JPH0575213A - Manufacture of semiconductor laser element - Google Patents

Abstract

PURPOSE:To get a current checking layer excellent in crystal property by performing the surface treatment using ammonium sulfide solution thereby removing the surface oxide when performing selective epitaxial growth. CONSTITUTION:With the SiO2 film 8 made on a base of multilayer structure as a mask, selective etching is performed, and a stripe shaped mesa part 9, which includes a p-GaAs ohmic contact layer 6, is made leaving only the p- AlGaAs second clad layer 5 by h in thickness. At this point of time, the surface treatment by ammonium sulfide solution is applied to remove the oxide produced, whereby the stable surface condition of the mesa part 9 is gotten. Then, n-GaAs is buried in the mesa part 9 so as to form current checking layers 7 on both sides of the mesa part 9. In the current checking layer 7 being made this way, marked improvement of the crystal property can be seen. Lastly, a p-type electrode 10 and an n-type electrode 11 are made by removing the SiO2 film, whereby a semiconductor element is gotten.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor laser device.

[0002]

2. Description of the Related Art Generally, a semiconductor laser device is used as a light source for a compact disc, a video disc, etc., and therefore the structure of the device is designed to reduce light loss and unnecessary recombination as much as possible. It is necessary to confine energy and injected current, and further to confine light to a minute spot of the order of 1 μm, and confine light in a direction parallel to the active layer of the device, that is, have a structure capable of controlling transverse mode oscillation. In fact, it is known that a ridge-embedded semiconductor laser device satisfying these structural conditions is effective.

FIG. 2 is a schematic sectional view showing the structure of this ridge-embedded semiconductor laser device. As shown in FIG. 2, this device comprises an n-GaAs substrate 1, an n-GaAs buffer layer 2, an n-AlGaAs first cladding layer 3, and an Al layer.
A GaAs active layer 4 and a p-AlGaAs second cladding layer 5 are formed in this order, and both side surfaces of the stripe-shaped mesa portion formed on the second cladding layer 5 and the ohmic contact layer 6 are parallel to the laser light traveling direction. Are embedded with the current blocking layer 7. The current blocking layer 7 has a role of a light absorbing layer, and by appropriately selecting the width of the mesa portion on the second cladding layer 5 when viewed from the front, stable transverse mode oscillation of the device is possible, Further, since the current blocking layer 7 is close to the light emitting region of the active layer 4, the current concentrates in a part of the active layer 4 and the oscillation threshold current can be reduced.

Such a ridge-embedded semiconductor laser device is usually manufactured as follows. Figure 1 (a)
(D) shows the order of the main steps, and the same parts as those in FIG. 2 are represented by the same reference numerals. First, n-GaAs
Low pressure MOCVD method (metal organic chemical vapor deposition method) on the substrate 1
N-GaAs buffer layer 2, n-AlGaA
s first cladding layer 3, AlGaAs active layer 4, p-Al
After the GaAs second cladding layer 5 and the p-GaAs ohmic contact layer 6 are sequentially grown, a mask of the SiO ₂ film 8 is formed on the upper surface of this stack [FIG. 1 (a)].

Next, using the SiO ₂ film 8 as a mask, p-
GaAs ohmic contact layer 6 and p-AlGa
Selective etching is performed up to the middle of the As second clad layer 5 using an SH etching solution consisting of sulfuric acid, hydrogen peroxide solution and water, leaving the p-AlGaAs second clad layer 5 by a thickness h and leaving the p-GaAs. A stripe-shaped mesa portion 9 including the ohmic contact layer 6 is formed [FIG. 1 (b)].

Next, the SiO ₂ film 8 is used as a mask for selective growth and selective epitaxial growth is performed using a low pressure MOCVD method to remove the portion where the SiO ₂ film 7 is adhered.
GaAs is embedded in the mesa portion 9 and the current blocking layer 7 is formed on both sides of the mesa portion 9 [FIG. 1 (c)].

After the SiO ₂ film 8 is removed, a p-type electrode 10 and an n-type electrode 11 are formed to obtain a semiconductor laser device having the structure shown in FIG. 2 [FIG. 1 (d)]. ..

[0008]

However, when the semiconductor laser device is manufactured by the above method, there are the following problems. This is because the semiconductor laser device having this structure has p-AlGa by selective epitaxial growth using the low pressure MOCVD method when forming the current blocking layer 7 as described above.
GaAs must be crystal-grown on the As second cladding layer 5. At this time, since AlGaAs is a material that is very easily oxidized, a considerable oxide film is formed on the surface after the selective etching. Is observed. Therefore, if the selective epitaxial growth is directly performed on the surface after the selective etching, a large number of defects due to the oxide are generated in the current blocking layer 7, and it becomes impossible to form the good current blocking layer 7. The formation of the current blocking layer 7 having good crystallinity is intended to suppress the reactive current and to efficiently pass the current only to the stripe-shaped mesa portion 9 and to efficiently release the heat from the surface of the assembled element. Is also very important.

The present invention has been made in view of the above-mentioned points, and an object thereof is to perform surface treatment using an ammonium sulfide solution to remove surface oxides during selective epitaxial growth to obtain crystals. It is an object of the present invention to provide a method for manufacturing a semiconductor laser device that can obtain a current blocking layer having good properties.

[0010]

In order to solve the above-mentioned problems, the present invention provides a method of manufacturing a semiconductor laser device, in which a stripe-shaped mesa portion is formed by selective etching, and then surface treatment is performed using an ammonium sulfide solution. Then, a step of burying the current blocking layer by selective epitaxial growth is added.

[0011]

According to the present invention, by using the above method, a stable surface can be obtained by removing the oxide film formed on the surface of the convex stripe mesa portion. Therefore, the current blocking layer subsequently embedded in the mesa portion is obtained. Eliminates the crystal defects caused by the oxide film, and can form a high-quality current blocking layer having good crystallinity uniformly and with good reproducibility.

[0012]

EXAMPLES The present invention will be described below based on examples. Since the structure of the semiconductor laser device obtained by the method of the present invention is the same as that shown in FIG. 2, illustration thereof is omitted, and the manufacturing process related to the method of the present invention is basically the same as that of FIG. Here too, description will be given with reference to FIGS.
The point that the method of the present invention is different from the conventional method is in the process of moving to the process of FIG. 1C after the process of FIG. That is, since the surface of the mesa portion 9 is in an oxidized state at the time when the stripe-shaped mesa portion 9 is formed, the present invention performs the surface treatment with the ammonium sulfide solution, and the oxide film formed there. Is taken in and a process for obtaining a stable surface state of the mesa portion 9 is incorporated.

The ammonium sulfide solution has a property of dissolving oxides of GaAs and AlGaAs, and the S (sulfur) atom contained in the ammonium sulfide solution forms a stable bond of a monoatomic layer on the surface of GaAs or AlGaAs. It has the effect of reducing the defect level on the surface. The S concentration in the ammonium sulfide solution used in the present invention is preferably 0.5 to 2%. It etches the oxide film, but does not etch GaAs or AlGaAs itself. The S concentration needs to be 0.5% or more. When the S concentration increases to 2% or more, GaAs or AlG
This is because aAs itself will also be etched.
After being immersed in an ammonium sulfide solution for 5 minutes in this S concentration range, it is washed with ultrapure water for 10 minutes.

After that, the process starting from FIG. 1C is started as described above. The current blocking layer 7 thus formed was remarkably improved in crystallinity by performing the above-mentioned ammonium sulfide treatment, as compared with the conventional case where this treatment is not performed. The method of the present invention is
The same effect can be obtained also in the semiconductor laser device having a structure having a conductivity type opposite to that of each laminated film described above.

[0015]

According to the present invention, when manufacturing a semiconductor laser device, as described in the embodiments, an oxide film formed on the surface of a convex stripe mesa formed by selective etching is treated with an ammonium sulfide solution. The current blocking layer embedded in the mesa portion by selective growth after that has been incorporated by the use, because the current blocking layer having good crystallinity is formed with good reproducibility without being adversely affected by the oxide film. The obtained semiconductor laser device exhibits uniform and excellent characteristics.

[Brief description of drawings]

1A to 1D are manufacturing process diagrams of a semiconductor laser device.

FIG. 2 is a schematic sectional view of a semiconductor laser device.

[Explanation of symbols]

1 substrate 2 buffer layer 3 first clad layer 4 active layer 5 second clad layer 6 ohmic contact layer 7 current blocking layer 8 SiO ₂ film 9 mesa portion 10 p-type electrode 11 n-type electrode

Claims (2)

[Claims] 1. A one conductivity type AlGaAs first cladding layer, an active layer, and a reverse conductivity type A on one main surface of a one conductivity type semiconductor substrate.
A method of manufacturing a semiconductor laser device, comprising: a 1 GaAs second clad layer and an ohmic contact layer, and embedding a current blocking layer of one conductivity type in a convex striped mesa portion formed by the second clad layer and the contact layer. And forming the mesa portion by selective etching, performing a surface treatment using an ammonium sulfide solution, and subsequently burying the current blocking layer by selective epitaxial growth. 2. The method for manufacturing a semiconductor laser device according to claim 1, wherein the S concentration of the ammonium sulfide solution is 0.5 to 2%.