JPH0556675B2 - - Google Patents

Description

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

Structures of conventional examples and their problems Chemical etching of GaAs and GaAlAs-based compound semiconductors has been studied for some time, and there are many reports on their 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.

The cavity surface of semiconductor lasers is generally formed by the cleavage method, but when attempting to integrate a semiconductor laser and elements such as a detector drive circuit into a monolink, such as in an optical IC, the cleavage method should not be used at all. I can't. for that,
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. FIG. 1 shows the relationship between the inclination θ of the cavity surface and the normalized reflectance. As we will see, a tilt of the cavity surface of just 5 degrees reduces the reflectance by as much as 50%, 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-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 a chemical 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 Ga _1-x Al _x As on the active layer.
The mixed crystal ratio x of the cladding layer and the
The difference z-x from the mixed crystal ratio z of the Ga _1-z Al _z As layer formed via the GaAs layer is set between 0 and 0.2, and the above-mentioned
It consists of chemical etching through a mask with edges parallel to the <011> direction above the Ga _1-z Al _z As layer.

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 x. x
When the value of is around 0.2 and 0.4, the tilt angle θ ₁ is about 90°
becomes. On the other hand, the angle θ ₂ generated at the interface with the GaAs substrate
is almost 0 at x<0.1 and x~0.4. Focusing on x in the vicinity of 0.4, θ ₁ to 90° and 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 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 are _formed as shown in FIG.
A GaAs type contact 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 along the <011> direction on the type GaAs contact layer 5, and etching was performed to the GaAs substrate 1 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, the p-type GaAs contact layer 5 has an inverted mesa shape with θ ₁ =65° with respect to the surface, and the angle between the p-type GaAs contact layer 5 and the p-type Ga _0.6 Al _0.4 As cladding layer 4 is θ ₂ = Since it is 0°, it becomes an inverted mesa shape with an angle of 65° as shown in Figure 4, and a vertical cavity surface is never obtained. Therefore, in the present invention, p
A fifth layer Ga _1-z Al _z As layer 7 is provided on the type GaAs contact layer 5 (FIG. 5a). A striped photomask 6 is formed on it along the <011> direction, and GaAs is Etching was carried out up to substrate 1 (FIG. 5b). The conditions for vertically etching the p-type cladding layer 4 and below are the 5th layer Ga _1-z Al _z As
The difference z−x in the AlAs mixed crystal ratio between the layer 7 and the Ga _1-x Al _x As cladding layer 4 exists within a certain range.
Figure 6 shows the difference in AlAs mixed crystal ratio z−x and the cladding layer 4.
shows the relationship between the slope of the etched side surface _θ3 . As is clear from this figure, θ ₃ is 90° in the range of z−x from 0 to 0.2. This has an important meaning in obtaining vertical cavity surfaces by chemical etching. That is,
No matter what the AlAs composition ratio x of the Ga _1-x Al _x As cladding layers 2 and 4 is, a vertical etched side surface can be obtained with the value of z of the fifth layer Ga _1-z Al _z As. That's what it means. The fact that the AlAs mixed crystal ratio of the cladding layer can be changed arbitrarily means that the composition of the active layer, that is, the oscillation wavelength, can be freely designed.
Therefore, according to the present invention, a vertical cavity surface can be obtained by chemical etching regardless of whether the oscillation is in the infrared or visible region.

As an embodiment of the present invention, x of the cladding layers 2 and 4 is set to 0.4, and the AlAs mixed crystal ratio z of the fifth layer 7 is set to x+0.1.
In other words, epitaxial wafers were prepared with a value of 0.5. Fifth
A vertical cavity surface was prepared by etching with a sulfuric acid-based etching solution through a striped photomask 6 formed in the <011> direction on the layer 7 (FIG. 7). Thereafter, the fifth layer 7 is selectively etched and removed, a positive electrode 8 is formed on the exposed p-type GaAs contact layer 5, and a negative electrode 9 is formed on the substrate side, and then the etched grooves are etched. By the way, a semiconductor laser device having a vertical cavity surface as shown in FIG. 8 was obtained.

FIG. 9 shows the optical output-current characteristics of the semiconductor laser device shown in FIG. 8. 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 As described above, in the method for manufacturing a semiconductor laser device of the present invention, a cavity surface that is perpendicular to the bonding surface and has a mirror surface can be fabricated by chemical etching. The advantages of the etching method are that it is easy to integrate with other elements on the same substrate, that short cavity lasers can be fabricated, that the protective film on the laser end face can be formed by batch processing, and that the characteristics can be inspected on the wafer. There are many things you can do on your own, and the practical effects are great.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between the inclination of the cavity surface and the reflectance, and Figure 2 is a diagram showing the relationship between the inclination of the cavity surface and the reflectance.
A diagram showing the relationship between the AlAs mixed crystal ratio and the tilt angle of the cavity plane, Figure 3 is a manufacturing process diagram of a conventional semiconductor laser device, Figure 4 is a cross-sectional view of the main part of a conventional semiconductor laser device, and Figure 5 is a diagram of the main part of the conventional semiconductor laser device. FIG. 6 is a diagram showing the manufacturing process of the semiconductor laser device of the invention. FIG. 6 is a diagram showing the relationship between the difference in the AlAs mixed crystal ratio and the tilt angle of the cavity surface of the same device. FIG. 7 is a diagram showing the tilt of the cavity end face of the same device. , FIG. 8 is a perspective view of the same device, and FIG. 9 is a diagram showing the relationship between current and optical output in the same device. 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.

Claims (1)

[Claims] 1 Ga _1-x Al _x As (0<x<
1) Ga _1-y Al _y As (0<y
<1) A Ga _1-z Al _z As (0<z<1) layer in which the difference between the active layer, the GaAs contact layer, and the cladding layer has a mixed crystal ratio z ranging from 0 to 0.2. a step of forming a mask having an edge in the <011> direction on the Ga _1-z Al _z As layer; and a step of performing chemical etching through the mask. A method for manufacturing a semiconductor laser device.