JPH09320969A - Formation of gaas layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide formation of a GaAs layer which dopes carbon and indium into a GaAs layer at a temperature, e.g. about 600 deg.C, appropriate for forming the GaAs layer using an organometal vapor growth method. SOLUTION: A GaAs layer, where carbon and indium are doped, is formed on a GaAs substrate by using the organometal vapor growth method, with halide carbon such as carbon tetrabromide (CBr4 ), carbon tetrachloride (CCl4 ) or carbon tetraiodide (ICl4 ), and organometallic indium such as trimethyl indium or ethyldimethyl indium, as dopant. Then, the halide carbon and organometallic indium as dopant are supplied, not simultaneously but alternately, at a growth temperature of at about 600 deg.C which is an appropriate temperature for GaAs deposition.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an improvement in a method for forming a GaAs layer. In particular, in the temperature range suitable for forming a GaAs layer on a GaAs substrate by using the metal organic chemical vapor deposition method, both carbon and indium are reduced to G
It relates to an improvement making it possible to dope the aAs layer.

[0002]

2. Description of the Related Art In order to form a GaAs layer or an AlGaAs layer used for a hetero bipolar transistor or the like, a metal organic chemical vapor deposition method is preferably used.

By the way, using the metal organic chemical vapor deposition method,
To form a GaAs layer on a GaAs substrate by
It is known to have a degree. For example, carbon tetrabromide (C
Br _Four) As a dopant and GaA doped with carbon
The optimum temperature range for forming the s layer is 580 ° C to 650 ° C.
° C, collector of the hetero-bipolar transistor
Optimum temperature range for forming the GaAs layer used for the layer
Is 600 ° C to 650 ° C, and AlGaAs
The optimum temperature range for forming a layer is 650 ° C to 700 °
It is C.

Carbon having a small diffusion coefficient is preferably used as an impurity for forming a GaAs layer used as a base layer of a hetero bipolar transistor. And, in order to dope carbon, carbon tetrabromide (CB
A halogenated carbon such as r ₄ ) is used.

By the way, since a GaAs layer doped with carbon at a high impurity concentration of about 10 ¹⁹ cm ^-3 has a small atomic radius of carbon, a GaAs layer used for a collector layer of a hetero bipolar transistor or a hetero bipolar transistor. The lattice constant is smaller than that of the AlGaAs layer or the like used for the emitter layer. Therefore, when considering forming a heterobipolar transistor using the above base layer, collector layer, and emitter layer, in order to improve the reliability of this heterobipolar transistor, carbon used as the base layer is Doped G
It is desirable to increase the lattice constant of the aAs layer. To realize this purpose, it is known that it is effective to dope not only carbon but also indium having a large atomic radius into the GaAs layer.

In order to form a multilayer film while maintaining a good crystal state between layers, it is desirable to carry out the growth step continuously without interrupting the growth step between the layers. For that purpose, it is desirable that the growth process of each layer is performed at the same temperature and the growth temperature is not changed between the layers.

However, as described above, since the metal organic chemical vapor deposition method has an optimum temperature range, it is generally not easy to form a multilayer film at a constant growth temperature.

Further, if one layer is formed at a low temperature and then another layer is formed thereon at a high temperature, the lower layer formed earlier is eventually annealed, and the lower layer formed earlier is formed. The crystal quality may be adversely affected.

[0009]

In the above technical environment, trimethylgallium is used as a Ga source and arsine (A
GaAs layer doped with carbon and indium using an organometallic vapor phase epitaxy method in which sH ₃ ) is an As source, carbon tetrabromide (CBr ₄ ) is a carbon dopant, and trimethylindium is an In dopant. GaAs
An experiment for forming on a substrate was performed. At this time, the growth temperature was set to about 600 ° C., the gas arsine (AsH ₃ ) was allowed to flow from the beginning, and all other materials (trimethylgallium / carbon tetrabromide (CBr ₄ ) / trimethylindium) were used. The supply was started at the same time, and the supply was ended at the same time. The amount of trimethylindium supplied was increased to 2% over the stoichiometric composition, but indium was not incorporated into the formed GaAs layer. The reason for this is
Since the growth temperature is as high as about 600 ° C., trimethylindium reacts with carbon tetrabromide (CBr ₄ ) before being taken into GaAs, or indium adsorbed on the GaAs crystal surface is It is considered that this is because it is removed by etching.

Then, when the growth temperature was lowered to 550 ° C. and a similar experiment was conducted, it was confirmed that both indium and carbon were incorporated into GaAs.
The growth temperature of 50 ° C. was lower than the above-mentioned optimum temperature (the optimum temperature for depositing GaAs using the metal organic chemical vapor deposition method), and a GaAs layer with good crystal quality could not be formed.

An object of the present invention is to eliminate this drawback, and in a temperature range suitable for forming a GaAs layer using a metal organic chemical vapor deposition method, for example, about 600 ° C.,
It is an object of the present invention to provide a method for forming a GaAs layer, which makes it possible to dope the GaAs layer with both carbon and indium.

[0012]

The above-mentioned object is to supply carbon dopants such as carbon tetrabromide (CBr ₄ ), carbon tetrachloride (CCl ₄ ), carbon tetraiodide (ICl ₄ ), and the like. And indium dopants such as trimethylindium / ethyldimethylindium and other indium organometals are not simultaneously supplied, but they are alternately supplied, and carbon dopants such as carbon tetrabromide (CBr ₄ )・ Carbon tetrachloride (CCl ₄ ), carbon tetraiodide (ICl ₄ ) and the like react with indium dopants such as trimethylindium and ethyldimethylindium, and the indium adsorbed on the GaAs crystal formed is This is achieved by preventing it from being removed by etching.

More specifically, G according to the present invention
The aAs layer is formed by using a metal organic chemical vapor deposition method to form a GaAs layer doped with carbon and indium on a GaAs substrate. Carbon dioxide (CBr ₄ ), carbon tetrachloride (CCl ₄ ), carbon tetraiodide (ICl ₄ ), and the organic metal of indium such as trimethylindium / ethyldimethylindium are used, and the growth temperature is GaAs deposition. The optimum temperature is about 580-650 ° C
That is, the carbon halide, which is a dopant, and the organometallic indium are to be supplied alternately instead of simultaneously.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a method of forming a GaAs layer according to two examples of an embodiment of the present invention will be described to further clarify the constitution of the present invention and its unique effect.

First Example See FIG. 1. Trimethylgallium was used as a Ga source, and arsine (As
H ₃ ) as an As source, carbon tetrabromide (CBr ₄ ) as a carbon dopant, and trimethylindium as an indium dopant, using a metal organic chemical vapor deposition method at a growth temperature of 600 ° C. Was formed. At this time, as shown in the raw material supply diagram of FIG. 1, trimethylindium and carbon tetrabromide (CBr ₄ )
And were alternately supplied for 5 seconds so as not to mix with each other.

In other words, an indium-doped GaAs layer initially containing 4% indium and having a thickness of 5 nm is formed, and then carbon is contained at 4 × 10 ¹⁹ cm ^-3 and having a thickness of 5 nm. The step of forming a certain carbon-doped GaAs layer was repeated 50 times so that the total thickness became 0.5 μm. As a result, a layer equivalent to a GaAs layer containing 2% indium and simultaneously containing carbon in 2 × 10 ¹⁹ cm ⁻³ was formed.

The formed crystal was measured for indium concentration and carbon concentration by using an X-ray two-crystal method for indium concentration and a hole measuring method for measuring hole concentration for carbon concentration. As a reference example, under the same conditions, the growth temperature is lowered to about 550 ° C., and a GaAs layer is formed according to a conventional technique of forming a GaAs layer while simultaneously doping a carbon dopant and an indium dopant.
Carbon-doped Ga performing method of forming aAs layer
An As layer and an indium-doped GaAs layer were formed, and indium concentration and carbon concentration were measured in the same manner as above. The results are shown together in Table 1.

[0018]

[Table 1] The indium concentration and carbon concentration contained in the GaAs layer formed by performing the GaAs layer forming method according to the present embodiment and the GaAs layer forming method according to the reference example (prior art) are used. Indium concentration and carbon concentration contained in the formed GaAs layer Reference example of the present embodiment (prior art) Indium concentration 1.5% 4% Carbon concentration 2 × 10 ¹⁹ cm ⁻³ 4 × 10 ¹⁹ cm ⁻³ Clear from Table 1 As described above, the GaAs according to the present embodiment
It was confirmed that the GaAs layer formed by carrying out the layer forming method is almost equivalent to the expected concentration of indium and codoped with carbon.

The crystal quality of the GaAs layer formed by performing the method for forming a GaAs layer according to the present embodiment is determined by the mobility of hole measurement, the emission wavelength of photoluminescence, the emission intensity of photoluminescence, and the full width at half maximum. Was inspected. As a result, the former two (the mobility of the hole measurement and the emission wavelength of the photoluminescence) are significant as compared with the case of the conventional technology (the method of forming the GaAs layer in which the growth temperature is lowered and the indium and carbon are simultaneously doped). Although no difference was observed, the latter two (photoluminescence emission intensity and full width at half maximum) were obviously of high quality in the present embodiment.

Furthermore, a GaAs-based heterobipolar transistor having a GaAs layer as a base layer according to the present embodiment was manufactured. The method of forming a GaAs layer according to the prior art (the growth temperature is lowered and indium and carbon are simultaneously formed). Method of forming GaAs layer for doping)
The performance was higher than that of the hetero bipolar transistor using the aAs layer as the base layer.

Second Example See FIG. 2, as shown in the raw material supply diagram of FIG. 2, except that a non-supply period of about 1 second is provided between the supply period of the indium dopant and the supply period of the carbon dopant. Growth was carried out under exactly the same growth conditions as in the case of the first example. The results are shown in Table 2 together with the results of the reference example.

[0022]

[Table 2] The indium concentration and carbon concentration contained in the GaAs layer formed by performing the GaAs layer forming method according to the present embodiment and the GaAs layer forming method according to the reference example (prior art) are used. Indium concentration and carbon concentration contained in the formed GaAs layer Reference example of the present embodiment (prior art) Indium concentration 1.9% 4% Carbon concentration 1.9 × 10 ¹⁹ cm ⁻³ 4 × 10 ¹⁹ cm ⁻³ Table 2 As is clear from the above, in the case of the second example, it is clear that the indium concentration is closer to the expected value.

The reason for providing the non-supplying period in this embodiment is to prevent indium and carbon (dopant) from being mixed in the growth apparatus. As a result of providing the non-supply period, the reaction between indium and carbon is suppressed, and the indium uptake efficiency is better than in the case of the first example. The non-supply time is effective for about 0.5 seconds, but if it is too long (5 seconds or more),
Since the supply of the dopant will be insufficient, about 1 to 2 seconds is optimal.

In the above examples, carbon tetrabromide (CBr ₄ ) is used as the carbon dopant and trimethylindium is used as the indium dopant, but this is one example, and ethyldimethyl is used as the indium dopant. Indium and other organic metals such as indium can be used, and carbon tetrachloride (C
Cl ₄ ). Carbon tetraiodide (ICl ₄ ) and other halogenated carbon can be used.

In the above example, the indium-doped or carbon-doped GaAs layer has a thickness of 50.
Although it is set to nm, this is also an example, and it is possible to form a film in a thinner range than this. That is,
It can be a monoatomic layer. Furthermore, the thickness of the indium-doped GaAs layer and the carbon-doped G
Although the thickness of the aAs layer is the same, the thickness is not necessarily the same.

[0026]

As described above, the Ga according to the present invention
In the method of manufacturing an As layer, a metal halide vapor phase growth method is used to form a GaAs layer doped with carbon and indium on a GaAs substrate. Carbon bromide (CB
r ₄ ) ・ Carbon tetrachloride (CCl ₄ ) ・ Carbon tetraiodide (IC
l ₄ ) and the like and an organic metal of indium, for example, trimethylindium / ethyldimethylindium,
The growth temperature is about 600 ° C which is the optimum temperature for GaAs deposition.
Since it is said that the carbon halide, which is a dopant, and the organic metal of indium are supplied alternately, not at the same time, a temperature suitable for forming the GaAs layer by using the metalorganic vapor phase epitaxy method. Range eg 600 °
In C, both carbon and indium are GaAs
It is possible to dope the layer.

[Brief description of drawings]

FIG. 1 is a raw material supply diagram according to the gist of a method for forming a GaAs layer according to a first example of an embodiment of the present invention.

FIG. 2 is a raw material supply diagram relating to the gist of the method for forming a GaAs layer according to the second example of the embodiment of the present invention.

Claims (2)

[Claims] 1. A GaAs layer doped with carbon and indium is deposited on a GaAs layer using a metal organic chemical vapor deposition method.
In the method for forming on an aAs substrate, a GaAs layer is formed by using carbon halide and an indium organometal as a dopant, and alternately supplying the carbon halide and the indium organometal. Method. 2. The carbon halide is carbon tetrabromide, carbon tetrachloride, or carbon tetraiodide, the organic metal of indium is trimethylindium or ethyldimethylindium, and the growth temperature is About 580
The temperature is 650 ° C. and the Ga according to claim 1.
Method of forming As layer.