JPH0361637B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a method for growing GaAs single crystals at low temperatures by vapor phase epitaxial method.

Prior Art and its Problems A halogen transport method is known as a vapor phase epitaxial growth method for GaAs. In this method, a Ga source previously saturated with As is heated to 800-900°C, and AsCl ₃ and H ₂ are introduced onto this source. The introduced AsCl ₃ generally decomposes into As ₄ and HCl as follows: AsCl ₃ +3/2H ₂ →1/4As ₄ +3HCl, and this decomposition product and the GaAs coating formed on the Ga source surface It is said that these are brought into equilibrium through the reaction GaCl+1/4As ₄ +1/2H ₂ ←→GaAs+HCl. When the gas in this state is guided downstream and supplied to the low temperature substrate surface, the equilibrium reaction equation described above proceeds to the right.
GaAs crystals are precipitated from the gas phase and epitaxial growth occurs. This method requires hydrogen reduction of AsCl ₃ as described above, and for this purpose, it must be heated to a high temperature of at least about 700° C. or higher, based on the measurement results in FIG. 2 by the present inventors.
However, as the temperature increases, contamination from Si and other substances generated from quartz reaction tubes increases, which becomes an obstacle to obtaining high-purity crystals. Therefore, a growth method that can lower the temperature of the entire reaction tube and the like as much as possible is required.

OBJECTS OF THE INVENTION The present invention provides a method for vapor phase epitaxial growth of high purity GaAs single crystals at low temperatures.

Structure of the Invention The present invention has the gist set forth in the claims, and is directed to the epitaxial growth of GaAs single crystals using the Ga/AsCl ₃ /H ₂ system halogen transport _method . It is characterized by promoting the hydrogen reduction reaction by irradiating it with light.

The present invention will be specifically explained below. First, _AsCl3
The effect of light irradiation on the hydrogen reduction reaction of was investigated using infrared absorption method.

AsCl ₃ was introduced with H ₂ as a carrier gas, and the infrared absorption spectrum was measured while irradiating it with light. Figure 1 shows the change in the infrared absorption spectrum when the temperature was maintained at approximately 500°C and 249 nm light from an excimer laser was irradiated. The concentration of AsCl ₃ decreases due to light irradiation, and HCl is newly generated. That is, the hydrogen reduction reaction of AsCl ₃ is promoted by light irradiation. Figure 2 shows a comparison of the temperature dependence of hydrogen reduction of AsCl ₃ with and without irradiation with 249 nm light.
The vertical axis indicates the absorbance of AsCl ₃ , which approximately corresponds to the concentration. At high temperatures, AsCl ₃ thermally reacts with H ₂ to generate HCl, which decreases, and at high temperatures of 700°C or higher, it is completely thermally reduced by hydrogen. However, in the case of light irradiation, approximately 30% of the introduced AsCl ₃ is reduced to HCl even at a low temperature of 325°C, and this value is equivalent to 615°C without light irradiation. This means that the effect is equivalent to that of 290℃. Figure 3 shows the hydrogen reduction of AsCl ₃ when the wavelength of the irradiated light was varied while keeping the power of the laser light constant at 0.35W and 2W. Light with wavelengths shorter than 300 nm is effective for hydrogen reduction.

Next, we applied the hydrogen reduction reaction of AsCl ₃ by light irradiation described above to the epitaxial growth of GaAs single crystals. FIG. 4 shows a schematic diagram of the apparatus used.
A Ga source 3 saturated with As and GaAs are placed in a predetermined position in a quartz reaction tube 2 having a light introduction window 1.
A crystal substrate 4 is installed. The electric furnace 5 heats the Ga source 3 and the substrate 4 to predetermined temperatures.
Light from an irradiation light source 6 is introduced into the reaction tube 2 through the light introduction window 1. GaAs single crystal is epitaxially grown by passing H ₂ gas through a flow meter 7 and then through an AsCl ₃ bubbler 9 kept at a predetermined temperature by a constant temperature bath 8 into the reaction tube 2. It will be done.

Using the device shown in Figure 4, the temperature of the Ga source was set to 600℃.
Crystal growth was performed with the substrate temperature at 550°C, the AsCl ₃ bubbler temperature maintained at 0°C, and the H ₂ gas flow rate at 100 ml/min. At this time, 249 nm light with an intensity of 3 W from an excimer laser was introduced into the reaction tube through the light introduction window. As a result of 2 hours of growth,
A GaAs single crystal with a thickness of 4 μm was grown on the substrate. The carrier density of the crystal thus obtained was 1×10 ¹³ cm ⁻³ .

In addition, FIG. 5 shows a device in which the direction of light introduction is changed to the direction perpendicular to the gas flow direction in the device shown in FIG. When this process was carried out, completely similar crystals were obtained.

Furthermore, FIG. 6 shows that in the apparatus shown in FIG.
The structure is such that the light introduction window is drawn out from the reaction tube main body, and it is possible to prevent the irradiated light from being attenuated due to adhesion of reaction products to the light introduction window.

Effects of the Invention As described above, according to the present invention, there is no need to heat to the high temperatures conventionally required for hydrogen reduction of AsCl ₃ , the temperature of the entire reaction tube etc. can be lowered, and high purity GaAs monomers can be produced. The epitaxial growth of crystals becomes easier, and its industrial effects are significant.

[Brief explanation of drawings]

Figure 1 shows the change in the absorption spectrum when a mixed gas of AsCl ₃ and H ₂ is irradiated with light.
AsCl ₃ B shows the absorption spectrum of HCl. FIG. 2 is a diagram showing the temperature dependence of hydrogen reduction of AsCl ₃ . FIG. 3 is a diagram showing the wavelength dependence of hydrogen reduction of AsCl ₃ by light irradiation. FIG. 4 is a diagram schematically showing a growth apparatus according to one embodiment of the present invention, FIG. It is a figure which shows the modification of a figure. 1...Light introduction window, 2...Quartz reaction tube, 3...
Ga source, 4...GaAs crystal substrate, 5...Electric furnace, 6...Irradiation light source, 7...Flowmeter, 8...Thermostatic chamber, 9...AsCl ₃ bubbler.

Claims (1)

[Claims] 1. AsCl ₃ vapor and hydrogen gas are used as Ga source or
By introducing a Ga source or a GaAs solid source saturated with As to cause a reaction, and supplying the gas generated by this reaction to the surface of a substrate crystal installed downstream of the source, 1. A method for producing a GaAs single crystal, which comprises promoting the hydrogen reduction reaction of AsCl ₃ by irradiating light when epitaxially growing the GaAs single crystal. 2. The method for producing a GaAs single crystal according to claim 1, wherein the irradiated light has a wavelength shorter than 300 nm.