JPH0533550B2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field This invention requires two MBE growth steps.
This invention relates to a method for manufacturing a semiconductor laser having an AlGaAs double heterojunction structure.

(b) Prior Art Generally, when manufacturing this type of semiconductor laser, an etching process is performed to form a stripe groove deep enough to expose the surface of the first upper cladding layer in the first growth layer stacked in the first growth process. By carrying out this process, impurities such as oxides are directly attached to the surface of the first upper cladding layer, so that good growth of the second growth layer to be laminated in the second growth step cannot be expected.

Therefore, the applicant proposed a method for manufacturing a semiconductor laser as disclosed in Japanese Patent Application No. 165334/1982. In the etching process, stripe grooves are formed deep enough to leave the light absorption layer, and the light absorption layer has a passivation effect so that impurities do not directly adhere to the surface of the first upper cladding layer. is evaporated using so-called thermal cleaning.

However, when the light absorption layer is left relatively thick during thermal cleaning in which the temperature is raised while exposing the substrate to an arsenic molecular beam, it becomes difficult for the light absorption layer to evaporate in the depth direction, and the width of the stripe grooves increases. It was found that evaporation becomes easier in this direction. However, it is very difficult to leave the light absorption layer thin, and if thermal cleaning is performed, the light absorption layer will evaporate in the width direction of the stripe grooves until all the remaining light absorption layer evaporates. There were cases where the was deformed. In this case, if a second grown layer is laminated later, a cavity will be formed between the second grown layer and the deformed portion, resulting in a problem that the laser characteristics will deteriorate.

(C) Purpose It is an object of the present invention to provide a method for manufacturing a semiconductor laser, which can form striped grooves with good reproducibility using a simple manufacturing technique, and can also stack a second growth layer well.

(d) Structure This invention comprises a lower cladding layer, an active layer, and a first layer.
A first growth step in which a first growth layer consisting of an upper cladding layer, a protective layer made of P-type GaAs, and an evaporation prevention layer made of N-type AlGaAs is laminated on the substrate surface, and an etching rate where B≫P. an etching step in which the evaporation prevention layer is selectively etched with a solvent having the following properties to form a striped groove having a depth that exposes the surface of the protective layer and a tapered surface that becomes narrower toward the substrate side; ,
By performing the etching process, impurities deposited on the first growth layer and the protective layer whose surface is exposed are evaporated, thereby making the stripe grooves deep enough to expose the surface of the first upper cladding layer. a second growth step of laminating a second growth layer composed of a second upper cladding layer made of P-type AlGaAs and a cap layer made of P ⁺ type GaAs on the thermally cleaned substrate; The reason is that it is equipped with the following.

(E) Embodiment FIG. 1 is an explanatory diagram showing an embodiment of a semiconductor laser according to the present invention. In the figure, 1 is a semiconductor laser, and 1a and 1b are Fabry-Perot reflective surfaces. 10 is a substrate made of N-type GaAs, 21 is N-type Al×Ga _1-x As (Al composition x=0.55)
22 is Al×Ga _1-x As
(Al composition x=0.12) active layer, 23 is P type
The first upper cladding layer is made of Al×Ga _1-x As (A1 composition x=0.55), 24 is a protective layer made of P-type GaAs, and 25 is N-type Al×Ga _1-x As (Al composition x=0.12).
41 is a second upper cladding layer made of P-type Al _Y Ga _1-Y As (Al composition Y=0.55);
42 is a cap layer made of P ⁺ type GaAs, 50 is P
type electrode, 51 indicates an N-type electrode, respectively.
The thickness of the protective layer 24 is set so that it can be easily evaporated by thermal cleaning.

Specifically, the lower cladding layer 21 and the active layer 2
2, a first upper cladding layer 23, a protective layer 24, and an evaporation prevention layer 25 constitute a first growth layer 20. The first growth layer 20 has a stripe groove 30' having a depth that exposes the surface of the first upper cladding layer 23 and a tapered surface 31 that becomes narrower toward the substrate 10. It is formed along the resonator wavelength. The second upper cladding layer 41 and the cap layer 42 constitute a second growth layer 40. This second growth layer 40
is laminated on top of the first growth layer 20 in a concave shape corresponding to the shape of the striped groove 30'.

FIG. 2 is a reference diagram for explaining the method of manufacturing a semiconductor laser according to the present invention, and the following description will be made with reference to the same diagram.

Board 10 installed in an MBE device (not shown)
is heated in a prescribed manner. The raw materials and impurities stored in the evaporation sources are evaporated in the form of molecular beams. The first growth layer 20 is laminated by monitoring the raw materials with a mass spectrometer (not shown) and controlling the temperature and shutter of the evaporation source with a computer (not shown).
(See Figure 2a).

It is assumed that the thickness of the protective layer 24 is set to about 10 to 1000 Å.

The substrate 10 on which the first growth layer 20 is laminated is
After taking it out from the MBE device, the board 10
Next, the evaporation prevention layer 25 other than the portion where the stripe grooves are to be formed is covered with a photoresist 60. The substrate 10 using the photoresist 60 as a mask is immersed in a solution having an etching rate of N≫P under light irradiation from, for example, a halogen lamp, and the evaporation prevention layer 25 is selectively etched, thereby exposing the surface of the protective layer 24. The stripe groove 3 has a tapered surface 31 that has a depth that is narrower toward the substrate 10 side.
0 (etching step, see FIG. 2b). As the solution, an aqueous solution of 1,2-dihydroxybenzene-3,5-disulfonic acid, disodium salt is used.

The substrate 10 from which the photoresist 50 has been removed is organically cleaned. After that, the substrate 10 is replaced again.
Installed inside the MBE device. Here, the substrate 10 is heated to about 720° C. while applying an arsenic molecular beam to the substrate 10.
Heat above. As a result, impurities such as oxides deposited during the etching process are evaporated, and the protective layer 24 whose surface is exposed is evaporated to form striped grooves 30' where the surface of the first upper cladding layer 23 is exposed (thermal Cleaning step, see Figure 2c). 70 indicates the evaporated area.

In the process, the temperature of the substrate 10 is set to about 600°C, and the second growth layer 40 is grown in the same manner as in the process.
(Second growth step, see FIG. 2d).

Thereafter, a P-type electrode and an N-type electrode are respectively formed in the same manner as in a normal semiconductor laser manufacturing method.

FIG. 3 shows the relationship between temperature and evaporation rate of GaAs and AlGaAs. According to the figure, it can be seen that as the temperature increases, AlGaAs hardly evaporates, but GaAs evaporates at a faster rate. In other words, even if you perform thermal cleaning
Since the evaporation prevention layer 25 made of AlGaAs hardly evaporates, it can be said that deformation of the stripe grooves 30 is minimized.

In addition, in the embodiment of this invention, Al×Ga _1-x As
Although the Al composition of each layer consisting of and Al _Y Ga _1-Y As is shown, it is of course possible to change it as appropriate. In the above embodiment, since the Al composition of the lower cladding layer 21 and the first upper cladding layer 23 is set to 0.55, the optical confinement effect of the lower cladding layer 21 and the first upper cladding layer 23 can be improved.

(f) Effects As explained in detail above, in this invention, only the protective layer can be selectively left in the etching process, so that the protective layer has a passivation effect on the first upper cladding layer and removes impurities from the first upper cladding layer. Since the second grown layer is not directly attached to the surface of the cladding layer, the laminated state of the second grown layer can be improved. Further, even when thermal cleaning is performed, deformation of the stripe grooves can be minimized. However, according to the present invention, a semiconductor laser having the characteristics described above can be easily manufactured since no particularly difficult technology is required in the manufacturing process.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing one embodiment of the semiconductor laser according to the present invention, FIG. 2 is a reference diagram for explaining the manufacturing method of the semiconductor laser according to the present invention, and FIG.
The figure is an explanatory diagram showing the relationship between temperature and evaporation rate of GaAs and AlGaAs. DESCRIPTION OF SYMBOLS 10... Substrate, 20... First growth layer, 21... Lower cladding layer, 22... Active layer, 23... First upper cladding layer, 24... Protective layer, 25... Evaporation prevention layer, 30,
30'...stripe groove, 31...tapered surface, 40...
Second growth layer, 41... Second upper cladding layer, 42...
cap layer.

Claims (1)

[Claims] 1. A lower cladding layer, an active layer, a first upper cladding layer, a protective layer made of P-type GaAs, and an N-type GaAs layer.
The first layer consists of an evaporation prevention layer made of AlGaAs.
a first growth step of laminating a growth layer on the substrate surface, and selectively etching the evaporation prevention layer with a solvent having an etching rate of N≫P to a depth where the surface of the protective layer is exposed; an etching step to form a striped groove having a tapered surface that becomes narrower toward the substrate; and by performing the etching step, impurities adhering to the first growth layer and the protective layer whose surface is exposed are evaporated. a thermal cleaning step of making the stripe grooves deep enough to expose the surface of the first upper cladding layer;
Second upper cladding layer made of AlGaAs and P ⁺ type
1. A method of manufacturing a semiconductor laser, comprising: a second growth step of laminating a second growth layer composed of a cap layer made of GaAs.