JP3985288B2 - Semiconductor crystal growth method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a vapor phase growth method of a semiconductor crystal thin film, and more particularly to a heteroepitaxial growth method.
[0002]
[Prior art]
In recent years, GaN-based compound semiconductor thin films have been put into practical use as blue LED materials. At present, since it is difficult to grow a GaN bulk crystal serving as a substrate, a GaN-based compound semiconductor thin film is grown on a sapphire substrate having a normal lattice constant. In this case, a GaN epitaxial layer is grown on a buffer layer formed by annealing a GaN layer grown at a low temperature in order to relax the lattice constant of GaN and sapphire.
[0003]
On the other hand, since a sapphire substrate is insulative, it is necessary to form an electrode by etching a GaN-based epitaxial layer in order to produce an LED structure. For this reason, a process becomes complicated and cost increases. Therefore, an example of investigating cost reduction of the process by forming a GaN buffer layer and a GaN-based epitaxial layer on a conductive substrate such as a GaAs semiconductor substrate and forming electrodes on the back surface of the substrate as described above. There is also.
[0004]
In addition, since a GaAs substrate that is frequently used as a compound semiconductor is difficult to increase in diameter and is expensive, it has been studied to form a GaAs layer on a Si substrate that is easy to increase in diameter and is inexpensive. Also in this case, the difference in lattice constant is mitigated by annealing a GaAs layer formed at a low temperature to form a buffer layer and growing a GaAs epitaxial layer thereon.
[0005]
[Problems to be solved by the invention]
As described above, conventionally, when forming a semiconductor crystal thin film on a substrate having a different lattice constant, a buffer layer formed at a low temperature has been inserted between the substrate and the epitaxial layer in order to alleviate the difference in lattice constant. However, the crystallinity of the epitaxial layer thus formed is often not perfect. In particular, when the lattice constant difference is large, such as GaN and GaAs, there is a problem in the crystallinity of the epitaxial layer.
[0006]
Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art and provide a method for producing a high-quality semiconductor epitaxial layer on a substrate having a different lattice constant.
[0007]
[Means for Solving the Problems]
According to the present invention, in a method of growing a semiconductor crystal thin film on a substrate having a different lattice constant by a vapor deposition method, the semiconductor crystalline thin film is formed on the substrate with a material equal to the semiconductor at a temperature lower than a temperature at which the crystalline thin film of the semiconductor is epitaxially grown. The step of forming an amorphous layer by vapor deposition and the step of raising the temperature of the substrate on which the amorphous layer is formed to a temperature at which the amorphous layer crystallizes are continuously repeated at least twice on the buffer layer formed. There is provided a semiconductor crystal growth method characterized by epitaxially growing the crystalline thin film of the semiconductor. In the method of the present invention, the semiconductor is GaAs, GaP, InAs, or InP, the substrate is a Si substrate, or the semiconductor is GaN, InN, or AlN, and the substrate is a sapphire substrate or A GaAs substrate is preferred. The GaAs substrate is preferably a GaAs (111) A surface or B surface.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The main feature of the method of the present invention is that the buffer layer, which has conventionally been formed of one layer, is formed of two or more layers by repeating the same process. This buffer layer is obtained by annealing an amorphous layer made of the same material as that of the semiconductor to be epitaxially grown and at a lower growth temperature than the semiconductor is epitaxially grown. The amorphous layer is crystallized by annealing, and at that time, the amorphous layer is crystallized so as to be oriented in the crystal structure of the substrate. This alleviates the difference in lattice constant between the substrate and the upper epitaxial layer. In the present invention, two or more buffer layers are formed to improve crystallinity.
[0009]
In the conventional method, since only one buffer layer is inserted, the lattice constant is not sufficiently relaxed. It is considered that the buffer layer surface has a lattice constant intermediate between the lattice constant of the lower layer crystal and the lattice constant of the upper layer crystal. Therefore, by forming the buffer layer in multiple layers, the lattice constant of the surface of the buffer layer becomes closer to the epitaxial layer. In addition, since there is a limit to the thickness of the buffer layer that can be formed in one step, the same effect cannot be obtained even if a buffer layer having a plurality of layer thicknesses is used. In addition, the effect of the present invention can be obtained even when the buffer layer having a thickness of one layer conventionally formed by two or more layers by the method of the present invention. For example, in the method of the present invention, the thickness of the buffer layer formed in one step is preferably 10 to 100 nm.
[0010]
Further, in general, in order to epitaxially grow semiconductor layers having different lattice constants on a substrate, the growth temperature (substrate temperature) must be increased. However, a substrate containing a volatile substance such as a GaAs substrate or InP substrate can be used. In this case, there is a problem that volatile components having a high vapor pressure such as As and P evaporate. In the method of the present invention, this problem can also be solved by increasing the overall thickness of the buffer layer formed at a low temperature to be a multilayer.
[0011]
【Example】
Example 1
FIG. 1 shows a cross-sectional structure of an epitaxial wafer produced by using the compound semiconductor growth method according to the present invention. The epitaxial wafer of FIG. 1 includes a GaAs (111) B surface substrate 1, a first GaN layer 21 having a thickness of 20 nm and a second GaN layer having a thickness of 20 nm formed on the GaAs (111) B surface substrate 1. A buffer layer 2 having 22 and a GaN epitaxial layer 3 having a thickness of 1 μm formed on the buffer layer 2. Both the buffer layer 2 and the GaN epitaxial layer 3 were formed by the MOC-VPE method. The first GaN layer 21 was formed at a growth temperature of 550 ° C. and a growth time of 30 minutes, and then heated to 850 ° C. and annealed for 10 minutes. The second GaN layer 22 was formed by annealing the first GaN layer 21 and then reducing the temperature to 500 ° C. for a growth time of 30 minutes, and then raising the temperature to 850 ° C. and annealing for 10 minutes. Thereafter, the GaN epitaxial layer 3 was grown at a growth temperature of 850 ° C. for 60 minutes.
[0012]
In the obtained GaN epitaxial layer 3, the peak half-value width of X-ray diffraction was reduced by half compared to the case where the buffer layer was one layer, and improvement in crystallinity was confirmed. In addition, the surface flatness was improved, and there were no vacancies due to As missing at the substrate and epitaxial interface.
[0013]
【The invention's effect】
As described above in detail, according to the present invention, an epitaxial wafer having better crystallinity and surface flatness than the conventional one can be obtained. The method of the present invention is particularly effective when a GaN epitaxial layer is formed on a GaAs substrate.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of an example of an epitaxial wafer produced by the method of the present invention.
[Explanation of symbols]
1 GaAs (111) B-side substrate 2 Buffer layer 3 GaN epitaxial layer

Claims (5)

In a method of growing a semiconductor crystal thin film on a substrate having a different lattice constant by vapor deposition, an amorphous layer is formed on the substrate with a material equal to the semiconductor at a temperature lower than the temperature at which the crystalline thin film of the semiconductor is epitaxially grown. forming by phase growth method, crystallinity of the temperature of the substrate formed with the amorphous layer in a step of the amorphous layer is heated to a temperature to crystallize at least two successive repeated forming the buffer layer on a semiconductor A method for growing a semiconductor crystal, comprising epitaxially growing a thin film of 2. The semiconductor crystal growth method according to claim 1, wherein the semiconductor is at least one compound semiconductor selected from the group consisting of GaAs, GaP, InAs, and InP, and the substrate is a Si substrate. . 2. The semiconductor crystal growth method according to claim 1 , wherein the semiconductor is at least one compound semiconductor selected from the group consisting of GaN, InN, and AlN, and the substrate is a sapphire substrate. 2. The semiconductor crystal growth method according to claim 1 , wherein the semiconductor is at least one compound semiconductor selected from the group consisting of GaN, InN, and AlN, and the substrate is a GaAs substrate. 5. The semiconductor crystal growth method according to claim 4, wherein the semiconductor is GaN, and the substrate is a GaAs (111) B plane or a GaAs (111) A plane.

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