JP2002270957A - Semiconductor laser element and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a GaN based semiconductor laser element having a highly reliable window structure by a simple method. SOLUTION: A p-type contact layer 20 of an Mg doped GaN semiconductor is formed on the uppermost layer of a multilayer sample 31 comprising a plurality of GaN based semiconductor layers. Under a state that a region of a 60 μm width around a cleavage line A on the end face of a resonator is covered with a UV-ray mask material 28, the p-type contact layer 20 is irradiated with UV-rays and then the multilayer sample 31 is heat-treated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a semiconductor laser device made of a GaN-based semiconductor and a method of manufacturing the same.

[0002]

2. Description of the Related Art In a semiconductor laser device, the current density at the end face increases under high-power oscillation, so that the light density increases and end face destruction occurs, making it difficult to obtain high reliability. I have. For this reason, a window structure has been proposed in which the band gap of the semiconductor layer constituting the vicinity of the cavity end face is increased to reduce light absorption.

For example, Japanese Patent Application Laid-Open No. 2000-31596 discloses that a dopant is diffused into a quantum well layer by etching a cladding layer to the vicinity of a quantum well active layer and forming a cladding regrowth layer to which a dopant is added. Although a window structure manufactured by being converted is disclosed,
There is a problem that the diffusion depth and the mixed crystal formation fluctuate due to variations in thermal diffusion due to the regrowth process, and the reproducibility of the window structure is poor. Therefore, it has been difficult to obtain a highly reliable semiconductor laser at a high yield under high output oscillation. Further, in this configuration, it is necessary to perform three crystal growths and two dry etching steps for device formation, and when manufacturing is assumed, there is a concern that the production is complicated and the cost is increased.

In Japanese Patent Application Laid-Open No. H11-298086, the band gap can be increased by lattice relaxation near the active layer by employing a compound semiconductor layer structure incorporating strain compensation around the active layer. A semiconductor laser capable of reducing light absorption at an end face has been proposed. However, with this configuration alone, the current injection region is formed up to the end face, and a small amount of carrier injection is performed, so that a complete window structure cannot be formed.

[0005]

SUMMARY OF THE INVENTION In view of the above circumstances, it is an object of the present invention to provide a semiconductor laser device having a window structure, which has a high reliability from low output to high output and has a window structure, which can be manufactured in a simple process with high yield. It is intended to provide a method.

[0006]

A semiconductor laser device according to the present invention is a semiconductor laser device comprising a plurality of GaN-based semiconductor layers, wherein a semiconductor layer in contact with a p-side electrode is opposed to each other forming a resonator. A p-type contact layer made of a Mg-doped p-type GaN semiconductor formed from one of the two end faces to the other, in the vicinity of at least one of the two end faces of the p-type contact layer; A region where the contact resistance with the p-side electrode is higher than the contact resistance in a portion other than the vicinity of the end face.

In the semiconductor laser device, the region where the contact resistance is high may be formed in a region including the end face and a distance from the end face in the cavity in the direction of 5 μm or more and 50 μm or less. desirable.

The method for manufacturing a semiconductor laser device according to the present invention comprises:
A method for manufacturing a semiconductor laser device comprising a plurality of GaN-based semiconductor layers laminated, wherein a p-type contact layer comprising a Mg-doped GaN semiconductor is formed on an uppermost layer of a laminate formed by laminating a plurality of GaN-based semiconductor layers. And forming the p-type contact layer,
In a state where at least one of the resonator end faces including the end face near the end face is covered with an ultraviolet mask material, and in a non-heated state, p
The mold contact layer is irradiated with ultraviolet rays, and after the irradiation with the ultraviolet rays, the laminate is subjected to a heat treatment.

In the above manufacturing method, the area near the end face covered by the ultraviolet mask material is an area including the end face of the resonator and extending from the end face to a distance of 5 μm or more and 50 μm or less in a resonator internal direction. Is desirable.

The wavelength of the ultraviolet light is 200 nm or more and 350 nm or more.
It is desirable that:

Further, the heating temperature in the heat treatment is
Desirably, the heating temperature is 600 ° C. or more and 800 ° C. or less, and the heating time is 5 minutes or more and 60 minutes or less.

[0012] The above GaN system indicates that Ga and N are included in the constituent elements.

[0013]

The semiconductor laser device of the present invention has a plurality of Ga layers.
A semiconductor laser device comprising an N-based semiconductor layer, wherein a semiconductor layer in contact with a p-side electrode is formed from one of two end surfaces facing each other constituting a resonator, from one to the other, Mg.
Is a p-type contact layer made of a doped p-type GaN semiconductor, and the contact resistance between the p-type contact layer and the p-side electrode in the vicinity of at least one of the two end faces is different from the vicinity of the end face. Since a region having a higher resistance than the contact resistance in the portion is provided, current injection into the cavity end face having this high resistance area is suppressed, and the current density at the end face can be reduced. In addition, heat generation at the end face can be reduced. Therefore, since disturbance of the oscillation mode due to heat generation can be suppressed, a high-quality Gaussian distribution beam from low output to high output can be obtained.

The region where the contact resistance is high includes the end face and the distance from the end face in the resonator inward direction is 5 mm.
If it is formed in a region ranging from μm to 50 μm, the spread of current due to the contact layer can be suppressed more favorably, and the reduction in light output due to light loss due to light absorption can be suppressed. .

As in the method of manufacturing a semiconductor laser device of the present invention, a p-type contact layer made of a Mg-doped GaN semiconductor is formed on the uppermost layer of a stacked body formed by stacking a plurality of GaN-based semiconductor layers. The p-type contact layer is irradiated with ultraviolet light in a non-heated state while covering a region near the end face including at least one resonator end face with an ultraviolet mask material, and after the irradiation of the ultraviolet light, stacks the p-type contact layer. By performing the heat treatment on the body, the p-type impurity in the p-type semiconductor layer can be easily activated. In particular, by activating Mg in the p-type contact layer, the contact resistance with the electrode can be reduced, and as a result, a semiconductor laser capable of achieving laser oscillation at a low current can be easily obtained. In addition, since ultraviolet rays are not irradiated to the region near the end surface by the ultraviolet mask material, Mg near the end surface is not activated, and the contact resistance with the electrode in this region is the contact resistance of the portion irradiated with the ultraviolet light. Higher than. That is,
A semiconductor laser device having, in the vicinity of at least one of two end faces of the p-type contact layer, a region in which the contact resistance with the p-side electrode is higher than the contact resistance in a portion other than the vicinity of the end face. It can be manufactured easily and reliably.

The region near the end face covered with the ultraviolet mask material is a region including the end face of the resonator and extending from the end face to a distance of 5 μm or more and 50 μm or less from the end face to the inside of the resonator. A semiconductor laser device having a resistance region can be obtained.

Further, when the wavelength of the ultraviolet light is 200 nm or more and 350 nm or less, the activation rate of the p-type impurity increases, which is effective. It is considered that this is based on the fact that the charge of hydrogen associated with the p-type impurity is excited into the valence band.

Further, the heating temperature in the heat treatment is set to 600
By setting the heating temperature to not less than 800 ° C. and the heating time to be not less than 5 minutes and not more than 60 minutes, the p-type impurity can be more effectively activated.

[0019]

Embodiments of the present invention will be described below in detail with reference to the drawings.

A semiconductor laser device according to an embodiment of the present invention will be described along with its manufacturing process. FIG. 1 is a partially sectional perspective view of a semiconductor laminated sample (wafer) in a process of manufacturing the semiconductor laser device, and FIG. 2 is a perspective view of the semiconductor laser device.

Trimethyl gallium (TMG), trimethyl indium (TMI), trimethyl aluminum (TMA) and ammonia are used as raw materials for growing each semiconductor layer described below, and silane gas is used as an n-type dopant gas. Cyclopentadienyl magnesium (Cp ₂ Mg) was used as the type dopant.

As shown in FIG. 1, a low-temperature GaN layer 2 having a thickness of 30 nm is formed on a (0001) C-plane sapphire substrate 1 on which etching holes for photolithography have been formed in advance by photolithography. The GaN buffer layer 3 was formed on the GaN low-temperature layer 2 at a low pressure of 1.33 × 10 ⁻⁴ Pa (100 torr) with a thickness of about 2 μm.
Next, a 0.1 μm thick SiO ₂ film 4 is formed on the GaN buffer layer 3.
A 5 μm-wide stripe was formed by photolithography and etching using a P-CVD apparatus, followed by SiO ₂
A 20 μm thick GaN film 6 was grown on the mask pattern.
Subsequently, the n-GaN contact layer 9 and n-Ga _1-z1 Al _z1 N (1 ≧ z
1 ≧ 0; 2.5 nm) / GaN superlattice cladding layer (2.5 nm) 11, n-Ga
_1-y2 Al _y2 N optical waveguide layer (0.4> y2 ≧ 0) 13, In _x2 Ga _1-x2 N (S
i-doped) / In _x1 Ga _1-x1 N multiple quantum well active layer (0.5> x1
> X2 ≧ 0) 14, p -Ga 1-y3 Al y3 N carrier blocking layer (1>y3> y2) 15 , p-Ga 1-y2 Al y2 N optical waveguide layer 16, p-Ga
_1-z1 Al _z1 N (2.5 nm) / GaN (2.5 nm) superlattice cladding layer 18, pG
An aN contact layer 20 was grown.

Next, a Ti / W film (0.1 / 1 μm)
Is formed on the p-GaN contact layer 20, and Ti / Ti is applied only to the 60 μm-wide stripe-shaped current non-injection portion centered on the cavity end face setting position indicated by the alternate long and short dash line A in FIG. 1 by photolithography and etching. The state was such that the W film 28 was formed.

Next, as shown in FIG. 3, an ultraviolet light source is applied to the semiconductor laminated sample (wafer) 31 in a shielding box 33.
Ultraviolet rays 30a from 30 to a wavelength of 200 to 350 nm and an energy light amount of 0.2 Joule measured by the light amount monitor 32 were emitted and irradiated for 1 hour. The atmosphere in the shielding box 33 was the atmosphere, and the temperature was room temperature.

Thereafter, the Ti / W film 28 is removed, and the wafer 31 is heated at 700 ° C. as shown in FIG.
It was placed on top and heated for about 30 minutes to activate the Mg dopant. The heater block 34 includes a temperature sensor 36 and a heater 35 connected to a temperature controller 37, and the temperature is controlled by the temperature controller 37.
Thereafter, the wafer 31 is treated with a 6: 1 (NH ₄ F: HF) solution for 1 hour.
Then, the contaminated layer (contamination layer) was removed.

Subsequently, a SiO 2 layer is formed on the contact layer 20._TwoMembrane (Figure
(Not shown) and a resist (not shown).
2.2 μm wide stripe-shaped resist
And SiO_TwoThe film was removed. In addition, RIE (reactive ion
P-Ga by selective etching_1-z1Al_z1N
(2.5 nm) / GaN (2.5 nm)
And p-Ga_1-y2Al_y2E from the N optical waveguide layer 16 to a distance of 0.1 μm.
To form a 2.2μm wide ridge stripe.
Was. At this time, the remaining of the p-type cladding layer 18 due to the etching is
Control the thickness of the ridge to propagate vertically at both sides of the ridge
Light propagating in the vertical direction of the equivalent refractive index nA and ridge
Difference from the equivalent refractive index nB of the light, nB-nA, is 1 × 10 ^-2> NB
-nA> 2 × 10^-3Range.

Thereafter, the resist is removed by oxygen plasma ashing, and SiO ₂ is removed by BHF (buffered hydrofluoric acid).
The film is removed, and a SiO ₂ film (not shown) and a resist (not shown) are formed again.
_Two stripe mask patterns were formed. Along the mask pattern, etching was performed up to the upper surface of the n-GaN contact layer 9 by ECR etching using chlorine ions, the resist was removed by oxygen plasma ashing, and the SiO ₂ film was removed by BHF. Thereafter, the insulating film SiO ₂ film 25 was formed again, and a resist was applied. Using an alignment mark formed in advance on the substrate, the resist and the SiO ₂ film 25 on the upper surface of the ridge stripe previously irradiated with ultraviolet rays are removed by ordinary photolithography and etching to form an opening. A p-side electrode 27 made of Ni / Au was formed on the surface of the p-GaN contact layer 20 exposed through the opening of the _second film 25. The p-side electrode 27 is formed by coating a p-side electrode material on the exposed portion of the p-GaN contact layer 20 and the resist, and then removing the p-side electrode material other than the exposed portion of the p-GaN contact layer 20 together with the resist by a lift-off method. It was formed by peeling. Thereafter, a resist is applied again, and 10 μm parallel to the p-side electrode 27 is formed on the SiO ₂ film 25 on the n-GaN contact layer 9 by ordinary photolithography and etching.
An m-width stripe opening was formed, and an n-side electrode 26 made of Ti / Al was formed on the exposed n-GaN contact layer 9. After the n-side electrode material is formed on the exposed portion of the n-GaN contact layer 9 and the resist, the n-side electrode 26 is formed on the n-side electrode 26 except for the exposed portion of the n-GaN contact layer 9 by a lift-off method.
It was formed by stripping the side electrode material together with the resist.

Thereafter, the sapphire substrate 1 is polished by a polishing method.
Polishing was performed to a thickness of 70 μm. The wafer 31 is cleaved at the center of the region not irradiated with ultraviolet light, that is, at the cavity end face setting position shown by the dashed line A in FIG. 1, and a high reflectance coat is applied to one of the cavity surfaces formed by the cleavage. On the other side, an anti-reflection coating was applied, and further, cleavage was performed at a device isolation cleavage position indicated by a dotted line B in FIG. 1 to form a chip, thereby forming a semiconductor laser device as shown in FIG. As a result, a region extending from the end faces of both resonators to the inside of the device in the direction of 30 μm has a region not irradiated with ultraviolet rays, that is, a high resistance region in which p-type impurities are not activated, and at the same time, a p-side electrode is formed in this region. A semiconductor laser device having a good end face non-injection structure (window structure) as a current non-injection region was obtained.

In the above embodiment, the current non-injection region is a region extending over a distance of 30 μm from the end face of the resonator toward the inside of the device. It is sufficient that the range is equal to or less than the area. If the current non-injection region is a region in which the distance from the end face to the inside of the resonator is smaller than 5 μm, the non-current injection region cannot be substantially formed due to the spread of current by the contact layer, and the end face is deteriorated due to heat generation. When the area is larger than 50 μm, light loss due to light absorption in the current non-injection area increases and the light output decreases.

In addition, even if the current non-injection region is not one end face but one end face, the effect of suppressing the end face destruction by increasing the light density can be obtained.

The mask material at the time of ultraviolet irradiation is not limited to the above-described Ti / W, and any material may be used as long as it reflects or absorbs ultraviolet light. May be covered.

The semiconductor laser device of the present invention emits a high-quality and high-reliability beam having a Gaussian distribution from a low output to a high output. Therefore, the fields of high-speed information / image processing and communication, measurement, medical care, and printing are provided. It can be applied as a light source in a computer.

[Brief description of the drawings]

FIG. 1 is a view showing a part of a semiconductor laminated sample in a manufacturing process of a semiconductor laser device according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a semiconductor laser device according to an embodiment of the present invention.

FIG. 3 is a diagram for explaining a manufacturing process of the semiconductor laser device shown in FIG. 2;

FIG. 4 is a view for explaining a manufacturing process of the semiconductor laser device shown in FIG. 2;

[Explanation of symbols]

Reference Signs List 1 (0001) C-plane sapphire substrate 2 GaN low-temperature layer 3 GaN buffer layer 4 SiO ₂ film 6 GaN layer 9 n-GaN contact layer 11 n-Ga _1-z1 Al _z1 N / GaN super lattice cladding layer 13 n-Ga _{1 -y2} Al _y2 N optical waveguide layer 14 In _x2 Ga _1-x2 N / In _x1 Ga _1-x1 N multiple quantum well active layer 15 p-Ga _1-y3 Al _y3 N carrier blocking layer 16 p-Ga _1-y2 Al _y2 N optical waveguide layer 18 p-Ga _1-z1 Al _z1 N / GaN superlattice cladding layer 20 p-GaN contact layer 25 insulating film 26 n-side electrode 27 p-side electrode 28 Ti / W film (UV mask material) 30 UV Light source 31 Wafer 32 Light intensity monitor 33 Shield box 34 Heater block 35 Heater 36 Temperature sensor 37 Temperature controller

Claims (6)

[Claims] 1. A semiconductor laser device comprising a plurality of GaN-based semiconductor layers, wherein a semiconductor layer in contact with a p-side electrode is formed from one of two opposing end faces constituting a resonator to one from the other. A p-type contact layer made of a Mg-doped p-type GaN semiconductor, the contact resistance of the p-type contact layer with the p-side electrode near at least one of the two end faces, A semiconductor laser device comprising a region having a resistance higher than a contact resistance in a portion other than the vicinity of the end face. 2. The region where the contact resistance is high is formed in a region including the end face and a distance from the end face in the cavity in the direction of 5 μm or more and 50 μm or less. 2. The semiconductor laser device according to 1. 3. A method for manufacturing a semiconductor laser device comprising a plurality of GaN-based semiconductor layers stacked, wherein M is formed on the uppermost layer of a stacked body formed by stacking a plurality of GaN-based semiconductor layers.
forming a p-type contact layer made of a g-doped GaN semiconductor, in a state in which a region near the end face including at least one resonator end face of the p-type contact layer is covered with an ultraviolet mask material, and in a non-heated state. A method for manufacturing a semiconductor laser device, comprising irradiating a p-type contact layer with ultraviolet rays, and performing heat treatment on the laminate after the irradiation with the ultraviolet rays. 4. The region near the end face covered by the ultraviolet mask material is an area including the end face of the resonator and extending from the end face in a range of 5 μm or more and 50 μm or less in a resonator inward direction. 4. The method for manufacturing a semiconductor laser device according to item 3. 5. The method for manufacturing a semiconductor laser device according to claim 3, wherein the wavelength of the ultraviolet light is not less than 200 nm and not more than 350 nm. 6. The heating temperature in the heat treatment is 600 ° C.
6. The method for manufacturing a semiconductor laser device according to claim 3, wherein the heating time is not less than 800 ° C. and the heating time is not less than 5 minutes and not more than 60 minutes.