JPH05160523A - Optical device manufacturing method - Google Patents

Abstract

(57) [Summary] [Purpose] This is a re-growth technology applicable to semiconductor lasers of arbitrary structure, etc. by dramatically improving the crystal quality of the re-growth interface. In a process of manufacturing an optical device having an active layer such as a semiconductor laser on a semiconductor substrate, the process includes at least two crystal growth steps, and the first epitaxial material for regrowth contains Al. By bringing oxidized AlGaAs into contact with high-purity Al _x Ga _1-x As (0 <x ≦ 1) 304, the oxygen concentration 102 near the regrowth interface is dramatically reduced by utilizing the gettering effect. Let

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an optical device used for optical communication, optical information processing and the like.

[0002]

2. Description of the Related Art In recent years, Photonics Integrat that integrates electronic and optical devices using compound semiconductors.
The ed Circuit (PIC) is of interest.
Among the elemental technologies for realizing PIC, crystal growth technology, particularly regrowth technology, occupies a large weight.

The most obstacle to regrowth is deterioration of crystal quality at the regrowth interface. Unlike normal crystal growth, it is difficult to make the crystal surface before regrowth suitable for growth. In particular, the crystal surface is Al
In the case of GaAs, it is easily affected by oxidation and contamination, and it is not easy to obtain good regrowth interface and regrowth crystal quality.

As an example of manufacturing a semiconductor laser (hereinafter, also abbreviated as LD) using re-growth by molecular beam epitaxy (MBE), the'Single Longitudin '
al-Mode Self-aligned (AlG
a) As Double-Heterostructu
re Lasers Fabricated by Mo
regular Beam Epitaxy '(Jap
anese Journal of Applied
Physics, Vol. 24, No. 2, 1985, L
89 to L90). FIG. 4 is a schematic diagram for explaining the laser manufacturing process. This will be briefly described below.

On a (100) GaAs substrate 400, n-
Al _0.6 Ga _0.4 As clad layer 401 (thickness 1.3 μ
m), undoped Al _0.15 Ga _0.85 As active layer 402
(Thickness 0.1 μm), p-Al _0.6 Ga _0.4 As first cladding layer 403 (thickness 0.25 μm), n-GaAs carrier block layer 404 (thickness 0.5 μm), n-AlG
aAs thermal etching stop layer 405 (thickness: 0.
1 μm), n-GaAs layer (thickness 0.2 μm) MBE
To stack (FIG. 4A). Next, width 3μm on the surface
Grooves are formed by wet etching. The etching depth is p-Al by using a sulfuric acid-based etching solution.
_0.6 Ga _0.4 As 1st clad layer (thickness 0.25 μm) 4
The etching is controlled so as to stop in the middle of 03 (FIG. 4B). Next, load the wafer into the MBE chamber,
The substrate temperature is 740 ° C while applying As ₄ (arsenic molecular beam).
The GaAs layer evaporates (thermal etching) when the temperature is raised to. This step is the most characteristic part of the conventional example. In this process, only GaAs evaporates and AlGa
Since As does not evaporate, the thermal etching stop layer 405 is formed outside the groove, and the p-AlGaAs first layer is formed inside the groove.
Thermal etching stops at the cladding layer 403 (FIG. 4C). After this step, a p-AlGaAs second cladding layer 407 (thickness 1.3 μm) and a p-GaAs cap layer 408 (thickness 0.3 μm) are laminated (FIG. 4).
(D)). The subsequent deviceization process is the same as a normal process.

[0006]

The greatest problem of the above-mentioned conventional example is that this manufacturing method can be applied only to a semiconductor laser having a specific structure. The LD structure of the conventional example is a so-called self-aligned semiconductor LD, and it is possible to perform current confinement and mode control of light at the same time. However, since re-evaporation of GaAs is used, mode control of light is a loss guide type. I cannot help becoming. This means that there is always a loss of light, which causes a problem that it is disadvantageous in increasing the LD output and decreasing the threshold value.

Therefore, an object of the present invention is to provide a re-growth technique applicable to a semiconductor laser or the like having an arbitrary structure by dramatically improving the crystal quality of the re-growth interface.

[0008]

In the method of manufacturing an optical device according to the present invention for achieving the above object, crystal growth is performed at least twice in the step of manufacturing an optical device having an active layer such as a semiconductor laser on a semiconductor substrate. And the initial regrowth epitaxial material comprises Al. More specifically, the crystal growth method is molecular beam epitaxial growth, the surface material of the wafer on which the crystal growth step is performed is AlGaAs, and the epitaxial material forming the regrowth interface is Al _x Ga _1-x As. (0 <
x ≦ 1) or the epitaxial material forming the regrowth interface is Al _x Ga _1-x As (0 <
It is characterized in that it consists of a superlattice of x ≦ 1) / GaAs.

[0009]

When the surface layer before regrowth is AlGaAs, Al
Is easily oxidized and its binding energy is large, so that it is extremely difficult to remove the influence of oxidation.
However, if this oxidizable property is actively used, it has a function of reducing the oxide (gettering function). The essence of the present invention is to dramatically reduce the oxygen concentration near the regrowth interface by bringing oxidized AlGaAs or the like into contact with high-purity AlGaAs.

It is considered that the gettering effect by Al is greater as the Al ratio is higher, the material is highly pure, the material is thicker, and the diffusion time (growth time) is longer. However, the Al ratio and the thickness cannot be increased excessively. This is because the device characteristics may be deteriorated. For example, regarding confinement of light,
Since the refractive index changes depending on the Al ratio, it may be difficult to control the light mode. In this case, the gettering effect and the mode control can be controlled independently by adopting the quantum well (QW) structure. That is, the gettering effect can be maintained by dividing the layer containing Al into multiple layers and making them close to each other, and the desired refractive index can be set by controlling the well width and the Al mixed crystal ratio and width of the barrier layer. You can However, the first epilayer of regrowth must be AlGaAs.

[0011]

EXAMPLE 1 FIGS. 3 (a) to 3 (d) are schematic views for explaining a manufacturing method of a first example of the present invention. Hereinafter, description will be given with reference to the drawings. Here, the manufacturing of the distributed Bragg reflection type (DBR) LD will be described as an example, but the present invention can be applied to any other device.

First, as shown in FIG. 3A, a molecular beam epitaxial growth method or a metal organic chemical vapor deposition method (MO) is used.
By using the CVD method) on the n-GaAs substrate 300.
-AlGaAs cladding layer 301 (thickness: 1.5 μm),
GaAs active layer 302 (thickness 0.07 μm), p-Al
_0.13 Ga _0.87 As Optical guide layer 303 (thickness 0.25μ
m) is epitaxially grown.

After the growth of these layers, a photolithography process and an etching process were performed to form a grating 310 on a part of the surface as shown in FIG. 3B. By carrying out this step, adsorption of oxygen and carbon concentration on the surface of 10 ²⁰ cm ^-3 level occurs. By performing sufficient plasma cleaning, it is possible to remove the carbon concentration to a level at which there is no practical problem, but it has almost no effect on oxygen. This is because Al is easily oxidized by oxygen in the atmosphere as described above.

A broken line 101 in FIG. 1 shows the oxygen profile of the epi surface immediately before the second crystal growth.
It can be seen that oxygen penetrates from the surface to a depth of over 200Å.

In the second growth step, AlAs30
4 is grown under the following conditions. Substrate temperature 720 ° C, As /
Al flux ratio (value obtained by dividing the number of incoming molecules of As in Group V by the number of incoming molecules of Group III Al) 4.0, growth rate of 0.
The thickness is 3 μm / h and the thickness is 200Å. This state is shown in Figure 3.
It is shown in (c). Subsequently, an epi layer having a desired structure is grown under desired growth conditions. In the case of this example, as shown in FIG. 3D, a p-type Al _0.5 Ga _0.5 As clad layer 305 (thickness: 1.5 μm) and a p-type GaAs cap layer 306 (thickness: 0.5 μm) were laminated.

A solid line 102 in FIG. 1 shows an oxygen concentration profile near the regrowth interface after the second MBE growth. Thus, it can be seen that by forming AlAs 304, the oxygen concentration sharply decreased near the regrowth interface and the high concentration portion disappeared.

Embodiment 2 FIG. 2 is a view similar to FIG. 1 for explaining a second embodiment of the present invention. In the second embodiment, in the second growth step, AlGa is used instead of AlAs 304 in FIG.
A superlattice structure of As / GaAs (50Å / 30Å) 5 periods was adopted. The rest is the same as the first embodiment.

The oxygen profile 103 after re-growth is slightly different from that of the first embodiment, but the oxygen concentration at the re-growth interface is reduced to the same extent. Moreover, since the superlattice structure can control the refractive index, the crystal quality of the regrowth interface can be improved without sacrificing the mode profile of light.

[0019]

The effects of the present invention having the above-described structure are as follows: 1) The oxygen concentration near the AlGaAs regrowth interface can be suppressed to a low level, and a good regrowth interface can be obtained. 2) It has become possible to regrow semiconductor lasers having an arbitrary structure.

[Brief description of drawings]

FIG. 1 is a graph illustrating the effects of the first embodiment of the present invention.

FIG. 2 is a graph illustrating the effect of the second embodiment of the present invention.

FIG. 3 is a schematic diagram illustrating steps of the manufacturing methods of the first and second embodiments.

FIG. 4 is a schematic diagram illustrating a process of a conventional example.

[Explanation of symbols]

101 ... Oxygen concentration profile before regrowth 102, 103 ... Oxygen concentration profile after regrowth 300, 400 ... GaAs substrate 301, 401 ... N-AlGaAs cladding layer 302, 402 ... GaAs active layer 303 ... Optical guide layer 304 ... AlAs layer or AlGaAs / GaAs superlattice layer 305, 403, 407 ... p-AlGaAs cladding layer 306, 408 ... p-GaAs cap layer 404 ... n-GaAs carrier block layer 405 ... ... n-AlGaAs thermal etching stop layer 406 ... n-GaAs layer

Claims (3)

[Claims] 1. A method of manufacturing an optical device having an active layer such as a semiconductor laser on a semiconductor substrate, comprising at least two crystal growth steps, and the first regrowth epitaxial material contains Al. A method for manufacturing a featured optical device. 2. The crystallization method is molecular beam epitaxial growth, the surface material of the wafer on which the crystal growth step is performed is AlGaAs, and the epitaxial material forming the regrowth interface is Al _x Ga _{1 -x} As (0). <X ≦ 1), The method for manufacturing an optical device according to claim 1, wherein 3. The optical device according to claim 1, wherein the epitaxial material forming the regrowth interface is a superlattice of Al _x Ga _1-x As (0 <x ≦ 1) / GaAs. Manufacturing method. 3. The method of manufacturing an optical device according to claim 3, wherein the first epitaxial material forming the regrowth interface is made of Al _x Ga _1-x As (0 <x ≦ 1).