JPH0376218A - Crystal growth method on roughened substrate - Google Patents

Abstract

PURPOSE:To make it possible to grow excellent epitaxial layer on which a defect is hardly generated by a method wherein an Al mixed crystal layer is crystal-grown on the substrate with crystal growth speed 4Angstrom /sec or below having roughened surface using an Al-containing organic metal chemical vapor growth method. CONSTITUTION:An active layer 44, consisting of undoped AlyGa1-yAs is epitaxially grown on an n-clad layer 43, having a trapezoidal cross-section, on a mesa protrusion 42. When a current block layer 46, consisting of n-type AlxGa1-xAs of the same composition as the n-type clad layer 43, is epitaxially grown using an MOCVD method, the relation between the value x (atomic ratio), namely, the value (x), with which no defect is generated in epitaxial growth against Al content, in other words, an oxide is not generated, and vapor- growth speed g.r. is calculated, and the region smaller than the straight line g.r.=-20x+13, in other words, the slunt-lined region on the left side of the diagram is obtained. As a result, the growth speed g.r. can be suppressed to 4Angstrom /sec., because the mixed crystal ratio (x) of Al is x approx.<0.45 in general.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is suitable for manufacturing semiconductor lasers, and is particularly applicable to forming an M mixed crystal growth layer on a textured substrate. Related to crystal growth methods.

[Summary of the invention]

The present invention relates to a crystal growth method on a textured substrate, in which an M mixed crystal layer is grown on a substrate having a textured surface by an organometallic chemical vapor deposition method containing Al at a growth rate of about 4 Å/second or less. By growing crystals, it is possible to reliably obtain, for example, a semiconductor device with desired characteristics.

[Conventional technology]

As a method for obtaining a semiconductor laser with a low threshold current tts, for example, there is an invention disclosed in Japanese Unexamined Patent Publication No. 183987/1987. In this case, a stripe-like mesa protrusion is formed in advance on the semiconductor substrate, and semiconductor layers are successively epitaxially grown on this to take advantage of the dependence of the epitaxial growth rate on the crystal plane orientation. This constitutes a buried heterojunction type low I semiconductor laser.

[Problem to be solved by the invention]

Furthermore, in the above-mentioned semiconductor laser, in order to further simplify the manufacturing and stabilize the characteristics, Japanese Patent Application No. 63-217829 and Japanese Patent Application No. 1983 filed by the present applicant have been proposed.
In the application No. 3-330136, a semiconductor laser was similarly proposed that utilized the dependence of epitaxial growth rate on crystal plane orientation.

As shown in FIG.
A striped mesa-like protrusion (2) extending in the <011> axis direction perpendicular to the paper plane of FIG. 3 is formed on the main surface (1a) of the aAs compound semiconductor substrate (1).
) on the main surface (1a) of the substrate (1) with MOCV
D(Metal Organic chen+1cal
A KlGaAs cladding layer (3) of a first conductivity type, for example, an n-type, and a low impurity or undoped GaAs cladding layer (3) are continuously formed by vapor deposition).
an active layer (4) and a first second conductivity type, for example p-type All
A G a As cladding fli (5) and a kl G a As current blocking layer of a first conductivity type, for example, an n-type (
6) and a second second conductivity type, for example, p-type MI Ga
A s cladding layer (7) and a second conductivity type cap layer (8
) are epitaxially grown.

(9) and (10) show first and second electrodes ohmically deposited on the back side of the cap layer (8) and the substrate (1).

The cladding layer (3) of the first conductivity type, the first and second cladding layers (5) and (7) of the second conductivity type, and the current blocking layer (6) of the first conductivity type are active layers. It is made of a material with a larger nod gap, that is, a smaller refractive index than in (4).

When such epitaxial growth is performed, mesa protrusions (2
) The epitaxially grown portion has a triangular cross section. This is because once a (111) B crystal plane is generated by epitaxial growth on the mesa protrusion (2), the epitaxial growth rate on this plane is several tenths or less of that of other crystal planes, such as the (100) plane. Therefore, epitaxial growth on this surface is almost stopped, and a fault section is generated due to this (111)B.

That is, by specifying the relationship between the crystal orientation of the protrusion (2) of the base (1), selecting its shape and size, and further selecting the thickness of each layer (3) to (6), the protrusion ( 2) On top of the (111) B crystal plane, a cladding layer (
3) and (5) and the active layer (4) sandwiched between them
It is separated from the others and has both bottoms in a stripe shape, and at both end faces thereof, facing the slope (11), a mesa groove (
12) Current blocking layer (
6) is arranged.

In this way, the active layer (4) separated and defined in stripes on the mesa protrusion (2) is surrounded by the current block 1 (6), so that the threshold current is small. This allows the laser to be manufactured in one continuous epitaxial operation.

However, when observing a semiconductor laser formed by such epitaxial growth of an M mixed crystal by MOCVD, depressions or irregularities often occur in a part of the electrode (9) corresponding to the striped protrusion (2). Furthermore, in this case, there are problems in terms of characteristics, such as no laser beam oscillation, low oscillation efficiency, and unstable characteristics.

On the other hand, in the case of MOCVD containing Al, it has been observed that the epitaxial growth rate becomes extremely high, especially as the M content increases.

As a result of various research and considerations, the present inventors have found that semiconductor lasers having problems in laser oscillation and characteristics have some relationship with their growth rate. One of the reasons for this is that, for example, in the example shown in FIG. 3, an oxide of M, for example, is formed on the stripe-like epitaxial semiconductor layer that is originally formed on the stripe-like protrusion (2) and separated from the others, so as to cross the stripe. products are generated, which cause depressions or unevenness in the electrode (9), and cause the active layer (4) to become depressed or uneven.
) or, conversely, block the current path, resulting in defective products that do not oscillate, as well as property problems such as deterioration of characteristics and instability of characteristics. I can think about it.

The present invention has been applied to the manufacturing method of semiconductor lasers, for example, to reduce the incidence of defective products and to obtain semiconductor lasers with stable and excellent characteristics. Provides a crystal growth method.

[Means to solve the problem]

The present invention is applied to a substrate having an uneven surface, such as a compound semiconductor substrate (41) having a mesa protrusion (42), as shown in FIG. , M mixed crystal layer is grown at a growth rate of about 4 seconds or less.

[Effect]

In the present invention, by lowering the crystal growth rate by M-based MOCVD, excellent M
We were able to perform epitaxial growth of mixed crystals.

〔Example〕

An example in which the method of the present invention is applied to a semiconductor laser manufacturing method will be described with reference to FIG. In this case AIG a A
In the case of obtaining an s-based ■-■ group compound semiconductor laser, in this case, first, as shown in FIG. 1A, for example, an n-type GaAs compound semiconductor substrate (41) is provided.

This base body (41) has a main surface (41a) of (100
) has crystal planes. The main surface (41) of this base (41)
a) A striped etching mask (51) with a required width W is selectively formed on the mask. Mask (51)
can be formed, for example, by coating a photoresist film, pattern exposure, and development. In this case, the plane along the plane of the paper is selected to be the (011) plane, and the extension direction of the stripes of the mask (51) is selected to be a direction perpendicular to this plane<O1b axis direction.

Next, from the main surface (41a) side of the substrate (41), for example, H1SO4, 1hOt, and H of a sulfuric acid-based etching solution are applied.
Crystallographic etching is carried out using an etching solution in which 2°C and 2°C are mixed in a ratio of 3:1:1. In this way, etching progresses from the part not covered by the mask (51), and mesa grooves (48) are formed as shown in FIG. A striped mesa protrusion (42) close to a regular mesa is generated.

Then, as shown in FIG. A first conductivity type cladding layer (43) of type klXGa,-,As is epitaxially grown.In this case,
As the epitaxial growth progresses, slopes (49) consisting of (111)B crystal planes forming an angle θ of approximately 55@ with respect to the (100) plane are naturally generated on both sides of the upper surface of the mesa protrusion (42). come. And something like this (111)
Epitaxial growth of the n-type cladding layer (43) is stopped in a state where the slope (49) due to the B-plane exists. Subsequently, by continuous MOCVD, an active layer (44) made of undoped A4'yGa+-yAs is formed, including the n-cladding M (43) having a trapezoidal cross section on the mesa protrusion (42).
grow epitaxially.

In this case, the (111)B crystal plane of the slope (49) has MO
Since epitaxial growth layers by CVD are difficult to form,
The active layer (44) does not substantially grow on this slope (49), but grows on the mesa protrusion (42) and the mesa grooves (42) on both sides thereof.
48) can be selectively separated from each other and formed only on the bottom surface.

Next, a first p-type M, Ga, -, As
A first cladding layer (45) of the second conductivity type is epitaxially grown by MOCVD. In this case, as shown in the second diagram, the growth of the p-type cladding layer (45) progresses to the point where the slopes (49) on both sides intersect on the mesa protrusion (42). 45>, while mesa protrusions (42) are grown on the mesa grooves (48).
) A p-type cladding layer (45) is grown up to the middle position of the slope (49) of the n-type cladding layer (43) on the top (45).

Next, as shown in Figure 1, for example, an n-type cladding layer (4
A current blocking layer (46) made of n-type Ai, Ga, -, and As having the same composition as in 3) is epitaxially grown by MOCVD. In this case, the current blocking layer (46) has slopes (49) on both sides of the active layer (44) on the mesa protrusion (42).
The film is grown by controlling the thickness to cover it. Further, the current blocking layer (46) is a p-type cladding layer (
45) and the first second conductivity type (p type) on the mesa groove (48>)
The cladding layers (45) are formed so as to be separated from each other.

Next, as shown in FIG. 1F, the first second conductivity type (p type)
A second conductivity type (p) having the same composition as the cladding layer (45).
Type) AJ! An XGa+-xAs cladding layer (47) and a highly doped cap layer (50) made of second conductivity type (p-type) GaAs are sequentially epitaxially grown by MOCVD. In this case, the second p-type cladding layer (
47) does not grow on the slope (49) in the initial stage, but as the growth progresses, (11) grows at the part where it meets the slope (49).
1) When a crystal plane other than the B-plane appears, it grows over the entire surface including the slope (49). Therefore, the cap layer (50) on this second p-type cladding layer (47) is also lengthened entirely.

Next, as shown in FIG.
A semiconductor laser according to the present invention is obtained by ohmically depositing the electrode (51) and the second electrode (52) on the back surface of the base (41).

Here, each layer (43), (44), (45)
, (46), (47), (50) are a series of M
By changing the raw material gas supplied by OCVD, it can be formed in one operation, that is, one continuous crystal growth.

As the raw material gas for MOCVD of each klGaAs-based epitaxial growth layer in this MQCVD, trimethylgallium, trimethylaluminum, arsine (AsH3) or triethylgallium, triethylaluminum, AsH can be used, but the above-mentioned When forming epitaxial growth having a triangular cross section on a mesa protrusion in a self-aligned manner, it is desirable to use a methyl-based source gas. In this case, now AI, the crystal growth of the Ga1-XAS system is
The value of X (atomic ratio), that is, M
When the relationship between the X value at which defects do not occur in the epitaxial growth, that is, the formation of oxides do not occur in the above-mentioned epitaxial growth, that is, the formation of oxides, and the vapor phase growth rate g''r for the content of , the straight line g- r = 20
It is smaller than x+13, that is, it is the shaded area on the left in the figure. From this, it is clear that the growth rate gr of M-based mixed crystal is generally x < 0.
．． 45, it can be seen that it must be marked at about 4 Å/sec or less.

In the example of FIG. 1, the set IvcM of the n-type cladding layer (43), the first P-type cladding layer Ji (45), the n-type current blocking layer (46), and the second P-cladding layer (47)
XGa+-Js and the composition M of the active layer (44), Ga
, −, As are selected such that x>y.

Note that, if necessary, an optical waveguide layer may be formed in contact with the active layer (44) by continuous MOCVD.

Further, the conductivity type of each layer may be the opposite conductivity type from that illustrated.

In the example described above, the present invention is applied to the case where a semiconductor laser is obtained by forming an AIG a As semiconductor layer on a substrate having unevenness due to striped mesa protrusions. By applying the present invention to the epitaxial growth of a mixed crystal containing Al, it is possible to obtain a semiconductor device which has excellent crystallinity and also avoids the generation of, for example, M oxide products.

FIG. 2 is a diagram showing the relationship between M content X and crystal growth rate g'r that can avoid defect generation in the method of the present invention, and FIG. 3 is a cross-sectional view of a comparative example.

(41) is a compound semiconductor substrate, and (42) is a mesa protrusion.

〔Effect of the invention〕

As described above, according to the present invention, mixed crystalline crystals containing Al are M
When formed by OCVD, good epitaxial growth with less defects can be achieved by regulating the growth rate, so it can be applied to the manufacture of semiconductor lasers, for example, to ensure the desired laser oscillation. It has great industrial benefits because semiconductor lasers that are stable and have excellent characteristics can be manufactured.

[Brief explanation of drawings]

Claims (1)

[Claims] Crystal growth on a textured substrate, characterized in that an Al mixed crystal layer is grown at a growth rate of about 4 Å/sec or less on a substrate having a textured surface by an organometallic chemical vapor deposition method containing Al. Law.