JPH0371796B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor laser, and in particular provides an optimal method for diffusing impurities in a semiconductor laser having a diffusion region formed by diffusing impurities, such as a planar stripe type semiconductor laser. That is.

FIG. 1 shows a typical laser of this kind, where 1 is n
type GaAs (gallium arsenide) substrate, 2 is an oscillation layer laminated on the substrate, and the oscillation layer is an n-type Ga _1-X
A 1 μm thick first cladding layer 3 made of Al _X As (gallium aluminum arsenide) (0<X<1), Ga _1-Y Al _Y As (0
_≦ Y<1 _, There is. 6 is a 1 μm thick cap layer made of n-type GaAs laminated on the oscillation layer 2;
The cap layer is for making ohmic contact with electrodes that will be formed later. 7 is P ⁺
This is a diffusion region of the mold, and the region is a diffusion region of the cap layer 6.
It is formed by diffusing Zn (zinc) from the surface to a depth that partially reaches the second cladding layer 5.

In such a laser, the diffusion region 7 surface and the substrate 1
When electrodes are formed on each back surface and a forward current is applied with the electrode on the side of the diffusion region 7 as the positive electrode, the current is constricted because the cap layer 6 and the diffusion region 7 are of opposite conductivity type, and the laser beam is emitted at a low current. can oscillate. Further, since the cap layer 6 is made of GaAs, the electrode formed on the surface of the diffusion region 7 can obtain good ohmic characteristics.

However, the formation of the diffusion region 7 is performed at a temperature of 700°C
Since the process is carried out at a high temperature of 1000°C and the cap layer 6 is as thin as 1 mμ, problems such as loss of As (arsenic) components in the active layer 4 and cladding layers 3 and 5 occur, resulting in loss of crystallinity. This impedes the improvement of performance.

In order to prevent such As leakage, the As in the diffusion device must be
Methods such as increasing the partial pressure have been used, but they have not been very effective. Furthermore, it is possible to increase the thickness of the cap layer 6 in order to reduce the thermal influence on the cladding layer, etc., but since the diffusion rate of impurities in the GaAs layer is very slow, this method is not suitable for mass production. I can't say that.

The present invention was made in view of the above problems.
This was done based on the knowledge that the impurity diffusion rate within the GaAlAs layer is higher than that within the GaAs layer. The invention will be explained below with reference to Examples.

FIGS. 2A to 2C are cross-sectional views showing steps of an embodiment of the present invention.

FIG. 2A shows the first step, in which the n-type GaAs substrate 1
The oscillation layer 2 and the cap layer 6 are formed in the same manner as in the laser shown in FIG. 1 above. Note that the same parts as in FIG. 1 are given the same numbers.

FIG. 2B shows the second step, in which about 100% of non-doped Ga _1-Z Al _Z As (1<Z<1) is formed on the cap layer 6.
A protective layer 11 with a thickness of 3 μm is laminated by epitaxial growth.

FIG. 2C shows the third step, from the surface of the protective layer 11 to the depth reaching the surface of the second cladding layer 5.
A diffusion region 7 is formed by diffusing Zn. Such diffusion is made of SiN etc. on the surface of the protective layer 11, and the window 12A
forming a mask 12 having a substrate of
Vacuum sealed in a closed tube with Zn source and heated to 700℃~1000℃
This is done by heat treatment at high temperatures. In this case, it is also desirable to increase the As partial pressure ratio in the closed pipe.

Thereafter, the protective layer 11 is removed to complete the semiconductor laser shown in FIG. To remove such a protective layer 11, for example, H ₃ PO ₄ (phosphoric acid) at 100°C to 150°C is used.
An etching solution is used that is strong in etching GaAlAs and weak in etching GaAs.

During impurity diffusion in this embodiment, the clad layer and active layer are located at a depth of about 4 to 5 μm from the surface, so thermal effects can be reduced compared to conventional methods. According to the inventor's experiments, it has been found that in high temperatures of 700°C to 1000°C, if the oscillation layer consisting of the cladding layer and active layer is at a depth of 3 μm or more from the surface, it is less susceptible to thermal effects. did. Furthermore, in this case As in the atmosphere
It is preferable to increase the partial pressure ratio.

Furthermore, as shown in FIG. 3, the diffusion rate of impurities in the GaAlAs layer is much higher than that in the GaAs layer. Forming the protective layer 11 made of GaAlAs as in the embodiment requires less diffusion time and is suitable for mass production.
In the graph of FIG. 3, the horizontal axis represents the square root of time, and the vertical axis represents the diffusion distance.

Figure 1: Oscillation threshold of a semiconductor laser in which a 10 μm wide diffusion region 7 is formed by directly diffusing impurities from the surface of a cap layer 6 with a thickness of approximately 1 μm, without forming a protective layer made of GaAlAs as in the laser. While the current was 120mA±40mA, the oscillation threshold current of the semiconductor laser obtained in this example was
The result was a good 100mA±20mA.

In this example, the protective layer 11 is non-doped.
Although it is formed of Ga _1-Z Al _Z As, it may be p-type or n-type. Further, the Al concentration (Z value) of the protective layer 11 is preferably set to 0.3 or more in order to increase the difference in etching rate from the cap layer 6 (GaAs) in the final etching process. It was set to 0.4.

Furthermore, in this example, a planar stripe type semiconductor laser was explained, but a TJS (transformer) type semiconductor laser was explained.
Needless to say, the present invention can also be applied to a device having an impurity diffusion region in the oscillation layer, such as a birth/junction type semiconductor laser.

As is clear from the above description, in the present invention, a high-performance semiconductor laser can be manufactured with almost no thermal influence on the oscillation layer and a short diffusion time, so it can be said that the method is suitable for mass production.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a typical semiconductor laser, Figure 2 is a cross-sectional view of a typical semiconductor laser.
Figures A to C are cross-sectional views by process showing embodiments of the present invention;
FIG. 3 is a graph showing the diffusion rate of impurities in GaAs and GaAlAs. DESCRIPTION OF SYMBOLS 1... GaAs substrate, 2... Oscillation layer, 6... Cap layer, 7... Diffusion region, 11... GaAlAs layer (protective layer).

Claims (1)

[Claims] 1 GaAs substrate, laminated on the GaAs substrate
A semiconductor comprising a double heterojunction type oscillation layer made of GaAlAs-based material, a cap layer made of GaAs laminated on the oscillation layer, and a diffusion region in which impurities are diffused from the surface of the cap layer to a depth reaching the oscillation layer. In the laser, the cap layer having the diffusion region is formed by forming a GaAlAs layer on the cap layer, and diffusing impurities from the surface of the layer to a depth that passes through the cap layer and reaches the oscillation layer.
A method of manufacturing a semiconductor laser, characterized in that the semiconductor laser is formed by removing the GaAlAs layer.