dividing the element so that the resonator length L becomes 700 μm.

  In the fifteenth embodiment, since the intermediate layer is composed of the multilayer structure intermediate layer 425, the resistance of the entire p-type cladding layer is not increased so much even if the narrow band gap portion is undoped. By making undoped, the crystallinity can be increased and the probability of luminescent recombination can be increased, and heat generation can be suppressed more effectively.

  In the fifteenth embodiment, holes are injected smoothly by configuring the multilayered intermediate layer 425 so that the forbidden bandwidth continuously changes. However, the step function It may be configured with a multilayer structure that changes with time.

  Although the thirteenth to fifteenth embodiments of the present invention have been described above, the present invention is not limited to the configuration of the embodiment. For example, in the thirteenth to fifteenth embodiments, an intermediate The layer is configured to be GaN or GaN at the lowest forbidden band width, but may be AlGaN or InGaN.

In the thirteenth to fifteenth embodiments described above, an SQW structure made of In _0.15 Ga _0.85 N / In _0.05 Ga _0.95 N is adopted as the active layer. The ratio may be changed within the range of Al _x Ga _y In _1-xy N (0 ≦ x <1, 0 <y ≦ 1), and accordingly, the mixing of the light guide layer and the cladding layer The crystal ratio may be changed within the range of Al _a Ga _b In _1-ab N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1).

In the thirteenth to fifteenth embodiments, the active layer has an SQW structure, but may have an MQW structure. In this case, for example, the thickness is 1 to 10 nm. For example, 5 nm of undoped In _0.05 Ga _0.95 N barrier layer and a thickness of 3 to 10 nm, for example, 5 nm of undoped In _0.15 Ga _0.85 N well layer alternately with 2 to 10 undoped In _0.15 Ga _0.85 N well layers, for example, The MQW active layer may be formed by growing it to have 5 layers.

  Furthermore, in the above embodiment, the p-side light guide layer is composed of an undoped layer, but it may be doped p-type.

Next, referring to FIG. 19 and FIG. 20, nonuniform injection of carriers is improved by controlling the thickness of the barrier layer constituting the MQW active layer, thereby reducing the threshold current density J _th . The sixteenth and seventeenth embodiments of the present invention will be described.
First, a short wavelength semiconductor laser according to a sixteenth embodiment of the present invention will be described with reference to FIG.
FIG. 19A is a perspective view of an MQW semiconductor laser according to the sixteenth embodiment of the present invention, and FIG. 19B is an MQW active layer indicated by a broken-line circle in FIG. It is an enlarged view which shows the layer structure of the vicinity.
19 (a) and 19 (b) First, on a n-type SiC substrate 511 made of hexagonal 6H—SiC having a (0001) plane, that is, a c-plane as a main surface, TMGa, TMAl, ammonia, and With a MOVPE method using hydrogen as a carrier gas as a growth gas, a growth pressure is set to 70 to 760 Torr, for example, 100 Torr, a growth temperature is set to 800 to 1200 ° C., for example, 950 ° C., and a thickness of 50 to 300 nm. For example, a 50 nm AlGaN buffer layer 512 is grown.

Subsequently, using TMGa, ammonia, SiH ₄ as the dopant source, and hydrogen as the carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 920 ° C. And an n-type GaN intermediate layer having a thickness of 0.1 to 2.0 μm, for example, 0.5 μm, and an impurity concentration of 5 × 10 ¹⁷ to 1 × 10 ¹⁹ cm ⁻³ , for example, 2 × 10 ¹⁸ cm ^−3. Grow 513.

Subsequently, using TMAl, TMGa, ammonia, SiH ₄ as a dopant, and hydrogen as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 950 ° C. In this state, the thickness is 0.1 to 2.0 μm, for example, 0.5 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ²⁰ cm ⁻³ , for example, 1.0 × 10 ¹⁸ cm. ⁻³ n-type Al _0.15 Ga _0.85 N cladding layer 514 is grown.

  Subsequently, using TMGa, ammonia, and hydrogen as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 930 ° C. An undoped GaN light guide layer 515 of ˜300 nm, eg, 100 nm is grown.

Subsequently, using TMGa, TMIn, ammonia, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 550 to 900 ° C., for example, 700 ° C. Thickness of 3 nm to 10 nm, for example, 4 nm of undoped In _0.15 Ga _0.85 N well layer 517 separated by an undoped In _0.05 Ga _0.95 N barrier layer 518 of, for example, 3 nm, The MQW active layer 516 is formed by growing three layers.

Subsequently, using TMGa, ammonia, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 1130 ° C. An undoped GaN light guide layer 519 having a thickness of 10 to 300 nm, for example, 100 nm is grown.

Subsequently, using TMAl, TMGa, ammonia, biscyclopentadienylmagnesium, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, In a state of 950 ° C., the thickness is 0.1 to 2.0 μm, for example, 0.5 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 2.0 × A 10 ¹⁷ cm ⁻³ p-type Al _0.15 Ga _0.85 N cladding layer 520 is grown.

Subsequently, using TMGa, ammonia, biscyclopentadienylmagnesium, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 930 ° C. In this state, the thickness is 0.1 to 2.0 μm, for example, 0.5 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 1.0 × 10 ^18. A cm ⁻³ p-type GaN contact layer 521 is grown.

  Next, an Ni electrode 522 having a thickness of 100 nm is provided on the back surface of the n-type SiC substrate 511 as an n-side electrode, and an Ni electrode having a thickness of 100 nm and a width W of 3 μm is provided on the p-type GaN contact layer 521 as a p-side electrode. An MQW semiconductor laser is completed by providing 523 and dividing the element so that the resonator length L is 700 μm.

  In the sixteenth embodiment of the present invention, since the thickness of the barrier layer constituting the MQW active layer 516 is less than 5 nm, carrier injection efficiency is improved and non-uniform carrier injection can be eliminated. it can.

  In addition, in the case of a semiconductor having a conventional zinc blende type crystal structure, there is a problem of oozing of the wave function when the barrier layer is thinned, but in the case of a nitride compound semiconductor as in the present invention. Since the effective mass of carriers is large, there is little oozing of the wave function, and even if the thickness of the barrier layer is less than 5 nm, the decrease in the generation of optical gain is not a problem.

  It is sufficient that the thickness of the barrier layer is less than 5 nm, and the In composition ratio of the barrier layer may be less than 0.04, but the strain reduction effect due to the reduction in the thickness of the barrier layer is effectively utilized. For this purpose, the forbidden band width of the barrier layer without causing deterioration of crystallinity by setting the thickness of the barrier layer to 3 nm or less and the In composition ratio of the barrier layer made of InGaN to 0.04 or more. The carrier injection efficiency can be further improved by reducing the height and the height of the barrier.

Next, an MQW semiconductor laser according to a seventeenth embodiment of the present invention using a sapphire substrate as a substrate will be described with reference to FIG.
FIG. 20 is a perspective view of an MQW semiconductor laser according to a seventeenth embodiment of the present invention. First, TMGa, ammonia, and carriers are formed on a sapphire substrate 531 having a (0001) plane as a main surface. A GaN low temperature buffer layer 532 having a thickness of 0.03 μm is grown at a growth temperature of 500 ° C. by a MOVPE method using hydrogen as a growth gas and a growth pressure of 70 to 760 Torr, for example, 100 Torr.

Subsequently, using TMGa, ammonia, SiH ₄ as the dopant source, and hydrogen as the carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 920 ° C. And an n-type GaN intermediate layer having a thickness of 0.1 to 2.0 μm, for example, 1.0 μm and an impurity concentration of 5 × 10 ¹⁷ to 1 × 10 ¹⁹ cm ⁻³ , for example, 2 × 10 ¹⁸ cm ^−3. Grow 533.

In the following, the thickness is 0.1 to 2.0 μm, for example, 1.0 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ²⁰ cm ⁻ as in the sixteenth embodiment. ³ , for example, 1.0 × 10 ¹⁸ cm ⁻³ n-type Al _0.15 Ga _0.85 N cladding layer 534, thickness 10 to 300 nm, for example, 100 nm undoped GaN light guide layer 535, MQW active layer 536, thickness 10 An undoped GaN light guide layer 537 having a thickness of 0.1 to 2.0 μm, for example, 0.5 μm, and an impurity concentration of 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ^−3. For example, a p-type Al _0.15 Ga _0.85 N cladding layer 538 having a thickness of 2.0 × 10 ¹⁷ cm ⁻³ and a thickness of 0.1 to 2.0 μm, for example, 0.5 μm and an impurity concentration of 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 1.0 × 10 ^{1 An 8} cm ⁻³ p-type GaN contact layer 539 is sequentially epitaxially grown.

In this case, the MQW active layer 536 is also 1 nm to less than 5 nm thick, for example, 3 to 10 nm thick, for example, 4 nm undoped In _0.15 Ga _0.85 N separated by a 3 nm undoped In _0.05 Ga _0.95 N barrier layer. The well layer is formed by growing 2 to 10 layers, for example, 3 layers.

  Next, a part of the n-type GaN intermediate layer 533 is exposed by dry etching to provide a Ti electrode 540 as an n-side electrode, and a Ni electrode having a width W of 3 μm as a p-side electrode on the p-type GaN contact layer 539. After providing 541, dry etching is performed to form a pair of parallel end faces having a cavity distance L of 700 μm, thereby completing the MQW semiconductor laser.

  Also in the seventeenth embodiment of the present invention, since the thickness of the barrier layer constituting the MQW active layer 516 is less than 5 nm, the carrier injection efficiency is improved, thereby eliminating the non-uniform carrier injection. be able to.

  Also in this case, in order to effectively use the strain reduction effect due to the thinning of the barrier layer, the thickness of the barrier layer is 3 nm or less, and the In composition ratio of the barrier layer made of InGaN is set to By setting it to 0.04 or more, the barrier height of the barrier layer can be lowered without causing deterioration of crystallinity, and thereby carrier injection efficiency can be further improved.

Although the sixteenth and seventeenth embodiments of the present invention have been described above, the present invention is not limited to the configurations of the sixteenth and seventeenth embodiments described above, and for example, the sixteenth and seventeenth embodiments. In this embodiment, the MQW structure made of In _0.15 Ga _0.85 N / In _0.05 Ga _0.95 N is adopted as the multiple quantum well active layer, but the mixed crystal ratio is changed to Al _x Ga _y according to the required wavelength. In _1-xy N (0 ≦ x <1, 0 <y ≦ 1) may be changed, and accordingly, the mixed crystal ratio of the light guide layer and the cladding layer is changed to Al _a Ga. _You may change within the range of bIn1 _-abN (0 <= a <= 1, 0 <= b <= 1).

Next, referring to FIG. 21 to FIG. 23, the hole injection efficiency is improved by making the overflow prevention layer, that is, the electron block layer, an undoped layer or a graded layer, and thereby the threshold current density J Eighteenth and nineteenth embodiments of the present invention that reduce _th will be described.
First, an MQW semiconductor laser according to an eighteenth embodiment of the present invention will be described with reference to FIG.
21. First, TMGa, TMAl, ammonia, and hydrogen as a carrier gas are grown on an n-type SiC substrate 611 made of hexagonal 6H—SiC having a (0001) plane, that is, a c-plane as a main surface. An AlGaN buffer layer having a thickness of 50 to 300 nm, for example 50 nm, with a growth pressure of 70 to 760 Torr, for example, 100 Torr and a growth temperature of 800 to 1200 ° C., for example, 950 ° C., by the MOVPE method used as the gas. 612 is grown.

Subsequently, using TMGa, ammonia, SiH ₄ as the dopant source, and hydrogen as the carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 920 ° C. And an n-type GaN intermediate layer having a thickness of 0.1 to 2.0 μm, for example, 0.5 μm, and an impurity concentration of 5 × 10 ¹⁷ to 1 × 10 ¹⁹ cm ⁻³ , for example, 2 × 10 ¹⁸ cm ^−3. 613 is grown.

Subsequently, using TMAl, TMGa, ammonia, SiH ₄ as a dopant, and hydrogen as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 950 ° C. In this state, the thickness is 0.1 to 2.0 μm, for example, 0.5 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ²⁰ cm ⁻³ , for example, 1.0 × 10 ¹⁸ cm. ^-3 n-type Al _0.09 Ga _0.91 N cladding layer 614 is grown.

  Subsequently, using TMGa, ammonia, and hydrogen as a carrier gas, a growth pressure of 70 to 760 Torr, for example, 100 Torr, a growth temperature of 800 to 1200 ° C., for example, 930 ° C., and a thickness of 10 An undoped GaN light guide layer 615 of ˜300 nm, eg, 100 nm is grown.

Subsequently, using TMGa, TMIn, ammonia, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 550 to 900 ° C., for example, 700 ° C. 2 to 10 layers, for example, 3 layers of undoped In _0.15 Ga _0.85 N well layer having a thickness of 3 to 10 nm, for example, 4 nm, separated by an undoped In _0.03 Ga _0.97 N barrier layer of 1 nm to 10 nm, for example, 5 nm An MQW active layer 616 is formed by growth.

Subsequently, using TMAl, TMGa, ammonia, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 950 ° C. An undoped Al _0.18 Ga _0.82 N electron blocking layer 617 having a thickness of 5 to 30 nm, for example, 20 nm is grown.

Subsequently, using TMGa, ammonia, biscyclopentadienylmagnesium, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 1130 ° C. P-type having a thickness of 10 to 300 nm, for example, 100 nm, and an impurity concentration of 1.0 × 10 ^{17 to} 5.0 × 10 ¹⁹ cm ⁻³ , for example, 1.0 × 10 ¹⁸ cm ⁻³ . A GaN light guide layer 618 is grown.

Subsequently, using TMAl, TMGa, ammonia, biscyclopentadienylmagnesium, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, In a state of 950 ° C., the thickness is 0.1 to 2.0 μm, for example, 0.5 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 2.0 × A p-type Al _0.09 Ga _0.91 N clad layer 619 of 10 ¹⁷ cm ⁻³ is grown.

Subsequently, using TMGa, ammonia, biscyclopentadienylmagnesium, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 930 ° C. In this state, the thickness is 0.1 to 2.0 μm, for example, 0.5 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁹ cm ⁻³ , for example, 1.0 × 10 ^18. A cm ⁻³ p-type GaN contact layer 620 is grown.

  Next, an Ni electrode 621 having a thickness of 100 nm is provided on the back surface of the n-type SiC substrate 611 as an n-side electrode, and an Ni electrode having a thickness of 100 nm and a width W of 3 μm is provided on the p-type GaN contact layer 620 as a p-side electrode. An MQW semiconductor laser is completed by providing 622 and dividing the element so that the resonator length L is 700 μm.

In the eighteenth embodiment, since the Al _0.18 Ga _0.82 N electron blocking layer is an undoped layer, the hole concentration is reduced and a high applied voltage V is required, but since scattering due to impurities is eliminated, it is effective. Therefore, the mobility is increased, and therefore the hole concentration with respect to the case where the electron block layer is formed with a p-type layer having an impurity concentration of about 5.0 × 10 ¹⁷ cm ⁻³ to 5.0 × 10 ¹⁹ cm ^{−3 as in the} prior art. As a result, the effect of improving the hole injection efficiency is generally expected.
Since the impurity concentration of the undoped layer in the GaN-based semiconductor is generally less than 1.0 × 10 ¹⁷ cm ⁻³ , even when intentionally doped, the impurity concentration is less than 1.0 × 10 ¹⁷ cm ⁻³ . If present, the same effect as the undoped layer can be obtained.

  The p-side light guide layer in the eighteenth embodiment is composed of a p-type layer for the sake of simplicity, but may be composed of an undoped layer, and n The side light guide layer is composed of an undoped layer, but may be composed of an n-type layer.

Next, an MQW semiconductor laser according to a nineteenth embodiment of the present invention is described with reference to FIGS.
FIG. 22A is a cross-sectional view perpendicular to the optical axis of the MQW semiconductor laser according to the nineteenth embodiment of the present invention, and FIG. 22B is a band diagram near the MQW active layer. Furthermore, FIG. 23 is an explanatory diagram of the effect.
First, as in the eighteenth embodiment, an AlGaN buffer layer 612, an n-type GaN intermediate layer 613, and an n-type Al _0.09 Ga _0.91 N cladding layer 614 are formed on the n-type SiC substrate 611. Then, an undoped GaN light guide layer 615 and an MQW active layer 616 are formed.

Subsequently, using TMAl, TMGa, ammonia, biscyclopentadienylmagnesium, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, In a state of 950 ° C., TMAl is gradually and continuously increased from 0 to a thickness of 1 to 20 nm, for example, 10 nm, and an impurity concentration of 1.0 × 10 ^{15 to} 3.0 × 10 ²⁰ cm ⁻³ , For example, a p-type graded AlGaN layer 623 of 1.0 × 10 ¹⁹ cm ⁻³ is grown, and then the TMAl / TMGA ratio is kept constant, the thickness is 1 to 20 nm, for example, 10 nm, and the impurity concentration is 1.0. A p-type Al _0.18 Ga _0.82 N layer 624 of × 10 ^{15 to} 3.0 × 10 ²⁰ cm ⁻³ , for example, 1.0 × 10 ¹⁹ cm ⁻³ is grown, and then TMAl / The TMGA ratio is continuously reduced to 0 to a thickness of 1 to 20 nm, for example, 10 nm, and the impurity concentration is 1.0 × 10 ^{15 to} 3.0 × 10 ²⁰ cm ⁻³ , for example, 1.0 × 10 ^19. A p − graded AlGaN layer 625 of cm ⁻³ is grown, and the forbidden band width is smoothed by the p type graded AlGaN layer 623, the p type Al _0.18 Ga _0.82 N layer 624, and the p type graded AlGaN layer 625. A p-type electron blocking layer 626 that continuously changes is formed.

Thereafter, the p-type GaN light guide layer 618, the p-type Al _0.09 Ga _0.91 N clad layer 619, and the p-type GaN contact layer 620 are successively grown again in exactly the same manner as in the eighteenth embodiment.

Next, the p-type GaN contact layer 620 and the p-type Al _0.09 Ga _0.91 N cladding layer 619 are mesa-etched by dry etching, and an Ni electrode 621 having a thickness of 100 nm is provided as an n-side electrode on the back surface of the n-type SiC substrate 611. At the same time, a Ni electrode 622 having a thickness of 100 nm is provided as a p-side electrode on the p-type GaN contact layer 620 via a SiO ₂ film 627 having a stripe-shaped opening, and the elements are divided so that the resonator length L is 700 μm. This completes the MQW semiconductor laser.

In FIG. 22 (b), in the nineteenth embodiment of the present invention, the p-type electron block layer 626 includes a p-type graded AlGaN layer 623, a p-type Al _0.18 Ga _0.82 N layer 624, and a p-type gray. Since it is constituted by the dead AlGaN layer 625, the forbidden band width can be continuously changed and the electron affinity can also be changed continuously, whereby the MQW active layer 616 can be changed on the n side. difference in electron affinity between the in _0.03 Ga _0.97 N barrier layer and the p-type graded AlGaN layer 623 constituting the can be eliminated almost, whereby an in _0.03 Ga _0.97 N barrier layer and the p-type graded AlGaN layer 623 A notch serving as a potential barrier against holes is not formed at the interface.

  Further, on the p side, the difference in electron affinity between the p-type GaN light guide layer 618 and the p-type graded AlGaN layer 625 can be eliminated, whereby the p-type GaN light guide layer 618 and the p-type graded AlGaN are eliminated. A notch serving as a potential barrier against holes is not formed even at the interface with the layer 625.

  Accordingly, since notches serving as potential barriers for holes are not formed on both sides of the p-type electron block layer 626, the hole injection efficiency is improved, thereby reducing the drive voltage.

FIG. 23 is a diagram showing voltage-current characteristics by simulation for explaining the effect when the p-type graded AlGaN layer 623 and the p-type graded AlGaN layer 625 are provided.
As is apparent from the figure, when the p-type graded AlGaN layer 623 and the p-type graded AlGaN layer 625 are provided, the overflow prevention layer, that is, when the graded layer is not provided in the electron block layer as in the prior art. In comparison, it is understood that the drive voltage can be lowered, and this is due to the suppression of notch formation as described above.

In the description of the nineteenth embodiment, graded layers are provided on both sides of a p-type Al _0.18 Ga _0.82 N layer 624 having a constant composition, but may be provided on only one of them. Although the degree of improvement in hole injection efficiency is low compared to the case where both are provided, the hole injection efficiency is improved compared to the case where no graded layer is provided.

In the nineteenth embodiment, as the impurity concentration of the p-type electron block layer 226, an impurity concentration that does not make a significant contribution due to impurity conduction on the valence band side as in the prior art is employed. However, it may be doped at a high concentration of 1.5 × 10 ¹⁹ cm ⁻³ or more, more preferably 7 × 10 ¹⁹ cm ⁻³ or more. In this case, holes are injected by impurity conduction. Contributions of both improvement in efficiency and improvement in hole injection efficiency due to the disappearance of notches are expected.

  Further, the p-type electron blocking layer 626 in the nineteenth embodiment may be an undoped layer, as in the eighteenth embodiment, and in this case, the effective movement of holes due to the undoping is performed. The improvement of the hole injection efficiency due to the improvement of the degree and the improvement of the hole injection efficiency due to the disappearance of the notch are expected to contribute.

  In the nineteenth embodiment and its modifications, the p-side light guide layer may be configured using an undoped GaN light guide layer instead of the p-type GaN light guide layer 618, and n The side light guide layer may be configured using an n-type GaN light guide layer instead of the undoped GaN light guide layer 615.

  The eighteenth and nineteenth embodiments of the present invention have been described above. However, the present invention is not limited to the configurations of the eighteenth and nineteenth embodiments described above. For example, the present invention is not a SiC substrate but a conventional one. A sapphire substrate may be used in the same manner as described above. In that case, TMGa, ammonia, and hydrogen as a carrier gas are first formed on a sapphire substrate having a (0001) plane as a main surface, as in the prior art. A GaN low temperature buffer layer having a thickness of 0.03 μm is grown at a growth temperature of 500 ° C. at a growth pressure of 70 to 760 Torr, for example, 100 Torr, and then TMGa, ammonia, and , Using hydrogen as a carrier gas, a growth pressure of 70 to 760 Torr, for example, 100 Torr, and a growth temperature of 800 1200 ° C., for example, while a 950 ° C., the thickness of 0.1 to 2.0 [mu] m, for example, to grow the n-type GaN intermediate layer of 1.0 .mu.m.

Thereafter, the n-type Al _0.09 Ga _0.91 N clad layer, the n-side GaN light guide layer, the MQW active layer, the electron block layer, and the p-side GaN light guide layer are exactly the same as in the eighteenth and nineteenth embodiments. Then, a p-type GaN optical guide layer, a p-type Al _0.09 Ga _0.91 N cladding layer, and a p-type GaN contact layer are sequentially epitaxially grown.
In this case, the electron block layer has a structure according to the corresponding embodiment.

Subsequently, similarly to the conventional example, the p-type GaN layer and the p-type Al _0.09 Ga _0.91 N cladding layer are mesa-etched by dry etching, and a part of the n-type GaN intermediate layer is exposed to form n An n-side electrode made of Ti / Au is provided on the exposed portion of the type GaN intermediate layer, and a p-side electrode made of Ni / Au is provided on the p-type GaN contact layer through a SiO ₂ film having a stripe-shaped opening, Next, dry etching may be performed to form a pair of parallel end faces to be a resonator surface.

In the eighteenth and nineteenth embodiments described above, the MQW structure made of In _0.15 Ga _0.85 N / In _0.03 Ga _0.97 N is adopted as the multiple quantum well active layer, depending on the required wavelength. Thus, the mixed crystal ratio may be changed within the range of Al _x Ga _y In _1-xy N (0 ≦ x <1, 0 <y ≦ 1), and accordingly, the light guide layer and the cladding The mixed crystal ratio of the layers may be changed within the range of Al _a Ga _b In _1-ab N (0 ≦ a ≦ 1, 0 ≦ b ≦ 1).

  For example, in the eighteenth and nineteenth embodiments described above, InGaN is used for the InGaN well layer as the barrier layer, but AlGaN or GaN may be used instead of InGaN. When AlGaN or GaN is used, the notch at the interface between the barrier layer and the electron block layer using the graded layer can be completely eliminated.

Next, referring to FIGS. 24 to 30, the electron block layer has an impurity concentration of 7 × 10 ¹⁹ cm ⁻³ or more and the electron block layer growth temperature is set to 600 ° C. to 900 ° C. A twentieth embodiment of the present invention will be described that prevents the overflow of the current and thereby reduces the threshold current density.
First, with reference to FIG. 24, the manufacturing process of the short wavelength semiconductor laser of the 20th Embodiment of this invention is demonstrated.
24. First, n-type SiC having a carrier concentration of 4 × 10 ¹⁸ cm ^{−3 made} of hexagonal 6H—SiC having a (0001) plane, that is, a c-plane as a main surface, is grown in bulk by the modified Rayleigh method. On the substrate 711, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 Torr by MOVPE using TMGa, TMAl, ammonia, SiH ₄ as a dopant source, and hydrogen as a carrier gas as a growth gas. ˜1200 ° C., for example, 1100 ° C., thickness 50 nm to 5 μm, eg 350 nm, impurity concentration 5 × 10 ¹⁷ to 1 × 10 ¹⁹ cm ⁻³ , eg 8 × 10 ¹⁸ cm ^-3 n-type Al _0.09 Ga _0.91 N buffer layer 712 is grown.

Subsequently, using TMAl, TMGa, ammonia, SiH ₄ as a dopant, and hydrogen as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 1100 ° C. In this state, the thickness is 0.1 to 2.0 μm, for example, 0.55 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ²⁰ cm ⁻³ , for example, 2.0 × 10 ¹⁸ cm. ^-3 n-type Al _0.09 Ga _0.91 N cladding layer 713 is grown.

Subsequently, using TMGa, ammonia, SiH ₄ as a dopant, and hydrogen as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 1100 ° C. Then, an n-type GaN light guide layer 714 having a thickness of 10 to 300 nm, for example, 100 nm, and an impurity concentration of 5 × 10 ¹⁷ to 1 × 10 ¹⁹ cm ⁻³ , for example, 2 × 10 ¹⁸ cm ⁻³ is grown.

Subsequently, using TMGa, TMIn, ammonia, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 600 to 900 ° C., for example, 780 ° C. 2 to 10 layers, for example, 3 layers of undoped In _0.15 Ga _0.85 N well layer having a thickness of 3 to 10 nm, for example, 4 nm, separated by an undoped In _0.03 Ga _0.97 N barrier layer having a thickness of 1 to 10 nm, for example, 5 nm An MQW active layer 715 is formed by growth.

Subsequently, using TMAl, TMGa, ammonia, biscyclopentadienylmagnesium, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 600 to 900 ° C., for example, A p ⁺ type Al _0.18 Ga _0.82 N electron block having a thickness of 5 to 30 nm, for example, 20 nm, and an impurity concentration of 7 × 10 ¹⁹ cm ⁻³ or more, for example, 1 × 10 ²⁰ cm ⁻³ at 780 ° C. Layer 716 is grown.

Subsequently, using TMGa, ammonia, biscyclopentadienylmagnesium, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 1100 ° C. P-type having a thickness of 10 to 300 nm, for example, 100 nm, and an impurity concentration of 1.0 × 10 ^{17 to} 1.0 × 10 ²⁰ cm ⁻³ , for example, 1.5 × 10 ¹⁹ cm ⁻³ . A GaN light guide layer 717 is grown.

Subsequently, using TMAl, TMGa, ammonia, biscyclopentadienylmagnesium, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, In a state of 1100 ° C., the thickness is 0.1 to 2.0 μm, for example, 0.55 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ²⁰ cm ⁻³ , for example, 1.5 × A p-type Al _0.09 Ga _0.91 N clad layer 718 of 10 ¹⁹ cm ⁻³ is grown.

Subsequently, using TMGa, ammonia, biscyclopentadienylmagnesium, and N ₂ as a carrier gas, the growth pressure is set to 70 to 760 Torr, for example, 100 Torr, and the growth temperature is set to 800 to 1200 ° C., for example, 1100 ° C. In this state, the thickness is 0.1 to 2.0 μm, for example, 0.1 μm, and the impurity concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ²⁰ cm ⁻³ , for example, 1.5 × 10 ^19. A p-type GaN first contact layer 719 of cm ⁻³ is grown, and subsequently, the impurity concentration is 5.0 × 10 ¹⁹ to 5.0 × 10 ²⁰ cm ^{− under the} same conditions as the p-type GaN first contact layer 719. ^3. A p ⁺ -type GaN second contact layer 720 having a thickness of, for example, 1.5 × 10 ²⁰ cm ⁻³ and a thickness of 5 to 50 nm, for example, 20 nm is grown.
The growth rate in this case is 2 μm / hr for the n-type layers 712 to 714, 0.3 μm / hr for the MQW active layer 715, and about the p ⁺ -type Al _0.18 Ga _0.82 N electron blocking layer 716. Is 0.9 μm / hr, and the p-type layers 717 to 720 are 2.6 μm / hr.

Next, after polishing the back surface of the n-type SiC substrate 711 to reduce the total thickness to about 100 μm, the p ⁺ -type GaN second contact layer 720 to the p-type Al _0.09 Ga _0.91 N clad layer 718 are formed by dry etching. Then, for example, a stripe mesa having a width of 4 μm and a height of 0.5 μm is formed.

Next, an n-side electrode 722 made of Ni / Ti / Au is provided on the back surface of the n-type SiC substrate 711, and a stripe-shaped opening having a width of 2 μm, for example, is formed on the p ⁺ -type GaN second contact layer 720. An MQW semiconductor laser is completed by providing a p-side electrode 723 made of Ni / Ti / Au via the SiO ₂ film 721 and dividing the element so that the resonator length L becomes 700 μm.
The stripe direction is the <1-100> direction, and the cleavage plane is the (1-100) plane.

FIG. 25 shows the current-light output characteristics of the element having the smallest threshold current among the results of measuring the current-light output characteristics of the MQW semiconductor laser of the twentieth embodiment. As is clear from the figure, the minimum value of the threshold current was 380 mA.
Although not shown, the maximum value measured this time is 600 mA, the average is 500 mA, and the threshold current is significantly larger than the previous threshold currents of 650 to 1600 mA and the average value of 900 mA. Reduced.

In order to confirm the effect of using such a p ⁺ -type electron block layer, a surface-emitting LED was fabricated in the same crystal growth process as the above semiconductor laser, and the emission spectrum was measured. 26 and FIG. 28 will be described.
26 (a) and 26 (b). FIG. 26 (b) is a schematic cross-sectional view of a surface-emitting LED manufactured for measurement, and FIG. 26 (a) is a top view. ) Plane, that is, on the n-type SiC substrate 731 having a carrier concentration of 4 × 10 ¹⁸ cm ^{−3 made} of hexagonal 6H—SiC with the c-plane as the principal plane, the thickness is 0.35 μm and the impurity concentration is n-type Al _0.09 Ga _0.91 n buffer layer 732 of impurity concentration 8 × 10 ¹⁸ cm ^-3, a thickness of 0.55 .mu.m, the impurity concentration is 2.0 × 10 ¹⁸ cm ^-3 n-type Al _0.09 Ga _0.91 n Clad layer 733, n-type GaN light guide layer 734 with a thickness of 100 nm and impurity concentration of 2 × 10 ¹⁸ cm ⁻³ , 4 nm thick undoped separated by an undoped In _0.03 Ga _0.97 N barrier layer with a thickness of 5 nm an In _0.15 Ga _0.85 N-well layer grown three-layer MQW Sex layer 735, a thickness of 20 nm p-type Al _0.18 Ga _0.82 N electron blocking layer 736, a thickness of 100 nm, p-type GaN optical guide layer 737 of impurity concentration is 5.0 × 10 ¹⁹ cm ^-3, thickness in but 0.2 [mu] m, p-type Al _0.09 Ga _0.91 N cladding layer 738 of impurity concentration is 5.0 × 10 ¹⁹ cm ^-3, a thickness of 0.1 [mu] m, the impurity concentration is 5.0 × 10 ¹⁹ cm ^-3 A p ⁺ -type GaN second contact layer 740 having a thickness of 20 nm and an impurity concentration of 1.5 × 10 ²⁰ cm ⁻³ is sequentially deposited.

Next, an n-side electrode 741 made of Ni / Ti / Au is provided on the back surface of the n-type SiC substrate 731, and an SiO ₂ film 742 having a substantially square opening on the surface of the p ⁺ -type GaN second contact layer 740. A p-side electrode is formed by providing a translucent electrode 743 made of Ni / Au, and a bonding pad 744 made of Ni / Au around the electrode.
The p ⁺ -type GaN second contact layer 740 visible through the semi-transparent electrode 743 has a 37 μm square dimension and an element dimension of 300 μm square.

In such a surface emitting LED, the Mg concentration of the p-type Al _0.18 Ga _0.82 N electron block layer 736 is changed in the range of 0 to 2 × 10 ²⁰ cm ⁻³ , and the p-type Al _0.18 Ga _0.82 N electron block is changed. Crystal growth was performed by setting the growth temperature of the layer 736 to two temperatures of 780 ° C. and 1100 ° C.

  Next, a 100 mA pulse current with a width of 100 μs and a frequency of 1 kHz is applied to the surface-emitting LED at room temperature in the forward direction, and the light emitted from the translucent electrode 743 is condensed by a lens, and then dispersed through a grating. The measurement was performed by detecting with a photomultiplier tube.

FIG. 27 shows a sample of a surface-emitting LED in which the electron concentration of the electron block layer as a conventional condition is 5 × 10 ¹⁹ cm ⁻³ and the growth temperature is 1100 ° C., and the electron block layer as a new condition. This is a comparison of measurement results with a sample having a Mg concentration of 1 × 10 ²⁰ cm ⁻³ and a growth temperature of 780 ° C.
As is apparent from the figure, the emission intensity in the vicinity of 400 nm, which is the emission center wavelength of the MQW active layer 735 made of InGaN, is significantly increased under the new conditions, and the intensity ratio is about 10 times.

  In addition, in the conventional condition LED, the p-type GaN light guide layer 737 has a light emission peaking at a wavelength of 363 nm. However, in the new condition LED, the light emission in this wavelength band is hardly seen. It is considered that the electrons overflowing into the p-type GaN light guide layer 737 have disappeared.

FIG. 28A is a diagram showing the Mg concentration dependence of the emission intensity in the MQW active layer 735 made of InGaN. As is clear from the figure, the vicinity of 7 × 10 ¹⁹ cm ⁻³ is shown. The light emission intensity suddenly increases at the boundary, and increases by about three orders of magnitude compared with the conventional condition.
Further, in the case of the same Mg concentration, the emission intensity increases by about two orders of magnitude or more under the new condition where the growth temperature is 780 ° C.

Refer to FIG.
FIG. 28B is a diagram showing the Mg concentration dependence of the emission intensity in the p-type GaN light guide layer 737. As is clear from the figure, the emission intensity is around 5 × 10 ¹⁹ cm ^−3. Although it decreases, in the case of the new condition where the growth temperature is 780 ° C., light emission is hardly observed when the Mg concentration is 7 × 10 ¹⁹ cm ⁻³ or more.

From the measurement results of FIGS. 27 and 28, the Mg concentration of the p ⁺ -type Al _0.18 Ga _0.82 N electron block layer 716 is 7 × 10 ¹⁹ cm ⁻³ or more, as in the twentieth embodiment. Preferably, the electron overflow can be prevented by setting it to 1 × 10 ²⁰ cm ⁻³ or more, and the recombination is efficiently performed in the MQW active layer 715, so that the threshold current density J _th can be reduced. It becomes possible.

In particular, when the crystal growth temperature of the p ⁺ -type Al _0.18 Ga _0.82 N electron block layer 716 is set to 600 ° C. to 900 ° C., for example, 780 ° C., in the same range as the MQW active layer 715, the effect becomes remarkable.
The lower limit of 600 ° C. is the lower limit of the temperature at which InGaN single crystal growth is possible, and the upper limit of 900 ° C. is the substantial upper limit of the InGaN growth temperature.

Thus, the reason why the overflow of electrons is almost completely suppressed by setting the Mg concentration of the p ⁺ -type Al _0.18 Ga _0.82 N electron block layer 716 to 7 × 10 ¹⁹ cm ⁻³ or more is unknown. Since 1.0 × 10 ²⁰ cm ⁻³ is a high impurity concentration higher than the concentration limit at which Mg is activated, it has a high density in the forbidden band on the valence band side of the p ⁺ -type Al _0.18 Ga _0.82 N electron blocking layer 716. An impurity level is formed, and this impurity level helps to improve the hole injection efficiency. As a result, it is considered that the overflow of electrons is suppressed. This situation will be described with reference to FIG.

29 is a band diagram in the vicinity of the MQW active layer 715. Holes in the p-type GaN light guide layer 717 are formed by tunnel conduction by the impurity level 724 or impurity conduction through the impurity level 724. As a result, the efficiency of hole injection is improved. As a result, electrons that have been attracted by the electric field of the holes staying in the p-type GaN light guide layer 717 can no longer be attracted. The threshold current density _Jth can be lowered.

29 and FIG. 42A. Further, when driving this MQW semiconductor laser, the applied voltage V may be set so that the band edge of the valence band of the p-type GaN light guide layer 717 reaches the impurity level 724. As is clear from the comparison between FIG. 29 and FIG. 42A, the drive voltage can be made lower than that of the conventional MQW semiconductor laser.

Next, the reason why the Mg concentration in the p-type electron block layer of the conventional short wavelength semiconductor laser, that is, the p-type overflow prevention layer is 5 × 10 ¹⁹ cm ⁻³ or less will be discussed with reference to FIG.
FIG. 30A is a diagram in which the p-type carrier concentration in the p-type GaN layer, that is, the Mg concentration dependence of the hole concentration is examined. When the Mg concentration is low, the p-type carrier concentration is Although it increases with the Mg concentration, it becomes maximum when the Mg concentration is about 5 × 10 ¹⁹ cm ⁻³ , and decreases when the Mg concentration is higher than that.

Such a dependency of the p-type carrier concentration in the p-type GaN layer on the Mg concentration also holds true for the p-type AlGaN layer. Therefore, even in the p ⁺ -type Al _0.18 Ga _0.82 N electron block layer 716, 5 × It is considered that the p-type carrier concentration decreases at 10 ¹⁹ cm ⁻³ as a boundary.

As described above, the phenomenon in which the carrier concentration is saturated or lowered at a dopant concentration higher than a certain dopant concentration is a phenomenon that is generally observed in other compound semiconductors. In a conventional short wavelength semiconductor laser, It is estimated that the value of 5 × 10 ¹⁹ cm ⁻³ is used as the Mg concentration of the p-type electron block layer due to the above-described circumstances.

Therefore, as in the twentieth embodiment of the present invention, setting the Mg concentration of the p-type electron block layer to 7 × 10 ¹⁹ cm ⁻³ or more is not quite effective as a means for increasing the p-type carrier concentration. However, since it is disadvantageous, it is a configuration that cannot be adopted without the new knowledge by the present inventors that the overflow of electrons is suppressed by setting the Mg concentration to 7 × 10 ¹⁹ cm ⁻³ or more.

In addition, in a high doping concentration region where the carrier concentration is saturated, a phenomenon of crystallinity deterioration due to overdoping is generally observed, and the mobility of the carrier decreases as the crystallinity decreases. This is a technique in which excessive doping is not employed unless there are other special circumstances. From this point of view, it is unpredictable that the Mg concentration of the p-type electron block layer is 7 × 10 ¹⁹ cm ⁻³ or more. is there.

FIG. 30B is a diagram in which the growth temperature dependence of the p-type carrier concentration in the p-type GaN layer grown by the MOVPE method is examined. As the growth temperature increases, the p-type carrier concentration increases. To increase.
That is, it can be seen that when the growth temperature is lowered, the p-type carrier concentration does not increase but decreases.

  The growth temperature dependence of the p-type carrier concentration in such a p-type GaN layer is also established for the p-type AlGaN layer. Therefore, the growth temperature of the p-type electron block layer is set to 600 ° C. as in the present invention. ˜900 ° C. is adopted without new knowledge by the present inventors that the overflow of electrons is suppressed by setting the temperature to 600 ° C. to 900 ° C., more preferably 730 to 830 ° C., for example, 780 ° C. It is a configuration that cannot be done.

  Further, when the growth temperature of the GaN layer or AlGaN layer is lowered to 900 ° C. or lower, the surface morphology is remarkably deteriorated. Therefore, the crystal growth temperature of the p-type GaN layer or p-type AlGaN layer is usually in the range of 900 ° C. to 1200 ° C. For example, a high temperature of 1100 ° C. is adopted, and from this point, it is unpredictable that the crystal growth temperature of the p-type electron block layer is 600 ° C. to 900 ° C.

The twentieth embodiment of the present invention has been described above. However, the present invention is not limited to the configuration described in the embodiment, and various modifications are possible. For example, a p-type electron block layer is used. Although it is composed of Al _0.18 Ga _0.82 N, it is not limited to such a composition ratio, AlGaN with other composition ratios may be used, and further, Al _x depending on the composition of the active layer and the p-type cladding layer. It may be changed within the range of Ga _y In _1-xy N (0 <x <1, 0 <y <1).

In the description of the twentieth embodiment of the present invention, the MQW active layer having three well layers is used as the active layer. However, the MQW active layer having another structure, for example, a 5 nm-thick layer is used. An MQW active layer or the like in which five In _0.15 Ga _0.85 N well layers having a thickness of 2.5 nm are alternately sandwiched by six In _0.03 Ga _0.97 N barrier layers may be used. It may be used.

  In the description of the twentieth embodiment of the present invention, the p-side light guide layer is a p-type layer and the n-side light guide layer is an n-type layer. It may be composed of an undoped layer.

It is explanatory drawing of the fundamental structure of this invention. It is explanatory drawing of the layer number dependence of the well layer of the correlation of mode gain and current density. It is explanatory drawing of the layer thickness dependence of the active layer of _Jth in the 1st Embodiment of this invention. 1 is a perspective view of a semiconductor laser according to a first embodiment of the present invention. It is a perspective view of the semiconductor laser of the 2nd Embodiment of this invention. It is a perspective view of the MQW structure semiconductor laser of the 3rd Embodiment of this invention. It is a perspective view of the MQW structure semiconductor laser of the 4th Embodiment of this invention. It is a perspective view of the SQW structure semiconductor laser of the 5th Embodiment of this invention. It is a perspective view of the SQW semiconductor laser of the 6th Embodiment of this invention. It is a perspective view of the SQW semiconductor laser of the 7th Embodiment of this invention. It is explanatory drawing of the SQW semiconductor laser of the 8th Embodiment of this invention. It is explanatory drawing of the SQW semiconductor laser of the 9th Embodiment of this invention. It is explanatory drawing of the SQW semiconductor laser of the 10th Embodiment of this invention. It is explanatory drawing of the SQW semiconductor laser of the 11th Embodiment of this invention. It is a perspective view of the short wavelength semiconductor laser of the 12th Embodiment of this invention. It is explanatory drawing of the growth rate dependence of the standard deviation of PL wavelength and PL light intensity in the 12th Embodiment of this invention. It is explanatory drawing of the 13th Embodiment of this invention. It is explanatory drawing of 14th and 15th embodiment of this invention. It is explanatory drawing of the MQW semiconductor laser of the 16th Embodiment of this invention. It is a perspective view of the MQW semiconductor laser of the 17th Embodiment of this invention. It is explanatory drawing of the MQW semiconductor laser of the 18th Embodiment of this invention. It is explanatory drawing of the MQW semiconductor laser of the 19th Embodiment of this invention. It is explanatory drawing of the effect in the 19th Embodiment of this invention. It is explanatory drawing of the MQW semiconductor laser of the 20th Embodiment of this invention. It is explanatory drawing of the electric current-light output characteristic of the MQW semiconductor laser of the 20th Embodiment of this invention. It is explanatory drawing of the surface emitting LED produced in order to confirm the effect in the 20th Embodiment of this invention. It is explanatory drawing of the structural condition dependence of the emission spectrum intensity | strength of surface emitting LED. It is explanatory drawing of Mg density | concentration dependence of the emitted light intensity in surface emitting type LED. It is a band diagram of the MQW active layer vicinity of the MQW semiconductor laser of the 20th embodiment of this invention. It is explanatory drawing of the structural condition dependence of the p-type carrier density | concentration in a p-type GaN layer. It is explanatory drawing of the conventional short wavelength semiconductor light-emitting device. It is explanatory drawing of the conventional short wavelength semiconductor laser. It is a band diagram at the time of the oscillation of the conventional MQW semiconductor laser. It is explanatory drawing of the layer position dependence of the hole current in the conventional MQW structure short wavelength semiconductor laser. It is explanatory drawing of the hole density distribution at the time of the oscillation of the conventional MQW semiconductor laser. It is explanatory drawing of the electron density distribution at the time of the oscillation of the conventional MQW semiconductor laser. It is explanatory drawing of the optical gain and radiation intensity distribution in the conventional MQW short wavelength semiconductor laser. It is explanatory drawing of the optical output-current characteristic of the conventional MQW semiconductor laser. A In _x Ga _1-x N In composition ratio of the barrier layer x dependency of illustration of the light emission efficiency of the quantum well structure active layer. It is explanatory drawing of the clad layer composition dependence of an overflow current. It is explanatory drawing of the element temperature dependence of the overflow current. It is explanatory drawing of the band diagram of the conventional short wavelength semiconductor laser. It is explanatory drawing of PL peak wavelength distribution of the conventional short wavelength semiconductor laser. It is explanatory drawing of the optical output characteristic in the conventional short wavelength semiconductor laser. It is explanatory drawing of the correlation of the histogram of PL peak wavelength, and light intensity in the conventional short wavelength semiconductor laser.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Clad layer 3 Light guide layer 4 Active layer 5 Light guide layer 6 Clad layer 11 n-type SiC substrate 12 AlGaN buffer layer 13 n-type GaN intermediate layer 14 n-type Al _0.15 Ga _0.85 N clad layer 15 Undoped GaN light guide layer 16 SQW active layer 17 p-type GaN optical guide layer 18 p-type Al _0.15 Ga _0.85 N cladding layer 19 p-type GaN contact layer 20 Ni electrode 21 Ni electrode 22 MQW active layer 111 n-type SiC substrate 112 AlGaN buffer layer 113 n-type GaN Intermediate layer 114 n-type Al _0.15 Ga _0.85 N cladding layer 115 undoped Al _0.05 Ga _0.95 N light guide layer 116 MQW active layer 117 p-type GaN light guide layer 118 p-type Al _0.15 Ga _0.85 N cladding layer 119 p-type GaN contact layer 120 Ni electrode 121 Ni electrode 122 Type Al _0.2 Ga _0.8 N cladding layer 123 an undoped GaN optical guide layer 124 an undoped Al _0.05 Ga _0.95 N optical guiding layer 125 SQW active layer 126 p-type Al _0.2 Ga _0.8 N overflow preventing layer 211 n-type SiC substrate 212 AlGaN buffer layer 213 n GaN intermediate layer 214 n-type Al _0.15 Ga _0.85 N cladding layer 215 undoped GaN light guide layer 216 SQW active layer 217 undoped GaN light guide layer 218 p-type Al _0.15 Ga _0.85 N cladding layer 219 p-type GaN contact layer 220 Ni electrode 221 Ni electrode 222 Undoped Al _0.05 Ga _0.95 N light guide layer 223 Undoped In _0.03 Ga _0.97 N light guide layer 224 Undoped In _0.03 Ga _0.97 N light guide layer 225 p-type Al _0.05 Ga _0.95 N light guide layer 226 Undoped G aN light guide layer 227 undoped graded light guide layer 228 p-type graded light guide layer 229 undoped Al _0.05 Ga _0.95 N light guide layer 230 p-type reverse graded light guide layer 311 n-type SiC substrate 312 AlGaN buffer layer 313 n-type GaN intermediate layer 314 n-type Al _0.15 Ga _0.85 N cladding layer 315 Undoped GaN light guide layer 316 MQW active layer 317 Undoped GaN light guide layer 318 p-type Al _0.15 Ga _0.85 N cladding layer 319 p-type GaN contact layer 320 Ni electrode 321 Ni electrode 411 n-type SiC substrate 412 AlGaN buffer layer 413 n-type GaN intermediate layer 414 n-type Al _0.15 Ga _0.85 n cladding layer 415 an undoped GaN optical guide layer 416 SQW active layer 417 an undoped GaN optical guide layer 41 p-type Al _0.15 Ga _0.85 N cladding layer 419 p-type GaN intermediate layer 420 p-type Al _0.15 Ga _0.85 N cladding layer 421 p-type GaN contact layer 422 Ni electrode 423 Ni electrode 424 graded intermediate layer 425 multilayer structure intermediate layer 511 n-type SiC substrate 512 AlGaN buffer layer 513 n-type GaN intermediate layer 514 n-type Al _0.15 Ga _0.85 N cladding layer 515 undoped GaN light guide layer 516 MQW active layer 517 undoped In _0.15 Ga _0.85 N well layer 518 undoped In _0.05 Ga _0.95 N barrier layer 519 undoped GaN optical guide layer 520 p-type Al _0.15 Ga _0.85 n cladding layer 521 p-type GaN contact layer 522 Ni electrode 523 Ni electrode 531 sapphire substrate 532 GaN low-temperature buffer layer 533 n-type GaN intermediate layer 534 -Type Al _0.15 Ga _0.85 N cladding layer 535 an undoped GaN optical guide layer 536 MQW active layer 537 an undoped GaN optical guide layer 538 p-type Al _0.15 Ga _0.85 N cladding layer 539 p-type GaN contact layer 540 Ti electrode 541 Ni electrode 611 n-type SiC Substrate 612 AlGaN buffer layer 613 n-type GaN intermediate layer 614 n-type Al _0.09 Ga _0.91 N clad layer 615 undoped GaN light guide layer 616 MQW active layer 617 undoped Al _0.18 Ga _0.82 N electron block layer 618 p-type GaN light guide layer 619 p Type Al _0.09 Ga _0.91 N clad layer 620 p type GaN contact layer 621 Ni electrode 622 Ni electrode 623 p type graded AlGaN layer 624 p type Al _0.18 Ga _0.82 N layer 625 p type graded AlGaN layer 626 p-type electron block layer 627 SiO ₂ film 711 n-type SiC substrate 712 n-type Al _0.09 Ga _0.91 N buffer layer 713 n-type Al _0.09 Ga _0.91 N clad layer 714 undoped GaN light guide layer 715 MQW active layer 716 p ⁺ type Al _0.18 Ga _0.82 N electron block layer 717 p-type GaN optical guide layer 718 p-type Al _0.09 Ga _0.91 N cladding layer 719 p-type GaN first contact layer 720 p ⁺ -type GaN second contact layer 721 SiO ₂ film 722 n-side electrode 723 p-side electrode 724 impurity level 731 n-type SiC substrate 732 n-type Al _0.09 Ga _0.91 N buffer layer 733 n-type Al _0.09 Ga _0.91 N clad layer 734 undoped GaN light guide layer 735 MQW active layer 736 p ⁺ type Al _0.18 Ga _0.82 N electron block layer 737 p-type GaN optical guide layer 738 p-type Al _0.09 Ga _0.91 N cladding layer 739 p-type GaN first contact layer 740 p ⁺ -type GaN second contact layer 741 n-side electrode 742 SiO ₂ film 743 semi-transparent electrode 744 bonding pad 811 sapphire Substrate 812 GaN buffer layer 813 n-type GaN buffer layer 814 n-type In _0.1 Ga _0.9 N layer 815 n-type Al _0.15 Ga _0.85 N clad layer 816 n-type GaN light guide layer 817 InGaN MQW active layer 818 p-type Al _0.2 Ga _0.8 N layer 819 p-type GaN optical guide layer 820 p-type Al _0.15 Ga _0.85 N cladding layer 821 p-type GaN contact layer 822 n-side electrode 823 p-side electrode 824 n-type GaN layer 825 In _0.15 Ga _0.85 N active layer 826 p-type GaN layer 831 Sapphire substrate 832 GaN back § layer 833 n-type GaN intermediate layer 834 n-type Al _0.09 Ga _0.91 N cladding layer 835 n-type GaN optical guide layer 836 MQW active layer 837 p-type Al _0.18 Ga _0.82 N overflow preventing layer 838 p-type GaN optical guide layer 839 p-type Al _0.09 Ga _0.91 N clad layer 840 p-type GaN contact layer 841 n-side electrode 842 SiO ₂ film 843 p-side electrode 844 Band edge of valence band when voltage is applied 845 notch 846 notch

Claims (53)

In a semiconductor laser using a nitride compound semiconductor, a multiple quantum well structure is used as an active layer, and the maximum position of the emitted light intensity distribution is shifted from the center position of the active layer to the p-type cladding layer side. A semiconductor laser. 2. The semiconductor laser according to claim 1, wherein the maximum position of the emitted light intensity distribution coincides with the position of the first quantum well from the p-type cladding layer side of the multiple quantum well structure. An n-side light guide layer and a p-side light guide layer are provided between the active layer and the n-type cladding layer and the p-type cladding layer, respectively, and the forbidden band width of the n-side light guide layer is set to the p-side light guide. 3. The semiconductor laser according to claim 1, wherein the semiconductor laser is larger than the forbidden band width of the layer. An n-side light guide layer and a p-side light guide layer are provided between the active layer and the n-type cladding layer and the p-type cladding layer, respectively, and the thickness of the p-side light guide layer is set to the n-side light guide layer. 4. The semiconductor laser according to claim 1, wherein the semiconductor laser has a thickness greater than the thickness of the semiconductor laser. 5. The semiconductor laser according to claim 1, wherein the forbidden band width of the n-type cladding layer of the semiconductor laser is larger than the forbidden band width of the p-type cladding layer. 6. In a semiconductor laser using a nitride compound semiconductor in which a single quantum well structure is used as an active layer and a wide band gap layer is provided between the active layer and the p-side light guide layer, the wide band gap A semiconductor laser characterized in that an n-side layer compensates for a deviation between the maximum position of the emitted light intensity distribution caused by the layer and the center position of the active layer. 7. The semiconductor laser according to claim 6, wherein the n-side layer is at least an n-side light guide layer, and the forbidden band width of the n-side light guide layer is larger than the forbidden band width of the p-side light guide layer. . 8. The semiconductor according to claim 6, wherein the n-side layer is at least an n-side light guide layer, and the layer thickness of the n-side light guide layer is made thinner than the layer thickness of the p-side light guide layer. laser. The n-side layer is at least an n-type cladding layer, and the forbidden band width of the n-type cladding layer is made larger than the forbidden band width of the p-type cladding layer. The semiconductor laser described. 2. The well layer constituting the active layer of the quantum well structure is composed of Al _x Ga _y In _1-xy N (where 0 ≦ x <1, 0 <y ≦ 1). 10. The semiconductor laser as described in any one of 1 to 9. A semiconductor laser using a nitride compound semiconductor, wherein the active layer has a multiple quantum well structure having two gain layers. A semiconductor laser using a nitride compound semiconductor, wherein the active layer is formed of a multiple quantum well structure having two or three gain layers each having a thickness of 6 nm or more. 13. The semiconductor laser according to claim 11, wherein the gain layer is composed of an undoped layer. The gain layer is described _{Al x Ga y In 1-xy} N ( where, 0 ≦ x <1,0 <y ≦ 1) any one of claims 10 to 13, characterized in that it is composed of Semiconductor laser. In a semiconductor laser using a nitride compound semiconductor, the p-side light guide layer is made of either InGaN or GaN, and the impurity concentration of the p-side light guide layer is less than 1 × 10 ¹⁷ cm ^−3. A semiconductor laser characterized by the above. 16. The semiconductor laser according to claim 15, wherein the p-side light guide layer is an undoped layer. 17. The semiconductor laser according to claim 15, wherein the hole mobility in the p-side light guide layer is 2 cm ² / V · s or more. A semiconductor laser using a nitride compound semiconductor, wherein the p-side light guide layer is thinner than the n-side light guide layer. A semiconductor laser using a nitride compound semiconductor, wherein the p-side light guide layer has a layer thickness of less than 0.1 μm. 20. The semiconductor laser according to claim 18, wherein the forbidden band width of the p-side light guide layer is larger than the forbidden band width of the n-side light guide layer. In a semiconductor laser using a nitride compound semiconductor, the forbidden band width of the p-side light guide layer is small in a portion adjacent to the active layer and large in a portion adjacent to the p-type cladding layer. Semiconductor laser. The semiconductor laser according to claim 21, wherein the forbidden band width of the p-side light guide layer changes stepwise. The semiconductor laser according to claim 21, wherein the forbidden band width of the p-side light guide layer continuously changes. In a semiconductor laser using a nitride compound semiconductor, the forbidden band width of the p-side light guide layer is continuously reduced from the side adjacent to the active layer toward the side adjacent to the p-type cladding layer. A semiconductor laser. 25. The layer according to any one of claims 21 to 24, wherein the layer having a small forbidden band width constituting the p-side light guide layer is made of InGaN or GaN, and the layer having a large forbidden band width is made of AlGaN. The semiconductor laser described. A semiconductor light emitting device using a nitride compound semiconductor, wherein the photoluminescence wavelength distribution of the active layer in the resonator is 90 meV or less. 27. The semiconductor light emitting device according to claim 26, wherein the photoluminescence wavelength distribution of the active layer in the resonator is 50 meV or less. A semiconductor light emitting device using a nitride compound semiconductor, wherein a dislocation density of an active layer in a resonator is 10 ⁹ cm ⁻² or less. 29. The semiconductor light emitting device according to claim 28, wherein the dislocation density of the active layer in the resonator is 10 ⁸ cm ⁻² or less. 30. The semiconductor light emitting element according to claim 25, wherein the active layer contains In as a constituent element. In the manufacturing method of the semiconductor light-emitting device using a nitride type compound semiconductor, the growth rate at the time of growing an active layer shall be 0.1 micrometer / hour or more, The manufacturing method of the semiconductor light-emitting device characterized by the above-mentioned. 32. The method of manufacturing a semiconductor light emitting element according to claim 31, wherein the growth rate is set to 0.2 [mu] m / hour or more. 32. The method of manufacturing a semiconductor light emitting element according to claim 31, wherein the growth rate is set to 0.3 [mu] m / hour or more. 34. The method of manufacturing a semiconductor light-emitting element according to claim 31, wherein a SiC substrate is used as a growth substrate, and a surface of the SiC substrate is etched. 35. The method of manufacturing a semiconductor light emitting element according to claim 31, wherein the active layer contains In as a constituent element. In a semiconductor laser using a nitride-based compound semiconductor, the p-type cladding layer has a multilayer structure in which an intermediate layer having a narrow forbidden band is sandwiched between two p-type semiconductor layers having a wide forbidden band. A semiconductor laser characterized by the above. 37. The semiconductor laser according to claim 36, wherein the intermediate layer is formed of a single narrow band gap layer. In the intermediate layer, the forbidden band width is continuously changed so that the forbidden band width becomes the lowest at an arbitrary position between the two wide forbidden band width p-type semiconductor layers. The semiconductor laser according to claim 36. 37. The semiconductor laser according to claim 36, wherein the intermediate layer has a multilayer structure in which a plurality of layers having a wide forbidden bandwidth and a narrow forbidden bandwidth are alternately stacked. 40. The semiconductor laser according to claim 39, wherein a forbidden band width between a wide forbidden band layer and a narrow forbidden band layer constituting the intermediate layer is continuously changed. 41. The semiconductor laser according to claim 36, wherein at least a part of the layer on the narrow band gap side of the intermediate layer is an undoped layer. The layer of wide forbidden band is made of AlGaN, and the layer of narrow forbidden band is made of any one of InGaN, GaN, or AlGaN. The semiconductor laser described in 1. A multi-quantum well structure semiconductor laser using a nitride compound semiconductor, wherein the barrier layer constituting the multi-quantum well active layer has a thickness of less than 5 nm. 44. The multiple quantum well structure semiconductor laser according to claim 43, wherein the barrier layer constituting the multiple quantum well active layer is made of InGaN having an In composition ratio of 0.04 or more. A semiconductor laser using a nitride compound semiconductor, wherein the impurity concentration of an electron block layer provided on the p side of the active layer is less than 1.0 × 10 ¹⁷ cm ⁻³ . 46. The semiconductor laser according to claim 45, wherein the electron block layer provided on the p side of the active layer is an undoped layer. A semiconductor laser using a nitride compound semiconductor, wherein a forbidden band width is gradually changed in a p-side region of an electron block layer provided on a p-side of an active layer. A semiconductor laser using a nitride compound semiconductor, wherein a forbidden band width is gradually changed in a region on an n side of an electron block layer provided on a p side of an active layer. A semiconductor laser using a nitride compound semiconductor, wherein the forbidden band width is gradually changed in the n-side and p-side regions of the electron block layer provided on the p-side of the active layer. A semiconductor laser using a nitride compound semiconductor, wherein the electron block layer provided on the p side of the active layer has a Mg concentration of 7 × 10 ¹⁹ cm ⁻³ or more. A method for manufacturing a semiconductor laser using a nitride compound semiconductor, wherein the growth temperature of an electron block layer provided on the p side of the active layer is set to 600 ° C. to 900 ° C. 52. The method of manufacturing a semiconductor laser according to claim 51, wherein the growth temperature of the electron block layer is the same as the growth temperature of the active layer. 53. The method for manufacturing a semiconductor laser according to claim 51, wherein Mg is doped so that the Mg concentration of the electron block layer is 7 × 10 ¹⁹ cm ⁻³ or more.

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