JPH0584075B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing a semiconductor laser device.

Structure of conventional example and its problems Chemical etching of GaAs-GaAlAs-based compound semiconductors has been studied for some time, and there are many reports on its etching characteristics. Etchant, etch rate, GaAs or GaAlAs
The details of the selected etching solution, etching profile, etc. are known. Using such chemical etching technology, surface treatment of GaAs and
Selective etching of GaAs/GaAlAs wafers has been performed. Furthermore, such techniques have also been used to fabricate cavity surfaces for semiconductor lasers and the like.

Semiconductor lasers generally use the cleavage method to form the cavity surface, but when attempting to monolithically integrate semiconductor lasers and elements such as detectors and drive circuits, such as in optical ICs, the cleavage method is not used at all. It is not possible. For this purpose, wet etching methods using chemical etching methods and dry etching methods using reactive 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.

Figures 1a and 1b show the relationship between the inclination θ of the cavity surface and the normalized reflectance. As you can see, if the cavity surface is tilted by about 5 degrees, the reflectance will be 50.
% also decreases, leading to an increase in the threshold value and a decrease in 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 drawbacks, the present invention provides a method for manufacturing a semiconductor laser device having a vertical and flat cavity surface by an etching method.

Structure of the Invention In order to achieve this object, the method for manufacturing a semiconductor laser device of the present invention includes forming GaAlAs on the cap layer.
After forming the GaAlAs layer, a mask having an opening end in the <011> direction is formed on the GaAlAs layer, and etching is performed through the opening to form a cavity surface.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. Figure 2 is on a (100) GaAs substrate.
The graph shows experimental results regarding the tilt angle of the etching profile when a Ga _1-x Al _x As layer was grown and etched through a striped mask along the <011> direction. The tilt angles θ ₁ and θ ₂ are
It changes greatly depending on the AlAs mixed crystal ratio. When the value of x is around 0.2 and 0.4, the inclination angle θ ₁ is about 90°. On the other hand, the angle θ ₂ generated at the interface with the GaAs substrate becomes approximately 0 at x<0.1 and x˜0.4. When x is in the vicinity of 0.4, θ ₁ to 90° becomes θ ₂ to 0°, and the etched end surface becomes a vertical and flat surface. If this result is applied to a semiconductor laser, a cavity surface almost equivalent to a cleavage surface can be obtained. As an example, a manufacturing method will be explained based on the results shown in FIG. 2, with the AlAs mixed crystal ratio of the cladding being set to 0.4.

As shown in FIG. 3a, an n-type GaAs (100) substrate 1 is coated with an n-type Ga _0.6 Al _0.4 As cladding layer 2, a GaAs active layer 3, a p-type Ga _0.6 Al _0.4 As cladding layer 4, and a p-type GaAs (100) substrate 1.
A type GaAs cap layer 5 is continuously grown.

Semiconductor lasers generally have a four-layer structure like this, and conventional chemical etching methods cannot remove the top layer p.
A striped photomask 6 was formed on the type GaAs cap layer 5 along the <011> direction, and the GaAs substrate 1 was etched through the mask. This method results in an inverted mesa-like etching profile as shown in FIG. 3b, and a vertical cavity surface cannot be obtained. This can also be explained from the results shown in FIG.

FIG. 4 explains the etching profile from the angles of inclination θ ₁ and θ ₂ . That is, p-type
On the GaAs cap layer 5, there is an inverted mesa shape with θ ₁ = 65° with respect to the surface, and the p-type GaAs cap layer 5 and p-type
Since the angle θ ₂ with the Ga _0.6 Al _0.4 As cladding layer 4 is 0°, an inverted mesa shape with an angle of 65° is formed as shown in FIG. 4, and a vertical cavity surface is never obtained. Therefore, in the present invention, a layer having a liquid crystal ratio y of 0.4≦y≦0.5 is provided on the p-type GaAs cap layer 5.
A 5Ga _1-y Al _y As layer 7 is provided (FIG. 5a), a striped photomask 6 is formed on it along the <011> direction, and a GaAs substrate 1 is formed through the mask.
Etching is performed up to (Fig. 5b).

As an example of the present invention, an epitaxial wafer was prepared with AlAs mixed crystal ratio y=0.5 in the fifth layer 7 and x=0.4 in both cladding layers 2 and 4, and 1H ₂ SO ₄ :8H ₂ was formed through a striped photomask 6. _O2 : _1H2O (20℃)
Etching was performed up to substrate 1 under the following conditions.

FIG. 6 illustrates the etching profile of the present invention based on the results shown in FIG. No.
The 5Ga _0.5 Al _0.5 As layer has an inclination θ ₁ =65° and has an inverted mesa shape, but at the interface of the p-type GaAs cap layer 5, the angle becomes θ ₂ =25°. Since θ ₁ = 65° and θ ₂ = 25°, it is already vertical at the end face of the p-type GaAs cap layer 5, and since both clad layers are set at 0.4, its verticality extends to the substrate as well as the p-type cap layer. is maintained.

After creating the cavity surface by etching, the
5GaAlAs layer 7 is selectively removed and the exposed p-type
After forming a positive electrode 8 on the GaAs cap layer 5 and a negative electrode 9 on the substrate side, a semiconductor laser device as shown in FIG. 7 is obtained by breaking at the etched groove.

FIG. 8 shows the optical output-current characteristics of the semiconductor laser device shown in FIG. 7. Achieved with very high yield through continuous oscillation, with a typical oscillation threshold of 72 mA (70 mA for the cleavage method) and a differential quantum efficiency of 29% per side.
(30% for the cleavage method), properties with almost no difference from the cleavage method were obtained.

Effects of the Invention A feature of the present invention is that a cavity surface that is perpendicular to the bonding surface and has a mirror surface can be produced by chemical etching. The advantages of obtaining a cavity plane equivalent to a cleavage plane by chemical etching are that it is easy to integrate with other elements on the same substrate, that short cavity lasers can be fabricated, and that a protective film can be formed on the laser end face. It has great practical effects, such as being able to perform batch processing and testing the characteristics of the wafer as it is.

[Brief explanation of the drawing]

Figures 1a and b are diagrams showing the relationship between the inclination of the cavity plane and the reflectance, and Figure 2 is _a graph showing the relationship between the inclination of the cavity surface and _the reflectance. Figure 3 shows the inclination angle of the etched end surface when etching is performed through a striped mask.
Figures a and b are diagrams showing a conventional method for manufacturing a cavity surface by etching from a GaAs cap layer, Figure 4 is a schematic diagram for explaining the inclination of the end face, and Figure 5 is a schematic diagram for explaining the inclination of the end face.
Figures a and b are diagrams showing a method for manufacturing a cavity surface by etching a semiconductor laser according to the present invention;
The figure is a schematic diagram for explaining the inclination of the end face of the semiconductor laser, FIG. 7 is a perspective view of a semiconductor laser manufactured by the manufacturing method of the present invention, and FIG. 8 is an optical output-current of the semiconductor laser. FIG. 3 is a diagram showing characteristics. 1...n-type GaAs (100) substrate, 2...n-type Ga _0.6
Al _0.4 As clad layer, 3...GaAs active layer, 4...
p-type Ga _0.6 Al _0.4 As cladding layer, 5... p-type GaAs
Cap layer, 6...Photomask, 7th...
5Ga _0.5 Al _0.5 As layer, 8... Positive electrode, 9... Negative electrode.

Claims (1)

[Claims] 1 Form an active layer and a Ga _0.6 Al _0.4 As clad layer sandwiching the active layer on a (100) GaAs substrate, further form a cap layer on the clad layer, and then form a mixed crystal layer on the cap layer. Ratio y is 0.4
A Ga _1-y Al _y As layer with ≦y≦0.5 is formed, and the
A mask with an opening end in the <011> direction is formed on the Ga _1-y Al _y As layer, and the etching solution is etched through the opening using an etching solution consisting of sulfuric acid, hydrogen peroxide, and water.
A method of manufacturing a semiconductor laser device characterized by etching down to the GaAs substrate to form a vertical and flat cavity surface.