JPH10247760A - Semiconductor blue light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a P-type layer lessened in resistance by a method wherein the P-side clad layer of a double hetero-structure is doped with Mg, and an N-side clad layer is doped with Si. SOLUTION: A Si-doped N-type BP layer 42 serving as a buffer layer, an Si-doped N-type GaAlN/BP super-lattice layer 43 as thick as 1μm or so, an undoped GaAlN super-lattice layer 44 as thick as 0.1μm or so, and an Mg-doped P-type GaAlN/BP super-lattice layer 45 as thick as 1μm or so are successively laminated on an N-type GaP substrate 41. The undoped super-lattice 44 serves as an active layer. The N-type supper-lattice layer 43 is doped with Si by the use of SiH4 and kept an high in carrier concentration as 1×10<17> /cm<3> , and the P-type super-lattice layer 45 is doped with Mg by the use of CP2 Mg and kept as high in carrier concentration as 1×10<17> /cm<3> . In electrodes 46 and 47 are provided to the top and bottom of a semiconductor blue light emitting device respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a blue semiconductor light emitting device using a wide band gap compound semiconductor material useful as a short wavelength light emitting device.

[0002]

2. Description of the Related Art With the development of high-speed and high-density information processing systems, it is desired to realize short-wavelength semiconductor lasers. Conventionally, as a material of a semiconductor laser, AlGaAs is used.
III-V group semiconductor materials, such as based, InGaAsP based, and AlInP based, have been used. However, each of these has a band gap value far from the requirement for green light emission. In order to realize green light emission, a material design based on a new idea, not an existing material, is desired.

[0003] In view of the large band gap of the group III-V compound semiconductor material, BN (4 or 8e
V), AlN (6 eV), GaN (3.4 eV), In
P (2.4 eV), AlP (2.5 eV), GaP
Lighter Group III element nitrides and phosphides, such as (2.3 and 2.8 eV), have large band gaps. However, among these, BN is a high-pressure phase (c-BN) having a large band gap but four-coordinate (sp3) bonds.
Cannot be used because it is difficult to synthesize, has three types of polymorphs, and is easy to form a mixture. Impurity doping is also difficult.

[0004] InN has a small band gap, poor thermal stability, and can usually only obtain polycrystal. AlP and GaP each have a slightly insufficient band gap. The remaining AlN and GaN have a large band gap and excellent stability, and can be said to be suitable for short-wavelength light emission. However, AlN and GaN have a wurtzite type (Wurzeite type, hereinafter abbreviated as WZ type) crystal structure, and have high ionicity, so that lattice defects are likely to occur and a low-resistance p-type semiconductor can be obtained. Can not.

[0005] In order to solve such a problem, a material which does not contain B and N, which are materials developed for a conventional semiconductor laser.
Attempts have been made to obtain a material having a larger band gap by mixing B and N with a II-V group compound. But,
Stable crystals have not been obtained because the lattice constants of the conventionally used materials and the materials containing B and N are greatly different from 20 to 40% and the lattice types are also different. For example, GaP
When N is mixed with N, N can be mixed in only 1% or less of GaP, and it is impossible to obtain a sufficiently wide band gap.

According to the study of the present inventors, GaN and Al
The reason that a low-resistance p-type crystal cannot be obtained with N is that defects due to high ionicity are liable to occur, and that these are zinc-blende type (Zinc Blende type, hereinafter abbreviated as ZB type) crystals. The essential reason is that it has a WZ structure instead of a structure. This situation will be described below with reference to the drawings.

FIG. 7A shows a band structure of a cubic semiconductor. Here, the bottom of the conduction band is indicated by a point 宜 for convenience, but there is no essential difference in the discussion even in other places. Near the top of the valence band in question, the bands of heavy holes and light holes are degenerated. In the valence band, there is an orbit shifted to a lower energy side due to spin-orbit interaction. In this case, the holes are present in both the heavy and light bands, so the effective mass is the average of both.

However, in the hexagonal WZ structure, the strong uniaxial anisotropy strongly influences the crystal field, and as shown in FIG. 7B, the degeneracy of the band of the heavy hole and the light hole is released, and the band of the heavy hole is released. Shifts to the higher energy side. As a result, holes will be present in this heavy hole band. As a result, the effective mass of the hole is increased, so that the energy of the acceptor level is also increased, and it becomes difficult to emit the hole, so that a p-type with low resistance cannot be formed.

[0009]

As described above, conventionally, the band gap required for realizing a green light emitting semiconductor laser or a high-brightness blue LED is sufficiently large, for example, 2.7 eV or more, and pn control is possible. There was no semiconductor material satisfying the condition that the crystal quality was good. Al
Although nitrides such as N and GaN are effective materials for obtaining a large band gap, a low-resistance p-type layer cannot be obtained.

The present invention has been made in view of the above points, and provides a blue semiconductor light emitting device having a large band gap, a pn control, and a compound semiconductor material capable of obtaining a stable crystal. The purpose is to do.

[0011]

[Means for Solving the Problems]

(Structure) In order to solve the above problem, the present invention employs the following structure.

That is, according to the present invention, in a blue semiconductor light emitting device having a pn junction, a buffer layer formed on a single crystal substrate and a light emitting layer formed on the buffer layer and having a light emitting layer of GaAs
a double heterostructure portion formed between the p-type and n-type cladding layers made of an 1N-based material, wherein the p-side cladding layer of the double heterostructure portion is doped with Mg;
The side cladding layer is characterized by being doped with Si. Here, the active layer is preferably made of a superlattice of AlGaN and BP.

(Function) According to the present invention, the p-side cladding layer made of GaAlN-based material is doped with Mg.
This has important implications.

GaAs, which is a well-known material,
In this case, Zn is used as the p-type impurity. This is because although the activation rate of Zn is not so high, the GaAs
This is because the p-type GaAs is sufficiently taken in, and the resistance of the p-type GaAs can be sufficiently reduced. Mg located in the same group as Zn
Does not function as a p-type impurity in theory, but has a strong bond with O.
O is taken into the As crystal, and the resistance of the p-type GaAs increases. For this reason, Mg was considered to be undesirable as a p-type impurity.

On the other hand, when N is contained as in the GaAlN-based material of the present invention, the bond between Mg and N is strong,
Even if AlN is doped with Mg, O is less likely to be taken in. Therefore, Mg can be used as the p-type impurity. Further, as in GaAlN-based materials, A
When l is included, the band gap is wider than GaN and the level to be formed is deeper, so that doping with an impurity causes a problem that the lattice is distorted. When such a material is doped with conventional general Zn as a p-type impurity, Zn and Al
Are different from each other, the lattice is distorted and the resistance is increased.
On the other hand, since Mg has the same period as Al and is in a close position (adjacent group), it is easy to substitute for Al and Ga
Even if AlN is doped, the lattice distortion is small.

Therefore, as in the present invention, by doping the cladding layer made of a GaAlN-based material with Mg,
As a result, a p-type clad layer having a lower resistance and a higher quality than that obtained when Zn is doped can be obtained.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the illustrated embodiments.

(First Embodiment) An embodiment of the present invention will be described below.

FIG. 1 shows a semiconductor wafer having a GaN / BP superlattice structure according to one embodiment. In this embodiment, a GaP layer 2 as a buffer layer is formed on a GaP substrate 1.
Are formed, on which BP layers 3 and GaN layers 4 are alternately stacked at a predetermined period.

FIG. 2 shows a multi-chamber type metal organic chemical vapor deposition (MOCVD) apparatus used for manufacturing such a superlattice structure semiconductor wafer. In the figure, 1
Numerals 1, 12 and 13 are reaction tubes made of quartz, and necessary raw material gases are taken in from gas introduction ports located above the respective reaction tubes. These reaction tubes 11, 12 and 13 are vertically mounted in one chamber 14 through the upper lid thereof. The substrate 15 is placed on a graphite susceptor 16, is arranged so as to face the openings of the reaction tubes 11, 12 and 13, and is heated to a high temperature by an external high-frequency coil 17.

The susceptor 16 is mounted on a quartz holder 18 and can be moved at high speed below each of the reaction tubes 11, 12, and 13 by a drive shaft via a magnetic fluid seal. Driving is performed by a computer-controlled motor installed outside. A thermocouple 20 is placed at the center of the susceptor, monitors the temperature immediately below the substrate, and takes it out. The cord portion uses a slip ring to prevent twisting due to rotation. The reaction gas is extruded by a fast down-flow of hydrogen gas from the upper outlet 21, and while the mixing with each other is suppressed as much as possible, the exhaust gas 22
Exhausted by a rotary pump.

With such an MOCVD apparatus, a desired source gas is flowed through each of the reaction tubes 11, 12, and 13, and the substrate 15 is moved by a computer-controlled motor. A multilayer structure can be produced with the composition. In this method, a sharp concentration change that cannot be obtained by the gas switching method can be easily realized. In addition, in this method, it is not necessary to switch the gas at a high speed in order to form a steep hetero interface, so the problem that the decomposition rate of NH ₃ or PH ₃ as a raw material gas is slow is solved by setting the gas flow rate low. can do.

Using the MOCVD apparatus shown in FIG. 2, the semiconductor wafer shown in FIG. 1 was specifically manufactured, and the properties of the crystal layer of the obtained wafer were examined. The results are described below.
The raw material gases used were methyl organic metal trimethylgallium (TMG), trimethylaluminum (TMA),
Diborane (B ₂ H ₆ ) or triethyl boron (TEB)
And phosphine (PH ₃ ) and ammonia (NH ₃ ).

The substrate temperature was 850 to 1150 ° C., the pressure was 0.3 atm, the total flow rate of the raw material gas was 1 l / min, and the gas flow rate was set so that the growth rate was 1 μm / h.
The specific flow rate of each raw material gas is 1 × 10 ⁻⁶ mol for TEB.
/ Min, TMG 1 × 10 ^-6 mol / min, PH ₃ 5 ×
10 ⁻⁴ mol / min, and NH ₃ is 1 × 10 ⁻³ mol / min. The lamination cycle was kept at 50 to 30 nm, and the thickness ratio (D _BP / D _{Ga N} = r) of the BP layer 3 to the GaN layer 4 was kept at 1 or 2.

The resulting superlattice layer was traced by Auger spectroscopy while B and Ga signals were etched with Ar ions. As a result, it was found that the concentration change was sharp at any of the interfaces. This sharpness was about 3 nm, which is about the same as the escape length of Auger electrons. In addition, when a long-period structure of a 50-period superlattice layer was examined by small-angle X-ray scattering, it also reflected a good long-range order.

In the hole measurement of the GaN layer of the manufactured superlattice layer, it was found that the carrier concentration showed n-type conduction of about 1 × 10 ¹⁶ / cm ^{3, and} that the number of vacancies of N atoms was very small. . When TMG is replaced with TMA, G
It was also confirmed that aN was mixed with Ga _x Al ₁ -xN to form a superlattice layer composed of Ga and Al and a BP layer. The electric resistance of this superlattice layer increased remarkably when x was 0.4 or more, and became a high resistance almost regarded as an insulator.

When the laminating period of the GaN / BP superlattice layer was reduced to 6 nm or less while maintaining r = 2, the reflection of the WZ structure caused by GaN became unclear from the diffraction pattern of the X-ray diffractometer. At 4 nm or less, reflection was considered to be considered to have a ZB structure. However, the grid is distorted. As a result, it was confirmed that GaN having a ZB structure was synthesized when the thickness of the laminated film was selected. When the BP layer was set to 7 nm and the thickness of the GaN layer was changed, a GaN layer having a ZB structure was grown up to the GaN layer of 5 nm, and the band gap increased linearly with respect to the GaN layer thickness.

Similar results were obtained when AlN was grown instead of GaN. Therefore, if the composition ratio x is changed by changing the film thickness ratio or by growing Ga _x Al ₁ -xN, the band gap can be changed while keeping the lattice constant constant. Ga _x Al _1-x N
When the film thickness ratio between the layer and the BP layer was 1.0 or more, it was recognized that the indirect transition type was changed to the direct transition type.

As described above, in the case of undoping, the superlattice layer according to this embodiment exhibits n-type conduction. However, by mixing dimethyl zinc (DMZ) with a source gas and doping with Zn, a p-type crystal is formed. I got it. DMZ
The carrier concentration can be controlled at the same time as the conductivity type by changing the amount of.

As described above, according to this embodiment, nitride (GaAlN, GaN, Al
A sharp heterojunction of N) and a phosphide (BP) can be produced, whereby a compound semiconductor wafer having a ZB structure and a pn controllable wide band gap (> 2.7 eV) can be obtained. If this semiconductor wafer is used, a high-intensity blue LE
D and green light semiconductor lasers can be configured.

FIG. 3 shows a semiconductor wafer according to another embodiment of the present invention. In this embodiment, Ga _x Al, which is a mixed crystal, is formed on a GaP substrate 1 via a GaP layer 2 as a buffer layer.
The _{y B 1-xy N z P} 1-z layer 5 is grown.

FIG. 4 shows an MOCVD apparatus used for producing the semiconductor wafer of FIG. Reference numeral 23 denotes a quartz reaction tube through which a raw material gas is introduced through a gas inlet 24 located above the tube. The gas in the reaction tube 23 is exhausted from the exhaust port 25. The substrate 27 is placed on a graphite susceptor 26 and arranged in the reaction tube 23, and is induction-heated by an external high-frequency coil 28. 29 is a thermocouple for detecting the temperature of the susceptor 26.

Using the MOCVD apparatus of FIG. 4, FIG.
A GaP layer 2 is grown on a GaP substrate 1 as shown in FIG.
Thereon _{Ga x Al y B 1-xy} N z P 1-z (0 ≦ x,
y, z ≦ 1) A mixed crystal layer 5 was grown. The raw material gas is a methyl organic metal such as trimethyl gallium (TMG), trimethyl aluminum (TMA), diborane (B ₂ H ₆ ) or triethyl boron (TEB) and phosphine (P
H ₃ ) and ammonia (NH ₃ ). Substrate temperature is 85
Each raw material gas flow rate was set so that N and Al, and B and P were mixed in substantially the same amount at 0 to 1150 ° C. and a pressure of 0.3 atm.

The obtained Ga _x Al _y B _1-xy N _z P _1-z
The layer 5 was subjected to surface analysis and composition analysis by characteristic X-rays using an electron probe.
It was confirmed that l, B and P were uniformly mixed by almost the same amount. At this time, it was confirmed by X-ray diffraction that the whole was epitaxially grown with a ZB structure. Observation with a transmission electron microscope revealed a clean lattice plane and no clustered area.

Further, in order to obtain a p-type crystal, the same crystal growth was carried out by mixing diethyl zinc (DEZ) with the raw material gas. Although the obtained crystal had a high resistivity of 10 ⁵ Ω · cm, it was recognized that it was a p-type, and the photoluminescence was examined.

Thus, also in this embodiment, a mixed crystal layer of BP and GaAlN having a large band gap, capable of controlling pn, and having good crystal quality can be obtained.

Next, an embodiment in which the present invention is applied to a specific element will be described.

FIG. 5 shows an embodiment of an LED using a GaAlN / BP superlattice layer. On a Si-doped n-type GaP substrate 31, a Si-doped n-type BP layer 3 is formed as a buffer layer.
2 is grown to about 2 μm, and Si-doped n-type Ga
The AlN / BP superlattice layer 33 is about 3 μm
A GaAlN / BP superlattice layer 34 is sequentially grown by about 2 μm. The crystal growth was performed by the MOCVD apparatus shown in FIG.

The superlattice layers 33 and 34 are, specifically, Ga
_0.5 Al _0.5 N and BP alternately laminated, 1 nm + 1 n
m. The n-type superlattice layer 33 uses silane (SiH ₄ ) as a dopant to obtain a carrier concentration of 1 × 10 ¹⁷ / cm ³ , and the p-type superlattice layer 34 uses cyclopentadienyl magnesium (CP ₂ Mg) as a dopant. And a carrier concentration of 2 × 10 ¹⁶ / cm ³ is obtained. In electrodes 35 and 36 are provided on both surfaces of the element wafer, respectively.

With this structure, high-luminance blue light emission can be obtained.

FIG. 6 shows an embodiment of a DH laser using a GaAlN / BP superlattice layer. As in the previous embodiment,
It is made using the MOCVD apparatus of FIG. That is, n-type Ga
First, an n-type B doped with Si as a buffer layer
A P layer 42 is formed, on which a Si-doped n-type GaAl
The N / BP superlattice layer 43 is about 1 μm, the undoped GaAlN superlattice layer 44 is about 0.1 μm, and the Mg-doped p-type GaAlN / BP superlattice layer 45 is further
μm growth. The undoped superlattice layer 44 is the active layer.

The composition of each of the superlattice layers 43 to 45 is Ga _0.5
It is an alternate stack of Al _0.5 N and BP. In the p-type and n-type superlattice layers 45 and 43, 2n of 0.7 nm + 1.3 nm is used.
The band gap is about 3.0 eV at m periods, and the band gap is 2.7 eV at 10 A periods of 5A + 5A in the undoped superlattice layer 44. The n-type superlattice layer 43 has a carrier concentration of 1 × 10
¹⁷ / cm ³ , and the p-type superlattice layer 45 is doped with Mg by using CP ₂ Mg to obtain a carrier concentration of 1 × 10 ¹⁷ / c.
It has gained m ^3. In electrodes 46 and 47 are formed on both surfaces.

The DH laser of this embodiment emits blue light.

The present invention is not limited to the above embodiment. For example, it is possible to mix a small amount of In, Tl, etc. in addition to Ga, Al, B as a group III element, and to mix As, Sb, Bi, etc. as a group V element. As a raw material gas, triethyl gallium (TEG) is used for Ga raw material, and triethyl aluminum (TE) is used for Al.
An ethyl group organic metal such as A) can be used, and trimethyl boron (TMB) can be used as a raw material of B. As the N raw material, instead of ammonia, nitrogen gas or hydrazine (N ₂ H ₄ ), furthermore, Ga (C ₂ H ₅ ) ₃ .NH ₃ ,
_{Ga (CH 3) 3 · N} · (CH 3) 3, Al (C
_{2 H 5) 3 · NH 3} , Al (CH 3) 3 · N · (C
An organometallic compound called an adduct such as H ₃ ) ₃ can be used.

The compound semiconductor material according to the present invention, ie, Ga
Superlattice structure semiconductor or mixed crystal semiconductor Ga of AlN and BP
_x Al _y B _1-xy N _z P _1-z is a combination of direct transition type and indirect transition type and WZ structure and ZB structure having different characteristics as described above. The problem is that the bond length is particularly short as compared with other bond lengths, and AlN has a high resistance. As described above, it is necessary that x + y is approximately equal to z in order for the semiconductor material to exist stably.

Next, the problem of the crystal structure is important. Generally, highly ionic crystals tend to have a hexagonal structure,
Mold doping tends to be difficult. This is thought to be due to the effect of the crystal field due to the strong uniaxial anisotropy of the hexagonal structure, where heavy holes break the band degeneracy and form a band that forms the top of the valence band. For this reason, it is believed that satisfactory pn junctions of II-VI compounds, which often have a WZ structure, cannot be obtained.

From the above points, a crystal having a cubic structure is indispensable for producing a pn junction. AlN, GaN
Is preferably a direct transition type having a large band gap of 6.2 eV and 3.4 eV, respectively, and both crystals have a WZ structure. The remaining constituent B, P compound BP has a small band gap of about 2.0 eV and is an indirect transition type, but has a ZB type structure. Therefore, the lower limits of the ZB type components B and P necessary for keeping the crystal in the ZB type should be determined. According to our experiments,
The lower limit of the B and P components is 0.2, that is, x + y to z ≦ 0.8
It was necessary to be. Above this point, some of the crystals begin to take on a WZ structure.

Another problem is the band structure. BP
Is an indirect transition type having a conduction band bottom at point X, and AlN,
GaN is a direct transition type with a bottom at the Г point. FIG. 8 shows changes in the band gap and the position of the bottom of the conduction band depending on the composition of the mixed crystal assumed from these substances. Here, BP
And AlN, and the composition of two pseudo-binary systems of BP and GaN (Al
_{a N a B 1-a P} 1-a, Ga b N b B 1-b P 1-b; 0 ≦
a, b ≦ 1) shows a change in the band structure. In the figure, X, Г, and A are symbols indicating the position of the bottom of the conduction band.

Such a linear approximation is made of GaAs-AlAs
It is a sufficiently accurate approximation for mixed crystals of the system. It can be said that there is no indirect transition type steady laser oscillation example, and it is important that a direct transition type is used when a light emitting element is realized. Therefore, it is necessary to increase the ratio of the nitride component to the boride component to obtain a direct transition type. FIG.
, The band structure is almost determined by the value of x + y, and x
It can be seen that it does not depend much on the ratio between y and y. From this, in order to be a direct transition type, the superlattice layer and the mixed crystal layer are limited to the range of the majority nitride composition of 0.6 ≦ x + y to z in the co-average composition.

Also, the composition ratio of the group III element must be considered. Increasing the Al concentration increases the AlN component and effectively widens the band gap.
aN, the shorter lattice constants or binding length than BP, unfavorable also AlN in terms of lattice matching is typically 10 ¹⁰
It has a high resistance of Ω · cm or more and has a problem as a component of the element. In the case of a mixed crystal, if an Al--P bond is formed, the bond is cubic and has low resistance. However, the bond length is as large as 0.236 nm, and the formation of an indirect transition type compound AlP which is unstable in air is frequently performed. Therefore, it is not preferable to increase the Al concentration.

FIG. 9 shows the change in the bond length of the mixed crystal AlGaN depending on the composition. In the Al: Ga = 1: 1 composition, the band gap is about 4.8 eV, which is wide enough to correspond to the ultraviolet region, but the mismatch of the bond length reaches 2% with respect to BP. From the above, it is appropriate to suppress the Al composition y to about y ≦ 2x.

In the case of a superlattice layer, there is a problem that electrons are localized in one layer. If the electrons are localized in a layer thicker than the mean free path of the electrons, not only the characteristics of the superlattice structure do not appear, but also the electrical conductivity is lowered, and it becomes difficult to fabricate the device. Therefore, the stacking cycle naturally has an upper limit.

An embodiment in consideration of the above-described preferable composition and the like will be described below.

FIG. 10 shows the GaAlN of such an embodiment.
/ BP superlattice structure wafer. The MOCVD apparatus shown in FIG. 2 was used for producing the superlattice structure wafer. The wafer is
A GaP layer 52 as a buffer layer is formed on a GaP substrate 51, on which a BP layer 53 and a GaAlN layer 54 are alternately stacked. The lamination period is 5 to 30 nm,
The thickness of the BP layer 53 and the GaAlN layer 54 was set to be 1: 1. The source gas is trimethyl aluminum (TMA), trimethyl gallium (TMG), triethyl boron (TEB), ammonia (NH ₃ ), and phosphine (PH ₃ ).

The substrate temperature is about 850 to 1150 ° C., the pressure is 0.3 atm, and the total flow rate of the raw material gas is 1 l / min.
The gas flow rate was set so that the growth rate was 1 μm / h. The approximate gas flow rates are as follows: TMA: 1 × 10 ⁻⁶ mol /
min, TMG: 1 × 10 ⁻⁶ mol / min, TEB: 1 × 1
0 ^-6 mol / min, PH ₃ : 5 × 10 ^-4 mol / min, NH
₃ : 1 × 10 ⁻³ mol / min. Further, silane (S
iH ₄ ) and cyclopentadienyl magnesium (C
Doping was also performed by mixing P ₂ Mg) with the source gas.

The characteristics of the obtained super lattice structure wafer were measured. First, in the hole measurement of the undoped GaN layer grown in the preparation stage, the carrier concentration was 1 × 10 ¹⁶ / c.
m ³ , n with a hole mobility of about 150 cm ² / V · sec
It showed type conduction, and it was confirmed that vacancies of N atoms were very few. On the other hand, the AlN layer showed a high resistance of 1 × 10 ⁶ Ω · cm or more. In the superlattice with a lamination period of 4 nm, when the nitride portion is mixed with AlN, the electric resistance becomes 0.6 in the composition Al _w Ga _1-w N (0 ≦ w ≦ 1).
In the region of 5 or more, the number increased remarkably, and the crystal itself became imperfect.

FIG. 11 shows a change in resistivity ρ depending on the Al composition of the superlattice structure. From this figure, it can be seen that Al and Ga
It should be understood that the composition ratio should be limited to at most about 2: 1.

FIG. 12 further shows the composition ratio of the nitride layer as Ga
It is a result of examining a change in specific resistance when only the laminating cycle is changed while fixing to _0.5 Al _0.5 N. Lamination cycle is 2
When the thickness is extremely small, such as about 3 atomic layers, the effect of structural disorder and defects is strong, and the resistance is high.
The same size as the layer alone. However, when the lamination period is 5
The resistance starts to increase from about 0 A, and reaches 10 times or more, which is three times or more that of a short cycle. This is considered to be a result of localization of electrons in one layer.

In the method of the present invention, the ratio of the thickness of AlGaN to BP (r = D _AlGaN / D _BP ) or Al _w Ga _{1 -w}
If the composition w of N is changed, the band gap can be changed while the lattice constant is kept constant. Therefore, the semiconductor layer with the required characteristics
It is considered that the composition and the laminated structure can be obtained by predicting and growing the composition and the laminated structure according to the theory using the growth apparatus of FIG. However, it has been found from the production of a multilayer wafer that a desired wide band gap semiconductor layer cannot be obtained with an arbitrary composition and a laminated structure.

FIG. 13 shows a cross-sectional structure of a single-heterojunction type LED prototyped using the above-described superlattice semiconductor. First, a p-type BP layer 62 having a thickness of 2 μm and a carrier concentration of 3 × 10 ¹⁷ / cm ³ is formed as a buffer layer on a Zn-doped p-type GaP substrate 61 having a carrier concentration of 5 × 10 ¹⁷ / cm ³ . On top of this, a thickness of 2 μm and a carrier concentration of 1 × 1
0 ¹⁷ / cm ³ p-type Al _0.5 Ga _0.5 N / BP superlattice layer 63, thickness 2 μm, carrier concentration 1 × 10 ¹⁶ / cm ³
The n-type Al _0.5 Ga _0.5 N / BP superlattice layer 64 is sequentially formed. The band gap was changed by changing the thickness ratio r of the superlattice in this portion. Then, an n-type GaN layer 65 was formed thereon as a contact layer. Ohmic electrodes 66 and 67 were formed on both surfaces, respectively.

FIG. 14 shows the change in the luminance of the LED obtained as described above depending on the average composition. Here, the average composition satisfies x + y = z, which means that a superlattice structure is expressed using the nitrogen composition ratio z as a parameter. z is small and the indirect transition BP emits little light in most regions. As z is increased, the band structure changes directly to a transition type near z = 0.5, so that the luminance sharply increases. As the band gap increases with increasing z,
The emission wavelength also becomes shorter. The increase in brightness is z = 0.7
It reaches a local maximum in the vicinity, after which the brightness sharply drops again.

This decrease in luminance is due to the fact that a part of the crystal has a WZ structure and a good p-type cannot be obtained. That is, in this region, it is difficult to form a low-resistance p-type crystal, and even in X-ray diffraction, the peak due to the ZB-type structure is unclear, and reflection that seems to be due to the WZ-type structure is recognized. When z = 0.85 or more, the majority is W
Z-type was formed, no p-type layer was obtained, and no light emission was observed.

FIG. 15 is a sectional view of a double heterojunction (DH) type laser employing a similar superlattice structure. ^On an n-type GaP substrate 71 having a Si doping and a carrier concentration of 1 × 10 ¹⁸ / cm ³ , a Si doping and a carrier concentration of 5 × 10 ¹⁷ / c are provided.
An m ³ p-type BP buffer layer 72 is formed to a thickness of 2 μm. An n-type AlGaN / BP superlattice layer (Si-doped, carrier concentration of 1 × 10 ¹⁷ / cm ³ ,
1 μm) 73, undoped AlGaN /
BP superlattice layer (carrier concentration 2 × 10 ¹⁶ / cm ³ ;
1 μm) 74, and p-type Al as the second cladding layer
GaN / BP superlattice layer (Mg doped, carrier concentration 1 ×
10 ¹⁷ / cm ³ , 1 μm) 75 are sequentially formed.

Next, an n-type BP layer (Si-doped, carrier concentration 2
× 10 ¹⁷ / cm ³ , 1 μm) 76 is formed, and a p-type BP layer (Mg doped, carrier concentration 5 × 1) is formed as a contact layer.
0 ¹⁷ / cm ³ ) 77 was formed. Ohmic electrodes 78 and 79 are formed on both sides to complete.

FIG. 16 shows the result of measuring the change in the threshold current density with respect to the DH laser while changing the composition z of the superlattice semiconductor in the same manner as in the LED described above. However, as in the case of the above LED, the relationship of x + y = z is satisfied. When the nitrogen composition ratio is z = 0.45, about 100 kA / cm
² and a minimum value of 50 kA / cm ² around z = 0.75.
When z = 0.85 or more, the value rapidly increases and oscillation becomes impossible. Again, it was confirmed that a satisfactory pn junction could not be formed only with nitride, and that a light-emitting element could not be manufactured.

In the above-described embodiments of the LED and the DH laser, a superlattice semiconductor is used for the light emitting layer, and the composition ratio of Al and Ga and the lamination period of the superlattice layer are fixed in order to change the band gap. The thickness ratio r was changed.
Changing the composition ratio of 1 to Ga can easily change the band gap. However, in this case, there is a problem that if the Al concentration is easily increased, only a high-resistance n-type layer can be obtained. When the band gap is changed by this method, it is necessary to reduce the ratio of the nitride component to some extent.

In the above-described embodiment of the LED and the DH laser, the superlattice semiconductor portion is replaced with a ZB-type Ga _x
Al _y B _1-xy N _z P _1-z (0 ≦ x, y, x + y to _z )
It can be replaced with a mixed crystal semiconductor having the following composition.
For example, in order to obtain such a mixed crystal with the MOCVD apparatus shown in FIG. 2, the movement of the substrate during the crystal growth is stopped, and instead, a reaction gas mixed with a predetermined component may be introduced through one reaction tube. However, in this case, it is important to mix the reaction gas immediately before the reaction tube in order to prevent the mutual reaction of the source gases.

As a result of actually producing such a mixed crystal, x +
In the range of y = z ≦ 0.75, it was recognized by X-ray diffraction that the entire crystal was epitaxially grown with a ZB type. In observation with a transmission electron microscope, a regular lattice plane was observed, and no clustered region was particularly observed. Without adding Ga, the composition of Al and B was set to 1:
In the sample set to 1, the electric resistivity of the crystal is 10 ⁵ Ω · cm.
As described above, in the Hall measurement, the carrier concentration is 1 in the n-type.
It is about 0 ¹⁸ / cm ³ . This is presumed to be caused by N atom vacancies in the AlN layer, as generally said. The mobility was as low as about 50 cm ² / V · sec. z = x +
When a mixed crystal deviated from the condition of y by 5% or more was formed, it was confirmed that the half-width of the Bragg peak in X-ray diffraction increased to 0.2 degrees or more, and the peak intensity was significantly reduced.

FIG. 17 shows that x = 0.2, y = 0.3, z =
The change of the half width with respect to the composition deviation δ when 0.5 ± δ is shown. When the deviation δ is large, it cannot be said that a uniform mixed crystal layer is epitaxially grown on the substrate. Although the growth of mixed crystals has a large degree of freedom in the composition ratio range,
In many cases, a single crystal having a uniform composition cannot be obtained even in a minute region.

When a light emitting device is made of a new compound semiconductor material according to the present invention, it is difficult to select a substrate that is transparent to the emission wavelength and can achieve lattice matching. Problem. In addition, stress is applied to the light emitting layer due to lattice mismatch. An embodiment that solves this point will be described below. In the following embodiments, after forming a semiconductor layer having a wide band gap composed of a superlattice structure or a mixed crystal on a substrate in the same manner as the above-described embodiment, the substrate and the buffer layer are removed to improve the light extraction efficiency. Improve.

FIG. 18 shows an LED having a double hetero junction structure according to such an embodiment. This LED is a p-type AlGa
N / BP superlattice layer 81, undoped AlGaN / BP
Superlattice layer 82 and n-type AlGaN / BP superlattice layer 83
And a thick WZ structure n-type AlGaN contact layer 84 formed thereon. Ohmic electrodes 85, 8 on the n-side and p-side, respectively.
6 are formed.

This LED is manufactured using the MOCVD apparatus shown in FIG. A specific manufacturing process will be described below.

The source gases are TMA, TMG, TEB, N
H ₃ and PH ₃ . Substrate temperature is 850 ° C to 1150
℃, pressure 0.3 atm, total flow rate of raw material gas is 1 l / min
And the gas flow rate was set such that the growth rate was 1 μm / h. The approximate flow rate of each source gas is TMA;
10 ^-6 mol / min, TMG; 1 × 10 ^-6 mol / min, T
EB; 1 × 10 ^-6 mol / min, PH ₃ ; 5 × 10 ^-4 mol
/ Min, NH ₃ ; 1 × 10 ⁻³ mol / min. As the dopant, Si was used for the n-type and Mg was used for the p-type. Si was doped by mixing silane (SiH ₄ ) and Mg by cyclopentadienyl magnesium (CP ₂ Mg) by mixing them into the source gas.

First, on a Zn-doped p-type GaP substrate,
A 0.1 μm p-type BP buffer layer is formed. Next, on this buffer layer, a p-type AlGaN / BP superlattice layer 81 is formed.
(Carrier concentration 1 × 10 ¹⁷ / cm ³ , thickness 2 μm, band gap 3.0 eV), undoped AlGaN / B
P superlattice layer 82 (thickness 0.5 μm, band gap 2.
7 eV), and an n-type AlGaN / BP superlattice layer 83 (carrier concentration 1 × 10 ¹⁷ / cm ³ , thickness 2 μm, band gap 3.0 eV) is sequentially grown. Laminate portion of the DH structure, the portion of band gap 3.0 eV, Al _0.5
Ga _0.5 N (1.3 nm) / BP (0.7 nm), an undoped part having a band gap of 2.7 eV and Al _0.5 G
a _0.5 N (1 nm) / BP (1 nm), and the lamination period is 2 nm.

Then, on this DH structure, a contact layer 84 of Si-doped n-type AlGaN (carrier concentration 5 × 10 ¹⁷ / cm ³ , band gap 3.4 eV) is grown to 30 μm. This contact layer 84 is made of n-type A
The vicinity of the interface with the lGaN / BP layer 83 is a ZB type,
Most of them become WZ type by growing thickly. This is not only transparent to the emission wavelength, but also has a high growth rate and is suitable for growing a thick layer such as a contact layer.

After each semiconductor layer is grown in this manner, Ga
The P substrate side is polished and etched with a 2% bromine methyl alcohol solution to completely remove the substrate and the BP buffer layer. Finally, the In electrodes 85 and 86 are formed on both surfaces to complete the LED of FIG.

According to this embodiment, by removing the substrate and the buffer layer while leaving the thick contact layer, a loss due to light absorption is avoided, and the luminance of 20 mcd blue, which is nearly twice as bright as that without removing the substrate, is eliminated. Light emission was confirmed. Also, unnecessary stress is not applied to the light emitting layer portion by removing the substrate, and the reliability is improved.

The same effect can be obtained when a mixed crystal layer having the same composition as that of the light emitting layer is used instead of the AlGaN / BP superlattice structure. Also, the light emitting layer is not limited to the DH structure, and the effect of removing the substrate can be similarly expected in the case of a homo junction or a single hetero junction.

FIG. 19 shows a single heterojunction type L according to another embodiment in which a contact layer is left only near the electrodes.
ED. The raw materials and manufacturing method are basically the same as in the embodiment of FIG. First, a p-type BP layer (carrier concentration: 2 × 10 ¹⁷ / cm ³ , thickness: 5 μm) 91 is grown as a buffer layer and a contact layer on a Zn-doped p-type GaP substrate.
Next, a p-type AlGaN / BP superlattice layer (carrier concentration: 1 × 10 ¹⁷ / cm ³ , thickness: 3 μm, 1.
3 nm / 0.7 nm stack) 92, n-type AlGaN / B
P superlattice layer (carrier concentration 2 × 10 ¹⁶ / cm ³ , thickness 3
μm, 1 nm / 1 nm stack) 93 are sequentially grown, and an n-type BP layer 94 is formed thereon as a contact layer by 5 μm.
m. Again, the composition of the superlattice layer is Al _0.5 G
a _0.5 N / BP, and the lamination cycle was unified to 2 nm.

After the crystal growth, the GaP substrate is removed by etching in the same manner as in the previous embodiment. Then, In electrodes 95 and 96 are formed on both surfaces, and the BP layers 91 and 94 on both surfaces are etched by using these electrodes as an etching mask, and FIG.
9 is obtained.

Also in this embodiment, a blue LED with high luminance and a long life was obtained by etching and removing the substrate and unnecessary contact layers. Also in this embodiment, an equivalent mixed crystal film can be used instead of the superlattice layer.

FIG. 20 shows an LED according to another embodiment having a buffer layer and a contact layer that are thin enough that light absorption does not matter. A p-type B having a thickness of 0.1 μm and a carrier concentration of 3 × 10 ¹⁷ / cm ^{3 is formed on} a Zn-doped p-type GaP substrate.
A P buffer layer 101 is formed. Next, on this buffer layer, a p-type AlGaN / BP superlattice layer 102 (carrier concentration 1 × 10 ¹⁷ / cm ³ , thickness 2 μm, band gap 3.0 eV), undoped AlGaN / BP superlattice layer 103 (thickness 0.5 μm, band gap 2.7e
V), an n-type AlGaN / BP superlattice layer 104 (carrier concentration 1 × 10 ¹⁷ / cm ³ , thickness 2 μm, band gap 3.0 eV) is sequentially grown. The structure of the DH structure is the same as that of the embodiment shown in FIG.

As a contact layer on the DH structure,
Si-doped n-type BP layer (carrier concentration 3 × 10 ¹⁷ / c
m ³ ) 105 is grown 0.1 μm. After each semiconductor layer is grown, after mechanical polishing, the GaP substrate is removed by etching with a 2% bromine methyl alcohol solution, and In electrodes 106 and 107 are formed.

Even if the contact layer is left as in this embodiment, if it is very thin, light absorption is small,
High luminance characteristics can be obtained.

As described above, one problem is that the compound semiconductor material according to the present invention does not have a high quality substrate capable of achieving lattice matching. As described in the above embodiments, when a GaP substrate is used, there is about 15% lattice mismatch, which causes a defect and a large stress is applied to the light emitting layer. is there. An embodiment of a highly reliable light emitting element which solves this point will be described below. In the following embodiments, a multi-layered buffer layer having the same configuration as that used for the light emitting layer is grown as a base of the light emitting layer.

FIG. 21 shows a semiconductor laser of such an embodiment. First, an n-type GaP layer 112 is formed as a buffer layer on an n-type GaP substrate 111, and an n-type GaAlN / BP superlattice layer having a different average composition and an n-type GaAl
A multilayer buffer layer 113 in which N / BP superlattice layers are alternately stacked is formed. On this buffer layer 113,
An n-type GaAlN / BP superlattice layer 114 as a first cladding layer, an undoped GaAlN / BP superlattice layer 115 as an active layer, and a p-type GaAs as a second cladding layer
1N / BP superlattice layers 116 are sequentially formed.

On the double hetero structure thus formed, an n-type BP layer 117 as a current confinement layer having a stripe-shaped opening at the center is formed, and a p-type BP layer 118 as a contact layer is further formed thereon. Is formed.
A p-side metal electrode 119 is formed on the p-type BP layer 118, and an n-side metal electrode 110 is formed on the substrate.

This semiconductor laser uses a multi-chamber type MOCVD apparatus shown in FIG.
The doping and the like are basically manufactured under the same conditions as in the above-described embodiment. A typical lamination period of the GaAlN / BP superlattice layer is 50A, and the ratio of the thickness of the nitride to the thickness of the boride is 1: 1. When this ratio is smaller than 1, the band structure changes from the direct transition type to the indirect transition type, and the luminous efficiency decreases. When the laminating cycle exceeds 50A,
Localization of electrons and holes occurs, and the conductivity is reduced.

The specific configuration will be described.
11 has Si doping and a carrier concentration of 1 × 10 ¹⁷ / cm ^3.
The GaP buffer layer 112 is Si-doped,
The carrier concentration is 1 × 10 ¹⁷ / cm ³ , the thickness is 1 μm, and the multi-layer buffer layer 113 is formed of n-type Ga _0.5 Al _0.5 N /
The BP layer and the n-type Ga _0.4 Al _0.6 N / BP layer were formed at 1 μm (Si-doped, carrier concentration 1 × 10 ¹⁷ / c
m ³ ) grown. The n-type first cladding layer 114 is
A Ga _0.4 Al _0.6 N / BP superlattice layer (Si-doped, carrier concentration 1 × 10 ¹⁷ / cm ³ , thickness 1 μm) is used, and the undoped active layer 115 is a Ga _0.5 Al _0.5 N / BP superlattice layer (thickness 0). .1 μm), and the p-type second cladding layer 116 is a Ga _0.4 Al _0.6 N / BP superlattice layer (Mg doped, carrier concentration 1 × 10 ¹⁷ / cm ³ , thickness 1 μm)
And

On the p-type cladding layer 116, S was formed into a stripe having a width of 5 μm by thermal decomposition of silane gas and photolithography.
a current blocking layer 11 made of an iO ₂ film and made of an n-type BP layer
7 (Si doped, carrier concentration 1 × 10 ¹⁷ / cm ³ , 1
μm) is selectively grown. Next, the SiO ₂ film is removed, and a p-type BP layer 118 (Mg doped, carrier concentration 1 × 10 ¹⁷ / cm ³ , thickness 1 μm) is grown as a contact layer. Then, an Au / Zn electrode 119 is provided on the p side, and Au is provided on the n side.
/ Ge electrodes 110 are respectively formed.

The wafer thus obtained was cleaved to obtain a laser having a cavity length of 300 μm. In a pulse operation at a liquid nitrogen temperature and a pulse width of 100 μsec, green light laser oscillation was confirmed. The threshold current density is about 50 kA
/ Cm ² . Although no laser oscillation was observed at room temperature, stable light emission for 100 hours or more was confirmed in the operation in the LED mode. This stable operation is considered to be due to a reduction in stress on the active layer.

FIG. 22 shows a semiconductor laser according to an embodiment obtained by modifying the embodiment of FIG. In the embodiment of FIG.
Although the n-type BP current blocking layer 117 is formed on the p-type cladding layer 116 by selective growth, in this embodiment, the surface of the p-type cladding layer 116 is selectively etched in advance to form stripe-shaped protrusions. N-type BP
A current blocking layer 117 is formed.

FIG. 23 shows a semiconductor laser according to an embodiment obtained by further modifying the embodiment of FIG. In the previous embodiment, n
While a GaAlN / BP superlattice layer is used for the p-type cladding layer 114, the active layer 115, and the p-type cladding layer 116, in this embodiment, an n-type GaAlBNP mixed crystal layer having the same composition as the superlattice layer is used. Mold cladding layer 11
4 ', an active layer 115', and a p-type cladding layer 116 '.

According to these embodiments, a stable light emitting operation can be achieved by providing a multilayer (superlattice) structure buffer layer. As the multi-layered buffer layer, Ga _x Al _y B _{1 -xy} N _z P _{1 -z} mixed crystal layers having different average compositions may be laminated in multiple layers. GaAlN having different average compositions
The / BP superlattice layer and the Ga _x Al _y B _1-xy N _z P _1-z mixed crystal layer may be stacked in multiple layers. The multilayer buffer layer as described above is also effective for LEDs.

In the embodiments shown in FIGS. 21 to 23, the composition ratio is changed to obtain the DH structure. However, in the case of a superlattice layer, the film thickness ratio is changed. The DH structure can be similarly obtained by changing the crystal ratio. In Ga _x Al _y B _{1-x- y} N _z P _1-z ,
Although the case where x + y = 0.5 has been described, other compositions may be used. However, as for the light emitting layer, when x + y is smaller than 0.5, the band structure changes to an indirect transition type.
Not preferred. It is also possible to improve lattice matching between the BP layer and GaAlN by adding In or the like to GaAlN or GaAlBNP.

Next, an embodiment will be described in which the problem of lattice mismatch between the light emitting layer portion using the compound semiconductor layer according to the present invention and the substrate is solved by the substrate material. When growing a compound semiconductor layer containing boron or nitrogen having a wide band gap by MOCVD, it is desirable to grow at a high substrate temperature. However, the GaP substrate described in the above embodiments has a melting point of 146.
7 ° C., so that high-temperature growth cannot be performed to avoid substrate damage. In contrast, in the following embodiment, the melting point is 283.
The use of a SiC substrate having a high lattice constant of 0 ° C. and a lattice constant smaller than that of GaP enables high-temperature growth and enhances lattice matching between the substrate and the light emitting layer.

FIG. 24 shows a DH structure semiconductor laser of such an embodiment. First, on the n-type SiC substrate 121, n
A BP layer 122 is formed as a buffer layer, on which a first cladding layer 123 composed of an n-type GaAlN / BP superlattice layer, an active layer 124 composed of an undoped GaAlN / BP superlattice layer, and a p-type GaAlN / BP superlattice layer. A second cladding layer 125 composed of a lattice layer is sequentially formed to form a DH structure. A current blocking layer 126 made of an n-type BP layer is formed on the second cladding layer 125 except for a central stripe portion, and a contact layer 127 made of a p-type BP layer is formed thereon. . Ohmic electrodes 128 and 129 are formed on both sides of the device.

In this semiconductor laser, each semiconductor layer is grown by using the MOCVD apparatus shown in FIG. 2 as in the above embodiments. At this time, the growth conditions such as the source gas, the gas flow rate, and the dopant are the same as those in the above-described embodiment.
The substrate temperature is set to a higher temperature, for example, 1200 to 1400 ° C. as compared with the case where a GaP substrate is used.

The specific configuration will be described.
21 has Al doping and a carrier concentration of 1 × 10 ¹⁷ / cm ^3.
BP buffer layer 122 is doped with Si, has a carrier concentration of 1 × 10 ¹⁷ / cm ³ and a thickness of 1 μm.
Is a n-type Ga _0.4 Al _0.6 N / BP superlattice layer (Si-doped, carrier concentration 1 × 10 ¹⁷ / c).
m ³ , 1 μm) and the active layer 124 is undoped Ga _0.5 A
l _0.5 N / BP superlattice layer (0.1 μm) and second cladding layer 125 are p-type Ga _0.4 Al _0.6 N / BP superlattice layer (Mg-doped, carrier concentration 1 × 10 ¹⁷ / cm ³ , 1 μm)
m).

On the second cladding layer 125, an SiO ₂ film mask is formed in a stripe shape, and an n-type BP layer (Si-doped, carrier concentration 1 × 10 ¹⁷ / cm ³ , 1 μm) is selectively grown to block current. After the layer 126 is formed, the mask is removed and the p-type BP layer (Mg-doped, carrier concentration 1 × 1) is formed.
0 ¹⁷ / cm ³ , 1 μm). The p-side electrode 128 was formed using an Au / Zn film, and the n-side electrode 129 was formed using an Au / Ge film.

The obtained wafer is cleaved to have a cavity length of 3
As a result of producing a laser element of 00 μm, green light laser oscillation was confirmed by a pulse operation with a pulse width of 100 μsec at liquid nitrogen temperature. The threshold current was about 50 kA / cm ² . Laser oscillation at room temperature could not be confirmed.
A stable operation for 100 hours was confirmed in the operation in the ED mode.

FIG. 25 shows a configuration of an embodiment in which the light emitting layer portion of FIG. 24 is modified. In the embodiment of FIG. 241, the n-type BP current confinement layer 126 is formed on the p-type cladding layer 125 by selective growth, but in this embodiment, the surface of the p-type cladding layer 125 is selectively etched in advance to form a stripe-shaped convex. An n-type BP current blocking layer 126 is formed around the projection.

FIG. 26 shows a semiconductor laser according to an embodiment obtained by further modifying the embodiment of FIG. In the previous embodiment, n
While a GaAlN / BP superlattice layer is used for the p-type cladding layer 123, the active layer 124, and the p-type cladding layer 125, in this embodiment, the n-layer is made of a GaAlBNP mixed crystal layer having the same composition as the superlattice layer. Mold cladding layer 12
3 ', an active layer 124', and a p-type cladding layer 125 '.

According to these embodiments, a stable light emitting operation is possible. GaAln or GaAlB
It is also effective to add In to NP to improve the lattice matching between the BP layer and the GaAlN layer. In the above embodiments, the use of a Si substrate instead of the SiC substrate is also effective for enabling high-temperature growth. SiC substrate, Si
The use of a substrate is also effective in the manufacture of an LED.

The compound semiconductor material of the present invention has both the low ionicity of BP, the ZB structure, and the wide band gap of GaAlN. However, self-compensation such that N is released when an acceptor impurity enters the GaAlN layer portion. It is effective and it is difficult to do high concentration p-type doping. In order to solve this problem, it has been found that it is effective to selectively dope only the low ionic BP layer with impurities in the p-type when forming the GaAlN / BP superlattice layer.

If the entire GaAlN / BP superlattice layer is doped with a p-type impurity, in addition to the self-compensation effect in the GaAlN layer, many defects are generated and a high carrier concentration cannot be obtained as a whole. When only the p-type impurity is selectively doped into the GaN layer, the effect of the self-compensation effect is not exerted and no defect is generated, so that it is considered that many of the effectively doped impurities are effectively activated as carriers. .

FIGS. 27A and 27B are conceptual diagrams showing such a doping method. (A) shows the case of p-type doping, and (b) shows the case of n-type doping. In each case, a BP layer and a GaAlN layer are alternately stacked at a predetermined period, and the multilayer structure is basically used. In (a), only the BP layer is doped with Mg, and in (b), only the GaAlN layer is doped with Si.
Is doped.

The growth of the superlattice semiconductor layer and the selective impurity doping can be performed by the MOCVD apparatus shown in FIG. A GaAlN / BP superlattice layer was formed under the same conditions as in the formation of the superlattice layer in the above-described embodiment. For the n-type, the GaAlN layer was doped with Si, and for the p-type, the BP layer was doped with Mg. GaAs for n-type
The 1N layer and the BP layer may be doped with Si simultaneously.
P has a very large effective mass and is not suitable for n-type doping. By this selective doping, both p-type and n-type are 10 ¹⁸
It was confirmed that a superlattice semiconductor film having a carrier concentration on the order of / cm ³ was obtained.

It is to be noted that a slight amount of Mg is mixed in the GaAlN layer at the time of p-type doping, and that BP is
A small amount of Si may be mixed into the layer.

An embodiment in which the above-described selective doping of the multilayer film is applied to the manufacture of a specific device will be described below.

FIG. 28 shows a semiconductor laser of such an embodiment. First, an n-type GaP buffer layer 132 and an n-type BP buffer layer 133 are sequentially formed on an n-type GaP substrate 131, on which a first cladding layer 134 composed of an n-type GaAlN / BP superlattice layer and an undoped GaAlN / BP
Active layer 135 composed of a superlattice layer and p-type GaAlN / B
A second cladding layer 136 composed of a P superlattice layer is sequentially formed to form a DH structure. Second cladding layer 1
36, n-type BP except for the central stripe
A current blocking layer 137 made of is formed, and a contact layer 138 made of a p-type BP layer is further formed thereon. Ohmic electrodes 139 and 130 are formed on both surfaces of the device.

In this semiconductor laser, each semiconductor layer is grown by using the MOCVD apparatus shown in FIG. 2 as in the above embodiments. At this time, the growth conditions such as the source gas, the gas flow rate, and the dopant are the same as those in the above-described embodiment.
However, for doping of the p-type GaAlN / BP superlattice layer, Mg is doped only when the BP layer is grown, and for doping of the n-type GaAlN / BP superlattice layer, Ga is doped.
Si was doped only during the growth of the AlN layer.

A specific element configuration will be described. The GaP substrate 131 has Si doping and a carrier concentration of 1 × 10 ¹⁸ / cm.
Using ^three ones, n-type GaP buffer layer 132 is Si-doped, carrier concentration 1 × 10 ¹⁸ / cm ^3, a thickness of 1 [mu] m, n-type BP buffer layer 133 is likewise Si-doped, carrier concentration 1 × 10 ¹⁸ / cm ³ and a thickness of 1 μm.
Is a n-type Ga _0.4 Al _0.6 N / BP superlattice layer (Si-doped, carrier concentration 1 × 10 ¹⁸ / c).
m ^3, 1μm), the active layer 135 is undoped Ga _{0. 5} A
l _0.5 N / BP superlattice layer (0.1 μm), the second cladding layer 136 is a p-type Ga _0.4 Al _0.6 N / BP superlattice layer (Mg doped, carrier concentration 1 × 10 ¹⁸ / cm ³ , 1 μm)
m).

On the second cladding layer 136, an SiO ₂ film mask is formed in a stripe shape, and an n-type BP layer (Si-doped, carrier concentration 1 × 10 ¹⁸ / cm ³ , 1 μm) is selectively grown to block current. A layer 137 is formed, the mask is removed, and the p-type BP layer (Mg-doped, carrier concentration 1 × 1) is formed.
0 ¹⁸ / cm ³ , 1 μm). The p-side electrode 139 was formed using an Au / Zn film, and the n-side electrode 130 was formed using an Au / Ge film.

The obtained wafer is cleaved to have a cavity length of 3
As a result of producing a laser element of 00 μm, green light laser oscillation was confirmed by a pulse operation with a pulse width of 100 μsec at liquid nitrogen temperature. The threshold current was about 50 kA / cm ² . Laser oscillation at room temperature could not be confirmed.
A stable operation for 100 hours was confirmed in the operation in the ED mode.

FIG. 29 shows a semiconductor laser according to an embodiment obtained by modifying the embodiment of FIG. 28. After forming the second cladding layer 136, selective etching is performed so that a stripe-shaped projection is formed at the center of the second cladding layer 136. Thus, a current blocking layer 137 made of an n-type BP layer is formed around the protrusion. As a result, the same effect as in the embodiment of FIG. 28 can be obtained, and the convex portion of the second cladding layer 136 becomes an optical waveguide due to the difference in refractive index between the current blocking layer 137 and the current confinement and light confinement. Can be realized

FIG. 30 shows an embodiment in which selective doping of a superlattice layer with an impurity is applied to an LED. A p-type GaP buffer layer 142 and a p-type BP buffer layer 143 are sequentially formed on a p-type GaP substrate 141, and a p-type Ga _0.5 A
l _0.5 N / BP superlattice layer 144, n-type Ga _0.5 Al _0.5
A pn junction composed of the N / BP superlattice layer 145 is formed,
Further, an n-type GaN contact layer 146 is formed thereon. Ohmic electrodes 147 on both sides of the device wafer
148 are formed.

This LED is also formed using the MOCVD apparatus of FIG. 2 under substantially the same conditions as in the above embodiment.

The specific element configuration will be described. The GaP substrate 141 is Zn-doped and has a carrier concentration of 2 × 10 ¹⁷ / cm ^3.
It is. Both the p-type GaP buffer layer 142 and the p-type BP buffer layer 143 have a carrier concentration of 2 × 10 ¹⁷ / cm
^3. Thickness 3 μm, p-type Ga _0.5 Al _0.5 N / BP
The superlattice layer 144 has a laminated structure of 1.3 nm / 0.7 nm (band gap: 3.0 eV) and a carrier concentration of 1 × 10
¹⁷ / cm ³ , thickness 3 μm, n-type Ga _0.5 Al _0.5 N / B
The P superlattice layer 145 is a 1 nm / 1 nm stack (band gap 2.7 eV) and has a carrier concentration of 2 × 10 ¹⁶ / cm ³ ,
The thickness is 3 μm.

Most of the n-type GaN contact layer 146 is WZ type, is Si-doped, and has a carrier concentration of 1 × 10 ¹⁷ /
cm ³ and a thickness of 5 μm. p-type Ga _0.5 Al _0.5 N /
In forming the BP superlattice layer 144, Mg doping is performed only during the growth of the BP layer, and n-type Ga _0.5 Al _0.5 N / B
In forming the P superlattice layer 145, Si doping was performed only during the growth of the GaAlN layer.

FIG. 31 shows a state in which the LED chip 151 thus obtained is embedded in a resin case 152 also serving as a lens. One terminal of the element is connected to one of the external leads 154 via the internal lead 153.

As such a resin sealing type, blue light emission of about 10 mcd was confirmed.

FIG. 32 shows an embodiment in which selective doping of the superlattice layer is applied to an LED having a DH structure. p
P-type GaP buffer layer 162,
A p-type BP buffer layer 163 is sequentially formed, and
-Type Ga0.5 Al0.5 N / BP superlattice layer 164, an undoped Ga _0.5 Al _0.5 N / BP superlattice layer 165, n-type G
An a _0.5 Al _0.5 N / BP superlattice layer 166 is sequentially laminated, and an n-type GaN contact layer 167 is further formed thereon. Ohmic electrodes 1 on both sides of device wafer
68, 169 are formed.

This LED is also formed using the MOCVD apparatus of FIG. 2 under substantially the same conditions as in the above embodiment.

A specific device configuration will be described. The GaP substrate 161 is Zn-doped and has a carrier concentration of 2 × 10 ¹⁷ / cm ^3.
It is. Both the p-type GaP buffer layer 162 and the p-type BP buffer layer 163 have a carrier concentration of 2 × 10 ¹⁷ / cm
^3. Thickness 3 μm, p-type Ga _0.5 Al _0.5 N / BP
Superlattice layer 164 is 1.3 nm / carrier concentration in a laminated structure of ^{0.7nm 1 × 10 17 / cm 3} , a thickness of 2 [mu] m, an undoped Ga _0.5 Al _{0. 5} N / BP superlattice layer 165, 1
Carrier concentration of 2 × 10 ¹⁶ / c with a laminated structure of nm / 1 nm
m ³ , thickness 0.5 μm, n-type Ga _0.5 Al _0.5 N / BP
The superlattice layer 166 has a laminated structure of 1.3 nm / 0.7 nm and a carrier concentration of 2 × 10 ¹⁶ / cm ³ and a thickness of 2 μm.

Most of the n-type GaN contact layer 167 is WZ type, is Si-doped, and has a carrier concentration of 1 × 10 ¹⁷ /
cm ³ and a thickness of 5 μm. p-type Ga _0.5 Al _0.5 N /
In forming the BP superlattice layer 164, Mg doping is performed only during the growth of the BP layer, and n-type Ga _0.5 Al _0.5 N / B
When forming the P superlattice layer 166, Si doping was performed only during the growth of the GaAlN layer.

Such a DH structure LED was sealed with a resin as shown in FIG. 31, and higher luminance blue light emission was observed.

[0128]

As described above in detail, according to the present invention, in a light emitting device having a double heterostructure formed by sandwiching a light emitting layer between p-type and n-type cladding layers made of GaAlN-based material, By doping the cladding layer made of a GaAlN-based material with Mg, a p-type cladding layer having a lower resistance than that obtained by doping Zn can be obtained, which can contribute to the realization of a blue semiconductor light emitting device.

[Brief description of the drawings]

FIG. 1 is a view showing a compound semiconductor wafer according to one embodiment of the present invention.

FIG. 2 is a diagram showing an MOCVD apparatus for manufacturing a wafer.

FIG. 3 is a view showing a compound semiconductor wafer according to another embodiment.

FIG. 4 is a diagram showing an MOCVD apparatus for manufacturing a wafer.

FIG. 5 is a diagram showing an embodiment in which the present invention is applied to an LED.

FIG. 6 is a diagram showing an embodiment applied to a DH laser.

FIG. 7 is a diagram showing a band structure of a cubic semiconductor.

FIG. 8 is a graph showing a relationship between a composition of a compound semiconductor material according to the present invention and a band gap.

FIG. 9 is a graph showing the relationship between the composition and the bond length.

FIG. 10 is a diagram showing an example of a GaAlN / BP multilayer film wafer.

FIG. 11 is a diagram showing a relationship between a composition of a wafer and a resistivity.

FIG. 12 is a diagram showing a relationship between a lamination cycle and resistivity.

FIG. 13 is a diagram showing an embodiment of a single hetero-type LED using a GaAlN / BP superlattice layer.

FIG. 14 is a diagram showing a relationship between a nitrogen component ratio and luminance of an LED.

FIG. 15 is a diagram showing an embodiment of a double heterojunction laser using a GaAlN / BP superlattice layer.

FIG. 16 is a diagram showing a relationship between a nitrogen component ratio of a superlattice layer and a threshold current in a laser.

FIG. 17 shows a Ga _x Al _y B _1-xy N _z P according to the present invention.
FIG. 4 is a graph showing a relationship between a composition deviation of a _1-z mixed crystal layer and a half-value width of a Bragg peak in X-ray diffraction.

FIG. 18 shows an LE according to an embodiment in which the light extraction efficiency is improved.
The figure which shows D.

FIG. 19 shows an LE in an embodiment in which the light extraction efficiency is improved.
The figure which shows D.

FIG. 20 illustrates an LE of an embodiment in which the light extraction efficiency is improved.
The figure which shows D.

FIG. 21 is a diagram showing a laser according to an embodiment in which a multilayered buffer layer is interposed.

FIG. 22 is a diagram showing a laser according to an embodiment in which a multilayer buffer layer is interposed.

FIG. 23 is a diagram showing a laser according to an embodiment in which a multilayered buffer layer is interposed.

FIG. 24 is a diagram showing a laser according to an embodiment using a SiC substrate.

FIG. 25 is a diagram showing a laser according to an embodiment using a SiC substrate.

FIG. 26 is a diagram showing a laser according to an embodiment using a SiC substrate.

FIG. 27 is a diagram for explaining selective doping of a superlattice layer according to the present invention.

FIG. 28 is a diagram showing a laser according to an embodiment to which selective doping is applied.

FIG. 29 is a diagram showing a laser according to an embodiment to which selective doping is applied.

FIG. 30 is a diagram showing a single heterojunction LED of an embodiment to which selective doping is applied.

FIG. 31 is a diagram showing a single heterojunction LED of an embodiment to which selective doping is applied.

FIG. 32 is a diagram showing a double heterojunction LED of an embodiment to which selective doping is applied.

[Explanation of symbols]

1 ... GaP substrate 2 ... GaP layer 3 ... BP layer 4 ... GaN layer _{5 ... Ga x Al y B 1} -xy N z P 1-z layers 11 to 13 ... the reaction tube 14 ... chamber 15 ... substrate 16 ... susceptor 17 ... High frequency coil 18 Holder 19 Drive shaft 20 Thermocouple 23 Chamber 24 Gas inlet 25 Exhaust port 26 Susceptor 27 Substrate 28 High frequency coil 29 Thermocouple 31 GaP substrate 32 BP layer 33 n -Type GaAlN / BP superlattice layer 34 ... p-type GaAlN superlattice layer 35, 36 ... In electrode 41 ... GaP substrate 42 ... BP layer 43 ... n-type GaAlN / BP superlattice layer 44 ... undoped GaAlN / BP superlattice layer 45 ... p-type GaAlN superlattice layer 46, 47 ... In electrode

Claims (2)

[Claims] 1. A blue semiconductor light emitting device having a pn junction, comprising: a buffer layer formed on a single crystal substrate; and a light emitting layer formed on the buffer layer, wherein the light emitting layer is made of a GaAlN-based material.
A double-heterostructure portion formed between the mold and n-type cladding layers, wherein the p-side cladding layer of the double heterostructure portion is doped with Mg, and the n-side cladding layer is formed of Si.
A blue semiconductor light emitting device, characterized by being doped. 2. The blue semiconductor light emitting device according to claim 1, wherein said active layer comprises a superlattice of AlGaN and BP.