JPS6148917A - Forming method of selective pope-hetero structure of group iii-v compound semiconductor - Google Patents

Abstract

PURPOSE:To decrease remarkably concentration of carbon acceptor in a semiconductor layer containing Al, and to improve two dimensional electron gas mobility by using triethyl-aluminum as material for forming a semiconductor layer contain Al. CONSTITUTION:By an organic metal pyrolysis vapor-phase growth method, a selective dope GaAs/n-Al0.3Ga0.7As hetero structure consisting of semiconductor GaAs, a high fineness GaAs layer of the first andoped layer, the second andoped Al0.3Ga0.7As layer and the third Si doped n type Al0.3Ga0.7As layer, are formed. At this time, triethyl-aluminum is used as Al material of the second or third layer. As the result, two-dimensional electron gas mobility increases remarkably in lower temperature region tank 77K which Culomb scattering by ionized impurity comes to be dominant.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for forming a selectively doped heterostructure of a III-V compound semiconductor having higher electron mobility. The present invention relates to a method of forming a selectively doped heterostructure to obtain said structure.

Conventional technology Recently, chemical vapor deposition (MOC) using organometallic compounds has been developed.
VD) has attracted attention, and this method is excellent as a technology for forming multilayer epitaxial layers of compound crystals and solid solutions.
-It has been applied to the production of group compound semiconductors, etc. ■
Since all alkylated products of group elements are liquids with relatively high vapor pressure near room temperature, carrier gas such as H
It is easily gasified by bubbling etc. with 2, etc.
It can be advantageously used in the MOCVD method.

In this MOCVD method, the component elements to be grown and impurities can be supplied to the reactor as gases, and the properties of the growth layer can be easily controlled by switching valves and controlling the gas flow rate, and the composition and impurity concentration can be easily controlled. When changing the temperature, it is easy to replace the gas in the reactor, so the composition and impurity distribution can be made steep, and since only the substrate area needs to be heated uniformly, the equipment configuration can be simplified, making it possible to grow on large-area substrates. The crystal growth reaction proceeds thermally, allowing for heteroepitaxial growth on different types of substrates.Furthermore, since no halides are used, there is no possibility of autodoping, etc. that occurs when the substrate is etched. It has various advantages such as no fear.

The MOCVD method can be carried out using, for example, an apparatus configured as shown in FIG. The device includes a reactor 1 such as a quartz tube, a susceptor 3 made of carbon, for example, which is installed inside the reactor 1 to support a substrate 2 and to heat only the substrate, and a susceptor 3 made of carbon, which is installed outside the reactor 1. The reactor 1 is mainly composed of a high-frequency coil 4 as a heating means surrounding the reactor 1, and is further connected to a raw material introduction pipe system 5 and an exhaust pipe 6. For example, when growing a GaAs epitaxial layer for simplicity, ASH
37, Ga(CH3)* 8 and a dopant 9 (e.g. diethylzinc) and as carrier gas e.g.
Ga (CH3) 3
GaAs is formed according to the reaction +AsH3-GaAs+ 3 CH4 and grows on the substrate.

The flow rate of each raw material must be precisely controlled, and a mass flow controller device 11 or the like is used for this purpose. Further, since organic metals are generally liquid at room temperature, it is necessary to heat and control the temperature, and for example, a water jacket 12 equipped with a thermostat is used.

On the other hand, the requirements for transistors, integrated circuits, etc. have become increasingly sophisticated in recent years, and there is a trend towards higher frequencies and faster operation. Semiconductors suitable for high-speed, high-frequency devices must have high electron mobility and high saturation drift velocity. I-
BACKGROUND ART Group V compound semiconductors, such as GaAs, have attracted attention because they have higher electron mobility and saturation drift velocity than Si, and active research is being conducted.

Among these, by artificially producing various semiconductor mixed crystals, it is possible to obtain a heterojunction that can achieve lattice matching between different semiconductor crystals. For example, GaAs and IxGa
It is known that the lattice mismatch between +-x and S is 0.1% or less, and that there is almost perfect lattice matching between InP and Gaxin+-xAsyP ly.

Such heterojunctions can be used for ultrahigh-speed devices such as high electron mobility transistors and LDs that utilize modulation doping.
A variety of optoelectronic devices centered on , and electron-blocking devices such as multi-quantum well lasers that utilize superlattice structures are being developed.

Among the conventional selectively doped heterostructures of ■-■ group compound semiconductors, the most practical selectively doped GaAs/n-Al0.
3Ga0. When growing the Js heterostructure by the MOCVD method, the organic metals used include trimethylgallium (Ga(CH3)3), trimethylaluminumΔ1(CH3),
3) Trimethyl-based organic metals such as 3 were used.

However, in the GaAs epitaxial layer obtained using a trimethyl-based organometallic, carbon derived from the methyl group of the raw material trimethylaluminum molecule is affected by growth conditions (growth temperature, concentration ratio of arsine and group II organometallic) and Although it varies depending on the A1 composition of the AlGaAs layer, etc., 1
It was found that 017~10"m-' was also incorporated as an acceptor. Figure 4 shows selectively doped GaAs prepared by MOCVD using trimethyl organometallic as raw material.
/n-Al0. Ja0. A bandgap diagram of the Js heterostructure is shown.

As understood from this diagram, Si-doped n
Type Al0. aGa0. Js layer (3rd layer) and originally S1 doped n-type 8l0. 5Ga0. In the Js layer (third layer), an undoped layer 0.
,,Ga0. 7-A5tXi (second layer) also has IQ”~
As much as 10 cm-' of carbon acceptor is incorporated.As a result, due to the Coulomb interaction of this ionized carbon acceptor, Coulomb scattering by ionized impurities becomes dominant, as shown in Figure 5.77 The two-dimensional electron gas mobility in the low temperature region below is 40.0
It remained at a low value of 00 to 50.000 clTl/V, sec.

Similarly, selectively doped Ina using methyl organometallic,
s, Gaa-47AS/n IMa-ttln
0. Also in the 53AS heterostructure, Si-doped n
fiAlo-<tIn0. 53As layer and undoped Al0. The two-dimensional electron gas mobility remained at a low value due to the carbon acceptors incorporated into the 4tlna-53AS spacer layer.

Problems to be Solved by the Invention As described above, the MOCVD method has various advantages as described above, and can be applied to the production of various devices such as transistors and optoelectronic devices that have high-frequency and high-speed operation heterojunctions. However, traditional methods are insufficient,
There is still much room for improvement. That is, the carbon derived from the methyl group of the methyl-based organometallic used in the MOCVD method is converted into an undoped phase that is supposed to weaken the Coulomb interaction between the ionized Si donor and the two-dimensional electron gas in the Si-doped n-type epitaxial layer. It was taken in as an acceptor and became a factor that lowered the mobility of the two-dimensional electron gas.

For example, in the above-mentioned example, when a donor is added (modulation doping) only to GaAlAs1 in the superlattice structure in which ultrathin films of GaAs and GaAlAs are grown in layers, the donor is ionized and the generated electrons are accumulated in GaAs.

As a result, the electrons in GaAs are spatially separated from the ionized donors that serve as scattering sources, reducing Coulomb scattering and ensuring high mobility. High mobility transistor (HEM) applying the transfer i[ilJ layer to a field effect transistor
T), depletion type HEMT, enhancement type HEMT, and other devices will be increased by one.

However, for this purpose, it is necessary to develop a method that can advantageously prevent the carbon acceptor originating from the methyl group of the methyl-based organometallic from being incorporated into the undoped layer in the MOCVD method.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to eliminate the drawbacks of the conventional methods and provide a method for forming a selectively doped heterostructure of a ■-■ group compound semiconductor that provides high electron mobility. , with a selectively doped heterojunction -
It is also an object of the present invention to provide a V-group compound semiconductor device.

Means for Solving the Problems In view of the above-mentioned current state of formation of high mobility or superlattice type ■-V group compound semiconductor selectively doped heterostructures by MOCVD method, the present inventors have solved the above-mentioned drawbacks. As a result of various studies and studies, it has been found that using an ethyl organic metal instead of a methyl organic metal as a component for thin film crystal growth is extremely effective in achieving the above object. The present invention was completed based on such new findings.

That is, the present invention introduces an alkylated product of a group (1) element and a hydride of a group (2) element as a gas into a crystal growth reactor, and performs a thermal decomposition reaction of the gas on a heated substrate provided in the reactor. The present invention provides a method for forming a selectively doped heterostructure of a ■-■ group compound semiconductor by MOCVD, in which the reaction product is grown on a substrate. be.

Heterostructures contemplated by the present invention include, for example, semi-insulating GaA
s substrate, an undoped high purity GaAs layer as a first layer, an undoped AI0.3Ga0. 7A8 layer and a third layer of Si-doped n-type Al0. 3Ga0. 7A
Selectively doped GaAs/n with three-layer structure with s-layer
-Al0. 3Ga0.7As heterostructure or semi-insulating 1nP substrate, first layer of 771-'-p high purity 1n0. 53Ga0. +7As layer and the second layer of undoped Al0. , tln0. 5nAS layer and the third
Si-doped n-type 8 to layer 0. 4tuna, 5jAS
Selectively doped In0. 53Ga
0. 47As/n-Al0. <71n0. 53A
s heterostructure, etc. In these heterostructures, the carrier concentration is generally in the range of 0.5-2XIO18am-3, and the thickness of the first layer is generally 0.5-1μm
The second tier is 50-250 people and the third tier is 0.05-0.1
It is within the range of 5 μm.

Semi-insulating GaAs or InP as a base is a semi-insulating GaAs or InP with a large bandgap and Cr, ○, F.
It can be obtained by adding an impurity such as e to create a level in the center of the forbidden body, or it can also be obtained by using a native defect that creates a deep level.

The formation of these heterostructures can be carried out, for example, by using the apparatus shown in FIG. 1 with some modifications depending on the number of raw materials. In this case, in particular triethylaluminum is used as the aluminum raw material for the second and/or third layer. Thermal decomposition proceeds irreversibly, for example, Ga(CH3)3+As H3-GaAs+3C
H4Al (C2H5) 3 +As H3-AIAs
+ 3 C'2 Hs AlGaAs Creation The main feature of the method of the present invention is the use of an ethylated compound of at least AI as the alkylated compound of the group Ⅰ element in the MOCVD method.

AI of 3 molecules of triethylaluminum Al (C2H5)
The bond energy of C bond (58Kcal 1 mol) is
Trimethylaluminum AI (CH3) *molecule (7
) AI C bond energy (66Kcal 1
mole) and is easily thermally decomposed. In addition, in the thermal decomposition of trimethylaluminum, aluminum carbide A14C
Although island by-products have been observed, in the case of triethylaluminum, no carbide by-products have been observed. In fact, using a combination of triethylgallium (C2Hs) , , Ga, ) ethylaluminum (C2H5) 3A1, or a combination of trimethylgallium (CH3) 3Ga and triethylaluminum (C2H5) 3A1, M
According to the secondary ion mass spectrometry (SIMS) method, the AlGaAs epitaxial layer obtained by the OCVD method has 1
Only about 015 to 1016 cm-3 of carbon is incorporated, and Al grown using trimethylaluminum
Compared to GaAs, carbon content is reduced by nearly two orders of magnitude.

Therefore, it became clear that trimethylaluminum was responsible for the significant uptake of carbon.

Thus, according to the feature of the present invention, the ionized S in the third layer is reduced based on the reduction in the amount of carbon taken up in the second layer.
The Coulomb interaction between the i donor and the two-dimensional electron gas is the second
The mobility of the two-dimensional electron gas in the low temperature region below 77, where Coulomb scattering due to ionized impurities becomes dominant, is significantly improved (see FIG. 3). Therefore, the heterostructure obtained by the method of the present invention is extremely suitable for application as various semiconductor devices that exhibit excellent performance in the following low temperature range, as well as Josephson devices that operate at liquid helium temperatures. . That is, for example, the aforementioned enhancement type H
When applied to EMT, etc., it is possible to significantly improve mutual inductance at low temperatures (ie, in the region below 77°C).

EXAMPLES Hereinafter, the method of the present invention will be explained in more detail according to Examples. However, the present invention is not limited in any way by the following examples.

In FIG. 2, using the apparatus shown in FIG. 1 according to the present invention,
Selectively doped G formed by MOCVD using trimethylgallium and triethylaluminum as organic metals
aAs/n Al0. 3Ga0. A bandgap diagram of the 7AS heterostructure is shown.

Here, the first undoped high purity GaAs layer is 0,
1 μm, and the undoped A of the second layer is 10. a
, Ga0. The tAs layer has 200 people, and the third layer Si
Doped n-type Al0. 3Ga0. 7As layer is 1000
It was A. In addition, the formation conditions for these layers are growth temperature 6
50°C, growth rate 1.5 people/sec.

And so.

When the amount of carbon incorporated into the betaro structure thus prepared was measured by two-dimensional ion mass spectrometry (SIMS), it was found that Si-doped n-type Al0. 3Ga0. Js layer and undoped Al0. 3Ga0. Although 1015 to 1016 cm-3 of carbon acceptor is incorporated into the Js spacer layer, the carbon uptake is nearly two orders of magnitude lower than when trimethylaluminum is used.
The Coulomb interaction of the ionized carbon acceptor on the two-dimensional electron gas is significantly smaller. As a result, as shown in FIG. 3, the two-dimensional electron gas mobility increases significantly in the temperature range below 77 K, where Coulomb scattering due to ionized impurities becomes dominant, and at a temperature of 77 K, the two-dimensional electron gas mobility increases to 150,000. cnf/vsec, 450.000cnf/Vsec at a temperature of 2.

The value of was obtained. In FIG. 3, the two-dimensional electron gas mobility (cm''/Vsec, ) was measured according to a known method, ie, Van der Pauw's method.

Similarly, selectively doped In0. 53ca0
．． 47AS/n Al0. , tln0. 53
Also in the AS heterostructure, Si-doped n-type Al0.
4tln0. 53AS layer and undoped Al0.
<tln0. Due to the reduction of carbon acceptors in the sJs hexa layer, a significant increase in two-dimensional electron gas mobility was observed compared to the methyl-based case.

As described in detail of the invention, when growing a regressively doped heterostructure of a ■-■ group compound semiconductor by metal-organic pyrolysis vapor phase epitaxy,
By using triethylaluminum as a material for forming a semiconductor layer containing aluminum, it was possible to significantly reduce the concentration of carbon acceptors in the semiconductor layer containing aluminum. As a result, the two-dimensional electron gas mobility in the selectively doped heterostructure of the ■-■ group compound semiconductor is greatly improved, and the 15-characteristics of the field effect transistor using the selectively doped heterostructure of the ■-■ group compound semiconductor is significantly improved. was gotten.

[Brief explanation of the drawing]

FIG. 1 shows an MOCVD process useful in carrying out the method of the present invention.
FIG. 2 is a schematic diagram of a thin film forming apparatus by the method, and FIG. 2 shows a selectively doped GaAs/n-Al0. :+Ga0. 7As
Figure 3 shows the bandgap diagram of the heterostructure of GaAs/n'' obtained by the present invention.
81°, 5Ga0. 78S is a graph showing the temperature dependence of two-dimensional electron gas mobility in the heterostructure;
The figure shows a selectively doped GaAs/n-Al0. 3Ga0. Js
This shows the bandgap diagram of the heterostructure, and Figure 5 shows the GaAs/n structure obtained by the conventional method.
-Al0. 3Ga0. 2 in 7AS heterostructure
It is a graph showing the temperature dependence of dimensional electron gas mobility. (Main reference numbers) 1 Reactor, 2 Substrate, 3 Susceptor, 4 Heating means, 5 Piping system, 6 Exhaust pipe, ? --A s H3, 8 Organometallic, 9 Dopant, 10 H2, 11 Mass flow controller, 12 Walk jacket Patent applicant Nippon Telegraph and Telephone Public Corporation Representative Masahiko Arai Figure 2 Figure 3 Temperature (K)

Claims (2)

[Claims] (1) A group III element alkylate and a group V element hydride are introduced in a gaseous state into a crystal growth reactor, and the gases are subjected to thermal decomposition reaction on a heated substrate provided in the reactor. By metalorganic pyrolysis vapor phase epitaxy in which the reaction products are grown on the substrate, semi-insulating GaAs, the first layer of undoped high-purity GaAs, and the second layer of undoped Al_0
＿． _3Ga_0_. _7As layer and the third layer of Si-doped n-type Al_0_. _3Ga_0_. _3 with 7As layer
Selectively doped GaAs/n-Al_0_. with layer structure.
_3Ga_0_. The method for forming a 7As heterostructure, characterized in that triethylaluminum is used as an aluminum raw material for the second layer or the third layer.
A method for forming a selectively doped heterostructure of a II-V compound semiconductor. (2) A group III element alkylate and a group V element hydride are introduced in a gaseous state into a crystal growth reactor, and the gases are subjected to thermal decomposition reaction on a heated substrate provided in the reactor. A semi-insulating InP substrate and a first layer of undoped high-purity In_0_. _5_3-Ga_0_. ＿４
_7As layer and the second layer of undoped Al_0_. ＿４
_7In_0_. _5_3-As layer and the third layer of Si-doped n-type Al_0_. _4_7In_0_. _5_3A
Selectively doped In_0_. with a three-layer structure with an s layer. ＿５
_3Ga_0_. _4_7As/n-Al_0_. ＿４
_7In_0_. _5_3A method for forming an As heterostructure, characterized in that triethylaluminum is used as an aluminum raw material for the second layer or the third layer.
A method for forming a selectively doped heterostructure of a II-V compound semiconductor.