JPH03203316A - Epitaxial wafer and manufacture thereof - Google Patents

Abstract

PURPOSE:To diminish the development of strain, defects at the junction in a system having unmatched lattice by a method wherein the changing gradient in composition in an overshoot structure (corresponding to the changing gradient of lattice constant) is made more gentle. CONSTITUTION:After the epitaxial formation of lattice constant transition layers C, D (2) on the surface (a) of a substrate A (1) in lattice constant alpha, an epitaxial layer B (3) in a specific lattice constant beta is mounted on the surface (a). The lattice constant is gradually changed from the surface (a) to (c) so that the lattice constant(r) at the point (c) may exceed beta in the layer C. The excess level shall be 1/5-1/10 of the unmatched level of the lattice constant. After passing the point (c), the transition layer D (2) is provided to make the lattice constant approach to the lattice constant beta of the target layer B. The changing gradient shall be more gentle than that of the layer C so as to ease the strain. That is, about 1/3 of the gradient in the layer C will suffice for the changing gradient. In such a constitution, the changing rate of the lattice constant can be optimized, especially after exhibiting the overshoot structure, to be gradually changed thereby enabling a once imposed strain to be substantial ly eased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a wafer produced by an epitaxial growth method, and more particularly to an epitaxial wafer having a heterojunction with lattice mismatch and a method for growing the same.

[Conventional technology]

In recent years, there has been remarkable progress in the field of optoelectronics, with research and development of light emitting diodes (LEDs) and laser diodes (LDs) being actively conducted. One of the materials used here is GaAsP,
It is attracting attention because it can form a direct transition type crystal structure in the red to infrared color band depending on the mixing ratio of arsenic (As), which belongs to Group V of the periodic table, and gallium (Ga). The problem with this system is a decrease in crystallinity due to crystal lattice mismatch. For example, GaA used as a substrate
The lattice constant of the s single crystal is 5.653 angstroms, and when GaAs1-xPX is epitaxially grown on this GaAs substrate, the GaAs of x-0,3 is
The lattice constant of A S o, y P o, a crystal is 5.59
21 (person), and the lattice mismatch with the board is 1.1
%. Here, lattice mismatch refers to the ratio expressed by the following formula: (Lattice of epitaxially grown crystal (lattice constant of substrate crystal)
a A S o, e P o, the lattice constant of the four crystals is 5.
5718 (people), and the grid mismatch is 1.4%.

The lattice constant of the compound semiconductor single crystal used as a substrate is 5.853 for GaAs and 5.868 for InP.
7 people, and 5.450 people in GaP. The lattice mismatch when placing an epitaxial growth layer of GaAs1□PX on a GaP substrate is G, aAso, Po, 2 in the case of 3.
．． 6%, and in the case of G a A So, a P o, 4, it is about 2.2%.

In this way, the lattice constant of the epitaxially grown crystal may be larger or smaller than the lattice constant of the substrate crystal. In any case, since the lattice constants of the two are different, the larger the gap between them, the worse the crystallinity of the epitaxially grown crystal becomes, and the semiconductor devices produced from such epitaxial wafers also have inferior electrical properties.

Conventionally, when epitaxial growth with such lattice mismatch is performed, a method is used to provide a composition gradient layer that gradually changes the lattice constant from the lattice constant of the substrate to the lattice constant of the epitaxially grown crystal, as shown in Figure S3 (a). was being carried out. In this case, a method has also been proposed in which the composition of the composition gradient layer is changed until it exceeds the lattice constant of the constant composition layer on the surface, and then -constant composition epitaxial growth is performed (see Figure 3(b), Kaisho 51-8881
etc).

[Problem to be solved by the invention]

However, in this structure, the concentration gradient up to a constant composition layer is large, and the influence of lattice mismatch cannot be sufficiently reduced. In other words, in bonding systems with lattice mismatches, it is not possible to reduce distortion in the grown layer and the occurrence of defects, and therefore it is difficult to obtain a device with high brightness and high luminous efficiency when used as an LED device. Ta.

Therefore, it is an object of the present invention to optimize this concentration gradient, reduce the influence of lattice mismatch, and thereby obtain a light-emitting element with high luminance and high luminous efficiency.

[Means for solving problems]

In the present invention, the structure of the composition gradient region was improved and optimized in order to eliminate the influence of lattice mismatch on the crystallinity of epitaxially grown crystals. That is, the epitaxial wafer l) of the present invention is a semiconductor epitaxial wafer having a surface epitaxial growth layer on a semiconductor substrate with a lattice constant different from that of the substrate, in which a surface epitaxial growth layer is formed between the substrate and the surface epitaxial growth layer based on the lattice constant of the substrate crystal. It is characterized by providing an intermediate epitaxial growth layer whose lattice constant changes continuously up to a lattice constant exceeding that of the crystal, and then changes continuously up to the lattice constant of the surface epitaxial growth layer crystal.

Further, the method for manufacturing an epitaxial wafer of the present invention includes:
In a method for vapor phase growth of a semiconductor crystal that has a lattice constant different from that of a substrate, the reaction gas composition is set to be the same as the lattice constant of the substrate crystal at the start of vapor phase growth, and the target crystal is grown as the growth progresses. The lattice constant is changed so that the lattice constant becomes the same as that of the target crystal, and after the lattice constant of the target crystal is exceeded, the lattice constant is gradually changed so that the lattice constant becomes the same as that of the target crystal again, and the vapor phase growth is completed. do.

The lattice constant of a crystal is basically determined by the composition of the crystal. Furthermore, the lattice constant can be measured by the X1 diffraction technique. The relationship between the lattice constant obtained from X-ray diffraction and the crystal composition can be calculated by Vegard's law once the composition system is determined.

FIG. 1 shows the structure of an epitaxial wafer having mismatched lattice constants according to the present invention in terms of lattice constants. The substrate (A) in the figure is a single crystal substrate having a lattice constant α. It is desired to place an epitaxial growth layer (B) having a lattice constant β on Table 11ja of this substrate (A), but in this case, there is a difference of several percent between the lattice constants α and β. Therefore, first, lattice constant transition layers (C) and (D) are epitaxially grown on the surface j[a of the substrate (A), and then an epitaxial transition layer (B) having a -window lattice constant β is placed thereon. At this time, the lattice constant changes gradually from surface a to surface C of the substrate (A), and the lattice constant transition layer (C ).

The extent to which γ exceeds β is the amount of lattice constant mismatch, 115
~1/1O is appropriate. After reaching 0 points,
A lattice constant transition layer (D) is provided to gradually change the lattice constant again to bring it closer to the target lattice constant β of the epitaxial growth layer (B).

The degree of change in the lattice constant at this time may be the same as the slope of the (C) layer, as shown in graph 1 in Figure 1, or it may be greater than the slope of (C) W, as shown in graph 1 in Figure 1. You can make it more gradual. The gentler the distortion, the less strain will occur, which is preferable for later epitaxial growth of the window lattice constant. In this case, it is sufficient to set the gradient to about 1/3 of the gradient of layer (C).

Next, a method for manufacturing an epitaxial wafer according to the present invention will be explained. Since the lattice constant is determined by the composition of the crystal, the easiest way to change the lattice constant is to constantly change the composition of the epitaxially grown crystal. This can be achieved by changing the reaction gas composition using a vapor phase growth method. For example, M
When epitaxially growing a Q a A 81-x PX crystal by the OCVD method, after epitaxial growth starts at point a in Figure 1, the amount of arsine (A s Ha ) gas, for example, which serves as an arsenic source, is gradually reduced until reaching point C. For example, phosphin (PH3), which is a phosphorus source,
) Gradually increase the amount of gas. If it reaches 0 points,
The gas amount is changed in the opposite manner to the above, and when the point shown in Figure 1 is reached, the composition of the layer (B) is reached. L. Thereafter, a constant composition (B) layer is epitaxially grown.

[For production]

In the present invention, the rate of change in the lattice constant is optimized because the rate of change in the lattice constant has a significant effect on distortions and defects that occur in junctions between different lattice constants. In particular, it is presumed that by taking an overshoot structure and then gradually changing it, the distortion that has occurred is substantially alleviated.

〔Example〕

Next, examples of the present invention will be described.

M on a GaAsrlt viscous substrate with a lattice constant of 5.858.
Ga of lattice constant 5.5718 using OCVD method
A So, e Po, 4 crystals were epitaxially grown. In this case, the theoretical lattice mismatch degree is 1.4%
It is. MOCVD was carried out according to a conventional method, and the reaction gases used were TMG, As Hs (10% Ar dilution), and PH3 (10% Ar dilution), and ultra-high purity H2 gas was used as a carrier gas. The gas flow rate was adjusted as shown in Table 1.

Table 1 In other words, immediately after the start of epitaxial growth′! s1
At the point corresponding to point a in the diagram, A s H3: 845 (S
CCM), starting with no PH3, and then gradually reducing A s Ha and increasing PH 3 over the next 2 hours, and at the point corresponding to point C in Figure 1, A s H:
185 (SCCM), P Hs: 160 (SC
CM). After that, the A s Ha was gradually increased and the PH3 was decreased over 12 minutes, and at the point corresponding to the point shown in Figure 1, the A s Hs was 200 (SCCM).
.

The pH was set to 150 (SCCM), and epitaxial elongation was continued for 1 hour under constant conditions.

During this time, TMG continued to flow at a constant rate of 20 (SCCM) and H2 as a carrier gas continued to flow at a constant rate of 5.000 (SCCM).

FIG. 2 shows the results of measuring the lattice constant of the epitaxial wafer thus obtained. As a result of the measurement, Ga
The degree of lattice mismatch between the As substrate and the G a A 8 o, a P o, n epitaxial growth layer was 1.8%, but the degree of lattice mismatch at the overshooting part of point C was only 0.4%. It was. Further, the thickness of the lattice constant transition layer was approximately IIuIM, and the slopes of the tl and t2 portions were almost the same.

The half width of the X-ray rocking curve on the wafer surface of this structure was as steep as 200 seconds, indicating that good crystal growth was occurring.

〔effect〕

As described above, by reducing the gradient of composition change (corresponding to the gradient of lattice constant change) in the overshoot structure, it is possible to reduce the occurrence of distortion and defects in bonding systems with lattice mismatch. A big effect can be obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram explaining the structure of the lattice constant of the wafer of the present invention, FIG. 2 is a diagram showing the structure of the lattice constant of the wafer of the embodiment of the present invention, and FIG. 3 is the diagram of the lattice constant of the wafer of the conventional method. It is a figure showing the structure of a constant. 1...Substrate 2...Lattice constant transition layer 3
・・・Constant composition layer

Claims (1)

[Scope of Claims] 1) In a semiconductor epitaxial wafer having a surface epitaxially grown layer on a semiconductor substrate with a lattice constant different from that of the substrate, a method is provided between the substrate and the surface epitaxially grown layer based on the lattice constant of the substrate crystal. The lattice constant changes continuously until the lattice constant exceeds the lattice constant, and then until the lattice constant of the surface epitaxial growth layer crystal,
A semiconductor epitaxial wafer comprising an intermediate epitaxial growth layer with a continuously changing lattice constant. 2) In a method of vapor phase growth of a semiconductor crystal having a lattice constant different from that of the substrate, the reactive gas composition is set to be the same as the lattice constant of the substrate crystal at the start of vapor phase growth, and the target is set along with the growth process. The lattice constant is changed to match the lattice constant of the crystal, and once it exceeds the lattice constant of the target crystal, the lattice constant is gradually changed to the lattice constant of the target crystal again to complete the vapor phase growth. Characteristic vapor phase growth method.