JPH06232496A - Semiconductor laser and its manufacture - Google Patents

Abstract

PURPOSE:To prevent crystal defects by covering the edge plane of a semiconductor laser with a semiconductor layer which is formed of group II elements and group VI elements separately from the semiconductor crystal which forms the semiconductor laser element and permitting the thickness of the semiconductor film to be a quarter of the wavelength of the laser beams which the semiconductor laser element projects or less. CONSTITUTION:A semiconductor wafer is split in bar-shape at approximately 600mum intervals to be fixed with the split plane facing top and a ZnSe layer 12 is crystal-grown for approximately 10nm by introducing the wafer into a molecular-beam crystal growing device. Approximately 0-3% lattice unconformity is found between a ZnSe layer 12 and an AlGaAs, however, crystal defects are not generated since the film is thin. Then, the front edge plane of the element is coated with Al2O3 reflection preventing coating 13 and the rear edge plane is coated with highly reflecting coating 14 constituted of a-Si/Al2O3. The ZnSe layer allows less heat transmission compared with the AlGaAs layer and temperature increase at the edge plane is concerned, however, since the AnSe layer is very thin, heat is efficiently removed by Al2O3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high power semiconductor laser device used as a light source for a laser beam printer, an optical disk and a laser measuring device.

[0002]

2. Description of the Related Art In a conventional high-power semiconductor laser, as shown in FIG. 5, an AlGaAs 38 is additionally grown on the end face of a semiconductor laser element made of an AlGaAs-based material by the MOCVD method, and the active layer of the semiconductor laser is easily damaged by light. It was possible to obtain high output by preventing light damage by preventing the particles from directly appearing on the crystal surface.

[0003]

In the conventional high-power semiconductor laser described above, it is difficult to grow a crystal having good crystallinity on the cleaved surface of the semiconductor laser with good reproducibility, which causes deterioration of device characteristics. Further, in the conventional structure, the temperature at which the crystal is grown on the end face is higher than the temperature at which the electrode is formed on the laser element, so it is necessary to form the electrode after growing the crystal on the end face, which is also disadvantageous in terms of streamlining the manufacturing process. Met.

[0004]

In order to solve the above problems of the prior art, the present invention has devised to cover the end face of a semiconductor laser with a semiconductor layer composed of a group II element and a group VI element. Specifically, the Group II element is zinc or a mixture of zinc and cadmium, and the Group VI element is selenium or a mixture of selenium and sulfur. Further, in order to obtain the best possible crystallinity and uniform film thickness, the thickness of the semiconductor layer covering the end face prevents generation of crystal defects due to stress due to a difference in lattice constant between the semiconductor layer and the semiconductor layer constituting the semiconductor laser. Thin enough. Further, the inventors have also devised that the formation temperature of the semiconductor layer covering the end face is set to be lower than the maximum temperature reached in the step of forming the electrode on the semiconductor laser element. Further, in the present invention, the fact that the thickness of the semiconductor layer composed of the group II element and the group VI element described above is thin is utilized, and the thermal conductivity is higher than that of the semiconductor constituting the semiconductor laser on this layer and the laser On the other hand, a protective film made of an insulating material having no absorption is provided.

[0005]

[Function] Conventional Al is used as a layer for covering the end face of the semiconductor laser.
By using a II-VI group element having a wider band gap than GaAs, a barrier effect against surface recombination is large and a desired effect can be obtained by a thinner layer. Since the thickness of the film may be thin, the process of crystal growth on the end face of the semiconductor laser, which usually involves great difficulty, can be easily performed. Moreover, since the II-VI group semiconductor capable of crystal growth at a low temperature of about 300 ° C. is used, it becomes possible to perform crystal growth on the end face after forming the electrodes, and all the steps normally performed in a wafer state are completed. After that, it became possible to form a semiconductor layer covering the end face.

[0006]

EXAMPLE 1 An example of the present invention is shown in FIG. In this structure, first, n-Al _{0.5 is formed} on the n-GaAs substrate 1.
Ga _0.5 As clad layer 2, multiple quantum well active layer 3, p-
After the Al _0.5 Ga _0.5 As clad layer 4 and the p-GaAs contact layer 5 are successively grown, a SiO ₂ film is formed by the vapor phase chemical growth method, and a stripe of about 6 μm is formed on the SiO ₂ film by the photolithographic technique. Forming a photoresist pattern. The multiple quantum well active layer 3 is composed of an Al _0.1 Ga _0.9 As well layer 6 and an Al _0.3 Ga _0.7 As barrier layer 7. Next, a SiO ₂ film is formed on this structure by a thermal CDV method, and the SiO ₂ film, p is formed using the photoresist pattern as a mask.
After etching a part of -GaAs contact layer 5 and the p-Al _0.5 Ga _0.5 As cladding layer 4, further processed into a width of about 3μm to place a side etching only the SiO ₂ film by hydrofluoric acid etching solution. After removing the photoresist mask, the n-GaAs block layer 8 was selectively grown in the region without the SiO ₂ film by the metal organic chemical vapor deposition method. In order to reduce the series resistance of the device, after removing the SiO ₂ film, the p-Al _0.5 Ga _0.5 As embedded layer 9 and the p-GaAs cap layer 10 were formed. Next, after forming the electrode 11 containing Au as the main component on the surface of the wafer, the GaAs substrate is etched to about 100 μm by mechanical polishing and chemical etching, and the electrode 11 containing Au as the main component is also formed on the GaAs substrate side. Formed. FIG. 1A shows the sectional shape of the semiconductor laser at this stage.

Such a semiconductor wafer is cleaved in a bar shape at intervals of about 600 μm, fixed so that the cleaved surface faces upward as shown in FIG. 2, and introduced into a molecular beam crystal growth apparatus, ZnSe.
Layer 12 was crystal grown to about 10 nm. ZnSe layer 12 and A
There is a lattice mismatch of about 0.3% between 1 GaAs, but crystal defects do not occur because the film thickness is thin. The crystal growth temperature was about 300 degrees. After the same operation was performed on the other end face of the semiconductor laser, an Al ₂ O ₃ antireflection coating 13 (reflectance 5%) was formed on the front end face of the device, and a-Si / A high reflection coating 14 (reflectance 90%) composed of Al ₂ O ₃ was applied to obtain a laser chip having a structure as shown in FIG. ZnSe layer is A
The thermal conductivity is poorer than that of the 1GaAs layer, and the temperature rise of the end face may occur, but the ZnSe layer is very thin, so
It is efficiently removed by l ₂ O ₃ and a higher output operation becomes possible.

(Embodiment 2) A second embodiment of the present invention is shown in FIG.
Shown in. In this structure, first, n on the n-GaAs substrate 1
-(Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer 18, multiple quantum well active layer 19, p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5
After the P clad layer 20 and the p-GaAs contact layer 21 are sequentially crystal-grown, a SiO ₂ film is formed by the vapor phase chemical growth method, and about 6 μm is formed on the SiO ₂ film by the photolithography technique.
A photoresist pattern of m stripes is formed. The multiple quantum well active layer 3 is composed of a Ga _0.5 In _0.5 P well layer 22.
It is composed of (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P barrier layer 23. Next, the SiO ₂ film in this structure is provided by a thermal CDV method, SiO ₂ film photoresist pattern as a mask,
p-GaAs contact layer 5 and p- (Al _0.7 Ga _0.3 ).
After etching a part of the _0.5 In _0.5 P clad layer 20, the n-GaAs block layer 8 was selectively grown in the region without the SiO ₂ film by the metal organic chemical vapor deposition method. In order to reduce the series resistance of the device, after removing the SiO ₂ film, p-Al
_0.5 Ga _0.5 As buried layer 9 and p-GaAs cap layer 10
Was formed. Next, after forming the electrode 11 containing Au as a main component on the surface of the wafer, the GaAs substrate is etched to about 100 μm by mechanical polishing and chemical etching,
The electrode 11 containing Au as a main component was also formed on the GaAs substrate side. FIG. 3A shows the sectional shape of the semiconductor laser at this stage.

Such a semiconductor wafer is cleaved in a bar shape at intervals of about 600 μm, and is fixed so that the cleaved surface faces upward as shown in FIG.
The SSe layer 24 was crystal-grown to about 100 nm. Normally, it is difficult to obtain a perfect mirror surface by such crystal growth on the end face, but in the case of the present embodiment, the thickness of the ZnCdSSe layer 24 is 1/4 or less of the wavelength of light in ZnCdSSe. The fluctuation of the film thickness did not affect the laser light, and a good end face could be easily obtained. The crystal growth temperature was about 300 degrees. After performing the same operation on the other end face of the semiconductor laser, A is attached to the front end face of the device.
l ₂ O ₃ anti-reflection coating 13 (reflectance 5%),
The rear end face of the device is provided with a high reflection coating 14 (reflectance 90%) composed of a-Si / Al ₂ O ₃ .
A laser chip having a structure as shown in (b) was obtained.

(Embodiment 3) A third embodiment of the present invention is shown in FIG.
Will be described. This structure has MB on n-GaAs substrate 1.
According to the E method, n-Zn _0.43 Cd _0.57 S layer 25 (n = 1 × 1
0 ¹⁸ , 1.5 μm), ZnSSe / ZnCdSSe superlattice active layer 26, p-Zn _0.8 Mg _{0.2 .3} S _0.3 Se _0.7 layer 27 (p
= 5 × 10 ¹⁷ , 1.5 μm), p-ZnTe layer 28 (p
= 5 × 10 ¹⁹ , 10 nm) were sequentially laminated. ZnSSe
/ ZnCdSSe superlattice active layer 26 is ZnS _0.22 Se
_0.78 layer 29 (10 nm) and Zn _0.81 Cd _0.19 S _0.22 Se
Four _0.78 layers 30 (10 nm) were alternately laminated. Next, a SiO ₂ film 31 having a stripe-shaped hole is formed by using a thermal CVD method and a photolithography technique, and then Au electrodes 11 are provided on both surfaces of the wafer and cleaved at 600 μm intervals to obtain a bar-shaped sample. It was This bar-shaped sample
As shown in FIG. 2, the cleaved surface was fixed so that it was directed upward and introduced into a molecular beam crystal growth apparatus, and Zn _0.43 Cd was formed on the laser end surface.
_{The 0.57} S layer 24 was crystal-grown at about 5 nm. The crystal growth temperature was about 250 degrees. After performing the same operation on the other end face of the semiconductor laser, an Al ₂ O ₃ antireflection coating 13 (reflectance 5%) is provided on the front end face of the device, and a-Si / Al is provided on the rear end face of the device. _A high reflection coating 14 (reflectance 90%) made of ₂ O ₃ was applied to obtain a laser chip having a structure as shown in FIG.

[0011]

According to the present invention, it is possible to realize good crystal growth on the end face, which was difficult with the conventional high-power semiconductor laser, and to cover the end face after all the steps normally performed in a wafer state are completed. Since the semiconductor layer can be formed, the manufacturing process can be rationalized.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a semiconductor laser device according to an embodiment of the present invention.

FIG. 2 is a perspective view illustrating a method of fixing a sample during end face crystal growth.

FIG. 3 is an explanatory diagram of a semiconductor laser device according to a second embodiment of the present invention.

FIG. 4 is an explanatory diagram of a semiconductor laser device according to a third embodiment of the present invention.

FIG. 5 is a perspective view of a conventional semiconductor laser device.

[Explanation of symbols]

1 ... n-GaAs substrate, 2 ... n-Al _0.5 Ga _0.5 As clad layer, 3 ... Multiple quantum well active layer, 4 ... p-Al _0.5
Ga _0.5 As clad layer, 5 ... p-GaAs contact layer, 6 ... Al _0.1 Ga _0.9 As well layer, 7 ... Al _0.3 G
a _0.7 As barrier layer, 8 ... n-GaAs block layer, 9
... p-Al _0.5 Ga _0.5 As buried layer, 10 ... p-GaAs
Cap layer, 11 ... Electrode, 12 ... ZnSe layer, 13 ... A
Antireflection coating of l ₂ O ₃ , 14 ... a-Si / Al
₂ O ₃ highly reflective coating.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinichiro Yano 1-280, Higashikoigokubo, Kokubunji, Tokyo Inside the Central Research Laboratory, Hitachi, Ltd.

Claims (5)

[Claims] 1. A semiconductor laser device which is made of semiconductor crystals having different conductivity types and different forbidden band widths and which emits a laser beam when energized, wherein a radiation end face is formed separately from the semiconductor crystal forming the semiconductor laser device. Is covered with a semiconductor film composed of the group II element and the group VI element, and the semiconductor film is not more than a quarter of the wavelength of the laser light emitted by the semiconductor laser device in the semiconductor film. A semiconductor laser device having a thickness of 2. The semiconductor laser device according to claim 1, wherein the group II element is zinc or a mixture of zinc and cadmium, and the group VI element is selenium or a mixture of selenium and sulfur. 3. The crystal layer according to claim 1 or 2, wherein the thickness of the semiconductor layer covering the radiation end face is a crystal defect due to a stress generated due to a difference in lattice constant between the semiconductor layer and the semiconductor laser. A semiconductor laser device that is thin enough to prevent 4. The method for manufacturing a semiconductor laser device according to claim 1, wherein the semiconductor layer covering the radiation end face is formed at a temperature lower than the maximum temperature reached in the step of forming an electrode on the semiconductor laser device. . 5. The insulating material according to claim 1, 2, 3 or 4, which has a thermal conductivity higher than that of a semiconductor constituting the semiconductor laser element and is not absorptive of laser light on the semiconductor layer covering the radiation end face. A semiconductor laser device provided with a protective film composed of.