JPH07247196A - Method for growing crystal of compound semiconductor - Google Patents

Abstract

PURPOSE:To obtain a uniform crystal of a III-V compound semiconductor having a desired hole concentration by alternately feeding a gas containing a group V element and a gas containing a group III element, in either of which carbon is contained as an impurity, onto a substrate and vapor-growing the crystal. CONSTITUTION:This method for growing a crystal of a compound semiconductor is to prepare the first gas containing a group V element (e.g. As) and the second gas containing a group III element (e.g. Ga) as feed gases, add carbon as an impurity to either of the first and the second gases, e.g. use trimethylgallium as a raw material for the group III element, thereby comprise the carbon therein, then alternately feed the first and the second gases onto a substrate and vapor-grow the crystal of the compound semiconductor comprising the group V and III elements on the substrate. Accordingly, the carbon can uniformly be added at a desired concentration into the grown crystal with good controllability. As a result, the concentration of holes in the resultant crystal can uniformly be regulated to a desired value with the good controllability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crystal growth method for a III-V group compound semiconductor to which carbon is added as an impurity.

[0002]

2. Description of the Related Art I such as GaAs or AlGaAs
Carbon has attracted attention as an impurity that imparts p-type conductivity to II-V group compound semiconductors. Carbon has a characteristic that it has a small diffusion constant and can be doped at a high concentration, and is extremely excellent in practical use. For example, carbon-doped GaAs and AlGaAs are AlGaA
s / GaAs heterojunction bipolar transistor (H
It is widely used for the base layer of BT).

Conventionally, as a carbon doping method for GaAs, a method of using an alkyl group in the gas raw material of the base material as a carbon source has been widely used in the GaAs crystal growth by the MOCVD method. For example, by MOCVD, G
When aAs is crystal-grown, trimethylgallium (TMG) is used as a group III raw material, and arsine (AsH ₃ ) is used as a group V raw material.

At this time, by lowering the supply amount ratio (V / III ratio) of the group V source gas to the supply amount of the group III gas, the carbon in the methyl group bonded to the gallium atom in trimethylgallium becomes the carbon source. As a result, it becomes possible to dope carbon into the growing crystal. Also, V / I
It is also possible to change the II ratio to control the hole concentration due to carbon doping.

In this method, as shown by the curve 21 in FIG. 3, the hole concentration greatly depends on the V / III ratio.
It is considered that this is due to the following reasons. Since arsine has a high decomposition temperature, it reaches the substrate surface in the gas phase without being decomposed. Arsine reaching the substrate surface without being decomposed is decomposed on the substrate surface at a high temperature, and hydrogen radicals are generated on the substrate due to the decomposition of arsine.

The generated hydrogen radicals dissociate the methyl group (carbon source) bonded to the gallium atom in the trimethylgallium supplied at the same time from the gallium atom, and at the same time, bond to methane to become methane, and become methane. Dissociate. Since the methyl group in trimethylgallium serves as a carbon source for doping, if it diffuses into the gas phase as described above, the carbon source for doping will be lost.

As the V / III ratio increases, the amount of arsine relatively increases, so that the generation of hydrogen radicals increases on the substrate, and as a result of the above, the methyl group as a carbon source decreases. Then, it is considered that the hole concentration is reduced due to the reduction of carbon incorporation into the vapor-grown solid phase. Further, as the V / III ratio increases, the amount of As produced on the substrate also increases, as described above, and the As coverage ratio on the substrate surface increases. For this reason,
It is also conceivable that the number of sites where carbon is taken in is reduced, and thus carbon is suppressed from being taken into the solid phase and the hole concentration is decreased.

As described above, when carbon is doped while GaAs is vapor-grown by the MOCVD method, by changing the V / III ratio in the supply of the source gas, the vapor-phase-grown solid phase is changed. It is possible to change the hole concentration. However, as shown by the curve 21 in FIG. 3, since the V / III ratio dependency of this hole concentration is large,
There is a problem that the hole concentration is sensitive to the disturbance and distribution of the flow rate of the supplied source gas, and the controllability of the concentration and the in-plane uniformity of the substrate are poor.

On the other hand, as described above, V in vapor phase growth
A method using trimethylarsine as a group raw material has been reported (TF Kuech, MATischler, P.-J. Wang, G. Sci.
lla, R. Potemski and F. Cardone, Appl. Phys. Lett. 53 (198
8) 1317). According to this method, as shown by the curve 22 in FIG. 3, compared with the case where arsine is used, the hole concentration can be made higher at the same growth temperature and V / III ratio. There is. Further, since the hole concentration has a low dependency on the V / III ratio, the hole concentration is excellent in the uniformity of the hole concentration in the surface of the substrate on which the crystal is grown.

This can be considered as follows. Trimethylarsine does not generate hydrogen radicals when decomposed. Therefore, unlike the case where arsine is used as the group V raw material, there is no inhibition of carbon uptake by hydrogen radicals. Further, since trimethylarsine has a low decomposition temperature, the As coverage ratio on the substrate surface is almost saturated in the normal V / III ratio range, and this does not depend on the V / III ratio. Therefore, it is considered that the number of sites where carbon is taken in does not depend on the V / III ratio, and consequently the hole concentration does not depend on the V / III ratio.

[0011]

Since the conventional structure is as described above, when arsine is used as the group V raw material,
As mentioned above, the hole concentration can be changed,
There is a problem in that the controllability and variations are not good. On the other hand, when trimethylarsine is used as the group V raw material, the variation in hole concentration can be reduced,
Since the V / III group dependency is low, there is a problem that the hole concentration cannot be varied and a desired hole concentration cannot be obtained.

The present invention has been made to solve the above problems, and an object thereof is to obtain a desired hole concentration with good controllability and uniformity.

[0013]

The compound semiconductor crystal growth method of the present invention comprises a first gas containing a group V element and III.
A second gas containing a group element is alternately supplied to vapor-deposit a carbon-doped compound semiconductor. In addition to the above, in the compound semiconductor crystal growth method of the present invention, the carbon added to the compound semiconductor is supplied by the carbon compound contained in the second gas, and the carbon is added to the first gas. It is characterized in that it is free of substances that form reaction products with compounds.

[0014]

By supplying alternately, the decomposition reaction of the supplied gas is suppressed, and the cause of inhibition of carbon doping generated by decomposition in the gas phase is suppressed. In addition, the hydrocarbon compound, which is a carbon supply source generated when the second gas is supplied, is not dissociated into the gas phase from the solid surface on the substrate.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. Here, an example will be described in which trimethylgallium is used as a Group III raw material and carbon is doped into the GaAs layer to be formed. FIG. 1 shows a hole concentration and V for explaining a crystal growth method of a compound semiconductor according to one embodiment of the present invention.
It is a correlation diagram which shows the relationship with the / III ratio. In the figure, 1 is a curve showing the correlation between the V / III ratio and the hole concentration according to the present invention, and the growth temperature is 525 ° C. Others are the same as in FIG. 3, and V / I in the conventional method is used.
It shows the correlation between the II ratio and the hole concentration.

In this embodiment, one of the points is as follows. First, in vapor phase growth, trimethylarsine is used as a group V source gas, and, for example, trimethylgallium is used as a group III source gas.
The group raw materials are supplied alternately. As a result, first, the decomposition reaction of trimethylarsine in the gas phase is suppressed, and trimethylarsine is supplied onto the substrate without decomposition. As a result, the As coverage rate on the substrate surface is lowered so that the As coverage rate depends on the V / III ratio of the raw material to be supplied. This is because the efficiency of carbon incorporation into the vapor-grown crystal is considered to depend on the As coverage as described above.

Another point is that trimethylarsine is used. By this,
Unlike the conventional case, hydrogen radicals are not generated by the decomposition of the supplied group V raw material. Therefore, at the stage of supplying trimethylgallium, which is a Group III raw material, the methyl group does not become methane and dissociate in the gas phase.

Here, if the group III and V source gases are alternately supplied, each of them is naturally supplied individually. Compared to the case where both are supplied simultaneously as in the conventional case, when each is supplied alone, the decomposition reaction of the supplied source gas is suppressed. Conversely, for example, it has been reported that trimethylarsine promotes decomposition in the atmosphere in which trimethylgallium exists (SHLi, CALarsen and GBStringfello
w, J. Cryst. Growth, 102 (1990) 114). Therefore, by supplying alternately, the source gas reaches the substrate surface almost undecomposed even under a predetermined temperature condition in a range where vapor phase growth can be performed.

As described above, since the raw material gas trimethylarsine reaches the substrate surface without being decomposed, trimethylarsine is decomposed only on the substrate surface, and As produced by decomposition is generated. The amount of can be reduced. As a result, the coverage of As can be lowered, and this can be made dependent on the V / III ratio.

As described above, since the As coverage depends on the V / III ratio, the number of sites where carbon is incorporated depends on the V / III ratio, and as a result, the hole concentration becomes V / III. It becomes possible to make it depend on the III ratio. Further, in this case, since trimethylarsine is used as the group V raw material, there is no influence of hydrogen radicals, and thus the hole concentration can be gently dependent on the V / III ratio.

FIG. 2 is a distribution diagram showing the state of the hole concentration distribution in the substrate. In the figure, 2 is a curve showing the hole concentration distribution in the carbon-doped GaAs layer according to the present invention, and 3 is the hole concentration in the carbon-doped GaAs layer formed by using arsine as a group V raw material as in the conventional case. It is a curve shown. Regardless of the growth conditions, the growth temperature is 500.
C, V / III ratio is 3. Further, in the film formation according to the present invention shown by the curve 2, the supply flow rate of trimethylgallium is 4.0 × 10 ⁻⁵ mol / min, and the supply amount of trimethylarsine is 12.0 × 10 ⁻⁵ mol / min. The switching cycle of these supplies was set to 1 second.

GaA formed by the conventional method of FIG.
As is clear from the curve 3 showing the hole concentration distribution in the s layer, the hole concentration changes by about 50% when the position of 60 mm is different in the wafer on which the GaAs layer is formed. On the other hand, in the curve 2 according to the present invention, 60 mm in the wafer
Even if the position is different, the change in hole concentration is small, ± 4%
It fits within. As described above, according to the present invention, it is possible to improve the variation in hole concentration in the plane of the substrate on which the film is formed by one digit as compared with the conventional case.

By the way, in the above embodiment, the growth temperature is set to 5
Although the temperature is set to 00 ° C and 525 ° C, the present invention is not limited to this.
In the range of 00 to 550 ° C, the same effect can be obtained. When grown at a temperature higher than 550 ° C., even if the method of the present invention is used, the decomposition of trimethylarsine proceeds, so that the effect of the present invention becomes small. That is, the hole concentration in the growing crystal becomes less dependent on the V / III ratio. Further, when the crystal is grown at a temperature lower than 500 ° C., the crystal growth mode becomes a so-called reaction rate-determining mode, and the hole concentration also becomes less dependent on the V / III ratio.

Further, in the present invention, the most effect is obtained when the V / III ratio is in the range of 1-30. For example, in the above example, when the V / III ratio is less than 1, the desorption of As from the solid phase surface where the crystal is growing becomes remarkable. Therefore, it becomes difficult to obtain a good surface morphology of the growing crystal, and a crystal in a good state cannot be obtained.

Further, when the V / III ratio exceeds 30, as a result, the As coverage ratio on the substrate surface becomes saturated, so that the hole concentration becomes V / I as described above.
It becomes almost independent of the II ratio. In the above embodiment, the supply flow rate of the group V raw material was set to be three times the supply flow rate of the group III raw material, and the supply was switched every one second.
The supply time is not limited to this, and the V / III ratio may be set in the range of 1 to 30.

[0026]

As described above, according to the present invention, in the vapor phase growth of a III-V group compound semiconductor, when carbon is simultaneously added as an impurity, carbon is grown to a desired concentration uniformly with good controllability. It can be added into the crystal. As a result, the concentration of holes in the crystal can be made uniform to a desired value with good controllability.

[Brief description of drawings]

FIG. 1 is a correlation diagram showing a relationship between a hole concentration and a V / III ratio for explaining a crystal growth method of a compound semiconductor which is an embodiment of the present invention.

FIG. 2 is a distribution diagram showing a state of a hole concentration distribution in a substrate.

FIG. 3 is a correlation diagram showing a relationship between a hole concentration and a V / III ratio in a conventional example.

[Explanation of symbols]

 1, 2, 3, 21, 22, ... Curves.

Claims (4)

[Claims] 1. A state in which a first gas containing a group V element and a second gas containing a group III element are used as supply gases, and carbon contained in the first gas or the second gas is added as an impurity. In the crystal growth method of a compound semiconductor, which comprises forming a compound semiconductor composed of the group V element and the group III element on a substrate by vapor phase growth, supplying the first gas and the second gas alternately. Characteristic compound semiconductor crystal growth method. 2. The crystal growth method for a compound semiconductor according to claim 1, wherein the carbon added to the compound semiconductor is supplied by a carbon compound contained in the second gas, and the carbon added to the first gas is A method for growing a crystal of a compound semiconductor, which is free of a substance that forms a reaction product with a carbon compound. 3. The compound semiconductor crystal growth method according to claim 2, wherein the first gas is trimethylarsine. 4. The compound semiconductor crystal growth method according to claim 1, wherein the supply amount ratio of the first gas to the second gas is 1 to 3.
0, and the growth temperature is set to 500 to 550 ° C., The crystal growth method of the compound semiconductor.