JPH0212036B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a semiconductor laser device having a buried heterostructure.

The conventional - group compound semiconductor light emitting device is
The active region (region that directly contributes to light emission, etc.) such as GaAs is surrounded on the top, bottom, left and right by other compound semiconductors of different compositions, such as GaAlAs. Since the refractive index of GaAs is larger than that of GaAlAs, light can be confined in GaAs and can be used as a light waveguide. Generally, such a structure is called a buried heterostructure.

In actual production, the
GaAlAs and GaAs are grown by a liquid phase epitaxial method, and the epitaxially grown layer is mesa-etched to reach the substrate.
A buried heterostructure is obtained by growing a GaAlAs layer.

However, recently, compound semiconductor light-emitting devices based on GaAs are not necessarily a good idea in terms of material processability and strength, and there has been a shift toward using InP-based compound semiconductors as the basis, which are superior to these.

However, InP-based compound semiconductors generally still have difficulties in etching during processing. For example, when forming a surface layer made of InGaAsP in an inverted mesa structure into a predetermined shape, the etching plane orientation dependence of InGaAsP is significantly different from that of InP. There was a drawback that it was difficult to keep the width of the layer within a specified value.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a semiconductor laser device, which eliminates the above-mentioned drawbacks and makes it possible to obtain a semiconductor laser device that is easy to process and has good characteristics.

The purpose of the present invention to achieve the above object is to
It is characterized in that it is formed to have a composition of In _1-x Ga _x As _y P _1-y , 0≦y≦0.57, 0≦x<1, and mesa etching is performed with an alcohol solution of halogen.

According to the above structure, the surface layer formed on the optical confinement layer (also known as cladding layer) InP has a composition different from that of InP.
- It has been experimentally confirmed that etching occurs at the same etching speed when processed with a methanol-based etching solution.

Br-methanol is suitable as the halogen alcohol solution. Br is less than 10% in terms of capacity,
In particular, 0.1% to 5% is practically preferred.
I ₂ -methanol and the like can also be used. The solution temperature used during etching is 10°C to 30°C. According to the present invention, it is possible to perform reverse mesa etching to accurately form a desired pattern without excessively etching a specific surface or side etching, and it is possible to realize a semiconductor laser device with good electrical characteristics. Ta. This will be explained in detail below using specific examples.

InGaAsP-InP semiconductor lasers operate in the wavelength range of 0.9 μm to 1.6 μm and cover the low transmission loss band of optical fibers, so they are attracting attention as light sources for optical communications.

As a light source for optical communication, semiconductor lasers with various structures have been devised for the purpose of stably controlling the oscillation mode, and a buried heterostructure laser capable of oscillation in a transverse fundamental mode is a promising element.

As shown in Figure 1-a, the above-mentioned InGaAsP-InP laser has an active layer 3 grown on an InP substrate 1 (In _1-x Ga _x As _y P _1-y , 0<x<1, 0 <y<1)
It is composed of an optical confinement layer 2 (InP) and a surface layer 4 (InGaAsP) for improving electrical contact with the electrode. By the way, a buried heterostructure laser has a structure shown in FIG. 1-c. To manufacture this structure, an inverted mesa structure is formed by etching from the multi-layered growth layer shown in Figure 1-a.
Figure b) is further created by performing buried growth. The inverted mesa structure is an essential structure to achieve the active layer width of 2 μm or less required for fundamental transverse mode oscillation. The inverted mesa structure can be produced by forming oxide stripes of a predetermined shape on the surface after multilayer growth, and chemically etching the oxide using an etching solution whose etching rate is plane orientation dependent. By limiting the composition of the InGaAsP system to the following composition range, the etching rate and surface orientation dependence by chemical etching are almost the same as those of InP, and a good inverted mesa structure as shown in Figure 1-b can be obtained. It can be formed with good reproducibility.

1 In _1-x Ga _x As _y P _1-y When forming an inverted mesa by chemical etching, this composition range is 0<
Use y0.57.

2 In a system with In _1-x Ga _x As _y P _1-y as the surface layer,
When forming an inverted mesa through the surface layer by chemical etching, the composition range of the surface layer is 0<y
Use 0.57.

3 In the above, In _1-x is particularly lattice matched to InP
Ga _x As _y P _1-y has a composition of x=0.1894y/(0.4184
-0.0130y), but the composition range in the above composition is 0<y0.57 and the one satisfying the above formula is used.

Example When fabricating an InP-InGaAsP buried heterostructure laser, chemical etching was performed using a 1% Br-methanol solution to form an inverted mesa by leaving the (111) B plane. On the InP substrate 1,
The thickness of the first cladding layer InP2 is 2 to 5 μm, and the thickness of the active layer In1 _-x
Ga _x As _y P _1-y 3 (x = 0.26, y = 0.57) is 0.3 μm,
The second cladding layer InP2' is 2.5μm thick, and the surface layer 4
As In _1-x Ga _x As _y P _1-y (x=0.16, y=0.36)
0.5 μm, formed by normal liquid phase epitaxial growth method. As shown in FIG. 1a. This surface layer 4
SiO ₂ film 5 is placed on top of the
Form to 5.0 μm. The SiO ₂ film may be formed by a normal method. By selecting the width of the oxide film (SiO ₂ , PSG) stripe 5 to be 5.0 μm, the width of the active layer 3 can be made 2.0 μm with good reproducibility. The state after etching is as shown in FIG. 1b. The etching conditions are 20°C for 5 minutes under the above conditions. Next, after forming the above-mentioned inverted mesa, a cladding layer InP2' in the buried region is formed by a conventional liquid phase epitaxial method. Next, In _0.74 Ga _0.26 As _0.75 P _0.43 is formed on the cladding layer 2' by a conventional liquid phase epitaxial method. As shown in FIG. 1c. Next, a 1 μm SiO ₂ film is formed on the surface layers 4 and 4' by a conventional method to form striped windows, and then metal electrodes such as Cr-Au are formed corresponding to the windows to form a semiconductor laser. do.

It was also possible to perform the same process when the composition of the surface layer 4 was x=0.26 and y=0.57 or x=0.045 and y=0.10.

In addition, although InP was used as the InGaAsP cladding layer for the active layer in the example, the active layer and the cladding layer are not limited to this. The above-mentioned etching technique can also be used to manufacture a semiconductor laser in which both layers are made of InGaAsP material, or a semiconductor laser in which the cladding layer is made of InGaAsP material and the active layer is made of InGaAs material.

In the above embodiments, only the buried heterostructure laser has been described, but it goes without saying that the present invention is not limited to this and can be applied to the formation of inverted mesas and other mesas. Further, those skilled in the art will easily infer that the present invention is applicable not only to lasers but also to a wide range of compound semiconductors such as light emitting devices that require etching.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining an embodiment of a method for manufacturing a semiconductor laser device according to the present invention, and FIG. 2 is a cross-sectional view of a semiconductor laser device manufactured by a conventional method. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Optical confinement layer, 3... Active layer, 4... Surface layer, 5... Oxide film stripe.

Claims (1)

[Scope of Claims] 1. A method for manufacturing a semiconductor laser device, comprising the following steps. (1) On a compound semiconductor substrate, a first semiconductor layer having the same conductivity type as the compound semiconductor substrate, an active region layer, and a first semiconductor layer having a conductivity type different from that of the compound semiconductor substrate.
A first step of growing a semiconductor stacked structure including a second semiconductor layer made of InP in the above order. (2) On the semiconductor stacked structure, a conductivity type different from that of the compound semiconductor substrate and In _1-x Ga _x AsyP _1-y (However,
0<y0.57, 0<x1.0) A second step of growing a semiconductor surface layer. (3) A part of the semiconductor stacked structure and the semiconductor surface layer is chemically etched using an alcohol solution containing 10% or less of Br by volume to form a striped inverse structure including the second semiconductor layer and the semiconductor surface layer. A third step of forming a mesa-type semiconductor stacked region and determining the width of the upper front active region layer included in the semiconductor stacked region. (4) A fourth step of growing a third semiconductor layer surrounding the side surfaces of the striped semiconductor layer region. 2. In the method for manufacturing a semiconductor laser device according to claim 1, in the chemical etching, the temperature of the halogen alcohol solution is 10°C to 30°C.
A method for manufacturing a semiconductor laser device within the scope of. 3. The method of manufacturing a semiconductor laser device according to claim 2, wherein the alcohol solution is Br-methanol. 4. The method for manufacturing a semiconductor laser device according to claim 3, wherein the Br-methanol contains 0.1% to 5% Br by volume.