JPS61142786A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To decrease stress applied on an active layer, by forming a layer made of one material, which is selected among (GaAl)As, Ga(AsSb), or (InGa)As on a substrate, and forming a GaAlAs double heterostructure on the layer. CONSTITUTION:On a substrate, a layer made of one material selected among (GaAl)As, Ga(AsSb) or (InGa)As is formed. Multilayer films, having a GaAlAs double heterostructure is formed on said layer. For example, on a Ga1-xAlxAs mixed crystal substrate (0.02<=x<=0.4) 1, an N type Ga1-yAlyAs layer (0.5<=y<=0.8) 2, a Ga1-zAlzAs layer (0.15<=z<=0.35) 3, a P type Ga1-uAluAs layer (0.5<=u<=0.8)4 and P type GaAs layer 5 are grown by a liquid phase epitaxial method. Thereafter, a Zn diffused region 8, a P-side electrode 7 and an N-side electrode 6 are formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a highly reliable and long-life semiconductor laser device.

[Background of the invention]

Semiconductor laser devices are compact, highly efficient, and can be mass-produced, and are therefore being considered for a variety of applications as light sources for information terminal equipment such as laser printers, video disks, distance meters, and the like. In this case, the shorter the wavelength of the laser light, the better from the viewpoint of improving sensitivity and resolution, and the lower the threshold value from the viewpoint of ease of operation.

It is desired to put into practical use a highly reliable semiconductor laser device with an oscillation wavelength in the visible range.

In Gat-xAβz As semiconductor lasers that have been developed in the 0.8 μm band, the active layer X is 0.15-0.35 and the cladding layer X is 0.5.
~0.8, it is possible to easily produce a visible semiconductor laser with a wavelength of 7600 Å or less (for example, Kutsel et al.
Upride Physics Letters Volume 28, 197
6, p. 598 (H, Kressel et al.
, Appl, Phys, Lett.

Vol, 28. No. 10.1976, P. 598
)reference). In this case, the mismatching of the lattice constants between the GaAs substrate and the grown layer increases as the mixed crystal ratio An increase of one order of magnitude or more compared to that is an important issue in obtaining long life and high reliability of the device.

[Purpose of the invention]

An object of the present invention is to provide a new semiconductor laser device configuration that reduces stress applied to this active layer.

[Summary of the invention]

The first is to use a G a A s substrate as before and place G on the top of it.
A multilayer film having a GaAQAs-based double heterostructure is grown through an aAQAs-based buffer layer.

The second one uses a GaAs substrate as before and has Ga (
GaAQA through the buffer layer of the A s S b ) layer
This method grows a multilayer film with an s-based double heterostructure.

The third method uses a GaAs substrate as before, and on top of this (
A multilayer film having a GaAQAs-based double heterostructure is grown through an InGa)As buffer layer.

In addition, the fourth method is to grow a GaAQAs-based multilayer film having a double heterostructure on a Ga I X A 12
S b ) A multilayer film having a GaAQAs-based double heterostructure is grown on a mixed crystal substrate, and as a sixth method (I
There is also a method in which a multilayer film having a GaAl2As double heterostructure is grown on an nGa)As mixed crystal substrate.

[Embodiments of the invention]

Hereinafter, each will be explained in detail using examples.

The first form uses a GaAQAs mixed crystal substrate as the substrate.

FIG. 1 is a cross-sectional view taken along a plane parallel to a mirror surface constituting a Fabry-Perot resonator having a stacked structure of a GaAQAs semiconductor laser. At the same time, the thickness of each layer was indicated as d1 to d5.

The object of the present invention can be achieved by configuring each semiconductor layer as follows.

G a 1-z A Qz A S mixed crystal substrate (0,
02≦X≦0.4) (thickness d,) 8 layers of n-type Ga 1- y A Q y A on
≦y<0.8) (thickness dS) 2 , Get −z A Q z As layer (0,1
5≦2≦0.35) (thickness da) 3゜p type Ga t -LLA Q uASII (o,
s≦u<0,8) (thickness d4) 4, and the P-type GaAs layer 5 are grown by a well-known liquid phase epitaxial method. Layer 2 and N! I4 is of the opposite conductivity type. In this case, the mixed crystal substrate is selected so as to satisfy the relationship z −0, 075< x < z + 0, 025.

The thickness of each layer is selected within the following range.

50 membranes m≦d1≦200pm, 1μm≦d2≦3pm.

0.05 μm≦d2≦0.5pm, lpm≦d4≦3
p.m.

0.5pm≦d5<3pm.

Next, an Afi,03 film is formed on layer 5 to a thickness of 3000λ by CVD. The A2□03 film is selectively removed in stripes with a width of 5 μm using ordinary photolithography technology. Zn is diffused through this window to form a Zn diffusion region 8.

After removing the AQ203 film, Cr-A was used as the p-side electrode 7.
A u G e N i as the n side electrode 6
- Mutually parallel resonant reflection surfaces are produced by cleaving the opposing end faces 9 and 10 of the six semiconductor laser devices in which Au is formed by vapor deposition.

FIG. 2 is an example of calculating the stress in the active region in an element with this structure. Each parameter is illustrated in the figure. Solid lines indicate tensile stress and dashed lines indicate compressive stress.

The horizontal axis represents the mixed crystal ratio X of the substrate, and the vertical axis represents the stress in the active layer. Here, the mixed crystal ratio 2 of AnAs in the active layer is 0.15.
and 0.2 are shown. It can be seen that there is a range in which the stress in the active layer can be significantly reduced by setting Z within a certain range for 2 shown in the figure.

As a result of investigation, it was found that the mixed crystal ratio X of the substrate at which the stress in the active layer is minimized is X>z-0,025 (at this time, y=u=0.6). In addition, the stress in the active layer is 10”dyn/
It has been found that in order to make it within a#, it is sufficient to set z -0, 075≦X≦z+0.025. This situation is shown in Figure 3.

It has been confirmed through calculations that the stress in the active layer changes slowly with respect to the thickness of each layer d2 to d5, and for practical device structures, the above relationship is approximately within the error range. be satisfied. When the mixed crystal ratio 2 of A Q As in the active layer increases, y and U need to be 0.6 or more. In this case as well, the range where the stress is minimum is included in the area shown in FIG.

As stated above, stress concentration in the active layer can be reduced by using a substrate having a mixed crystal ratio (X) that satisfies the relationship z-0,075≦X≦z+0,025 in a GaAQAs-based visible semiconductor laser. is expected to be alleviated and the life of the device to be extended. Note that the mixed crystal substrate can be created by a liquid phase thick film growth method.

In the second form, a GaAQAs-based double heterostructure is formed on a GaAs substrate with a GaAQAs buffer layer interposed therebetween.

FIG. 4 shows an example of a semiconductor laser device of this form. FIG. 2 is a cross-sectional view of the main parts of the Fabry-Perot resonator taken along a plane parallel to a mirror surface constituting the Fabry-Perot resonator, similar to FIG. 1;

N-type GaAs substrate 41 with (100) plane on the surface
The following layers are grown thereon by a well-known liquid phase continuous epitaxial method.

n-type Ga1-zAQzAs (0<z≦0.8) (thickness d4z) 42゜n-type Ga1-yAQyAs (0,5
≦y≦Sail 8) (Thickness dsa) 43°Gat-xAQxA
s (0,15≦X≦0.35) (thickness d44) 44°Plj:! Ga1-uAQ uAs(o, s≦U≦0.
8) (Thickness d 45) 45゜P type QaAs (Thickness d
4e) 46. Here, the layer 42 is a buffer layer and is a particularly important layer in the present invention. A suitable thickness is 6 μm to 20 μm.

The layer 44 is an active layer, and the layers 43 and 45 sandwiching it are cladding layers. It can be designed in the same way as the conventional double heterostructure. Generally, the active layer 44 is 0.
Thickness of 05μm to 0.2μm, cladding layer approximately Iμm
The thickness is ~3 μm.

FIG. 5 shows how the stress in the active layer 44 changes with respect to the thickness of the buffer layer in the device of this structure. In the example of FIG. 5, z=Q, 5. y=u=0.2yd 4 □=100
u rn p d 43 =1 /j Tn t d
44 =Q, 1μm, d4s=2umt d46=1
It is μm. The horizontal axis represents the thickness d4□ of the buffer layer 42, and the vertical axis represents the stress in the active layer. Note that the point marked with an arrow A in FIG. 1 indicates the stress in the active layer in the conventional structure.

From the figure, it can be seen that in order to reduce the stress in the active layer to 18''dyn/cd or less, the buffer composition should be 13 μm or more when z=0.3, and 6 μm or more when z=0.6. The stress in the active layer is determined by the thickness d of each layer other than the buffer layer.
For 3 to d8, calculations have confirmed that the values change slowly when the respective thicknesses are approximately 2 μm or less, and for practical device structures, the above relationship is within the error range. I am almost satisfied with that.

As stated above, in a (GaAl)As-based visible laser, stress in the active layer can be reduced by providing a buffer layer with an AQAs mixed crystal ratio (z) of about 0.3 or more and a thickness of about 6 μm to 20 μm. can be expected to extend the life of the device.

In the third to sixth forms, when growing a (GaAl)As-based visible semiconductor laser, Ga (As S b ) or (InGa)As-based ternary mixed crystal is used as a buffer layer or
It is characterized by reducing stress in the active layer by using it as a mixed crystal substrate.

The contents will be explained below.

GaAs, AQAs, GaSb at room temperature.

The lattice constant of InAs is 5653, respectively.

They are 5662 people, 6095 people, and 6058 people, and when the difference is expressed as a percentage based on the lattice constant of Ga As, A! As +0.16%, GaSb +7.52%
, InAs is +6.92%. Mixed crystals of these systems (
GB 1+ x, AQX) As.

Ga(Asz-ySby)t(In2Ga1-z)
In As, Vegard's law that the lattice constant changes proportionally to the mixed crystal ratio x, y, z has been improved, so y of the mixed crystal ratio X = (0,16/7.52) X =0.0213XZ
= (0,16/6.92) When the buffer layer is provided with a thickness of about 6 to 20 μm, Ga (Ash-ySb) with y≧0.1065 corresponding to the same lattice constant
y) system or (InzGat X
) It can be replaced by adding seven layers of As-based buff with the same thickness.

Moreover, instead of using the mixed crystal substrate of X=O,t which is the first form, a Ga(As1-ySby) system with y 0.00213 or z>0.00231
(InzGat-x)As-based mixed crystal substrate can be used instead.

Therefore, Ga (Ash y 5by) (0< y
<0.003), (InzGal-2C)As (0
≦Z≦0.003), the object of the present invention can be achieved.

These forms have the following advantages over the case where a GaAQAs-based buffer layer or mixed crystal substrate is used.

When depositing a buffer layer with a thickness of 10 .mu.m to 20 .mu.m, this method can be carried out with great reproducibility if the components for depositing the buffer layer on the GaAs substrate and the growth for producing the laser structure thereon can be separated. (GaAffi)
In the case of an As-based buffer layer with x > 0.5, the surface is immediately oxidized in the air and cannot be separated into two such growths.On the other hand, Ga (Asl-ySby)
Or (InzGaneez)As, there is no such problem at all. Also, for example, at 800°C, y~2~0
．． When the mixed crystal of No. 1 is grown in a liquid phase from a Ga-rich solution, the segregation coefficient is about -0.5 for sb and -0.2 for In, and the composition can be easily controlled.

x Qt=0, 1 composition (Gaz −X A
QX) Even in the production of a mixed crystal substrate with the same lattice constant as As, yWZ is extremely small at 0.002 (0.2%), so the density of Sb and In in the crystal is -5X 101
g: I/cc and ordinary dopants are enough, and it can be manufactured without deteriorating the quality of the crystal as a substrate. Furthermore, since the segregation coefficients of Sb and In are small, it is easy to obtain a substrate with a uniform composition.

The fourth and sixth embodiments will be explained using specific examples.

This will be explained using FIG.

On the n-type GaAs substrate 41, n-type Ga (Aso, asS
bo, z2) layer or n-type (I no, tzGa o,
as) As layer 42, n-type (Ga O, 4A Q o,
s) As layer 43. P type (Qa□, B A Q g,
2) As layer 44. p-type (Ga o, a A Q o
, B) As layer 45. A P-type GaAs layer 46 is grown continuously using a liquid phase growth method. The liquid phase growth method was carried out using a normal slide boat method, and the thickness of each layer was 42 to 11) pm.
43 is 2pm, 44 is 0.1μm, 45 is 2μm, 46
is 1 μm.

Next, a SiO□ film is formed on the layer 46 to a thickness of 3 by CVD.
Formed to 000 people. The SiO□ film is selectively removed in stripes with a width of 5 μm using ordinary photolithography technology6.Then, AuZ
A u S n is formed by vapor deposition as the n and n side electrodes.

The laser length is 300 μm. Mutually parallel resonant reflection surfaces are created by cleaving the opposing end faces of the semiconductor laser device.

The above laser oscillates at 750 nm at room temperature,
The threshold current density is as low as lKA#J, and
．． A lifespan comparable to that of an 83 μm band element was obtained.

Furthermore, n-type Ga (Asz -0,002SbO,00
2) Substrate or n-type (I n O,002Ga + −
0,002) Prepare an As substrate, and place the above-mentioned 4 on top of it.
A zero-strand laser device in which a semiconductor layer with a composition and thickness of 3.44, 45°46 is continuously grown using the same liquid phase growth method also has the same low threshold current density and long length. You can get longevity.

As the Ga(AsSb)-based or (InGa)As-based buffer layer or mixed crystal substrate, one grown in vapor phase on a GaAs substrate or one grown by the CVD method can be used, and a similar one can be used. Characteristics were obtained.

In the present invention, an embodiment related to a semiconductor laser with a planar stripe structure has been described in detail, but a buried heterostructure, a channeled substrate
Similar characteristics were obtained by using the present invention in lasers with various structures such as , e P 1anar structure, etc.

〔Effect of the invention〕

The present invention has the effect of providing a practical visible semiconductor laser.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a semiconductor laser device of the present invention. Fig. 2 is a diagram showing the relationship between the mixed crystal ratio of the substrate and the stress in the active layer, and Fig. 3 is a diagram showing the range of the mixed crystal ratio of the active layer and the mixed crystal ratio of the substrate.
FIG. 4 is a cross-sectional view of a semiconductor laser device showing another embodiment of the present invention, and FIG. 5 is a diagram showing the relationship between the thickness of the buffer layer and the stress in the active layer. l...GaAQAs substrate, 2,4...cladding layer,
3... Active layer, 6, 7... Electrode, 9, 10... Crystal end face, 41... GaAs substrate, 42... Buffer layer. Foil 1 Funeral 2 (21 g a l l Lj a・J 4 (
(15 foils 3 times 64 pieces

Claims (1)

[Claims] 1. On the substrate (GaAl)As, Ga(As, Sb),
or (InGa)As, and has at least a GaAlAs-based double heterostructure on top of the layer. 2. The semiconductor laser device according to claim 1, wherein the substrate is made of GaAs.