JPH07176819A - Manufacture of semiconductor laser device - Google Patents

Abstract

PURPOSE:To provide a method of manufacturing a high-output semiconductor laser, which reduces reliably the surface level density of a laser crystal end face and inhibits a COD. CONSTITUTION:A method of manufacturing a semiconductor laser has a process, wherein a wafer, on which the formation of electrodes ends, is cleaved and after a sulfur monomolecular layer 5 is formed on a cleavage surface 4 using an ammonium sulfide resolution 2 during the time ending the formation of an insulating film 7, an ammonium polysulfide solution 3 is produced from the solution 2 utilizing a photochemical reaction and the surface 4 is completely passivated by forming further a sulfur polymolecular layer 6 on the above layer 5.

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 capable of obtaining high output.

[0002]

2. Description of the Related Art In recent years, in the field of optical disk memory, system speed and density have been increasing. Under such circumstances, the semiconductor laser device is required to have higher output for higher speed and shorter wavelength for higher density. In particular, the semiconductor laser device has been considerably advanced in output, and various structures have been proposed.

The largest cause of obstacles to higher output is optical damage (COD) on the end face of the laser device. Recently, a semiconductor laser device having a window-type structure capable of preventing COD by providing a non-implanted region near the end face of the laser device has been proposed, but it is still poor in mass productivity at this stage.

In a conventional high-power semiconductor laser device, COD occurs because the light density at the end face of the laser device increases as the light output increases. The cause of COD is that the surface level exists on the end face. The surface level of this end face exists in the band gap, and in particular, the surface level of GaAs, which is a typical material of the semiconductor laser device, exists almost in the center of the band gap. Become. Since heat is generated due to non-radiative recombination and the temperature of the active region rises, the band gap near the end face becomes smaller and the light absorption coefficient becomes higher. Therefore, many electron-hole pairs are generated. When these electron-holes recombine, heat is released again, and the temperature of the end face rises further.
COD is generated by repeating such a cycle. Therefore, in order to suppress COD, it is necessary to reduce the surface state density of the end face of the laser device. In order to reduce the surface state density, it is necessary to reduce impurities and lattice defects existing on the crystal surface.

In the conventional manufacturing process of a high-power semiconductor laser device, a wafer after the electrode process is cleaved, and the cleaved surface is coated with an insulating film without any treatment. In such a process, impurities such as oxides are formed on the laser crystal end face between the cleavage and the coating. Recently, a process of forming an insulating film after performing a surface treatment on the cleaved surface with an ammonium sulfide solution has been proposed. In this method, a bar cleaved from a wafer is immersed in an ammonium sulfide solution for 5 minutes, washed with water for several minutes and dried, and then an insulating film is formed.
By dipping in the ammonium sulfide solution, impurities on the laser crystal end face can be removed, and then a sulfur monomolecular layer can be formed to inactivate the laser crystal end face.

FIG. 4 shows the reaction mechanism of an ammonium sulfide solution with a simple model, using a GaAs crystal 12 as an example. Sulfur ions 8 in the ammonium sulfide solution are S ^2-
Exists in the state of. Ga and A on the surface of the GaAs crystal 12.
When the oxide 10 of s is present as an impurity, the sulfur ion 8 attacks a bond of Ga or As in the oxide 10 to remove the oxide from the GaAs crystal 12, and at the same time, G
A monolayer 5 of sulfur is formed on the surface of the aAs crystal. The removed oxide 10 is ammonium ion 11 in the solution.
Since they are coordinated by, they do not redeposit on the surface of the GaAs crystal 12. As a result, the GaAs crystal surface is protected by the sulfur monomolecular layer 5 and the surface unit due to impurities is reduced.

[0007]

However, in the above-mentioned conventional structure, the bond between the sulfur in the monolayer of sulfur formed by the surface treatment method using the ammonium sulfide solution and each atom on the end face of the laser crystal is covalent. Is believed to be strong, but this bond often breaks when exposed to ultraviolet light. The possibility that the cleaved surface will be attacked by ultraviolet rays during the period from the surface treatment with the ammonium sulfide solution to the step of forming the insulating film is generally high unless a method for preventing ultraviolet rays is taken. Therefore, the sulfur monolayer formed on the end face of the laser crystal may be destroyed, and oxidation may proceed again to form impurities.

The present invention solves the above problems, and an object of the present invention is to provide a method for manufacturing a high-power semiconductor laser device in which the surface state density of the laser crystal end face is reliably reduced and COD is suppressed. .

[0009]

In order to achieve the above object, the present invention provides a method of cleaving a wafer on which an electrode has been formed by cleaving a wafer with an ammonium sulfide solution and cleaving sulfur on the cleaved surface until an insulating film is formed. After forming the monolayer of, polyammonium sulfide solution is generated from the ammonium sulfide solution by utilizing the photochemical reaction, and on the above-mentioned sulfur monolayer,
Further, it is a method for manufacturing a semiconductor laser device, which includes a step of completely passivating the cleavage plane by forming a multi-layer of sulfur.

[0010]

With the above structure, the surface level density on the cleaved surface is reduced, the sulfur multi-molecular layer acts as an ultraviolet protective film, the cleaved surface is completely passivated, and COD
(Optical damage) is suppressed.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

FIG. 1A is a diagram showing a process of processing a laser end face. As a semiconductor laser device, a GaAlAs-based laser will be taken as an example. First, a bar 1 cleaved from a wafer is immersed in an ammonium sulfide (NH ₄ ) ₂ S solution 2 for 5 minutes, and then irradiated with light to change the ammonium sulfide solution 2 into a polyammonium sulfide (NH ₄ ) ₂ Sx solution 3
And then soak in the solution for an additional 1-2 minutes. After such treatment, it is washed with water for 5 minutes, dried and then coated. Through the above steps, a sulfur monolayer 5 is formed in the ammonium sulfide solution on the cleavage plane 4 as shown in FIG. 1B, and then a sulfur polylayer is formed in the polyammonium sulfide solution. 6 is formed. By coating in a high temperature atmosphere, the sulfur film is removed and the insulating film 7 is formed.

FIG. 2 is a diagram for explaining the reaction mechanism on the cleavage plane in the case of performing the end face treatment using the above ammonium sulfide solution by a simple model. Sulfur ions 8 in the ammonium sulfide solution exist in the state of S ²⁻ . GaA
When impurities such as oxide 10 are present on the surface of lAs crystal 9, sulfur ions 8 attack the bonds of Ga, Al, and As in the oxide to remove oxide 10 from the crystal surface,
At the same time, a monolayer 5 of sulfur is formed on the crystal surface. Since the oxide 10 is coordinated by the ammonium ion 11 in the solution, it does not adhere to the crystal surface again. Further, Sx ²⁻ having a cyclic structure is supplied by the polyammonium sulfide solution generated by the photochemical reaction. Sx
^{Since 2-} is an active ion, it easily bonds with the above-mentioned sulfur monolayer 5 to form a sulfur multi-layer 6 on the sulfur monolayer 5. Thus, the polylayer 6 of sulfur completely covers the crystal surface, thereby inactivating the crystal surface, reducing impurities and lattice defects, and reducing the surface state density. Further, since the sulfur multi-molecular layer 6 also functions as an ultraviolet ray preventive film, the cleavage plane can be completely passivated.

The bond between the atom on the cleavage plane and the sulfur monolayer 5 and the bond between the sulfur monolayer 5 and the polylayer 6 are broken when the temperature is raised to 300 ° C. or higher. If coating is performed under the above temperature atmosphere, the above-mentioned bond is broken and sulfur is sublimated to form the insulating film 7,
It does not affect the reflectance of the laser device after coating.

FIG. 3 shows current-light output characteristics of a semiconductor laser device manufactured by incorporating the above manufacturing method. It can be seen that COD is suppressed because the surface state density of the end surface of the laser device is reduced.

In this embodiment, the sulfur multi-layer film is formed by using the ammonium sulfide solution, but the same effect can be obtained by using the heterocyclic compound containing sulfur.

[0017]

As is apparent from the above embodiments, in the method of manufacturing a semiconductor laser device of the present invention, the insulating film is formed after the sulfur multi-molecular layer is laminated on the sulfur mono-molecular layer. It is possible to provide a high-power semiconductor laser device in which the surface state density of the end face of the laser device is reduced and COD is suppressed.

[Brief description of drawings]

FIG. 1A is a process step diagram showing a method for manufacturing a semiconductor laser device according to an embodiment of the present invention. FIG. 1B is a process step of forming an insulating film on a cleavage plane by the process step shown in FIG. Partial sectional view of a semiconductor laser device

2 is a cross-sectional view of a semiconductor laser device showing a reaction mechanism of a chemical reaction that occurs in the processing step of FIG.

3 is a diagram showing current-light output characteristics of a semiconductor laser device manufactured by the method for manufacturing the semiconductor laser device of FIG.

FIG. 4 is a diagram showing a reaction mechanism of a chemical reaction by a conventional method for manufacturing a semiconductor laser device.

[Explanation of symbols]

 1 Cleaved Bar 2 Ammonium Sulfide Solution 3 Poly Ammonium Sulfide Solution 4 Cleavage Surface 5 Sulfur Monolayer 6 Sulfur Multilayer 7 Insulating Film 8 Sulfur Ion 9 GaAlAs Crystal 10 Oxide 11 Ammonium Ion

Claims (1)

[Claims] 1. A wafer subjected to a predetermined treatment and cleaved on which the formation of electrodes has been cleaved, an ammonium sulfide solution is used to form a monolayer of sulfur on the cleaved surface, and the monolayer of sulfur is formed on the monolayer of sulfur. A method for manufacturing a semiconductor laser device, which comprises at least a step of forming a polyammonium sulfide solution from an ammonium sulfide solution using a photochemical reaction to form a sulfur multi-molecular layer and then forming an insulating film.