JPS6142186A - Manufacture of semiconductor laser device - Google Patents

Abstract

PURPOSE:To enable cavity surfaces vertical to junction surfaces to be manufactured by chemical etching by a method wherein a GaAlAs clad layer of constant AlAs mixed crystal ratio is formed on a GaAs substrate and provided with a GaAs cap layer. CONSTITUTION:An N type Ga0.5Al0.5As clad layer 5, a GaAs active layer 6, a P type Ga0.5Al0.5As clad layer 7, and a P type GaAs cap layer 8 are successively grown on the N type GaAs (100) substrate 1. Next, a stripe photo mask 2 is formed on the layer 8 along the <011> direction, and cavity surfaces equivalent to cleavage surfaces are obtained in the clad layers 5 and 7 by chemical etching to the substrate 1 through the mask 2. Thereafter, a positive electrode 9 is formed on the layer 8, and a negative electrode 10 on the substrate side.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method of manufacturing a semiconductor laser device.

Conventional Structures and Problems Chemical etching of GaAs and GaAlAs-based compound semiconductors has been studied for some time, and there have been many reports on their etching characteristics. Details of the etchant, etching rate, selective etching solution for GaAs or GaAlAs, etching profile, etc. are known. Such chemical etching techniques have been used for surface treatment of GaAs and selective etching of wafers made of GaAs/GaAβAs. moreover,
Such technology has also been used to fabricate cavity surfaces for semiconductor lasers and the like.

Semiconductor lasers generally have a cavity surface formed by the cleavage method, but when attempting to integrate a semiconductor laser and elements such as a detector and drive circuit into a monolink, such as in an optical IC, the cleavage method cannot be used at all. Can not. For this purpose, wet etching methods such as chemical etching methods and dry etching methods such as active ion etching (RIE) are being studied. Chemical etching is superior in terms of mass production and reliability, and because of its ease, various methods have been tried to fabricate the cavity surface. Problems in producing a cavity surface by chemical etching are the perpendicularity of the cavity surface and the flatness of the surface.

FIG. 1 shows the relationship between the inclination θ of the cavity surface and the normalized reflectance. As can be seen from this, the reflectance decreases by 50 degrees when the cavity surface is tilted by only about 5 degrees, which leads to an increase in the threshold value and a decrease in the external differential quantum efficiency. Furthermore, the reflectance is significantly reduced due to the roughness of the cavity surface.

Due to these problems, lasers fabricated by the conventional chemical etching method have a higher threshold current density than the cleavage method, making continuous oscillation extremely difficult.

OBJECTS OF THE INVENTION In view of the above-mentioned drawbacks, the present invention provides a method for manufacturing a semiconductor laser device in which a vertical and flat cavity surface can be formed by chemical etching.

Structure of the Invention In order to achieve this object, the method for manufacturing a semiconductor laser device of the present invention provides a method for manufacturing a semiconductor laser device according to the present invention. The method includes a step of forming a layer and a step of forming a cavity surface by chemical etching.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. Figure 2 shows a cross-sectional view when etching is carried out through a striped mask 2 along the (1oo) direction on the substrate 15. It becomes a cross section, and its angle θ1 is 66°. Figure 3 shows (1oo) Ga 1xAI J on substrate 1.
G layer 3 and GaAs layer 4 are grown, and similarly <ol
This is a cross section when etching is performed through a striped mask 2 along the <l> direction.

The uppermost GaAs layer 4 has an inverted mesa-shaped cross section with an angle of 65°, as in the case of the GaAs substrate shown in FIG. It has a bend of θ2. This angle θ2 varies greatly depending on the AlAs mixed crystal ratio X, as shown in FIG.

As is clear from this result, θ2 is X=Q, 25. It can be seen that the angle becomes 90° near 0.5. Applying this result to semiconductor lasers, chemical etching
A cavity surface equivalent to a cleavage surface is obtained.

Example 1 As shown in FIG. 6a, n-type GaAs (10
0) An n-type Ga, 6A (lo, 5As cladding layer 5) and a GaAs active layer active layer type Ga, 5A (1
, 5As cladding layer 7 and P-type GaAs cap layer 8 are successively grown. Next, a striped photomask 2 was formed on the KP type GaAs cap layer 8 along the <011> direction, and etching was performed through the mask to the GaAs substrate 1 (FIG. 6b). The etched cross section becomes perpendicular to the cladding layers 5 and 7, and a cavity surface equivalent to a cleavage surface is obtained. In the present invention, in order to ignore the non-uniformity of the interface between the active layer 6 and both cladding layers 6 and 7, the thickness of the active layer 6 is made extremely thin, thereby ignoring the influence of the non-uniformity. After forming a vertical cavity surface by chemical etching, a positive electrode 9 was formed on the P-type GaA+s cap layer 8, and a negative electrode 1o was further formed on the substrate side, and the etching was broken at the etched groove, as shown in FIG. A semiconductor laser device as shown in FIG. 1 was obtained.

Effects of the Invention A feature of the present invention is that the cavity surface perpendicular to the bonding surface can be created by chemical etching. The advantages of obtaining a cavity surface equivalent to a cleavage surface using the chemical etching method are that it is easy to integrate other elements on the same substrate, that short cavity lasers can be fabricated, and that the formation of a protective film on the laser end face is done in a batch process. It has great practical effects, such as being able to perform tests on the characteristics of a wafer.

The semiconductor laser fabricated according to the present invention is a continuous oscillation laser and is obtained at a very high yield, and the increase in the oscillation threshold is extremely small, 0.5% or less, compared to the same device fabricated by the cleavage method. It can be seen that the reflectance of the cavity surface due to chemical etching determined from the difference in external differential quantum efficiency is extremely high at approximately 29 inches (cleavage 32%), indicating that the cavity surface is excellent.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the relationship between the inclination of the cavity surface and the reflectance, and Fig. 2 is a cross-sectional view when etching is performed on a (100) GaAs substrate through a striped mask along the <oll> direction. Figure 3 shows the growth of a GaAlAs layer and a GaAs layer on a (100) GaAs substrate.
Figures 6a and 6b are diagrams showing the wafer structure manufactured based on the present invention. Figure 6 is a semiconductor laser device of the present invention. FIG. 1...GaAs i plate, 2...mask, 3...GaA/As layer, 4-...GaA+
s layer, 5-...n-type Gao, sA#, 6As cladding layer, 6...GaAs active layer, 7...
...P-type Ga, 5Al, 5As cladding layer, 8...
...P-type GaAs cap layer, 9...Positive electrode,
10... Negative electrode 0 Name of agent Patent attorney Toshio Nakao and 1 other person 1st
Figure 0 5 10 15 2
θ Kiibiki surface 9i angle 0 (crossing Fig. 2 Fig. 4 0 7), 2 0.4 0.6
(L, S /, 0 AIAs Mixed crystal ratio X Figure 5 (b)

Claims (1)

[Claims] On the GaAs substrate, the AlAs mixed crystal ratio X is 0.2 to 0.3.
or 0.45-0.55 Ga_1_-_xAl_x
The method includes a step of forming a cladding layer made of As, a step of forming a cap layer made of GaAs, a step of forming a mask on the cap layer, and a step of forming a cavity surface by chemical etching through the mask. A method of manufacturing a semiconductor laser device, characterized in that: