JP2877063B2 - Semiconductor light emitting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-excited oscillation type semiconductor light emitting device used for a light source of an optical disk system or the like.

[0002]

2. Description of the Related Art In recent years, in the field of optical information processing, a system for recording / reproducing information using light of an AlGaAs-based semiconductor laser having a wavelength of 780 nm has been put to practical use, and has been widely used in compact discs and the like. Recently, an increase in the storage capacity of these optical disk devices has been increasingly required, and accordingly, a demand for a laser having a short wavelength has been increasing.

Meanwhile, a semiconductor laser generates intensity noise due to feedback of reflected light from the disk surface or a change in temperature when reproducing an optical disk, thereby inducing a signal reading error.
Therefore, a laser with low intensity noise is indispensable for the light source of the optical disk. Therefore, it is attempted to reduce noise by multiplying the vertical mode. When the laser oscillates in single longitudinal mode, when a disturbance such as feedback of light or temperature change enters, the adjacent longitudinal mode starts to oscillate due to a small change in the gain peak, and the laser oscillates with the original oscillation mode. This causes a conflict, which causes noise. Therefore, when the longitudinal modes are multiplied, the intensity change of each mode is averaged, and since it does not change due to disturbance, stable low noise characteristics can be obtained.

A conventional self-sustained pulsation type semiconductor laser is disclosed in Japanese Patent Application Laid-Open No. Hei 6-260716. It has been reported that this laser has improved characteristics by making the energy gap of the active layer and the energy gap of the absorbing layer approximately equal. In particular, the energy gap of the strained quantum well active layer is almost equal to that of the strained quantum well saturable absorption layer. With this configuration, an attempt is made to obtain good self-excited oscillation characteristics.

[0005]

In order to perform high-density recording on an optical disk, it is desired to shorten the wavelength of a semiconductor laser. The reason for this is that if the wavelength is halved, the recording density is quadrupled. However, current light emitting devices having a blue wavelength band (for example, JP-A-4-242895 and JP-A-7-162038) do not take measures to reduce noise as described above. Even when such a semiconductor light emitting device is used for reproducing an optical disk, the intensity noise is generated due to the feedback of the reflected light from the disk surface or a change in temperature, which induces a signal reading error and is not practical. .

Accordingly, the present invention aims to shorten the wavelength by using a gallium nitride-based compound semiconductor having a large band gap,
It is another object of the present invention to provide a semiconductor light emitting device having self-sustained pulsation characteristics effective for low noise characteristics by providing a saturable absorption layer.

[0007]

In order to achieve the above object, a semiconductor light emitting device of the present invention uses a gallium nitride-based compound semiconductor for an active layer and has self-excited oscillation characteristics. Further, by controlling the energy gap between the ground levels of the saturable absorption layer and the active layer, the device has stable self-sustained pulsation characteristics.

[0008]

In the present invention, the oscillation wavelength is shortened by using a gallium nitride compound semiconductor for the active layer. By arranging the saturable absorbing layer in the light guide layer or the cladding layer, light from the active layer can be absorbed by the saturable absorbing layer. Excitation oscillation can be caused. Here, "saturable" means that when a large amount of light is absorbed, a certain amount or more of light is not absorbed.

Further, by setting the energy gap difference between the saturable absorbing layer and the active layer from 20 meV to 180 meV, the saturable absorbing layer efficiently absorbs laser light and saturates the light absorption. It became clear that stable self-excited oscillation was obtained. If it is lower than 20 meV, self-excited oscillation cannot be obtained. This is probably because the difference in energy gap is small and the saturable absorbing layer does not absorb much laser light. On the other hand, if the energy gap difference exceeds 180 meV, light absorption in the saturable absorption layer becomes too large, and the saturable absorption layer does not exhibit saturation characteristics, so that self-pulsation does not occur. Therefore,
It has been found that the energy gap difference is preferably 20 to 180 meV.

According to a more detailed study, the saturation condition of the saturable absorbing layer is optimal when the energy gap is in the range of 50 meV to 100 meV. When the energy gap difference exceeds 100 meV, the light absorption in the saturable absorbing layer gradually increases, and the operating current also slightly increases.
Therefore, it can be said that the energy gap difference is preferably 100 meV or less. In the range of 50 to 100 meV,
Not only does the operating current of the semiconductor laser not increase, but also a self-sustained pulsation characteristic stable against temperature changes can be obtained.

Further, when the volume of the saturable absorbing layer is reduced, the carrier density in the saturable absorbing layer can be easily increased. The saturable absorption layer absorbs the laser light emitted by the active layer, and generates a pair of electrons and holes.If the volume of the saturable absorption layer is small, the amount of light absorbed per unit volume increases,
This carrier density can be easily increased. Then, the state easily becomes saturated, and the effect of saturable absorption becomes remarkable. Therefore, strong and stable self-excited oscillation characteristics can be obtained.

Further, the semiconductor laser can have a configuration in which the small-volume saturable absorbing layer is arranged in the light guide layer. The reason for providing the light guide layer in the light guide layer is that, when the volume of the saturable absorption layer is reduced like a quantum well layer, the thickness becomes thinner, and the light confinement ratio is extremely reduced. As a result, stable self-pulsation It is because there is a possibility that it will not be. Therefore,
A saturable absorbing layer is arranged in the light guide layer to increase the confinement ratio. With this structure, when the light confinement ratio in the active layer is 0.5% or more, self-excited oscillation can occur when the confinement ratio in the saturable absorption layer is at least 1.2% or more. Becomes If the saturable absorption layer is a quantum well, even if its thickness is small and its volume is small, it can be effectively confined to the saturable absorption layer by arranging it in the light guide layer. Thereby, stable self-excited oscillation can be realized.

As described above, the saturable absorption layer may be formed in the light guide layer, or may be formed in the cladding layer. The position of the saturable absorbing layer to be set may be determined in consideration of the volume of the saturable absorbing layer and light confinement.

Further, the saturable absorption layer is a p-type light guide layer,
It may be formed in a p-type clad layer, furthermore, an n-type light guide layer or an n-type clad layer.

In the description of the present invention, "energy
The “gap difference” is an energy difference between ground levels. When the active layer includes a quantum well layer, it refers to the energy difference between the quantum levels, not the bottom of the conduction band and the valence band, and is larger than the difference in the band gap.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below.

(Embodiment 1) FIG. 1 is a sectional view showing the structure of a semiconductor laser according to the present invention. The configuration of the semiconductor laser of this embodiment is such that an n-type AlN buffer layer 102 doped with silicon is formed on a (100) plane n-type SiC substrate 101.
n-type AlGaN cladding layer 103n, n-type GaN light guide layer 104n, In0.05Ga0.95N quantum well active layer 10
5 (thickness 100A), p-type GaN light guide layer 104p,
p-type Al0.1Ga0.9N cladding layer 103p, p-type GaN
Contact layers 106 are sequentially formed. AlGaN
The n-type dopant of the layer is Si and the p-type dopant is Mg.

Further, in the p-type cladding layer 103p,
A p-type In0.1Ga0.9N saturable absorption layer 100 is formed at 50A. Although the lattice constant of the saturable absorption layer is larger than that of the cladding layer but is set to be equal to or less than the critical thickness, no dislocation occurs. Pt is formed as a p-type electrode 111 on the contact layer, and In is formed as an n-type electrode 110 on the SiC substrate 101 side.

The laser structure shown in FIG.
It is fabricated by MOCVD on m (100) SiC substrate. The n-type AlN buffer layer has a thickness of 3 μm with Si doping, the n-type cladding has a thickness of 0.5 μm with Si doping, and the n-type optical guide layer has a thickness of 0.1 μm with Si doping. Each of the p-type cladding layer and the p-type light guide layer is also 0.5 μm.
m, the thickness is 0.1 μm, and Mg is used as a dopant.

The saturable absorption layer is formed in the p-type cladding layer. The laser light from the active layer is 4
It is absorbed by this saturable absorbing layer having a small energy gap of 0 meV. The saturable absorption layer efficiently absorbs laser light and saturates the absorption of light, so that stable self-pulsation can be obtained.

The point for stably causing self-pulsation is that the energy between the quantum well layer of the active layer and the saturable absorption layer is high.
Gap difference. FIG. 2 shows a band diagram of this laser structure. In the first embodiment, the energy gap difference of the saturable absorption layer is smaller than that of the active layer by 40 meV, and stable self-pulsation can be obtained. The saturable absorption layer 100 is provided in the p-type cladding layer 103p.

Here, the energy gap difference between the quantum well layer of the active layer and the saturable absorbing layer is because the quantum well layer is used as the active layer and the saturable absorbing layer also has a quantum well structure.
The difference is defined as the energy gap difference of the ground level before laser oscillation.

In the semiconductor laser according to the present invention, the doping level of the saturable absorbing layer is set at 5.times.10@17 (cm @ -3) to reduce the carrier lifetime. As a result, the contribution of spontaneous emission to the time change rate of carriers increases, and self-sustained pulsation can be easily generated. Doping is 5 × 1
017 (cm −3) or more has the effect of reducing the carrier lifetime.

The impurity concentration is further increased to 1 × 10 18 (c
If m-3) or more, the life of carriers is further shortened, and stable self-sustained pulsation characteristics can be obtained. If the impurity concentration of the saturable absorbing layer is 1 × 10 18 (cm −3) or more, the energy gap difference between the saturable absorbing layer and the active layer should be zero or the saturable absorbing layer should be smaller. .

FIG. 3 shows a structure when the substrate is changed from silicon carbide to sapphire. When the sapphire substrate 1000 is used, the n-type GaN buffer layer 102
To the p-type GaN contact layer 106 are grown by MOCVD.
A mask is formed at a predetermined position on the surface and etched, and n
N-type GaN contact layer 109 for forming type electrode
To expose.

Thereafter, a p-type electrode 111 is formed on the p-type GaN contact layer 106 and an n-type electrode is formed on the n-type GaN contact layer 109, thereby completing the laser.

(Embodiment 2) In Embodiment 1, the saturable absorbing layer is formed in the p-type cladding layer. In this embodiment, however, the saturable absorption of the quantum well is formed in the p-type optical guiding layer 104p. An absorption layer 200 is formed. The structure and band gap energy diagrams are shown in FIGS.

As shown in the figure, the semiconductor laser has a configuration in which the saturable absorption layer 200 of the small quantum well is arranged in the light guide layer 104p. The reason for providing in the light guide layer is as described above. When the saturable absorption layer is a quantum well, even if its thickness is small and its volume is small, by providing the saturable absorption layer in the light guide layer,
Since effective light confinement can be achieved in the saturable absorption layer, stable self-pulsation can be realized by introducing this structure.

In the first and second embodiments, the active layer has a single quantum well structure. However, as shown in FIG. 6, a multiplexed barrier layer made of GaN and a well layer made of In0.05Ga0.95N are used. It may be a quantum well structure. In this case, the luminous efficiency in the active layer is increased, and the laser has a high light output. The well layer, the barrier layer, and the active layer include InxGa1-xN (0 ≦
x ≦ 1), and AlxGa1-xN (0 ≦ x ≦
Although 1) was used, generally, as a gallium nitride-based compound semiconductor, AlxGayInzN (x + y + z = 1, 0 ≦ x ≦
1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1) can be used.

(Embodiment 3) In this embodiment, a laser having a ridge structure is formed on a nitrogen-doped n-type SiC substrate. As the substrate, a silicon carbide (SiC) substrate is used. Since SiC is n-type by nitrogen doping, an electrode can be formed on the back surface of the substrate. Therefore, it is not necessary to etch the semiconductor layer epitaxially grown on the substrate to form an electrode. Hereinafter, a GaN-based semiconductor light emitting device using a SiC substrate will be described.

As shown in FIG. 8, an n-type SiC substrate 702
A semiconductor layer is vapor-phase grown using metal organic vapor phase epitaxy (MOVPE). First, prior to vapor phase growth, 6HSiC
The substrate 701 is placed on a susceptor in a reaction furnace, evacuated, and then heated at 1050 ° C. for 15 minutes in a 70 Torr hydrogen atmosphere to clean the substrate surface. The SiC substrate used here was 3.
The substrate is inclined at 5 degrees in the [11-20] direction.

Next, after lowering the substrate temperature to 1000 ° C.,
Ammonia was supplied at a flow rate of 2.5 L / min for 1 minute, and after nitriding the substrate surface, trimethyl aluminum (TMA) was
0 μmol / min, ammonia 2.5 L / min, monosilane (50 ppm based on hydrogen) 10 cc / min, carrier hydrogen 2 L
/ Minute each and the n-type AlN buffer layer
Deposit 0 nm. The reason why the buffer layer is made n-type is to prevent the electric resistance from increasing even if an n-type electrode is formed on the substrate. 1000 ° C. n-type AlN buffer layer
Since it is deposited at a high temperature, it is almost single crystal with few crystal defects.

Next, while changing the flow rate of trimethylaluminum (TMA) to 2 μmol / min, 20 μmol / min of trimethylgallium (TMG) and 10 cc / min of monosilane (50 ppm on a hydrogen basis) were additionally supplied. Then n
-Deposit an Al0.1Ga0.9N cladding layer 704.

Next, only the supply of TMA is stopped, and after the n-GaN guide layer 705n is deposited, only the supply of TMG and monosilane is stopped.
After the temperature is lowered to 0 ° C. to reach a constant temperature, trimethylindium (TMI) is supplied at 200 μmol / min and TMG is supplied at 20 μmol / min to deposit an undoped In0.05Ga0.95N well layer 705w of 3 nm. Under the same conditions as the n-GaN guide layer, an undoped GaN barrier layer 705b is grown to a thickness of 3 nm, and the GaN barrier layer and the InGaN
It has a multiple quantum well structure with a well layer.

After forming the last well layer of the multiple quantum well structure, p-GaN guide layer 705p is deposited by supplying TMG at 20 μmol / min and cyclopentadienyl magnesium (Cp2Mg) at 0.1 μmol / min. I do.

Next, TMA was further added at the same flow rate as the n-Al0.1Ga0.9N cladding layer, and the p-AlGaN first cladding layer 70 was added.
6a is deposited, the substrate temperature is lowered to 600 ° C., and TMG and TMI are again
And Cp2Mg to supply p-In0.1Ga0.9N saturable absorption layer 700
Grow. Furthermore, under the same conditions as the first cladding layer,
A second cladding layer 706b of p-Al0.1Ga0.9N is grown.

Then, on the p-AlGaN cladding layer,
An SiO2 mask is formed, and dry etching is performed using a mixed gas of chlorine gas and hydrogen gas as an etching gas. The p-AlGaN second cladding layer 706b is formed of p-
Etching to the InGaN saturable absorption layer 700,
Instead of completely removing the second cladding layer 706b by dry etching, the dry etching is temporarily stopped at a time of 0.2 μm after the removal, the wafer is taken out of the dry etching apparatus, and the concentrated phosphoric acid is heated to 100 ° C. Soak and remove the remaining 0.2 microns, including the damaged layer created by dry etching. In this manner, the p-AlGaN second cladding layer is first removed by dry etching, and subsequently removed by wet etching, thereby preventing damage to the saturable absorption layers on both sides of the ridge.

This saturable absorption layer 700 also functions as an etching stopper layer. Since this layer does not contain Al, it is hard to be etched by concentrated phosphoric acid, and the selectivity between the second cladding layer 706b and the saturable absorption layer 700 can be obtained.

Thereafter, the n-Al0.2Ga0.8N current blocking layer 707 is selectively grown on both sides of the ridge made of the second cladding layer 706b using the SiO2 mask as it is. The n-Al0.2Ga0.8N current block layer is composed of p-Al
The composition of Al is larger and the refractive index is smaller than that of the second cladding layer and the first cladding layer. Therefore, the light is easily confined under the p-AlGaN second cladding layer 706b having a high refractive index, becomes a refractive index waveguide, and a stable transverse mode can be realized. In addition, since laser light hardly absorbs in the current blocking layer, it is also promising as a high-output laser.

The SiO 2 mask is removed, and the p-type GaN cap layer 70 is formed under the same conditions as the p-type GaN guide layer 705p.
Then, a p-type GaN contact layer 709 is deposited. The p-type contact layer is more
Highly doped with impurities, the concentration is 1
× 10 18 cm -3.

Here, the p-type contact layer 709 is made of p-type GaN.
Ohmic contact with the p-type electrode can be easily obtained by using nGaN. To do so, set the substrate temperature to 60
At 0 ° C., TMG, TMI and Cp2Mg are supplied to deposit p-InGaN. By depositing p-InGaN 709 having a small band gap after depositing the p-GaN cap layer 708, the Schottky barrier with the p-type electrode (Pt) can be reduced, and the resistance can be reduced.

After depositing p-InGaN,
This can be realized by performing heat treatment in a reduced pressure hydrogen atmosphere at 70 ° Torr at 00 ° C. As a heat treatment effect, in a hydrogen atmosphere under reduced pressure, p-type activation can be performed by heat treatment at 400 ° C. or higher, and considering the suppression of dissociation of nitrogen atoms, the heat treatment temperature is preferably as low as 500 ° C. Finally, it is cooled to 500 ° C in a mixed atmosphere of ammonia and hydrogen,
At this temperature, the supply of ammonia is stopped, and heat treatment is performed for 5 minutes in a hydrogen atmosphere.

Finally, on the n-type SiC substrate 702 side, an n-type electrode 701 is formed using Ti, and on the p-type contact layer 709 side,
A p-type electrode 1412 is formed using a Pt electrode. The reason for choosing Pt is that Pt has a large work function and reduces the barrier to the p-type contact layer 709 of p-type GaN or p-InGaN. In addition to Pt, a combination of Ni and Pt may be used. Since Ni is difficult to peel off and has high adhesiveness, the reliability of the electrode is increased by stacking Pt through this layer.

The wafer having the laser structure completed as described above is transferred to a laser bar. Before cleavage, Si
The C substrate has been previously polished from the back surface and has a thickness of 200 microns. In order to work, the SiC substrate
It is preferable to keep it at about 200 to 300 microns.
If it is larger than 300 microns, a large stress is required for cleavage, and if it is smaller than 200 microns, there is a possibility that a portion other than the place to be cracked may be cracked.

As for the direction of the cleavage at the time of the cleavage, it is necessary to pay attention to the direction in which the stress is applied because the SiC substrate is not a just substrate but an inclined substrate.

FIG. 9 is a diagram schematically showing the crystal structure of the end face of the resonator. AB is the substrate surface,
The steps are atomic steps. This substrate is 3.5 [deg.] From the plane orientation of the (0001) plane, [11-2].
0] direction. FIG. 10 is a perspective view showing the configuration of this laser.
1) It is inclined 3.5 degrees from the plane orientation of the plane in the [11-20] direction. That is, as shown in FIGS. 9 and 10, this substrate is inclined by 3.5 degrees from the (0001) plane direction to the [11-20] direction. To change. The reason for this is that when stress is applied from A, the cracks in the direction B as shown in FIG. 9 progress from the middle to the (0001) plane direction, resulting in cracking failures and lowering the yield. Therefore, the cleavage is performed from the direction B to the direction A. This is true not only for the SiC substrate but also for a tilted substrate for a semiconductor substrate such as GaAs. From the direction in which the angle between the just surface (here, the (0001) plane) and the inclined substrate surface becomes smaller (here, B), stress is applied toward the inclined direction to cleave.

After forming the end face by cleavage, the end face of the resonator is coated. From the end face side, S with a film thickness of λ / 4
With one cycle of the SiO 2 film and the SiN film having a thickness of λ / 4, 3
The layers were periodically stacked, and the reflectance was set to 70%. ECR sputtering was used for laminating the SiO film and the SiN film.

When current is injected into the completed laser element and laser oscillation is performed, the operating voltage, which was about 30 V in the past, becomes 5 V
Could be reduced to

As in the present embodiment, n-type SiC substrate 7
By using a low-resistance n-type AlN buffer layer 703 deposited at a high temperature on the substrate 02, there is no need to form an n-side electrode by etching from the p-type contact layer side as in the related art. An electrode may be formed on the back surface.

The reason for using the inclined SiC substrate as the substrate will be described. In the present embodiment, an n-type SiC substrate is used which is polished by 3.5 degrees from (0001) in the [11-20] direction. This is to improve the flatness of the surface when AlGaN mixed crystal is deposited on SiC. FIG. 11 shows that the horizontal axis represents AlGa.
It is the result of taking the Al composition of N and the surface roughness of AlGaN on the vertical axis. The dotted line shows the case where a (0001) just substrate is used, and the solid line shows the case where a 3.5-degree inclined substrate is used. As the value on the vertical axis increases, the roughness increases and the surface becomes less flat. A comparison of the experimental results shows that the use of a tilted substrate results in an Al composition of 30%.
%, It was found that a good surface could be obtained.

Next, FIG. 12 shows the results obtained by plotting the inclination angle on the horizontal axis and the surface roughness on the vertical axis. Surface roughness is
It was found that the smaller the inclination angle was, the smaller the angle was, and the flatness was maintained from about 1 degree to about 18 degrees. In particular, it has been found that when the inclination angle is from 5 degrees to 15 degrees, the incorporation rate of the following p-type dopant is good.

Further, when a p-type AlGaN layer is produced, the use of a (0001) just substrate reduces the rate of incorporation of Mg, which is a p-type dopant, with an increase in Al composition, and increases the resistance of the device. I understood.
When an inclined substrate is used as in the present embodiment, as shown in FIG. 13, the rate of incorporation of Mg is higher than that of a just substrate. The vertical axis indicates the incorporation rate of Mg as a dopant into AlGaN, and the horizontal axis indicates the Al composition of AlGaN. From this figure, it was found that as the Al composition was increased, the incorporation rate of Mg decreased in the just substrate, but the incorporation rate did not decrease when the inclined substrate was used. This tendency is not limited to the case where Mg is used as the dopant, and is the same when Zn, C, and Ca are used.

As a result, the concentration of the p-type dopant can be increased, so that the operating voltage of the light emitting device can be reduced.

In this embodiment, an inclined substrate is used. Of course, even if a (0001) just substrate is used,
Since the resistance can be reduced by using the n-type AlN buffer layer, it is effective in reducing the operating voltage of the light emitting element.

In this embodiment, the p-type InGaN layer is used as the saturable absorbing layer, but the n-type InGaN
Layers may be used. The structure cross section at this time is as shown in FIG. That is, the saturable absorption layer is inserted in the p-AlGaN cladding layer.

As compared with the p-type saturable absorption layer, the n-type saturable absorption layer can increase the impurity concentration to about 1 × 10 20, and can shorten the life of carriers caused by light absorbed by the saturable absorption layer. Stable self-excited oscillation characteristics can be realized.
When the n-type saturable absorption layer is doped with an impurity of about 1 × 10 18 cm −3 or more, the energy gap difference between the saturable absorption layer and the active layer may be 0 to 180 meV.
It is sufficient that the energy gap of the saturable absorbing layer is small by the amount of the energy gap.

Although silicon is used as an impurity for the n-type, silicon has a low degree of diffusion, maintains a steep impurity concentration, and has a highly reliable device that can withstand long-term use. Becomes

Further, in this embodiment, the first p-type cladding layer has a refractive index waveguide type in which the refractive index is larger than that of the current blocking layer. On the contrary, the current blocking layer has a higher refractive index. By using a material or a current blocking layer, for example, a layer that absorbs light of 380 to 450 nm such as ZnO, an effective refractive index difference is provided in the lateral direction of the active layer, and light is applied to the active layer immediately below the ridge. It is also conceivable to have a structure that traps

(Embodiment 4) FIG. 15A shows a structural section of a semiconductor laser according to a fourth embodiment.

On an n-type SiC substrate 1502 inclined 3.5 degrees from “0001” in the [11-20] direction, an n-type A
1N buffer layer 1503 (100 nm thick), n-type Al
There is an xGa1-xN cladding layer 1504 (1 μm thickness). As the composition ratio x of AlN increases, the energy gap of AlGaN increases and the refractive index decreases.

[0062] determines the In _z Ga _1-z N InN composition ratio z of the oscillation when determining the wavelength active layer 1505 (thickness 50 nm), it will determine the value of x to it. When the oscillation wavelength is 410 nm (purple), z = 0.15, and x
Is about 0.1 to 0.2.

On the active layer 105, p-type AlyGa1-
yN first cladding layer 1506 (0.2 μm thickness), p
-Type In0.2Ga0.8N saturable absorption layer 1500 and n-type A
luGa1-uN current block layer 1507, 15
In 07, an opening is formed to reach the saturable absorption layer 1500 with a width of 1 to 10 μm. n-type current block layer 1
The thickness of 507 is 0.7 μm. The current is blocked by the n-type current blocking layer 1507 and flows only through the opening, and flows only through the active layer 1505 immediately below the opening.

In the opening and on the n-type current blocking layer, there is a p-type AlvGa1-vN second cladding layer (0.5 μm thick on the constriction layer). Here, by setting u> y, v, the refractive index of the block layer 1507 becomes smaller than the refractive indexes of the first cladding layer 106 and the second cladding layer 108. Is confined to form optical waveguide due to the difference in refractive index, and laser light without aberration is obtained.

The difference in refractive index is determined in consideration of the width of the opening, but if the width of the opening is 1 to 8 μm as in the present embodiment, the active layer immediately below the opening and the active layer immediately below the constriction layer are formed. Of the active layer (effective refractive index difference of the active layer) is 0.003 to
It is preferably in the range of 0.02. The reason for this is that if the refractive index difference is too large, higher-order modes will be established, and if the refractive index difference is too small, light will spread.

On the second p-type cladding layer 1508,
p-type GaN cap layer 1509 (0.5 μm thickness), 1
There is a p-type GaN contact layer 1510 (0.5 μm thick) having an impurity concentration of × 10 18 / cm 3 or more.
And 111 are formed on the n side and the p side, respectively. The electrode material is Ti and Au on the n side, and Ni and Au on the p side. The impurity of the n-type layer is Si, and the impurity of the p-type layer is Mg.

Since the width of the opening and the difference in the refractive index between the p-type cladding layer and the constriction layer determine the intensity distribution of light confined in the active layer, they must be set to appropriate values. In this embodiment, the width of the opening is 2 μm and the AlN composition ratio of the constriction layer is u =
0.25. The values of y and v are the same as x, ie, 0.15.
It is.

By doing so, the p clad layer 15
06, 1508 (Al0.15Ga0.85N) and the block layer 1507 (Al0.25Ga0.75N), the laser light in the direction parallel to the active layer is confined in the active layer by a refractive index distribution to be in a single mode, A GaN-based semiconductor laser device with low current and capable of obtaining laser light without aberration can be realized.

In this embodiment, (0001) to [11-
20] direction is used. this is,
This is because when AlGaN mixed crystal is deposited on SiC, the surface flatness is improved. This is because the flatness of the crystal surface is better when the inclined substrate is used than when the just substrate is used. Particularly, when the inclination angle is from 3 degrees to 12 degrees, the flatness is remarkably improved.

In this embodiment, an inclined substrate is used, but a (0001) just substrate may be used.

In another embodiment of the present invention, the blocking layer 150
7, ZnO is used. Since ZnO has a lattice constant close to that of GaN, crystal growth can be performed. Further, ZnO is an insulator, and further absorbs blue laser light generated in the active layer, so that a refractive index difference can be effectively provided in a direction parallel to the active layer. Also in this case, the refractive index difference between the active layer immediately below the ridge and the active layer outside the ridge is 0.003.
It is preferably in the range of 0.02. Other than ZnO, any material that absorbs laser light, has a refractive index difference in a direction parallel to the active layer, and can block current and allow current to flow through the ridge can be used for the constriction layer. .

Further, a layer having a smaller band gap than the active layer may be used as the block layer so as to absorb the laser beam of the active layer, so that a refractive index difference can be effectively provided in a direction parallel to the active layer. For example, if the active layer is InaGa1-aN
When (0 <a <1) is used, In _b Ga _1-b N (0 <a <b), which is a layer having a smaller band gap than this layer.
By using <1) for the block layer, a layer of the active layer that absorbs light can be realized. Moreover, by setting the conductivity type of the block layer to n-type, the current is concentrated on the ridge portion,
Current spreading in the active layer can be prevented.

Although the case where InGaN is used for the active layer is described, as shown in FIG. 15B, an active layer is provided between the n-type cladding layer 1504 and the p-type first cladding layer 1506. As 1505, the n-type GaN light guide layer 1
505n, an InGaN well layer 1505n, a multiple quantum well structure composed of a GaN barrier layer 1505b and a p-type GaN layer 1505p.

(Embodiment 5) Metal organic chemical vapor deposition (MOVP)
The crystal is grown using the method E). That is, prior to vapor phase growth, a sapphire C-plane substrate is placed on a susceptor in a reaction furnace, evacuated, and then heated at 1050 ° C. for 15 minutes in a 70 Torr hydrogen atmosphere to clean the substrate surface.

Next, after cooling to 600 ° C., ammonia was supplied at a flow rate of 2.5 L / min for 1 minute, and after nitriding the substrate surface, trimethylgallium (TMG) was added at 20 μmol / min.
By flowing ammonia at 2.5 L / min and carrier hydrogen at 2 L / min, a polycrystalline GaN buffer layer is deposited to a thickness of 50 nm.

Next, only the supply of TMG was stopped, and the temperature was lowered to 95%.
After the temperature was raised to 0 ° C, GaN was supplied by supplying 20 μmol / min of TMG.
A single crystal nucleus layer is formed.

Next, while the TMG is being supplied, the substrate temperature is set at 105.
The temperature is gradually increased to 0 ° C. and 1090 ° C. to form a GaN single crystal layer. Next, monosilane (50 ppm based on hydrogen)
Is supplied at an additional rate of 10 cc / min, and 2 μmol / min of trimethylaluminum (TMA) to deposit an n-AlGaN cladding layer.

Next, only the supply of TMG, TMA and monosilane was stopped, and 700 ° C. in a mixed atmosphere of ammonia and hydrogen.
After the temperature is lowered to a constant temperature, 200 μmol / min of trimethylindium (TMI) and 20 μmol / min of TMG are supplied to deposit an active layer 1605 of InGaN mixed crystal with a thickness of 10 nm.

Next, TMA and TMG were added at the same flow rate as above, and cyclopentadienyl magnesium (Cp2Mg) was added at 0.1%.
p-AlGaN first p-type cladding layer 160 by supplying μmol / min
After depositing 6a, again under the same conditions as those for depositing the active layer, the supply of TMG and Cp2Mg was stopped, and the substrate temperature was lowered to 6 ° C.
P-InGaN by supplying TMG, TMI and Cp2Mg again
Deposit a saturable absorbing layer. A p-type InGaN saturable absorption layer 1600 is deposited. The In composition is larger than that of the active layer.

Further, on this saturable absorption layer, the first p
A p-AlGaN cladding layer 1606b is deposited under the same conditions as the mold cladding layer. Thereafter, as described in the third embodiment, an SiO2 mask is formed to form a ridge structure composed of a p-AlGaN cladding layer. The etching is the same as that described in the third embodiment.

After forming a ridge in this way and filling the ridge with the current blocking layer 1607, the SiO mask is removed and a p-GaN cap layer 1608 and a p-type GaN contact layer 1609 are deposited. Thus, a current-confined-type laser structure can be manufactured even when a sapphire substrate is used.

(Embodiment 6) FIG. 17 shows a laser using a sapphire substrate and having an opening for passing a current through the second p-type cladding layer.

Al 2 O 3 (sapphire) was used as the substrate 1702, and a GaN layer (thickness: 1) was used as the buffer layer 1703.
00 nm). The subsequent configuration is the same as that of FIG.

The n-type cladding layer 1704 is thickened to 2 μm, and the ridge-free portion is etched and exposed until the n-type cladding layer 1704 has a thickness of 1 μm.
701 are formed. The refractive index difference in the direction parallel to the active layer 1705 is also high below the opening. The difference in the refractive index in the direction parallel to the active layer is preferably in the range of 0.003 to 0.02.

[0085]

As described above, according to the present invention, a semiconductor light emitting device having stable self-sustained pulsation characteristics in a short wavelength region can be obtained by using a gallium nitride compound semiconductor. Further, by using the saturable absorption layer, stable self-sustained pulsation characteristics can be obtained in a short wavelength region. Further, by controlling the energy gap between the saturable absorption layer and the active layer, a laser having self-pulsation characteristics in a short wavelength region can be reliably realized. As a result, a semiconductor laser having a low relative noise intensity can be realized.

[Brief description of the drawings]

FIG. 1 is a structural sectional view of a semiconductor laser according to a first embodiment.

FIG. 2 is a band gap energy diagram of the first embodiment.

FIG. 3 is a structural sectional view when the substrate is sapphire in the first embodiment.

FIG. 4 is a structural sectional view of a semiconductor laser according to a second embodiment.

FIG. 5 is a band gap energy diagram of a second embodiment.

FIG. 6 is a structural sectional view of a semiconductor laser according to another embodiment.

FIG. 7 is a structural sectional view of a semiconductor laser according to an embodiment of the present invention;

FIG. 8 is a sectional view showing a manufacturing process of the semiconductor laser according to the embodiment of the present invention;

FIG. 9 is a sectional view illustrating a cleavage direction.

FIG. 10 is a sectional view illustrating a cleavage direction.

FIG. 11 is a diagram showing the relationship between AlGaN surface roughness and Al composition when a silicon carbide substrate is used.

FIG. 12 is a diagram showing a relationship between a tilt angle of a silicon carbide substrate and AlGaN surface roughness.

FIG. 13 is a diagram showing the relationship between the incorporation rate of Mg in AlGaN and the Al composition when a silicon carbide substrate is used.

FIG. 14 is a structural sectional view of a semiconductor laser according to an embodiment of the present invention;

FIG. 15 is a structural sectional view of a semiconductor laser according to an embodiment of the present invention;

FIG. 16 is a structural sectional view of a semiconductor laser according to an embodiment of the present invention.

FIG. 17 is a structural sectional view of a semiconductor laser according to an embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 saturable absorption layer 101 n-type SiC substrate 102 n-type GaN buffer layer 103 n n-type AlGaN cladding layer 103 p p-type AlGaN cladding layer 104 n n-type GaN light guide layer 104 p p-type GaN light guide layer 105 InGaN active layer 106 GaN contact layer 200 Saturable absorption layer

──────────────────────────────────────────────────の Continuing on the front page (72) Masahiro Kume, 1006 Kadoma Kadoma, Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Akihiko Ishibashi 1006 Kadoma, Kadoma, Kadoma, Osaka Matsushita Electric Industrial Co., Ltd (56) References JP-A-6-196810 (JP, A) JP-A-6-260716 (JP, A) JP-A-7-176826 (JP, A) JP-A-58-159349 (JP, A) Japanese Unexamined Patent Publication No. 7-302951 (JP, A) Japanese Unexamined Patent Publication No. 9-129951 (JP, A) Proceedings of the Spring Society of Materials Science, 1994 (Heisei 6) 28p-K-9 p. 990 IEICE Technical Report LQE95-2 (1995) p. 7-12 IEEE Photonics Tech. Lett. 7 [12] (1995) p. 1406-1408 (58) Fields investigated (Int. Cl. ⁶ , DB name) H01S 3/18 H01L 33/00

Claims (11)

(57) [Claims] 1. A semiconductor light emitting device comprising at least an active layer and a saturable absorbing layer, wherein the active layer is made of a gallium nitride-based compound semiconductor, and an energy between ground levels of the saturable absorbing layer. The gap is larger than the energy gap between ground levels of the active layer by 20 to 180 me.
A semiconductor light emitting device having a small V and having self-excited oscillation characteristics. 2. The semiconductor light emitting device according to claim 1, wherein the saturable absorption layer is formed of a gallium nitride compound semiconductor. 3. The semiconductor light emitting device according to claim 1, wherein the saturable absorption layer is a quantum well . 4. The active layer has a multiple quantum well structure.
Or the semiconductor light emitting device according to 2. 5. A semiconductor light emitting device comprising at least an active layer, a light guide layer adjacent to the active layer, a pair of cladding layers sandwiching the active layer and the light guide layer, and a saturable absorption layer. The saturable absorbing layer is formed in the at least one cladding layer or in the light guide layer, and the active layer is formed of a gallium nitride-based compound semiconductor, and a ground standard of the saturable absorbing layer. A semiconductor light emitting device having a self-oscillation characteristic in which an energy gap between potentials is smaller than an energy gap between ground levels of the active layer by 20 to 180 meV. 6. The semiconductor light emitting device according to claim 5, wherein the saturable absorption layer is made of a gallium nitride compound semiconductor. 7. The saturable absorption layer is a quantum well.
7. The semiconductor light emitting device according to item 6. 8. The active layer is a multiple quantum well structure according to claim 5
Or a semiconductor light emitting device according to 6. 9. The (0001) plane is tilted in the <11-20> direction.
In a substrate having a beam surface, the substrate surface and
This is a method of cleaving on a plane perpendicular to the (11-20) plane.
To cleave in the <11-20> direction of the substrate
The method of cleaving the substrate. 10. The cleavage method according to claim 9, wherein the substrate is made of SiC. 11. The (0001) plane in the <11-20> direction
On a substrate with a semiconductor multilayer film formed on an inclined surface
Perpendicular to the surface and the (11-20) plane of the substrate
And cleaving on the surface of the substrate.
Semiconductor having a step of cleaving in the direction of -20>
A method for manufacturing a light-emitting element.