JPH02194587A - Manufacture of semiconductor laser - Google Patents

Abstract

PURPOSE:To form an embedded structure without reducing light-emitting efficiency and obtain a semiconductor laser with a small contact resistance with an electrode by diffusion impurities into only the bottom part of a mesa stripe and putting a quantum well active layer of this region into disorder selectively. CONSTITUTION:An n-type clad layer 2, an n-type guide layer 3, an active layer 4, a P-type guide layer 5, a P-type clad layer 6, and a P-type cap layer 2 are subjected to crystal growth on an n-type GaAs substrate 1, a mask 8 is formed, and then a mesa stripe 9 is formed with it as a mask. Then, an Si film 10 is deposited and then a protection film 11 on diffusion is deposited. Then. the Si film 10 and the protection film 11 are eliminated, heat treatment is performed, and then Si diffusion is made. At this time, since the Si film 10 is located only at the bottom part of the mesa stripe 9, an Si diffusion region 12 is formed only at this location. thus putting quantum well of the active layer 4 of this region into disorder and forming an embedded structure.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for manufacturing a high-performance semiconductor laser used in fields such as optical information processing and optical communication, and particularly relates to a method for manufacturing a high-performance semiconductor laser used in fields such as optical information processing and optical communication. The present invention relates to a method of manufacturing a semiconductor 1/-.

(Prior Art) It has been known that introducing impurities causes disorder in a quantum well structure.
In the third volume of the 9th (Autumn 1986) Applied Physics Hall 1 τf Lecture Proceedings, page 863, 5p-ZC-18, there is a ``G
a, As/AlGaAs threshold direct quantum laser j
It is reported under the title. This semiconductor! 2.--The '3-7 method for manufacturing A first involves the production of n-type Ga
On an As substrate 1, an n-type cladding layer 2 of about 111 m, an n-type guide layer 3 of about 100 m and an active layer 4 made of GaAs of about 100 m and a P-type guide layer 5 of about 100 m and a thickness of about 100 m are formed. P-type cladding layer 6 of 1 pm and Ga thickness of about 1000 nm
A P-type cap layer 7 made of As is sequentially formed (FIG. 2(a)). Thereafter, a mask 8 made of photoresist is formed using photolithography technology, and mesa stripes 9 are formed using this as a mask (see FIG. 2(b).
)). Next, a Si film was deposited under vacuum, and after removing the Si film on the mesa stripe by lift-off method (Fig. 2(C)), a SiN film was formed on the entire surface as a protective film 11 for diffusion.
By performing heat treatment at 0°C for about 1 hour, Si is diffused (Fig. 2 (d)), selectively disordering only the quantum well active layer at the bottom of the mesa stripe, and forming P-type and n-type
The manufacturing method involves forming a mold electrode (FIG. 2(e)).

(Problems to be Solved by the Invention) However, in the conventional semiconductor laser manufacturing method described above, a diffusion protective film is formed over the entire surface. There is a problem in that the diffusion causes crystal defects such as vacancies to be introduced from the protective film into the quantum well active layer, reducing the luminous efficiency of the laser.

Further, even in the upper part of the mesa stripe, external diffusion of Ga atoms into the protective film and reaction between the GaA, S cap layer and the protective film occur during high-temperature heat treatment, resulting in a problem of high contact resistance with the electrode. Furthermore, in order to avoid these problems, if heat treatment is performed under an arsenic pressure high enough to prevent the desorption of arsenic atoms without using any protective film, Si will not diffuse at all, and therefore a buried structure cannot be formed. There was a problem.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a semiconductor laser that can form a buried structure without reducing luminous efficiency and has low contact resistance with electrodes.

(Means for Solving the Problem) The present invention provides a method for manufacturing a buried structure semiconductor laser having a quantum well active layer and a structure in which the quantum well active layer is disordered. a step of forming a cladding layer of a first conductivity type; a step of forming a quantum well active layer including at least one quantum well on the first conductivity type cladding layer; and a step of forming a quantum well active layer including at least one quantum well on the first conductivity type cladding layer; forming a conductive type cladding layer; forming a stripe mask for selective etching on the second conductivity type cladding layer; and etching the second conductivity type cladding layer using the stripe mask. A step of forming a mesa stripe by etching a part of the surface, a step of vapor-depositing an impurity of the first conductivity type after this etching step, a step of vapor-depositing a protective film after this step, and a step of vapor-depositing a protective film after this vapor-deposition step. A process of removing impurities and a protective film on the stripe mask by removing only the stripe mask, and then performing heat treatment to diffuse the impurities only to the bottom of the mesa stripe, thereby reducing the quantum density in this region. A method of manufacturing a semiconductor laser includes a step of selectively disordering a well active layer.

(Function) Since there is no protective film on the sides and top of the mesa stripe, external diffusion of Ga atoms and introduction of crystal defects such as vacancies do not occur in these areas even during high-temperature heat treatment, leading to a decrease in laser light emission efficiency. There is no. Furthermore, since there is a protective film at the bottom of the stripe where the impurity is deposited, diffusion of the impurity occurs under stable conditions as before, and a buried structure can be formed. Further, since there is no protective film on the upper part of the mesa stripe during high-temperature heat treatment, no reaction with the cap layer occurs, and the contact resistance with the electrode can be reduced.

(Example) Next, an example of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a method for manufacturing a semiconductor laser according to an embodiment of the present invention. First, as shown in FIG. 1(a), an n-type cladding layer 2 (n-Al
xcGal-xAs, 0.45≦Xe≦0.85. thickness 0.8 to 311 m), n-type guide layer 3 (n-AIXg
Gal-xgA, s Xg<Xc, thickness 500-300
0 people (typically 1000 people), active layer 4 (GaAs, thickness 50-200 people), P-type guide layer (p4N, xgGa
l-xgAs thickness 500-3000 typically 100
), P-type cladding layer (p-AlxeGal-xeAs
, thickness 0.8-3 pyn), P-type cap layer (p-Ga
As (1000 to 5000 layers thick) is grown as a crystal. Next, as shown in FIG. 1(b), a mask 8 made of photoresist is formed by photolithography, and this is used as a mask to form mesa stripes. The width of the mesa stripe is 1-10 pm, typically 2-3 pm, and the depth is 100 pm from the bottom of the mesa stripe to the active layer 4.
It is preferable that the current is about 0 to 5000A. If the AI composition of the P-type guide layer 5 is 0.35 or less, if an HF-based etching solution is used, only the P-type cladding layer 6 with a high AI composition will be etched, and once the P-type guide layer 5 is reached, the etching will stop. It is convenient to use because it can be stopped automatically. In this case, it is necessary to remove the P-type cap layer 7 by separate etching before using the HF-based etching solution.

Further, dry etching such as reactive ion beam etching (RIBE) may be used as the etching method. In this case, since the etching depth can be precisely controlled, the etching can be stopped at the targeted location, and there is less side etching, so the stripe width is narrow (~
lpm) is easy to form.

Next, as shown in 1.a (c), the Si film 10 (thickness ~5
00A). A vacuum evaporation method is preferable as this forming method. This is because the Si film 10 is formed with discontinuities as shown in the figure. When using a method such as sputter deposition that involves a large amount of wrapping around the side surfaces, Si is vapor deposited on the side surfaces without causing the L break shown in the figure, and 8i is diffused into this area, so that the upper part of the mesa stripe 9 is When the P-type electrode 14 is formed, the pn junction made of the active layer 4 may be short-circuited, which is not preferable. Following this step, a protective film 11 for diffusion (for example, a 5i02 film with a thickness of 500 to 3
000A). A vacuum evaporation method is also preferable as this forming method. This is because the protective film 11 is formed with discontinuities as shown in FIG. 1(C) and is therefore not formed on the side surfaces of the mesa stripes.

Next, as shown in FIG. 1(d), the Si film 10 and protective film 11 on the mesa stripe 9 are removed by lift-off. If the mask is a positive resist, lift-off can be easily performed using an organic solvent such as acetone. then 850°
Si is diffused by heat treatment with C for about 1 hour. Desorption of arsenic atoms can be prevented by vacuum-sealing the sample together with, for example, GaAs powder or As powder, and performing the diffusion under an arsenic pressure higher than the equilibrium vapor pressure of arsenic with respect to GaAs.

At this time, since the Si film 10 is present only at the bottom of the mesa stripe 9, the Si diffusion region 12 is formed only there, and the quantum wells of the active layer 4 in this region become disordered, forming a buried structure. Furthermore, since there is no protective film on the side surfaces and the top of the mesa stripe 9, external diffusion of Ga atoms and introduction of crystal defects such as vacancies do not occur, and the P-type cap layer 7
No reaction occurs between the film and the protective film. Therefore, a good buried structure can be formed without deteriorating the light emitting characteristics of the active layer 4, and the P-side ohmic electrode can also be formed easily.

Next, as shown in FIG. 1(e), after removing the Si film 10 and the protective film 11 by dry etching or the like, the insulation film 13 is removed.
form. Next, the insulating film 13 above the mesa stripe 9
Remove only. This is a normal photolithography technique (]
: Buttering by f. Next, a P-type chamber (>14) and an n-type electrode 15 are formed to complete the process.

In the embodiments described above, the active layer has a single layer structure, but the active layer is not limited to this, and may have a multilayer structure such as a multiple quantum well structure. In addition, in this example, AlGaAs/GaAs is used as the material system.
InGaAsP/InP system, but is not limited to this.
Needless to say, it is also applicable to materials such as InAlGaAs/InP. In addition, in the embodiments described above, Si was used as the diffusing element 7, but it is not limited to this.
Impurities such as n, Mg, and Ga can be used. However, when using P-type impurities such as Zn and Mg, it is necessary to form a laser structure on a P-type substrate. Furthermore, the present inventors have recently found that when Ga is introduced into AlGaAs, it behaves as an n-type impurity, so it is thought that it can be applied to a laser structure on an n-type semiconductor substrate.

Furthermore, in the above embodiments, the protective film during diffusion was the 5i02 film, but it is not limited to this, and other protective films that can be vacuum evaporated,
For example, the present invention can be applied to an Al2O3 film. Further, in the above embodiments, diffusion is performed in a vacuum-sealed container, but the method is not limited to this. For example, an open tube method in a hydrogen atmosphere can be used to
The present invention can be applied even when carrying out the process using the e to face method (a method in which GaAs substrates are placed facing each other to prevent As atoms from being desorbed) or in a gas atmosphere containing arsine.

Further, in the above embodiment, the Si film 10 and the protective film 1
Although the insulating film 13 is formed after removing the Si film 10 and the protective film 11, the present invention is applicable to the case where the insulating film 13 is formed thereon without removing the Si film 10 and the protective film 11.

(Effects of the Invention) As described above, according to the present invention, it is possible to form a buried structure without reducing luminous efficiency, and a semiconductor laser having low contact resistance with an electrode can be obtained.

[Brief explanation of the drawing]

FIGS. 1(a) to (e) are process diagrams for explaining a semiconductor laser manufacturing method according to an embodiment of the present invention, and FIG. 2(a) is
-(e) are process diagrams according to a conventional manufacturing method. In the figure, 1 is an n-type GaAs substrate, 2 is an n-type cladding layer, and 3 is an n-type GaAs substrate.
is an n-type guide layer, 4 is an active layer, 5 is a p-type guide layer, 6 is a p-type rad layer, 7 is a p-type cap layer, 8 is a mask, 9
is a mesa stripe, 10 is a Si film, 11 is a protective film, 12
is a Si diffusion region, 13 is an insulating film, 1.4 is a P pear-shaped pole, 1
5 is an n-type electrode.

Claims (1)

[Claims] A method for manufacturing a semiconductor laser with a buried structure having a quantum well active layer and a structure in which the quantum well active layer is disordered, comprising: forming a cladding layer of a first conductivity type on a semiconductor substrate of a first conductivity type; , forming a quantum well active layer including at least one quantum well on the first conductivity type cladding layer; forming a second conductivity type cladding layer on the quantum well active layer; forming a stripe mask in a predetermined portion of the second conductivity type cladding layer; forming a mesa stripe by etching a part of the second conductivity type cladding layer using the stripe mask; a step of depositing an impurity of a first conductivity type; a step of depositing a protective film after this step; and removing the impurity and the protective film deposited on the stripe mask by removing the stripe mask. and a subsequent step of diffusing the impurity only to the bottom of the mesa stripe to selectively disorder the quantum well active layer in this region by applying heat treatment. manufacturing method.