JP2777432B2 - Manufacturing method of semiconductor laser - Google Patents

Description

The present invention relates to a method for manufacturing an AlGaInP-based semiconductor laser capable of oscillating visible light.

(B) Conventional technology Conventionally, as a semiconductor laser capable of oscillating visible light, for example, as disclosed in JP-A-62-200786, AlGa
InP-based semiconductor lasers have been proposed. In such a semiconductor laser, laser light of 670 to 680 nm is obtained by using GaInP for the active layer.

In recent years, it has been desired to shorten the wavelength of a semiconductor laser. As a method for shortening the wavelength of the AlGaInP-based semiconductor laser, Al is added to the active layer, the active layer has a superlattice structure, and the Ga of the active layer is A method of increasing the ratio of / (Ga + In) has been considered.

(C) Problems to be Solved by the Invention However, in the above method, the oscillation threshold value increases with an increase in the Al composition ratio, making continuous operation difficult.
In the methods (1) and (2), it is difficult to grow a crystal having good film quality, and there is a problem that reproducibility of characteristics and reliability of the device are poor.

Accordingly, the present invention is to provide a method for manufacturing a semiconductor laser that can shorten the wavelength of an AlGaInP-based semiconductor laser and that can be manufactured with good reproducibility.

(D) Means for Solving the Problems According to the present invention, a buffer layer made of Ga _x In _1-x P is laminated on a GaAs substrate, and (Al _z Ga _1-z ) _y In _{1 is formed} on the buffer layer. _-y P
A method of manufacturing a semiconductor laser in which an oscillation layer composed of (0 ≦ z ≦ 1, y> 0.5) is stacked.
The buffer layer is formed by gradually increasing the composition ratio x of Ga and simultaneously increasing the crystal growth temperature.

(E) Function According to the method of the present invention, when a buffer layer made of Ga _x In _1-x P is laminated on a GaAs substrate, this buffer layer is
By gradually increasing the composition ratio x of Ga from 0.5 and simultaneously increasing the growth temperature, the lattice constant of the buffer layer gradually decreases and the lattice defects generated on the buffer layer surface decrease.

(F) Example FIG. 1 shows a manufacturing process of an AlGaInP semiconductor laser.
An embodiment of the method of the present invention will be described below with reference to the drawings.

FIG. 1 (a) shows a first step, in which a substrate (1) made of n-type GaAs is first prepared, and a growth pressure is set to 70 Torr on this one main surface (1a) using a well-known MOCVD method. , N-type Ga _x
A buffer layer (2) made of In _1-x P is laminated.

Such a buffer layer (2) has a Ga composition ratio x at the start of growth.
Is a value matching the lattice of GaAs, for example, about 0.5, more preferably 0.51, and the growth temperature is 630 ° C., and the growth is performed for 5 to 10 minutes, and then the Ga composition ratio is maintained while the V / III supply ratio is kept constant. The growth is performed while gradually increasing x to 0.58 and gradually increasing the growth temperature to 680 ° C.

FIG. 1 (b) shows the second step, in which the surface composition is Ga
_On the buffer layer (2) of _0.58 In _0.42 P, an n-type (Al
_0.7 Ga _0.3 ) _0.58 In _0.42 P n-type cladding layer (3), undoped Ga _0.58 In _0.42 P active layer (4), p-type (Al _0.7 Ga _0.3 ) _0.58 In _0.42 P cap layer (6) is laminated in this order. The growth temperature of each of these layers is constant at 680 ° C.

FIG. 1 (c) shows a third step, in which a cap layer (6) and a p-type clad (5) are formed using a well-known photolithography technique.
Is removed by etching to form a stripe-shaped ridge (7) extending in the direction perpendicular to the paper surface. Here, the width of the top of the ridge (7) was 5 μm, and the cavity length was 250 μm. The cap layer (6) and the p-type clad layer (5)
Hydrobromic acid is used as an etchant for the removal.

FIG. 1D shows a fourth step, in which a cap layer (6) is formed.
P-type cladding layer and the upper and exposed (5) sputtering deposited a SiO ₂ film (8) by using the on ridge (7) by lift-off top, or cap layer (6) on the SiO ₂ The film (8) is removed.

FIG. 1 (e) shows a fifth step, in which Cr, Sn and Au are deposited on the other main surface (1b) of the substrate (1) in this order, on the n-type electrode (9), on the cap layer (6) and Cr on the SiO ₂ film (8)
Au is deposited in this order to form a p-type electrode (10).

The current-light output characteristics and the oscillation spectrum characteristics at an output of 2 mW of the semiconductor laser formed by such a method were measured. The results are shown in FIGS. 2 and 3. The measurement conditions are all those at the time of pulse operation at room temperature.

As is clear from these characteristic diagrams, in the device prepared by using the method of the present embodiment, as shown in FIG. 2, a linear characteristic can be obtained up to an oscillation threshold current of about 90 mA and an optical output up to 4 mW. As shown in FIG. 3, a laser oscillation wavelength of 634 nm was obtained.

Here, for comparison, an apparatus similar to that of the present example was manufactured with the growth temperature of each layer kept constant at 630 ° C. The other growth conditions are the same as in the method of this embodiment. From such a comparison device,
A laser oscillation wavelength of 650.4 nm was obtained.

This shows that even if the composition of the active layer (4) is the same, the wavelength can be further shortened by using the method of the present invention.
This is considered to be due to the fact that the band gap changes in the AlGaInP meter semiconductor laser depending on the growth temperature (Nikkei Electronics, August 10, 1987, No. 4).
27, p.136).

Next, a comparative device was manufactured under the same conditions as in the method of this example except that the growth temperature of each layer was fixed at 680 ° C. However, no laser oscillation occurred in such a comparison device. This is because the single-crystal GaInP-based buffer layer (2) did not grow on the GaAs substrate (1) at the growth temperature of 680 ° C. and was polycrystalline. If the temperature of the buffer layer (2) is increased to 680 ° C. before the growth of the buffer layer (2) at 630 ° C. and the growth of the n-type cladding layer (3) is started, it usually takes several minutes to increase the temperature. P having a high vapor pressure evaporates from the surface of the buffer layer (2), which is the formation layer, and it becomes difficult to grow a film having good crystallinity on this. Of course, a similar decrease occurs when the growth temperature is increased immediately before the growth of the active layer (4).
The crystallinity of the active layer (4) deteriorates.

(G) Effects of the Invention According to the method of the present invention, a buffer layer made of Ga _x In _1-x P is formed on a GaAs substrate by gradually increasing its Ga composition ratio x and gradually increasing its crystal growth temperature. A semiconductor laser with a shorter wavelength is formed by forming an oscillation layer of (Al _z Ga _1-z ) _y In _1-y P (0 ≦ z ≦ 1, y> 0.5). Can be manufactured with good reproducibility.

[Brief description of the drawings]

1 (a) to 1 (e) are cross-sectional views for explaining steps of an embodiment of the method of the present invention, and FIGS. 2 and 3 are views of a semiconductor laser manufactured using the method of the embodiment. It is a current-light output characteristic diagram and an oscillation spectrum characteristic diagram.

Continuation of front page (56) References JP-A-63-42114 (JP, A) JP-A-1-251684 (JP, A) JP-A-63-177487 (JP, A) JP-A-61-166186 (JP) , A) JP-A-3-104183 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01S 3/18

Claims (1)

(57) [Claims] 1. A buffer layer comprising Ga _x In _1-x P is laminated on a GaAs substrate, and (Al _z Ga _1-z ) _y In _1-y P is formed on the buffer layer.
In the method for manufacturing a semiconductor laser in which an oscillation layer composed of (0 ≦ z ≦ 1, y> 0.5) is laminated, the buffer layer is
Characterized by gradually increasing the composition ratio x and simultaneously increasing the crystal growth temperature thereof.