JPS64834B2 - - Google Patents

Description

[Detailed Description of the Invention] (a) Field of Industrial Application The present invention relates to a method for manufacturing a semiconductor laser by a molecular beam epitaxial growth method in which material is incident on the surface of a substrate in the form of a molecular beam to cause epitaxial growth. Regarding.

(b) Conventional technology Generally, molecular beam epitaxial growth (MBE)
In the case of a semiconductor laser formed by a semiconductor laser, the first cladding layer, the active layer, the second cladding layer, etc. are grown epitaxially at the same temperature, and the optical characteristics of the cladding layer near both sides of the active layer are is dependent on.

Thus, the first and second cladding layers are formed of high aluminum composition GaAlAs (e.g.
Since Al>0.3) is used, each optical crystallinity differs depending on the epitaxial growth temperature. For example, when molecular beam epitaxial growth is performed at a low growth temperature (approximately 600°C), the surface state (interface with the active layer) of the first and second cladding layers becomes flat; , a problem arises in that both of the cladding layers have poor optical crystallinity. Furthermore, when molecular beam epitaxial growth is performed at high temperatures (approximately 700°C), the optical crystallinity of both cladding layers improves, but on the other hand, the surface conditions of the first and second cladding layers (the active layer and (interface) is poor, and Ga re-evaporates at high temperatures, resulting in the problem that it is very difficult to control the film thicknesses of the first and second cladding layers.

That is, with conventional semiconductor laser manufacturing methods, it is difficult to improve the luminous efficiency.

(c) Purpose The present invention improves luminous efficiency by flattening the surface state (interface with the active layer) of the first and second cladding layers and improving the optical crystallinity of both the cladding layers. It is an object of the present invention to provide an improved method of manufacturing a semiconductor laser.

(D) Structure The method for manufacturing a semiconductor laser according to the present invention is a method for manufacturing a semiconductor laser by a molecular beam epitaxial growth method in which a material is incident on the surface of a substrate in the form of a molecular beam and epitaxially grown, A first lower cladding layer is formed on the surface of the substrate by epitaxial growth at a relatively low temperature until an appropriate film thickness is reached, and when the desired film thickness is exceeded, epitaxial growth is performed at a relatively high temperature. forming a thin first upper cladding layer; forming an active layer with a suitable thickness on the surface of the first upper cladding layer by epitaxial growth at a relatively high temperature; A relatively thin second cladding layer is formed on the surface of the active layer by epitaxial growth, and when a predetermined thickness is exceeded, a second upper cladding layer is formed by epitaxial growth at a relatively low temperature. It is characterized by comprising a process.

(E) Embodiment FIG. 1 is a cross-sectional explanatory view schematically showing an embodiment of the method for manufacturing a semiconductor laser according to the present invention, and the following description will be made with reference to the same figure.

(a) N-type GaAs substrate 10 (for example, 100
After organic cleaning of the substrate), e.g.
Etched with a mixture of H ₂ SO ₄ :H ₂ O ₂ :H ₂ O=5:1:1, dried with N ₂ blow, attached to a molybdenum substrate holder with molten In, and sent to the growth chamber. Introduce. This N-type GaAs substrate 10
Then, raise the temperature of the substrate while applying an As molecular beam.
The temperature rises to a level (approximately 700°C to 750°C) where Ga starts to re-evaporate from the GaAs substrate 10, and
At the same time, the adsorbed impurities (especially oxides, carbides, etc.) of the substrate holder are removed (duration: 20 to 30 minutes). Next, the temperature of the substrate 10 is lowered to 600°C and Al _x Ga _1-x As (for example, N-type Si
Or Sn-doped carrier concentration CC=~3×10 ¹⁷
cm ^-3 , Al composition x = ~0.3 to 0.7) by growing it to an appropriate film thickness (approximately 2 μm).
A first lower cladding layer 20 is formed.

(b) The substrate 10 is heated to a high temperature of 700°C to 720°C.
And Al _x Ga _1-x As (for example, N-type Si or
Sn-doped carrier concentration CC = ~3×10 ¹⁷ cm ^-3 )
The first upper cladding layer 20a is formed by growing Al _Y Ga _1-Y As (non-doped, Al
The active layer 30 is formed by growing a composition y=x−0.3) to a thickness of 1000 Å to 1500 Å,
_{Al _} ^{_ _}
A second lower cladding layer 40a is formed by growing the cladding layer 40a until the second lower cladding layer 40a is grown. Note that the active layer 3
0 is a layer where electrons and holes recombine and emit light.

(c) The substrate 10 is brought to a low temperature (e.g., about 600°C) and Al _x Ga _1-X As (e.g., P-type Be doped carrier concentration CC=~3×10 ¹⁷ cm ^-3 ) is formed to a thickness of about 2 μm. A second upper cladding layer 40 is formed by growing the second upper cladding layer 40 to a certain point.

(d) GaAs for making ohmic contact with the electrode on the surface of the second upper cladding layer 40;
(For example, P-type Be doped carrier concentration CC=~
1×10 ¹⁹ cm ^-3 ) to a thickness of 3000 Å, thereby forming the cap layer 50. Next, a striped photoresist 60 is patterned on the surface of this cap layer 50.

(e) Using the photoresist 60 as a mask, the cap layer 50 is selectively etched. Next, an insulating film 70 such as a silicon nitride film is grown in a vapor phase on the selectively etched substrate surface.

(f) After patterning the photoresist to open windows for electrode contacts, the insulating film 70 is
Select and etch. Next, a surface electrode 80 made of Ti, Au, etc. is placed on the surface of the substrate 10 with the window opened.
However, a back electrode 81 made of, for example, Au-Ge is formed on the back surface of the substrate 10 by vapor deposition.

Therefore, when growing an AlGaAs system using an MBE apparatus, when the temperature of the substrate 10 is as high as 700° C. to 720° C., it is possible to grow a crystal with good optical properties and fewer non-radiative bonding centers. Also, at this high temperature, if the Al composition is x > 0.3, the surface condition will be uneven if the grown film thickness is 1 μm or more, but if it is 1 μm or less, the surface condition can be made flat. . That is, the surface state (interface with the active layer 30) of the first upper cladding layer 20a and the second active layer cladding layer 40a can be made flat.

In addition, steps (a) to (d) in the above-mentioned example are as follows:
Even in the MBE equipment, it is formed continuously.

Further, in the above-mentioned embodiments, a striped structure semiconductor laser is explained as an example, but the present invention is not limited to this, and the steps (d) to (f) described above are as follows:
Needless to say, appropriate methods may be used depending on various striped semiconductor lasers.

Furthermore, in the above embodiment, the thickness of the active layer 30 is
If the thickness is 5000 Å to 1 μm, it can be used as a light emitting diode.

(f) Effects As described above, the present invention is characterized in that the first lower cladding layer is first epitaxially grown on the surface of the substrate at a relatively low temperature until it reaches an appropriate thickness, and when the desired thickness is exceeded. A relatively thin first upper cladding layer is epitaxially grown at a relatively high temperature, an active layer is then epitaxially grown at a relatively high temperature on a surface of the first upper cladding layer, and then the first upper cladding layer is epitaxially grown at a relatively high temperature. A relatively thin second lower cladding layer is epitaxially grown on the surface of the active layer at a relatively high temperature, and when the thickness exceeds a predetermined thickness, a second upper cladding layer is epitaxially grown at a relatively low temperature. .

Therefore, according to the present invention, the surface state (interface with the active layer) of the first upper cladding layer and the second lower cladding layer is made flat, and the optical crystallinity of both said cladding layers is improved. be able to. Therefore, the light emission efficiency of the semiconductor laser can be easily improved.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional explanatory diagram schematically showing an embodiment of a method for manufacturing a semiconductor laser according to the present invention. DESCRIPTION OF SYMBOLS 10... Semiconductor substrate, 20... First lower cladding layer, 20a... First upper cladding layer, 30
... Active layer, 40 ... Second upper cladding layer, 4
0a...Second lower cladding layer.

Claims (1)

[Claims] 1. A method for manufacturing a semiconductor laser by a molecular beam epitaxial growth method in which a material is incident on the surface of a substrate in the form of a molecular beam to grow epitaxially, the method comprising: A first lower cladding layer is formed on the surface of the substrate by epitaxial growth, and when the desired film thickness is exceeded, a relatively thin first upper cladding layer is formed by epitaxial growth at a relatively high temperature. forming an active layer with an appropriate thickness on the surface of the first upper cladding layer by epitaxial growth at a relatively high temperature; forming a relatively thin second lower cladding layer, and forming a second upper cladding layer by epitaxially growing at a relatively low temperature once a predetermined thickness is exceeded. A method for manufacturing a semiconductor laser.