JPS6339114B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a highly reliable and long-life semiconductor laser device.

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 GaAlAs double hetero semiconductor lasers that have been developed in the 0.8 μm band, the active layer's mixed crystal ratio z is 0.15 to 0.35, and the clad layer's mixed crystal ratio y and u are 0.5.
By setting it to 0.8, a visible semiconductor laser with a wavelength of 7600 Å or less can be easily manufactured. in this case,
As the mismatching of the lattice constants between the GaAs substrate and the grown layer increases as the mixed crystal ratio z, y, and u increases, the in-plane stress in the grown layer, especially the stress applied to the active layer, increases by 1 compared to the conventional 0.83 μm laser. Increasing the size by an order of magnitude or more is an important issue in obtaining long life and high reliability of the device. We propose a new semiconductor laser device configuration that reduces the stress applied to the active layer.

In the first form, a GaAlAs-based multilayer film having a double heterostructure is grown on a Ga _1-x1 Al _x1 As mixed crystal substrate.

The second form is on a GaAs _1-x2 Sb _x2 mixed crystal substrate.
This method grows a GaAlAs-based multilayer film with a double heterostructure.

The third form is on an In _x3 Ga _1-x3 As mixed crystal substrate.
This method grows a GaAlAs-based multilayer film with a double heterostructure.

Each will be explained in detail below.

The first form uses a Ga _1-x1 Al _x1 As 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-based double hetero semiconductor laser. At the same time, the thickness of each layer was expressed as _d1 to _d5 .

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

Ga _1-x1 Al _x1 As mixed crystal substrate (0.02x ₁ 0.4) (thickness
d ₁ ) n-type Ga _1-y Al _y As layer (0.5y0.8) on 1
(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)
A p-type GaAs layer (thickness d ₄ ) 4 and a p-type GaAs layer (thickness d ₅ ) 5 are grown by a well-known liquid phase epitaxial method. Layer 2 and layer 4 are of opposite conductivity type. In this case z
A mixed crystal substrate is selected so as to satisfy the relationship -0.075x ₁ z + 0.025.

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

50μmd ₁ 200μm, 1μmd ₂ 3μm, 0.05μm
d ₃ 0.5μm, 1μm d ₄ 3μm, 0.5μm d ₅ 3μ
m Next, an Al ₂ O ₃ film is deposited on layer 5 to a thickness of
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 diffuses through this window, and Zn
A diffusion region 8 is formed.

After removing the Al ₂ O ₃ film, Cr-
As the n-side electrode 6, AuGeNi-Au is formed by vapor deposition. Opposing end surfaces 9 and 1 of the semiconductor laser device
0 creates mutually parallel resonant reflection surfaces by cleavage.

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 ₁ of the substrate, and the vertical axis represents the stress σ 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 ₁ within a certain range for a certain z.

As a result of investigation, it was found that the mixed crystal ratio x ₁ of the substrate at which the stress in the active layer is minimized is x ₁ z-0.025 (at this time, y=u=0.6). Also, the stress σ in the active layer is
It turned out that in order to keep it within 10 ⁸ dyn/cm ² z−0.075x ₁ z+0.025 ……(1). This is the third
Shown in the figure. The stress in the active layer varies with the thickness of each layer d ₂ ~ _{d 5}
It has been confirmed through calculations that the amount changes slowly, and for practical device structures, the above relationship is almost satisfied within the error range. When the mixed crystal ratio z of AlAs in the active layer increases, y and u must be set to 0.6 or more, but in this case as well, the range where the stress is minimum is included in the region shown in FIG.

The prototype device showed the following characteristics.

A semiconductor laser prototyped with z = 0.2, x ₁ = 0.175, and y = u = 0.5 continuously oscillated at room temperature at an oscillation wavelength of 745 nm and a threshold current density of 1.5 KA/cm ² .
Furthermore, when operating at a constant light output of 5 mW at an environmental temperature of 50°C, it operated stably for over 1000 hours.

Furthermore, z=0.2, y=u=0.5, and x ₁ is Z−
Results similar to those described above were also obtained in the case of a semiconductor laser that was prototyped by changing it in the range of 0.075x ₁ z + 0.025.

As mentioned above, in a GaAlAs-based visible semiconductor laser, by using a substrate with a mixed crystal ratio x ₁ that satisfies the relationship z-0.075x ₁ z+0.025, stress concentration in the active layer is eased and the length of the device is increased. Expected to last longer. Note that the mixed crystal substrate can be manufactured by a liquid phase thick film growth method.

The second and third embodiments are characterized in that stress in the active layer is reduced by using GaAsSb or InGaAs ternary mixed crystal as a mixed crystal substrate during growth of the GaAlAs visible semiconductor laser.

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-x1 Al _x1 As, GaAs _1-x2 Sb _x2 , In _x3
In Ga _1-x3 As, Vegard's law that the lattice constant changes proportionally to the mixed crystal ratio x ₁ , x ₂ , x ₃ is becoming better, so Ga _1-x1 Al _x1 with a mixed crystal ratio x ₁ x ₂ and x _{3 ,} which have the same lattice constant as As, are x ₂ = (0.16/7.52) x ₁ = 0.0213x _{1 ……} ( ₂ ) 3) becomes.

This _means that instead of using a mixed crystal substrate with a mixed crystal ratio of x ₁ 0.1 in the semiconductor laser of the first form,
0.00213 GaAs _1-x2 Sb _x2 system, or x ₃ 0.00231
This shows that it can be replaced with an In _x3 Ga _1-x3 As mixed crystal substrate.

Furthermore, when x 1 , x 2 , and x ₃ are calculated from equations ( ₁ ), ( ₂ ), and (3), they become 0.075x ₁ 0.375 0.00160x ₂ 0.00799 0.00173x ₃ 0.00866.

Therefore, GaAs _1-x2 Sb _x2 (0.00160x ₂
0.00799), In _x3 Ga _1-x3 As (0.00173x ₃ 0.00866)
By using this, the object of the present invention can be achieved.

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

Even in the production of a mixed crystal substrate with the same lattice constant as Ga _1-x1 Al _x1 As with a composition of x ₁ 0.1, x ₂ x ₃ 0.002
(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 second and third embodiments will be explained using specific examples.

This will be explained using FIG.

n-type GaAs _1-0.002 Sb _0.002 substrate 42 or n-type In _0.002
A Ga _1-0.002 As substrate 42 is prepared, and on top of it are formed an n-type Ga _0.4 Al _0.6 As layer 43, a p-type Ga _0.8 Al _0.2 As layer 44, a p-type Ga _0.4 Al _0.6 As layer 45, and a p-type GaAs layer 46. Continuously grows using liquid phase growth method. The liquid phase growth method was carried out using the usual slide board method, and the thickness of each layer was 4
2 is 10μm, 43 is 2μm, 44 is 0.1μm, 45 is
2 μm, 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 conventional photolithography technology. After that, as a p-side electrode
AuZn and AuSn are formed by vapor deposition as the n-side electrode.
The laser length is 300 μm. Opposing end faces of the semiconductor laser device are cleaved to create mutually parallel resonant reflection surfaces.

The above laser oscillates at 750 nm at room temperature, and has a low threshold current density of about 1 KA/ ^cm2 .
In addition, in a life test in which the device operated at a constant light output at an ambient temperature of 50°C and a light output of 5 mW, it operated stably for over 1000 hours, achieving a lifespan comparable to that of conventional 0.83 μm band elements.

GaAsSb-based or InGaAs-based mixed crystal substrates are
Vapor phase growth on GaAs substrate or CVD
It was also possible to use those grown by the method, and similar properties 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
Similar characteristics were obtained by using the present invention in lasers with various structures such as a substrate planar structure.

[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, Fig. 3 is a diagram showing the range of the mixed crystal ratio of the active layer and the liquid crystal ratio of the substrate, and Fig. 4 is a diagram showing another embodiment of the present invention. FIG. 2 is a cross-sectional view of a semiconductor laser device showing its configuration. 1...GaAlAs substrate, 2, 4...cladding layer,
3... Active layer, 6, 7... Electrode, 9, 10... Crystal end face, 42... GaAsSb substrate, InGaAs substrate.

Claims (1)

[Claims] 1 Ga _1-x1 Al _x1 As, GaAs _1-x2 Sb _x2 or In _x3
Ga _1- y Al _y As layer (0.5y0.8), Ga _1-z Al _z As layer (0.15z0.35) on a mixed crystal substrate consisting of Ga _1- x3 As.
In a semiconductor laser device having a double heterostructure in which Ga _1-u Al _u As layers (0.5u0.8) are sequentially laminated, the mixed crystal ratios x ₁ , x ₂ , x ₃ of the mixed crystal substrate are each 0.075x ₁ 0.375, 0.00160x ₂ 0.00799, 0.00173x ₃ 0.00866. 2. The semiconductor laser device according to claim 1, wherein y, z, and u have a magnitude relationship of z<uy.