JPS61222217A - Molecular beam epitaxial growth - Google Patents

Abstract

PURPOSE:To execute growth at a low cell temperature without reducing the growing speed, by employing a plural of cells for a molecular beam of at least one of elements constituting compound semiconductor. CONSTITUTION:A plural of cells are employed for a molecular beam of at least one of elements constituting compound semiconductor. For example, an MBE apparatus which has several Ga cells 2 and several As cells 3 in a growth chamber evacuated into very high vacuum ( -10<10> Torr) and which has an introducing inlet 4 for H2 gas, is employed. Under a condition in which H2 gas with about (2-5)X10<-7> Torr is being introduced preliminarily in the growth chamber 1, heating every cell 2, 3 results in Ga and As molecular beams, which are bumped to a substrate 5 being heated preliminarily to a given temperature, thus to epitaxial-grow GaAs.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a molecular beam epitaxial growth method, which is most suitable for use in epitaxially growing various compound semiconductors such as GaAs.

, [Summary of the Invention] The present invention uses a plurality of cells to obtain a molecular beam of at least one of the constituent elements of a compound semiconductor to be grown in a molecular beam epitaxial growth method, thereby producing a compound semiconductor with extremely few surface defects. This makes it possible to grow compound semiconductors.

[Conventional technology]

Conventionally, GaAs crystals have been grown using the molecular beam epitaxial growth method (M
When growing by BE method), one Knudsen cell (hereinafter abbreviated as cell) was used as a molecular beam source for Ga and As.

[Problem that the invention seeks to solve]

In this case, in order to obtain a GaAs crystal layer with few surface defects, it is preferable to lower the temperature of both the Ga and As cells, but if the cell temperature is too low, the crystal growth rate may become extremely low. However, in severe cases, crystal growth may become impossible.

In view of the above-mentioned problems, it is an object of the present invention to provide a molecular beam epitaxial growth method that corrects the above-mentioned drawbacks of conventional molecular beam epitaxial growth methods.

[Means for solving problems]

In the molecular beam epitaxial growth method according to the present invention, when a compound semiconductor (e.g., GaAs) is epitaxially grown using a molecular beam, a plurality of molecular beams of at least one element (e.g., Ga) among the constituent elements of the compound semiconductor are grown. It is obtained by using cells (for example, three cells 2).

[Effect]

By doing so, it becomes possible to perform growth at a lower cell temperature without reducing the growth rate.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

As shown in Fig. 1, in this example, ultra-high vacuum (
Several Ga cells 2 and several As cells 3 (two of each are shown in FIG. 1) are provided in a growth chamber l which is evacuated to ~10" Torr, and an H2 gas inlet 4 is provided. Using the provided MBE device, inlet 4
H in advance (e.g. 2 to 3 hours before growth)
Molecular beams of Ga and As are obtained by heating each cell 2°3 while introducing two gases at approximately (2 to 5) 5 to epitaxially grow GaAs. The intensity of the molecular beam of As is
Growth is performed at, for example, about 10 times the intensity of the Ga molecular beam.

Such epitaxial growth of GaAs was performed while varying the temperatures of Ga cell 2 and As cell 3, and therefore the vapor pressures of Ga and As, and the surface defect density existing in the resulting GaAs crystal layer was observed by optical microscopy. Upon investigation, the results shown in Figures 2 and 3 were obtained. Furthermore, the second
In the figure and FIG. 3, the results obtained when growth was performed using one Ga or As cell are also shown for comparison.

As is clear from FIG. 2, whether one Ga cell 2 is used or three Ga cells 2 are used, the lower the vapor pressure of Ga, that is, the lower the temperature of the cell 2, the more the GaAs crystal layer Although the defect density inside is low, when three Ga cells 2 are used, a practically sufficient growth rate (1 μm/hour or more) can be achieved compared to when one Ga cell 2 is used. It can be seen that the defect density is extremely small even at a vapor pressure of about 1X10-'Torr or more required to obtain the same. This is the same value of G
a When obtaining the vapor pressure, it is better to use three Ga cells 2.
This is because the cell temperature can be lowered compared to the case where the actual Ga cell 2 is used. Note that from FIG. 2, the activation energy ΔE ~0.79 eV is obtained.

Furthermore, as is clear from Fig. 3, when one As cell 3 is used, the defect density increases as the vapor pressure increases, but when three As cells 3 are used, the defect density decreases. It is possible to increase the As vapor pressure while maintaining the same value.

Next, we measured the defect density in the GaAs crystal layer obtained when growth was performed by introducing H2 gas into the growth chamber 1 of the MBE apparatus and when growth was performed without introducing H2 gas. , the results shown in FIG. 4 were obtained.

As is clear from FIG. 4, when the growth is performed by introducing H2 gas into the growth chamber 1, the resulting GaAs crystal layer is smaller than when the growth is performed without introducing the H2 gas. Defect density has been reduced by almost half.

This is due to the following reasons. That is, the H2 gas introduced into the growth chamber 1 forms a reducing atmosphere near the cells 2 and 3, and therefore remains in the growth chamber 1. zo
, C0 molecules, etc. and Ga in cells 2 and 3.

The formation of oxides (e.g. Ga, O) due to oxidation reactions with As is prevented, and as a result, these oxides are mixed with GaAs during growth.
This is thought to be due to the fact that there is no possibility of contamination. As can be easily seen from this, it is actually sufficient to introduce H2 gas only in the vicinity of the Ga cell 2 and As cell 3.

In this way, according to the above embodiment, GaAs is epitaxially grown using several Ga cells 2 and several As cells 3, so that the surface defect density can be extremely low without reducing the growth rate. A GaAs crystal layer can be obtained. Furthermore, since the growth is performed with H2 gas introduced into the growth chamber 1 in advance, the defect density can also be reduced by this.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made based on the technical idea of the present invention.

For example, the number of Ga cells 2 and As cells 3 can be changed as necessary, and the pressure of Ht gas introduced into the growth chamber 1 can also be changed to a value different from that in the above embodiment as necessary. It can be used. Furthermore, a large diameter cell 2.3 can be used if necessary, and in this way the cell temperature can be further lowered. Further, in the above-mentioned embodiments, the case where the present invention was applied to the growth of GaAs was explained, but the present invention can also be applied to various compound semiconductors such as AJXGa, -, and As.

〔Effect of the invention〕

According to the molecular beam epitaxial growth method according to the present invention, since a plurality of cells are used to obtain a molecular beam of at least one of the constituent elements of the compound semiconductor to be grown, the growth rate cannot be reduced. The growth can be performed at a low cell temperature, and therefore a compound semiconductor with an extremely low defect density can be grown.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the MBE apparatus used in the examples of the present invention, and FIGS. 2 and 3 show the relationship between the vapor pressure of Ga and As and the defect density in the obtained GaAs crystal layer, respectively. The graph, Figure 4, shows the relationship between the vapor pressure of Ga and the defect density in the GaAs crystal layer when the growth was performed with H2 gas introduced into the growth chamber of the MBE apparatus and when the growth was performed without introducing H2 gas. It is a graph showing the relationship. In addition, in the symbols used in the drawings, 1----------------Growth chamber 2,
3------------Cell 5------
------------ It is a substrate.

Claims (1)

[Claims] When a compound semiconductor is epitaxially grown using a molecular beam, the molecular beam of at least one of the constituent elements of the compound semiconductor is obtained using a plurality of cells. Molecular beam epitaxial growth method.