JP2002237648A - Semiconductor laser element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a Gaussian-type laser light of high quality and high reliability in a range starting from low output to high output, in a semiconductor laser element composed of InGaAlN-based material. SOLUTION: In a resonator end surface, an N-GaN contact layer 9, an N- Ga1-z1Alz1N/GaN superlattice clad layer 10, an N-Ga1-z2Alz2N optical waveguide layer 11, an Inx2Ga1-x2N (Si-dope)/Inx1Ga1-x1N multi-quantum well active layer 12, a P-Ga1-z3Alz3 carrier blocking layer 13, a P-Ga1-z2Alz2N optical waveguide layer 14, an P-Ga1-z1Alz1N/GaN superlattice clad layer 15, and a P-GaN contact layer 16, are formed on a GaN layer 8. An SiN film is formed almost 1 nm in thickness on the resonator end surface. After that, a high reflectivity coating which consists of a dielectrics multiplayer film composed of SiO2/TiO2 is carried out, and low reflectivity coating, which uses SiO2 is performed. Since the SiN film is formed, in contact with the resonator end surface, the number of non- luminescent recombination centers can be reduced, and reliability of with time passage can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor laser device made of an InGaAlN-based material.

[0002]

2. Description of the Related Art A semiconductor laser device in the 400 nm band having a minute spot is a highly reliable Gaussian type semiconductor in fields such as an optical disk memory where recording density is increasing and a photosensitive material sensitive to a short wavelength region is used. It is expected to have a high quality beam and to oscillate in a fundamental transverse mode. For example, Jpn.J.Appl.phys.Lett., Vol.37, pp.
L1020, InGaN / GaN / AlGaN-Based Laser by Nakamura et al.
Diodes Grown on GaN Substrates with a Fundamental
In Transverse Mode, a short-wavelength semiconductor laser in the 410 nm band is introduced. In this semiconductor laser device, after GaN is formed on a sapphire substrate, a GaN layer is selectively grown using SiO ₂ as a mask, and an n-GaN buffer layer, an n-InGaN Anti-crack layer, n-AlGaN / GaN modulation-doped superlattice cladding layer, n-GaN
Optical waveguide layer, n-InGaN / InGaN multiple quantum well active layer, p-AlGaN
Carrier blocking layer, p-GaN optical waveguide layer is obtained by laminating a p-AlGaN / GaN modulation-doped superlattice cladding layer and p-GaN contact layer, a facet coating, formed by laminating a SiO ₂ and TiO ₂ are alternately Is used.

[0003]

In the above-mentioned semiconductor laser device, a modulation-doped superlattice cladding layer is used to reduce the device resistance, but this is not sufficient. Has been confirmed. Further, the light output is only about 30 mW in the fundamental transverse mode oscillation. Therefore, in the above-described semiconductor laser device, it is necessary to remove the non-radiative recombination center on the end face, which is the cause of the end face deterioration.

In view of the above circumstances, it is an object of the present invention to provide a semiconductor laser device which emits a high quality Gaussian beam with high reliability from low output to high output.

[0005]

According to the semiconductor laser device of the present invention, at least a first conductive type contact layer, a first conductive type clad layer, an active layer, a second conductive type clad layer and a second conductive type contact layer are formed. A current injection window is formed above the active layer of the resonators stacked in order, and in a semiconductor laser device made of an InGaAlN-based material, the resonator is in contact with the resonator surface of the resonator. And a dielectric film made of nitride is formed.

The dielectric film is preferably made of silicon nitride, aluminum nitride or gallium nitride.

It is desirable that the dielectric film has a thickness of 1 nm or more.

The above-mentioned “InGaAlN-based” refers to InGaAlN.
Includes compositions of N, GaN, InGaAlN and AlGaN.

The first conductivity type and the second conductivity type have opposite polarities. For example, if the first conductivity type is n-type conductivity, the second conductivity type is p-type conductivity. Is shown.

[0010]

According to the semiconductor laser device of the present invention, since the dielectric film made of nitride is formed in contact with the end face of the resonator, the composition of the dielectric film and the composition of the resonator are reduced. Are the same nitride, the bonds cut at the cavity facets are connected by nitrogen, so that a level contributing to non-radiative recombination is hardly formed in the band gap. Therefore, non-radiative recombination can be reduced and the end face can be prevented from deteriorating due to heat generated by non-radiative recombination current at the end face. Beam can be obtained.

[0011]

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

A description will be given of a semiconductor laser device according to an embodiment of the present invention. FIG. 1 shows a cross-sectional view of the semiconductor laser device.

As shown in FIG. 1, trimethylgallium (TMG), trimethylindium (TMI), trimethylaluminum (TMA) and ammonia are used as growth materials, and silane gas is used as an n-type dopant gas. Cyclopentadienyl magnesium (Cp ₂ Mg) is used as a p-type dopant. A temperature of 500 on a (0001) plane sapphire substrate 1 by metal organic chemical vapor deposition.
At 20 ° C., a GaN buffer layer 2 is formed with a thickness of about 20 nm. Subsequently, the temperature is set to 1050 ° C., and the GaN layer 3 is grown to about 2 μm. After that, an SiO ₂ film 4 (not shown) is formed,
After applying a resist 5 (not shown), use normal lithography

(Equation 1) The stripe region where the 5 μm SiO ₂ film 4 was removed in the direction
A line and space pattern is formed at a period of about μm. Using the resist 5 and the SiO ₂ film 4 as a mask, the GaN buffer layer 2 and the GaN layer 3 are removed to the upper surface of the sapphire substrate 1 by dry etching using a chlorine-based gas. At this time, the sapphire substrate 1 may be etched. After removing the resist 5 and the SiO ₂ film 4, the GaN layer 6 is
Selectively grow by about μm. At this time, the stripes finally merge due to the lateral growth, and the surface is flattened. After this,
An SiO ₂ film 7 is formed, and GaN is formed by ordinary lithography.
The SiO ₂ film 7 having a width of about 7 μm is removed so as to cover the upper portion where the layer 3 is present, and is striped. Subsequently, the GaN layer 8 is grown, and finally the stripes are united by the lateral growth to flatten the surface.

Subsequently, the n-GaN contact layer 9, n
_{-Ga 1-z1 Al z1 N (} 2.5nm) / GaN (2.5nm) superlattice cladding layer _{10, n-Ga 1-z2} Al z2 N optical waveguide layer 11, an In _x2 G
a _{1-x 2} N (Si- _{doped) / In x1 Ga 1-x1} N multiple quantum well active layer (0.5>x1> x2 ≧ 0 ) 12, p-Ga 1-z3 Al z3 N carrier blocking layer 13, p growing -Ga _1-z2 Al _z2 N optical guide layer _{14, p-Ga 1-z1} Al z1 N (2.5nm) / GaN (2.5nm) superlattice cladding layer 15 and p-GaN contact layer 16. Subsequently, an SiO ₂ film and a resist are formed, and the resist and the SiO ₂ film outside the stripe region having a width of 1 to 3 μm are removed by ordinary lithography. The ridge (reactive ion etching device) is selectively etched to a part of the p-type superlattice cladding layer 15 to form a ridge stripe. The remaining thickness of the cladding layer in this etching is a thickness that can achieve the fundamental transverse mode oscillation. After that, the resist and the SiO ₂ film are removed, and the SiO ₂ and the resist are formed again.
remove the SiO ₂ and the resist except for the area outside the area m,
Etching is performed by RIE until the n-GaN contact layer 9 is exposed. After removing the SiO ₂ and the resist, an insulating film 17 is formed. The p-GaN contact layer is removed by removing the insulating film 17 on the ridge using a normal lithography technique.
16 is exposed to form a current injection window. Ni / Au in stripes so as to be in contact with the surface of p-GaN contact layer 16
A p electrode 19 made of Ti / Au is formed so as to be in contact with the n-GaN contact layer 9. After that, the substrate is polished and the sample is cleaved to form a cavity surface with energy of about 30 eV.
After irradiating r ions to remove oxides and impurities on the end face, silicon nitride is formed to a thickness of about 1 nm by ECR sputtering, and a high reflectivity coat made of a dielectric multilayer film of SiO ₂ / TiO ₂ is formed on one end face. Then, a low reflection coating made of SiO _{2 is applied} to the other end face. Then, the semiconductor laser device is formed by chipping.

The composition of AlGaN is such that 1>z1> z2 ≧ 0 and 0.4>
Let z3> z2.

As a method for growing each layer, a molecular beam epitaxial growth method using a solid or gas as a raw material may be used.

Although the above structure grows the n-type layer first, it may grow from the p-type layer and only needs to reverse the conductivity of each layer.

In this embodiment, a ridge-structured index-guided laser has been described. However, a laser having a current confinement structure therein or a semiconductor laser having a ridge structure embedded therein to form a refractive-index-guided mechanism. You may.

As a film formed in contact with the laser end face,
Aluminum nitride or gallium nitride may be used.

The oscillation wavelength λ of the semiconductor laser device can be 380 <λ <550 (nm) depending on the composition of the active layer.

In the above embodiment, each layer is formed by growing on a sapphire substrate. However, a SiC substrate, ZnO, LiGaO ₂ , Li
AlO ₂ , GaAs, GaP, Ge or Si may be used.

Further, each of the above layers may be grown on a conductive GaN substrate formed by removing a sapphire substrate serving as a base and a GaN layer to which conductive impurities are not added.

In the above description, the formation of a semiconductor laser that oscillates in a fundamental transverse mode has been described. However, the stripe width is set to 3 μm or more, and a wide stripe semiconductor laser with low noise that can be used for exciting a wavelength conversion element or a fiber laser is used. Is also good.

Next, the reliability over time of the semiconductor laser device according to the present embodiment will be described. FIG. 2 shows the graph. In the figure, (a) shows the result of the semiconductor laser device of the comparative example, and (b) shows the result of the semiconductor laser device according to the present invention. The semiconductor laser device of the present invention, in the configuration of the semiconductor laser device, the composition ratio, z1 = 0.16, x
2 = 0.02, x1 = 0.14, z3 = 0.15 and z2 = 0, the stripe width is 3 μm, the resonator length is 500 μm, and the p-electrode 19 is 3 μm × 500 μm. As the semiconductor laser device of the comparative example, a semiconductor laser device having the same layer configuration as the above-described semiconductor laser device and having a reflection film formed on the resonator surface without sputtering silicon nitride is used. In both devices, before coating the reflective film, the end face is irradiated with Ar ions having energy of about 30 eV to remove oxides and impurities on the end face. In the test, the ambient temperature was 50 ° C., the light output was 1 mW, and the APC was driven.

As shown in FIG. 2A, the semiconductor laser device of the comparative example in which no silicon nitride is formed has deteriorated within 100 hours, and the semiconductor laser device of the present invention has
As shown in (b), although the current is increased up to 400 hours, the driving is continued. Therefore, it can be seen that the reliability over time is high by forming silicon nitride in contact with the end face of the resonator.

The semiconductor laser device of the present invention emits a high-quality beam and has high reliability over time, so that it can be applied as a light source in the fields of high-speed information / image processing and communication, measurement, medicine, and printing.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a semiconductor laser device according to an embodiment of the present invention;

FIG. 2 is a graph showing the reliability over time of a semiconductor laser device according to an embodiment of the present invention and a semiconductor laser device having a reflective film formed without providing a SiN film on a cavity end face;

[Explanation of symbols]

1 (0001) plane sapphire substrate 2 GaN buffer layer 3 GaN layer 6 GaN layer 7 SiO ₂ film 8 GaN layer 9 n-GaN contact layer 10 n-Ga _1-z1 Al _z1 N / GaN superlattice cladding layer 11 n-Ga _1-z2 Al _z2 N optical waveguide layer 12 In _x2 Ga _1-x2 N (Si-doped) / In _x1 Ga _1-x1
N multiple quantum well active layer 13 p-Ga _{1 -z 3} Al _z3 N carrier blocking layer 14 p-Ga _{1 -z 2} Al _z2 N optical waveguide layer 15 p-Ga _{1 -z 1} Al _z1 N / GaN superlattice cladding layer 16 p -GaN contact layer 17 Insulating film 18 N electrode 19 P electrode

Claims (3)

[Claims] At least a first conductivity type contact layer,
A current injection window is formed above the active layer of the resonator in which the first conductive type clad layer, the active layer, the second conductive type clad layer, and the second conductive type contact layer are stacked in this order, A semiconductor laser device in which a device is formed of an InGaAlN-based material, wherein a dielectric film made of nitride is formed in contact with a resonator surface of the resonator. 2. The semiconductor laser device according to claim 1, wherein said dielectric film is made of silicon nitride, aluminum nitride or gallium nitride. 3. The semiconductor laser device according to claim 1, wherein said dielectric film has a thickness of 1 nm or more.