JPS6343913B2 - - Google Patents

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 from the viewpoint of ease of operation, a semiconductor laser device with an oscillation wavelength in the visible range with a low threshold and high reliability is used. It is hoped that it will be put into practical use.

In Ga _1-x Al _x As semiconductor lasers that have been developed in the 0.8 μm band, the active layer X is 0.15-0.35,
By setting X of the cladding layer to 0.5 to 0.8, a visible semiconductor laser with a wavelength of 7600 Å or less can be easily produced (for example, Kutsel et al., Applied Physics Letters Vol. 28, 1976, p. 598 (H.
Kressel et al., Appl.Phys.Lett.Vol.28, No.10,
(1976, p. 598)). In this case, the mismatching of the lattice constants between the GaAs substrate and the grown layer increases as the mixed crystal ratio Increasing the size 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 GaAs substrate as before.
A GaAlAs double heterostructure multilayer film is grown through a GaAlAs buffer layer.

The second method uses a GaAs substrate as before, and Ga on the top of it.
This method grows a GaAlAs-based multilayer film with a double heterostructure through a buffer layer of (AsSb) layers.

The third method uses a GaAs substrate as in the past, and grows a GaAlAs-based double heterostructure multilayer film on top of the GaAs substrate with a buffer layer of (InGa)As layer interposed therebetween.

The fourth method is to grow a multilayer film with a GaAlAs-based double heterostructure on a Ga _1-x Al _x As mixed crystal substrate, and the fifth method is to grow a GaAlAs-based double heterostructure on a Ga(AsSb) mixed crystal substrate. A sixth method is to grow a multilayer film having a GaAlAs double heterostructure on an (InGa)As mixed crystal substrate.

[Embodiments of the invention]

Hereinafter, each will be explained in detail using examples.

The first form uses a GaAlAs 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 GaAlAs semiconductor laser. At the same time, the thickness of each layer is d ₁
Shown at ~ _d5 .

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

Ga _1-x Al _x As mixed crystal substrate (0.02x0.4) (thickness d ₁ ) n-type Ga _1-y Al _y As layer (0.5y0.8) (thickness d ₂ ) 2 Ga _{1 -z} Al _z As layer (0.15z0.35) (thickness d ₃ ) 3 p-type Ga _1-u Al _u As layer (0.5u0.8) (thickness d ₄ ) 4 and each layer of p-type GaAs layer 5 is grown by the well-known liquid phase epitaxial method. Layer 2 and layer 4 are of opposite conductivity type. In this case, the mixed crystal substrate is selected so as to satisfy the relationship z-0.075xz+0.025.

Note that the thickness of each layer is approximately selected within the following range.

50μmd ₁ 200μm, 1μmd ₂ 3μm, 0.05μmd ₃ 0.5μm, 1μmd ₄ 3μm, 0.5μmd ₅ 3μm.

Next, an Al ₂ O ₃ film is deposited on layer 5 to a certain thickness using the CVD method.
Formed at 3000Å. The Al ₂ O ₃ film is selectively removed in stripes with a width of 5 μm using a conventional photolithography technique. Zn is diffused through this window to form a Zn diffusion region 8. After removing the Al ₂ O ₃ film, Cr-Au is used as the p-side electrode 7, and Cr-Au is used as the n-side electrode 6.
Form AuGeNi-Au by vapor deposition. Mutually parallel resonant reflection surfaces are fabricated by cleaving opposing end surfaces 9 and 10 of the semiconductor laser device.

FIG. 2 shows an example of calculating the stress in the active layer 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, cases are shown in which the AlAs mixed crystal ratio z in the active layer is 0.15 and 0.2. The figure shows that there is a range in which the stress in the active layer can be significantly reduced by setting x within a certain range for a certain z.

As a result of the study, it was found that the mixed crystal ratio x of the substrate at which the stress in the active layer is minimized is Xz-0.025 (at this time, y=u=0.6). Also, the stress in the active layer
To keep it within 10 ⁸ dyn/cm ² , use z−0.075xz+
It turned out that 0.025 is sufficient. This situation is shown in Figure 3. The stress in the active layer depends on the thickness of each layer.
It has been confirmed through calculations that the values d ₂ to _{d 5} change slowly, and the above relationship is almost satisfied within the error range for a practical device structure. As the AlAs mixed crystal ratio z in the active layer increases,
It is necessary to make y and u 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 mentioned above, in GaAlAs-based visible semiconductor lasers, by using a substrate with a mixed crystal ratio (x) that satisfies the relationship z-0.075xz+0.025, stress concentration in the active layer is alleviated and the device has a long lifespan. It is expected that Note that the mixed crystal substrate can be created by a liquid phase thick film growth method.

In the second form, a GaAlAs-based double heterostructure is formed on top of a GaAs substrate with a buffer layer of GaAlAs 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;

The following layers are grown on an n-type GaAs substrate 41 having a (100) plane on its surface by a well-known liquid phase continuous epitaxial method.

n-type Ga _1-z Al _z As (0<z0.8) (thickness d ₄₂ ) 42, n-type Ga _1-y Al _y As (0.5y0.8) (thickness d ₄₃ ) 43, Ga _{1- x} Al _x As (0.15x0.35) (thickness d ₄₄ ) 44, p-type Ga _1-u Al _u As (0.5<u0.8) (thickness d ₄₅ ) 45, p-type GaAs (thickness d ₄₆₎ )46. Here, the layer 42 is a buffer layer and is a particularly important layer in the present invention. Thickness: 6μm~
20 μm is appropriate.

Layer 44 is an active layer, and layers 43 and 45 sandwich this layer.
is the clad layer. It can be designed in the same way as conventional double heterostructures. In general,
The active layer 44 has a thickness of 0.05 .mu.m to 0.2 .mu.m, and the cladding layer has a thickness of approximately 1 .mu.m to 3 .mu.m.

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. The example in Figure 5 is x=0.2, y=u=0.6, d ₄₁ =
100μm, _d43 = 1μm, _d44 = 0.1μm, _d45 = 2μm, _d46
= 1 μm. The horizontal axis is the thickness d ₄₂ of the buffer layer 42,
The vertical axis indicates stress in the active layer. Note that the point marked with an arrow A in the figure 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 ⁸ dyn/cm ² 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 of each layer d ₃ to d ₆ other than the buffer layer.
It has been confirmed through calculations that the amount changes slowly when it is about 2 μm or less, and for a practical device structure, the above relationship is almost satisfied within the error range.

As mentioned above, in (GaAl)As-based visible lasers, when the AlAs mixed crystal ratio (z) is about 0.3 or more and the thickness is
By providing a buffer layer with a thickness of approximately 6 μm to 20 μm, stress in the active layer is alleviated, and a longer life of the device can be expected.

In the third to sixth forms, when growing a (GaAl)As-based visible semiconductor laser, Ga(AsSb) 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.

At room temperature, the lattice constants of GaAs, AlAs, GaSb, and InAs are 5653 Å, 5662 Å, 6095 Å, respectively.
6058 Å, and when the difference is expressed as a percentage based on the lattice constant of GaAs, it is +0.16% for AlAs,
GaSb is +7.52%, and InAs is +6.92%. Mixed crystals of these systems (Ga _1-x Al _x As, Ga(As _1-y Sb _y ),
(In _z Ga _1-z )As, the lattice constant is the mixed crystal ratio x, y,
Since Vegard's law that changes proportionally to z has become better, the mixed crystal ratio X y = (0.16/7.52) Among the first and second stress-reduced semiconductor laser forms, the second form of semiconductor laser has a buffer layer with a composition of about 6 to 20 μm having a mixed crystal ratio of z0.3, which has the same lattice constant. It can be replaced by applying a Ga (As _1-y Sb _y )-based buffer layer with y≧0.00639 or (In _z Ga _1-z ) As-based buffer layer with z0.00693 to the same thickness. _Moreover , instead of using _the mixed crystal _{substrate of} Can be replaced with a mixed crystal substrate.

Therefore, Ga(As _1-y Sb _y ) (0y0.003), (In _z
The object of the present invention can be achieved by using Ga _1-z )As (0z0.003).

These forms have the following advantages over the case of using a GaAlAs-based buffer layer or a mixed crystal substrate.

When applying a buffer layer with a thickness of 10 μm to 20 μm,
If the growth of the buffer layer on the GaAs substrate can be separated from the growth of the laser structure on top of it, this method can be performed with great reproducibility. In the case of a (GaAl)As-based buffer layer of x0.5 or more, the surface is immediately oxidized in the air, so it cannot be separated into two growths like this. on the other hand,
In the case of Ga(As _1-y Sb _y ) or (In _z Ga _1-z )As, there is no such problem at all. For example, when a mixed crystal of y~z~0.1 is grown in liquid phase from a Ga-rich solution at 800°C, the segregation coefficient is -0.5 for Sb and -0.2 for In.
The composition can be easily controlled.

Even in the production of a mixed crystal substrate with the same lattice constant as (Ga _1-x Al _x )As with a composition of x0.1, yz0.002
(0.2%), the density of Sb and In in the crystal can be -5×10 ¹⁹ co/cc, which is about the same as a normal dopant, 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 (As _0.88 Sb _0.12 )
layers or n-type (In _0.12 Ga _0.88 ) As layer 42, n-type (Ga _0.4 Al _0.6 ) As layer 43, p-type (Ga _0.8 Al _0.2 ) As layer 44, p-type (Ga _0.4 Al _0.6 ) As layer 45, p-type GaAs
Layer 46 is grown continuously by liquid phase epitaxy. The liquid phase growth method was carried out by the usual slide boat method, and the thickness of each layer was 10 μm for 42, 2 μm for 43, 0.1 μm for 44,
45 is 2 μm, and 46 is 1 μm.

Next, a SiO ₂ film is formed on layer 46 to a thickness of 3000 Å by CVD. The SiO ₂ film is selectively removed in stripes with a width of 5 μm using a conventional photolithography technique. After that, as a p-side electrode
AuZn and AuSn are formed by vapor deposition as the n-side electrode.
The laser length is 300μm. Mutually parallel resonant reflection surfaces are created by cleaving the opposing end faces of the semiconductor laser device.

The above laser oscillated at 750 nm at room temperature, had a low threshold current density of about 1 KA/cm ² , and had a lifetime comparable to conventional 0.83 μm band devices.

Furthermore, an n-type Ga (As _1-0.002 Sb _0.002 ) substrate or an n-type Ga (As 1-0.002 Sb 0.002 ) substrate or
A (In _0.002 Ga _1-0.002 ) As substrate was prepared, and semiconductor layers having the compositions and thicknesses 43, 44, 45, and 46 described above were successively grown on the substrate by the same liquid phase growth method. The laser device with this structure can also achieve a low threshold current density and a long life similar to those described above.

Ga(AsSb)-based or (InGa)As-based buffer layers or mixed crystal substrates can be grown in vapor phase on a GaAs substrate or by CVD, and similar characteristics can be obtained. It was done.

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
Similar characteristics were obtained by using the present invention in lasers with various structures such as a substrate planar structure.

〔Effect of the invention〕

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

[Brief explanation of the drawing]

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, 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, and Fig. 4 is a diagram showing the relationship between the mixed crystal ratio of the substrate and the stress of the active layer. FIG. 5, which is a cross-sectional view of the semiconductor laser device according to the embodiment, is a diagram showing the relationship between the thickness of the buffer layer and the stress of the active layer. 1...GaAlAs substrate, 2, 4...cladding layer,
3... Active layer, 6, 7... Electrode, 9, 10... Crystal end face, 41... GaAs substrate, 42... Buffer layer.

Claims (1)

[Claims] 1 GaAs substrate and (G _a1-x Al _x ) As, Ga (As _1-y S _by ) or (I _oz
In a semiconductor laser device having a buffer layer made of (G _a1-z ) As and a GaAlAs-based double heterostructure formed on the buffer layer, the mixed crystal ratios x, y, and z of the buffer layer are each 0.3× 0.8，
0.00639y0.01704, 0.00693z0.01848,
, and the thickness of the buffer layer is 6 μm ~
A semiconductor laser device characterized by a diameter of 20 μm.