JPH02260636A - Etching of algainp crystal - Google Patents

Abstract

PURPOSE:To form a ridge, whose side surfaces have a large angle of inclination, by a method wherein an AlGaInP crystal is etched using a hydrobromic acid. CONSTITUTION:In a semiconductor laser of a prescribed structure, a hydrobromic acid containing 47% of HBr and a hydrochloric acid-phosphoric acid mixed solution of HCl:H3PO4=1:6 are used as an etching liquid for forming a ridge of a clad layer 4. At this time, a face (1-1-1) appears on each side surface of the ridge 5 and the angle of inclination of the face (1-1-1) becomes 55 deg. and is larger than the angle of inclination which is formed by a conventional method. If the layer 4 is generally a (AlxGa1-x)yIn1-yP (0<=x, Y<=1) crystal, the face (1-1-1) appears on each side surface of the ridge. In case an AlGaAsP multilayer film containing a GaAs layer is simultaneously etched, an oxidizing reagent like a nitric acid is added to the hydrobromic acid. An etching rate can be changed by adding a dilution substance, such as water and the like. By this constitution, a threshold current can be reduced and a stable transverse mode can be controlled in a ridge waveguide type laser.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial application field
This invention relates to a method of etching RGalnP-based crystals.

(b) Conventional technology Aj2GaI nP crystal has a band gap of 6μ
Since it is compatible with m-band light, it can be used in optoelectronic devices such as visible light semiconductor lasers and LEDs.

FIG. 1 shows a conventional semiconductor laser using an ApGaInP crystal, which is disclosed, for example, in 1985 Autumn Proceedings of the Japan Society of Applied Physics, 4p-ZC-11, page 836.

In the figure, (1) is a substrate made of n-type GaAs; (2) is a substrate made of n-type GaAs;
) is n-type (Aj2o, 7Gao, i) o, sI no
, n-type cladding layer consisting of sP, (3) is undoped G
Active layer consisting of a6.5Ino, sP, (4) is p-type A
(to.

It is a pfi cladding layer consisting of tGao, 3)o, sI no, and sP. Each of these layers is formed using the well-known metal organic chemical vapor deposition method (MOCVD method) or molecular beam epitaxial method (MB
E method) is used to sequentially epitaxially grow on the -main surface of the substrate (1). In addition, the n-type cladding layer (4) has a stripe width (5 μm) formed by selective etching with a stripe width of 5 μm.
is formed.

(6) is a block layer made of n-type GaAs epitaxially grown on the n-type cladding layer (4), and is not laminated on the top of the ridge (5) of the n-type cladding layer (4) due to a mask. (7) is a cap layer made of p-type GaAs that is epitaxially grown on the top of the ridge (5) of the exposed n-type cladding layer (4) and on the block layer (6).

(8) is the AuZn/
A p-type electrode made of A u, and (9) an n-type electrode made of A u G e /A u formed on the other main surface of the substrate.

In such a device, the effective refractive index of the semiconductor portion immediately below where the ridge (5) is not formed is smaller than the effective refractive index of the semiconductor portion directly below where the ridge (5) is formed. As a result, the generated laser light is confined in the region directly under the ridge (5), and the transverse mode is controlled.

In such Aj2Ga I nP crystal, the ridge (5)
Conventionally, H
C72: A hydrochloric acid-phosphoric acid mixture consisting of H3P04=1:6 was used (Electronics
Letters, 17th, March 1988,
Vol. 24, No. 6, p. 326-327).

(c) Problems to be Solved by the Invention The hot topic is that when such a hydrochloric acid-phosphoric acid mixture is used, AgG
In the a I nP crystal, etching progresses along the (211) plane. That is, in the above-mentioned semiconductor laser, one main surface of the substrate is the (100) plane, each semiconductor layer up to the p-type cladding layer is laminated thereon, and such a mixed liquid is used on the surface of the p-type cladding layer. When a striped ridge along the [011] direction is formed by etching, the inclination angle of the side surface of the ridge is 35°, and the lower part of the ridge is wide. When the width of the lower part of the ridge increases, the current spreads through the active layer, leading to an increase in the threshold current of the laser.Furthermore, the region that confines light in the lateral direction becomes wider, making it impossible to obtain a stable transverse mode. Further, if the stripe width at the top of the ridge is narrowed in order to reduce the width at the bottom of the ridge, the contact resistance with the layer provided thereon increases and the electrical characteristics deteriorate.

Furthermore, since the etching rate of such a conventional etching solution differs greatly depending on the difference in the A1 composition ratio of the AρGaInP crystal, it is difficult to control the shape of the ridge side surface when etching multilayer films with different AI2 composition ratios at the same time. For example (AρxGal-z) o, sI no, 5P
In a crystal, the etching rate when x=O is 1,
0 gm/min, and when x=05, it is 0.3 to 0.
It is 4 μm/-in.

Therefore, the present invention provides an etching method that can increase the slope of the ridge side surface when selectively etching an AgGa I nP-based crystal.

(d) Means for solving the problems In order to solve the above problems, the method of the present invention has the following features:
A feature of this method is that hydrobromic acid is used when etching P-based crystals.

(e) Action Etching progresses in hydrobromic acid along the (111) plane of the AgGaInP crystal.

(f) Example In the semiconductor laser having the structure shown in FIG. 1, as an etching solution for forming the ridge (5) of the second cladding layer (4),
Hydrobromic acid containing 47% hydrogen bromide (HBr) and hydrochloric acid consisting of HCN:H3P04=1:6
The shape of the ridge (5) when using the phosphoric acid mixture is shown in FIGS. 2(a) and 2(b), respectively.

Here, the first cladding layer (2), the active layer (3), and the second cladding layer (4) are epitaxially grown on the (100) plane of the substrate (1), and the composition of each layer is as shown in Figure 1. It is the same as the thing. In addition, the second cladding layer (4) glue (
5) is formed by etching using a striped mask with a width of 5 μm.

As shown in FIG. 2(a), [Affo, sGa.

s) A second cladding layer consisting of o, sI no, sP (
When 4) is selectively etched with hydrobromic acid, ridges (
5) A (111) plane appears on the side, and its inclination angle is 55
It becomes ゛. On the other hand, in the conventionally used hydrochloric acid-phosphoric acid mixed solution, a (211) plane appears on the side surface of the ridge (5), and the inclination angle thereof is 35°.

From the above, when forming the ridge (5) by etching, if hydrobromic acid is used as the etching liquid, the angle of inclination of the side surface of the ridge (5) can be increased, and the width of the lower part of the ridge (5) can be narrowed. It is possible.

When hydrobromic acid is used as the etching solution, the etched crystal is (Aj2o-sGao).

s) o, sI no, not limited to sP crystals, A#Ga
I nP crystal JIII (A Q x G a I-X
) yI n 1-yP (0≦x, y≦1) crystal, a <111) plane appears on the side of the ridge, as shown in Figure 2 (a
) has a similar shape.

Furthermore, the etching rate at 120°C for hydrogen bromide 'eJ containing 47% hydrogen bromide is as follows: Aρ composition ratio x=0 and x=
0.5, 0.8 μm/1fi, 1, 0 pm, respectively
lwin, and the difference is sufficiently smaller than that of a hydrochloric acid-phosphoric acid mixture. That is, by using such hydrobromic acid, it becomes possible to etch multilayer films having different A2 composition ratios substantially uniformly.

However, such hydrobromic acid hardly etches GaAs. Therefore, ApGa InP containing a GaAs layer
When simultaneously etching a series of layers, an oxidizing agent such as nitric acid can be added to hydrobromic acid, or the etching rate can be increased by adding a diluent such as water to hydrobromic acid. Of course, it may be changed.

(G) Effects of the Invention According to the present invention, by using hydrobromic acid as an etching solution for ANGa I nP-based crystals, a ridge with a large side surface inclination angle can be formed, for example, a ridge waveguide. When applied to a type laser, it becomes possible to reduce the threshold current and stably control the transverse mode.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an AgGa r nP semiconductor laser, FIG. 2(a) is a sectional view showing a ridge shape formed by the method of the present invention, and FIG. 2(b) is a sectional view showing a ridge shape formed by the conventional method. FIG. 3 is a cross-sectional view showing a ridge shape.

Claims (1)

[Claims] (1) A method for etching an AlGaInP-based crystal, characterized by using hydrobromic acid when etching the AlGaInP-based crystal.