JPS6367350B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a single mode oscillation semiconductor laser device that is easy to manufacture and has a high production yield.

Semiconductor laser devices have made remarkable progress over the past ten years or so, and in recent years, their practical use has begun mainly in the field of optical communications. Along with this, research has been progressing at a rapid pace to improve the performance of semiconductor lasers, one of which has been the basic unification of the oscillation mode. Several types of semiconductor lasers that oscillate in a single mode have already been developed.

For example, in the Spring 1979 Proceedings of the Society of Applied Physics, page 173, etc.
n-InGaAsP (n-conductivity type InGaAsP) embedded in p-InP (p-conductivity type InP) above the active layer
Proposals have been made to simultaneously confine current and light in this area.

However, with any of the crystals, a laser element with good characteristics cannot be obtained. In particular, when crystals with completely different compositions are stacked in the central part of the device, the effects of strain or defects occurring at each crystal interface extend to other regions, resulting in single-mode oscillation and other This makes it extremely difficult to manufacture semiconductor lasers with good characteristics (for example, low threshold current values) with a high yield.

An object of the present invention is to solve the above-mentioned drawbacks and provide a method for manufacturing a laser that oscillates in the fundamental mode with good reproducibility.

The structure of the present invention for achieving the above object is to provide a liquid phase growth improvement layer with a low mixed crystal ratio close to that of either one of the cladding layers and the absorption layer on the active layer.

This liquid phase growth improvement layer is a cladding layer Ga _1-z Al _z As (z=0.3 to 0.7) formed on the active layer GaAlAs.
It is obtained by further forming Ga _1-u Al _u As (u = 0.05 to 0.25) on top, which is smaller than the AlAs mixed crystal ratio in the cladding layer and larger than the AlAs mixed crystal ratio in the active layer. Takes a value. In addition, the improvement layer has a thickness of 0.1 to 0.4 μm so that the light distribution partially penetrates into the light absorption layer.
The thickness is .

Since the present invention has the above-described structure, the large amount of distortion and defects caused by mismatching that conventionally occurred between the light absorption layer GaAs and the cladding layer GaAlAs can be avoided.
Between the absorption layer and the growth improvement layer,
Since it is relaxed in two stages, between the growth improvement layer and the cladding layer, it hardly occurs, and no electrical or optical adverse effects occur. By interposing this growth-improving layer, even (GaAl)As-based crystals, for which lamination of liquid-phase growth layers has traditionally been difficult due to the problem of crystal matching, can have a transparent linear structure on the top of the active layer. It has become easier to form a DH laser device (double hetero type laser device). This will be explained in detail below using examples.

FIG. 1 is a schematic cross-sectional view of a semiconductor laser device as an embodiment of the present invention.

1 is n-GaAs substrate, 2 is n-Ga _1-x Al _x As (x
3 is Ga _1-y Al _y As (y
4 is a cladding layer of p-Ga _1-z Al _z As layer (z = 0.3-0.7), 5 is p-Ga _1-u
Liquid phase growth improvement layer of Al _u As (u=0.05~0.25), 6 is light absorption layer of n-GaAs layer, 7 is transparent line of p-Ga _1-v Al _v As layer (v=0.05~0.7) Strata, 8 is p-GaAs
This is the contact layer. 9 and 10 are ohmic electrodes. In addition, here, in particular, the thickness of the active layer of layer 3 is set to 0.1 μm or less, and the thickness of the cladding layer 4 and the liquid phase growth improvement layer 5 is set to 0.1 μm or less.
The total thickness including this is 0.5 μm or less. This is determined by the value of the seepage portion of the light distribution generated in the active layer applied to the light absorption layer. The thickness of the active layer plus the clad layer and liquid phase growth improvement layer is 0.1 μm.
Particularly good characteristics can be obtained when the thickness is 0.4 μm, that is, the thickness ratio is 1:4. In order to fabricate the above structure, layers 2 to 6 are successively grown on an n-GaAs substrate by liquid phase growth, and then the central part of layer 6 is made to resonate with a laser using photolithography technology. Etching is carried out in the longitudinal direction to form a striped window reaching the layer 5 and a pair of striped light absorption layers 6 on both sides of the window. The stripes run perpendicular to the cross section of the figure. Note that chemical etching, plasma etching, etc. are effective as the etching method. Especially in plasma etching,
Plasma etching using CCl ₂ F ₂ gas is ideal for creating this structure because it can selectively etch only GaAs. Next, layer 7,
Grow 8. Ga _1-u Al _u As of liquid phase growth improvement layer 5
The effects of the layers are explained below.
In liquid phase growth of GaAs-(GaAl)As system, as the AlAs mixed crystal ratio of the underlying (GaAl)As system crystal increases, the difference in crystal composition from that of the GaAs crystal increases.
Liquid phase growth of GaAs becomes difficult. So p-
In order to avoid discontinuous liquid phase growth on the Ga _1-z Al _z As layer 4 (z=0.3 to 0.7), a layer 5 having a small AlAs mixed crystal ratio is inserted in between. The relationship between the AlAs mixed crystal ratio z of the liquid phase growth improved layer 5 and the Al mixed crystal ratio y of the active layer is zy, that is, the relationship of the AlAs mixed crystal ratio is active layer<liquid phase growth improved layer<cladding layer. The absorption in layer 5 is made small for the wavelength of light generated in the active layer.

According to this structure, the laser light generated in the active layer is spread and distributed to each layer above and below, and reaches as far as the transparent striated layer 7 (with low absorption) in the center. However, the light reaches the light absorption layer 6 on both sides of the groove and is greatly absorbed by GaAs. Therefore, there is a difference in absorption loss between the center and both sides of the groove, and light is confined in the center. For the reasons for this, for example, JP-A-52-
143787 etc. in detail. This absorption loss is a built-in structure and is stable against changes in current, temperature, and other factors. Therefore, a stable laser oscillation mode can be obtained. Furthermore, in this structure, since current is also confined in the center by the light absorption layer 6, injection light emission occurs efficiently, and a semiconductor laser with a low threshold current value can be obtained with high yield.

In the above embodiment, a GaAs light absorption layer and a (GaAl)As-based cladding layer were described.
It goes without saying that the light absorption layer may be made of other compound semiconductors such as InGaAsP, and the cladding layer may also be made of other compound semiconductors such as InP. However, in that case, it goes without saying that consideration must be given to the mixed crystal ratio and the like so that the laser efficiency and the like do not deteriorate. Furthermore, it goes without saying that the conductivity types p and n may be reversed.

As mentioned above, in the present invention, GaAs-
Since the disadvantages of liquid phase growth between different types of crystals such as (GaAl)As systems do not become an obstacle, oscillation occurs in a single mode.
A semiconductor laser with stable characteristics can be manufactured with good reproducibility, and its practical effects are significant.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a semiconductor laser device as an embodiment of the present invention. 1...Substrate, 2...Clad layer (n-
3... active layer (GaAlAs), 4... cladding layer (p-GaAlAs), 5... liquid phase growth improvement layer, 6... light absorption layer (n-GaAs), 7... transparent filament layer (p-GaAlAs), 8...contact layer,
9,10... Electrode.

Claims (1)

[Scope of Claims] 1. A first semiconductor layer that does not contain or contains Al that acts as an active layer, and a semiconductor layer that has a larger forbidden band width and a refractive index than the first semiconductor layer laminated on the first semiconductor layer. a second semiconductor layer of one conductivity type containing a small amount of Al; a third semiconductor layer of the same conductivity type as the second semiconductor layer containing Al laminated on the second semiconductor layer; a pair of striped fourth semiconductor layers having at least a light absorption function and extending in the laser resonator length direction, laminated on a partial region of the semiconductor layer; and at least the fourth semiconductor layer of the third semiconductor layer. A semiconductor laser element made of a compound semiconductor having a fifth semiconductor layer of the same conductivity type as the second semiconductor layer containing Al and laminated in a portion not covered with the fourth semiconductor layer between the semiconductor layers. A semiconductor laser device, wherein the Al composition ratio of the third semiconductor layer is larger than the Al composition ratio of the first semiconductor layer and smaller than the Al composition ratio of the second semiconductor layer. 2 The first semiconductor layer is Al _x1 Ga _1-x1 As (0≦X ₁
≦0.2), the second semiconductor layer is Al _x2 Ga _1-x2 As (0.3
≦X ₂ ≦0.7), the third semiconductor layer is Al _x3 Ga _1-x
3 As (0.05≦X ₃ ≦0.25), the fourth semiconductor layer is
GaAs, the fifth semiconductor layer is Al _x5 Ga _1-x5 As (0.05
≦X ₅ ≦0.7).