JP2003124454A - Compound semiconductor epitaxial wafer and element using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable reduction of crystal defect of a conventional strain- relaxation buffer layer and a burden on a growing device in III-V compound semiconductor epitaxial wafer having an operative region where a substrate crystal and a grating constant are different equal to or greater than 0.15%. SOLUTION: In the III-V compound semiconductor epitaxial wafer having the operative region where the substrate crystal and the grating constant are different equal to or greater than 0.15%, the buffer layer 20 or 200 between the substrate and the operative region is provided with a crystal layer containing Al, Ga, In which has grown through MOVPE technique (ex. InAlGaAs quaternary mixed crystal 111, 121, 131, 141, 151 or 113, 123, 133, 143, 153) and a crystal layer containing Al, In from which difference in the grating constant is within 30% (ex. a layer of InAlAs ternary mixed crystal 112, 122, 132, 142, 152 or 114, 124, 134, 144, 154) in a pair or plural pairs, or in a state that the number of one layer is larger than that of the other.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a compound semiconductor epitaxial wafer and a device using the same.

[0002]

2. Description of the Related Art III-V group compound semiconductors have different band gaps depending on their materials, and devices utilizing hetero-physical properties which appear depending on their selection and combination are being utilized. Liquid phase epitaxial (LP
E) method, molecular beam epitaxy (MBE) method, metal organic vapor phase epitaxy (MOVPE) method and the like are known.

Here, the crystal lattice constants of the individual compounds of the materials are different, and when the epitaxial layer is grown, stress is generated due to lattice mismatch, warpage and distortion of the crystal lattice are generated, and various characteristics are deteriorated. Is well known. Only in the hetero system of GaAs / AlGaAs, the lattice constant difference (Δa / a) is as small as 0.14%, and the utilization is progressing over the entire range of the mixed crystal ratio. As a crystal, a crystal that is epitaxially grown only with a mixed crystal composition such as GaAs or InP that lattice-matches the substrate crystal is used. Therefore, the hetero-physical properties that can be used are very limited in terms of functionality and cost.

Therefore, in order to expand the range of application of the mixed crystal combination, various attempts have been made on material systems containing lattice distortion.

As a first example, a unipolar type electronic device represented by FET and HEMT is put into practical use. Since an InGaAs mixed crystal with excellent electron transport characteristics is used for this operating layer (channel layer),
A method of making a so-called pseudomorphic structure in which the lattice of the InGaAs layer is in a distorted state where lattice relaxation does not occur by making the In composition 0.2 or less and about 15 nm or less in a hetero system of / InGaAs / AlGaAs is put into practical use.

The second example is a system in which the lattice constants of the substrate crystal and the active layer are largely different, that is, the lattice constant of the substrate crystal is 0.1.
In a III-V group compound semiconductor epitaxial wafer having an operation region different by 5% or more, after the lattice relaxation is caused between the substrate crystal and the active layer (channel layer), the crystal through the buffer layer whose crystallinity is restored There is a growth method.
This buffer layer is called a metamorphic buffer layer (metamorphic buffer layer). The structure of the metamorphic buffer layer is such that the composition of the buffer layer between the crystal substrate and the active layer (channel layer) is gradually changed, or the composition is changed in a stepwise manner. Have been reported to reduce the effect of the.

A molecular beam epitaxial (MBE) method has been mainly used as a crystal growth method of the metamol buffer layer of the second example. The reason for this is that when the lattice strain is relaxed, it is necessary to grow at a low temperature centering on the relaxation point so as not to impair the orientation of crystal growth and surface flatness. This is because it is necessary to grow at a low temperature because it is difficult to obtain a flat thin crystal layer when three-dimensional growth occurs at a high temperature when crystal growth containing a large amount of the elements In and Ga is required.

Also in terms of purity, in order to obtain a high-purity compound semiconductor crystal by low-temperature growth, MB is a raw material of high-purity single-element metal, the atmosphere is ultra-high vacuum, and the crystal can be grown at a low temperature.
Method E has been used.

[0009]

However, the above-mentioned M
The BE method is highly safe for workers, but has a serious drawback as a production apparatus. That is, it takes a long time to perform maintenance for obtaining the ultra-high vacuum necessary for crystal growth, lack of stability of the apparatus against troubles, and the like.
Further, the group V raw material is practically limited to only As,
For example, the cost of the device will be extremely high for the realization of a large-area growth device.

On the other hand, regarding production, recently, metal-organic vapor phase epitaxial (MOVPE)
The phase epitaxy method has come into wide use. However, with respect to crystal growth including strain, the MOVPE method involves decomposition reaction of raw material organic substances and hydrides.
It was thought that the growth temperature was higher than that of the E method, and it was not suitable for the growth of the metamol buffer layer.

On the other hand, the present inventors have adopted InAlAs for the buffer layer, and found that a higher growth temperature gives a better surface depending on the growth conditions, and a good surface condition can be obtained. I've been doing so.

However, in the InAlAs ternary mixed crystal buffer layer, when the In composition is as low as 0.1, the remaining Al composition becomes as high as 0.9, and the durability to the process is high. There is a risk that the device will be lost or the reliability of the device will be reduced. Further, the growth conditions are very difficult for the MO growth apparatus, and the growth of the front and rear growth layers is also adversely affected.

Therefore, an object of the present invention is to solve the above-mentioned drawback of the conventional crystal of the strain relaxation buffer layer in the III-V group compound semiconductor epitaxial wafer having an operation region having a lattice constant different from that of the substrate crystal by 0.15% or more. The purpose is to reduce the load on the growth apparatus, and for that reason, to provide a strain relaxation buffer layer having good surface flatness and capable of low temperature growth.

[0014]

In order to achieve the above object, the present invention is configured as follows.

A compound semiconductor epitaxial wafer according to a first aspect of the present invention is a III-V compound semiconductor epitaxial wafer having an operation region having a lattice constant different from that of a substrate crystal by 0.15% or more, and a buffer between the substrate and the operation region. A layer having a crystal constant difference of 30% or less between the crystal layer containing Al, Ga and In grown by the MOVPE method and the layer.
It is characterized in that one set or a plurality of sets of crystal layers containing l and In are provided in a state where there are many layers.

According to the present invention, for example, in a III-V group compound semiconductor epitaxial wafer having an operating region having a lattice constant different from that of a substrate crystal by 0.15% or more, InAlGaAs quaternary mixed crystal and InAlA are used in all or part of the buffer layer.
One set or more sets of s3 ternary mixed crystals are alternately provided, whereby a structure having a strain relaxation buffer layer having good surface flatness and capable of low temperature growth is provided. Therefore, the field effect transistor (FET, HEMT
Etc.) or a compound semiconductor epitaxial wafer for a bipolar transistor (HBT etc.), it is possible to reduce the above-mentioned defects of the crystal of the strain relaxation buffer layer and the burden on the growth apparatus.

According to a second aspect of the invention, in the compound semiconductor epitaxial wafer according to the first aspect, the structure of the operation region is a structure of a field effect transistor or a bipolar transistor.

A compound semiconductor device according to a third aspect of the present invention uses the compound semiconductor epitaxial wafer according to the second aspect, and after subjecting the compound semiconductor epitaxial wafer to photolithography, etching, etc., an electrode is provided to the field effect transistor or the bipolar transistor. It is characterized by being configured as.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to illustrated examples.

(Embodiment 1) As a first embodiment of the present invention, the In composition of the InGaAs channel layer is 0.4 I.
The crystal growth of an HEMT epitaxial wafer having an nAlAs / InGaAs / InAlAs heterostructure is shown.

FIG. 1 is a schematic sectional view of a semiconductor epitaxial wafer having a HEMT structure. With the MOVPE device,
An undoped GaAs buffer layer 2 was grown to a thickness of 20 nm on a semi-insulating GaAs substrate 1 at a substrate temperature of 550 ° C.
_0.15 (Ga _0.5 Al _0.5 ) _0.85 As buffer layer 111 5
0 nm, followed by In _0.15 Al _0.85 As buffer layer 112
Of 50 nm, followed by In _0.23 (Ga _0.3 Al _0.7 ) _0.77 A
s undoped layer 121 to 50 nm, followed by In _0.23 Al
_0.77 As undoped layer 122 with 50 nm, In _0.30 (G
a _0.15 Al _0.85 ) _0.70 As undoped layer 131
m, In _0.30 Al _0.70 As undoped layer 132 to 50 n
m, In _0.35 (Ga _0.15 Al _0.85 ) _0.65 As undoped layer 141 at 50 nm, In _0.35 Al _0.65 As undoped layer 142 at 50 nm, In _0.40 (Ga _0.15 Al _0.85 ).
_0.60 As undoped layer 151 with 50 nm, In _0.40 Al
_0.60 As undoped cladding layer 152 with 100 nm, S
i-doped (doping concentration 5 × 10 ¹⁸ / cm ³ ) In
_0.40 Al _0.60 As carrier supply layer 21 with 5 nm, In
_0.40 Al _0.60 As spacer layer 22 of 2 nm, In _0.41 G
a _0.59 As channel layer 23 of 30 nm, In _0.40 Al
_0.60 As spacer layer 24 is 2 nm, Si-doped (doping concentration 5 × 10 ¹⁸ / cm ³ ) In _0.40 Al _0.60 As carrier supply layer 25 is 12 nm, In _0.40 Al _0.60 As undoped Schottky layer 26 is 30 nm, Si-doped (doping) Concentration 5 × 10 ¹⁸ / cm ³ ) In _0.41 Ga _0.59 As
To In _0.50 Ga _0.50 As with a contact layer 31 having a linear composition change of 50 nm, and Si-doped (doping concentration 5 × 10 ¹⁸ / cm ³ ) In _0.50 Ga _0.50 As
The contact layer 32 was epitaxially grown in order of 50 nm by MOVPE method.

In described above_0.15(Ga_0.5Al_0.5)_0.85
As buffer layer 111, In_0.15Al_0.85As buffer
Layer 112, In_0.23(Ga_0.3Al_0.7)_0.77As and
Layer 121, In_0.23Al_0.77As undoped layer 12
2, In_0.30(Ga_0.15Al _0.85)_0.70As undoped
Layer 131, In_0.30Al_0.70As undoped layer 132,
In_0.35(Ga_0.15Al_0.85)_0.65As undoped layer 1
41, In_0.35Al_{0. 65}As undoped layer 142, In
_0.40(Ga_0.15Al_0.85)_0.60As undoped layer 15
1, In_0.40Al_0.60As undoped cladding layer 152
Constitute the lattice-mismatched strain relaxation buffer layer 20.
It The strain relaxation buffer layer 20 has almost the same lattice constant.
A pair of InAlGaAs layer and InAlAs layer,
5 sets, and the In mixed crystal ratio of each set is set to semi-insulating GaAs.
0.15, 0.23, 0.30, 0.3 from the substrate 1 side
It is composed of gradually increased values of 5, 0.40. The film thickness is
Si-doped In_0.40Al_0.60As carrier supply layer 21
Immediately below In_0.40Al_0.60As undoped layer 152 is 10
Other InAlGaAs layers 11 except that the thickness is 0 nm
1, 121, 131, 141, 151 and InAlAs
The layers 112, 122, 132, 142 have the same 50 nm
It

With respect to the compound semiconductor epitaxial wafer having the strain relaxation buffer layer 20 composed of the lattice mismatched compound semiconductor multilayer thin film thus formed, the electrical characteristics of the semiconductor crystal having the HEMT structure are measured by the Hall effect measuring method. I asked. As a result, the electron mobility was 8.90.
The sheet carrier concentration was 0 cm ² / Vs, which was slightly smaller due to the influence of the n-GaAs layer as the underlayer, but the sheet carrier concentration could be significantly increased to 4.8 × 10 ¹² / cm ² .

In the above embodiment, I having almost the same lattice constant is used.
Although a total of five nAlGaAs layers and InAlAs layers have been described, a plurality of groups each having a plurality of nAlGaAs layers may be provided, and either of the layers may be large. The layer immediately below the spacer layer is preferably a ternary InAlAs layer having a large band gap, but InGaAlAs
It may be a layer.

(Embodiment 2) Next, as a second embodiment,
InG in which the In composition of the InGaAs channel layer is 0.4
aAs / InGaAs / InGaP H with heterostructure
The crystal growth of the BT epitaxial wafer will be described.

FIG. 2 is a sectional view of an epitaxial wafer having an HBT structure according to the second embodiment.

Semi-insulating GaAs by MOVPE device
An undoped GaAs buffer layer 2 was grown to a thickness of 20 nm on the substrate 1 at a substrate temperature of 550 ° C., and In _0.15 (Ga _0.5 Al _0.5 )
_0.85 As layer 113 of 100 nm, followed by In _0.15 Al
_0.85 As layer 114 of 100 nm, followed by In _0.23 (Ga
_0.3 Al _0.7 ) _0.77 As Undoped layer 123 100 n
m, followed by In _0.23 Al _0.77 As undoped layer 124 of 100 nm, In _0.30 (Ga _0.15 Al _0.85 ) _0.70 As undoped layer 133 of 100 nm, In _0.30 Al _0.70 As
The undoped layer 134 is formed with 100 nm, In _0.35 (Ga _0.15
Al _0.85 ) _0.65 As undoped layer 143 of 100 nm,
In _0.35 Al _0.65 As undoped layer 144 of 100 n
m, In _0.40 (Ga _0.15 Al _0.85 ) _0.60 As undoped layer 153 of 50 nm, In _0.40 Al _0.60 As undoped layer 154 of 100 nm, carrier concentration 5 × 10 ¹⁸ / cm ³
Of In _0.40 Ga _0.60 As subcollector layer 212 of
nm, carrier concentration 3 × 10 ¹⁶ / cm ³ In _0.40 Ga
_0.60 As collector layer 222 is 800 nm, p-type In _0.40 Ga _0.60 As base layer 223 having a carrier concentration of 4 × 10 ¹⁹ / cm ³ is 150 nm, carrier concentration is 5 × 10 ¹⁷ / cm 3.
³ of In _0.40 Al _0.60 As emitter layer 231 80n
m, carrier concentration 2 × 10 ¹⁸ / cm ³ of InAlAs cap layer 232 of 100 nm, doving concentration 5 × 10
¹⁸ / cm ³ of In _0.41 Ga _0.59 As to In _0.50 Ga
Contact layer 24 with composition changed linearly to _0.50 As
1 with 50 nm and a doping concentration of 5 × 10 ¹⁸ / cm ³
An n _0.50 Ga _0.50 As contact layer 242 was grown to a thickness of 50 nm.

In described above_0.15(Ga_0.5Al_0.5)_0.85
As layer 113, In_0.15Al_0.85As layer 114, In
_0.23(Ga_0.3Al_0.7)_0.77As undoped layer 123,
In_{0. twenty three}Al_0.77As undoped layer 124, In
_0.30(Ga_0.15Al_0.85)_0.70As undoped layer 13
3, In_0.30Al_0.70As undoped layer 134, In
_0.35(Ga _0.15Al_0.85)_0.65As undoped layer 14
3, In_0.35Al_0.65As undoped layer 144, In
_0.40(Ga_0.15Al_0.85)_0.60As undoped layer 15
3, and In_0.40Al_0.60The As undoped layer 154 is
The strain mitigating buffer layer 200 of the lattice mismatch system is formed.
It The strain relaxation buffer layer 200 has almost the same lattice constant.
The same InGaAlAs layer and InAlAs layer are combined as
Five sets of these are provided, and the In mixed crystal ratio of each set is set to semi-insulating GaA.
0.15, 0.23, 0.30, 0.
35, 0.40 and gradually increased. Film thickness
Is In_0.04Al_0.60Immediately below the As undoped layer 154
In_{0.40 (Ga0.15Al0.85) 0.60}As undoped layer 153
Other InAlGaAs layers 1 except 100 nm
13, 123, 133, 143, and InAlAs layer 1
14,124,134,144,154 are the same 100n
m.

The In composition of the npn interface of the hetero-bipolar transistor of this embodiment was designed to be 0.40, but any In composition provided the effect of the present invention.

Next, the HEMT and HBT devices manufactured by using the compound semiconductor epitaxial wafers according to the first and second embodiments and subjecting the compound semiconductor epitaxial wafers to photolithography, etching, etc., and then providing the electrodes are amplified. The rate and the maximum operating frequency fmax could be greatly increased, and especially for the HBT, the turn-on voltage could be lowered and the performance could be greatly improved.

[0031]

As described above, according to the present invention, the following excellent effects can be obtained.

The present invention has a lattice constant of 0.15 with the substrate crystal.
% Of Al, Ga, I grown on the buffer layer between the substrate and the operating region by the MOVPE method in the III-V group compound semiconductor epitaxial wafer having the operating region different by more than 1%.
The crystal layer having n and the crystal layer having Al and In having a lattice constant difference of 30% or less from the crystal layer having n are provided in one set or a plurality of sets or in a state in which either of the layers is large. Alternatively, one set or more of InAlGaAs quaternary mixed crystal and InAlAs ternary mixed crystal are alternately laminated in part.

With this structure, the strain relaxation buffer layer having a good surface flatness can be grown at a low temperature by the MOVPE method, and the field effect transistor (FE) can be formed.
T, HEMT, etc.) or bipolar transistor (HBT)
And the like) can be easily obtained. Therefore, according to the present invention, it is possible to reduce the defect of the crystal of the strain relaxation buffer layer in the conventional lattice mismatch system and the burden on the growth apparatus.

Further, in the HEMT and HBT devices manufactured by using the compound semiconductor epitaxial wafer of the present invention, the amplification factor and the maximum operating frequency fmax can be greatly increased, and especially for HBT, the turn-on voltage can be lowered. The performance can be improved significantly.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a compound semiconductor epitaxial wafer having a HEMT layer structure according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a compound semiconductor epitaxial wafer having an HBT layer structure according to an embodiment of the present invention.

[Explanation of symbols]

1 semi-insulating GaAs substrate 2 GaAs buffer layer 20 strain relaxation buffer layer 21 Si-doped In _0.40 Al _0.60 As carrier supply layer 22 In _0.40 Al _0.60 As spacer layer 23 In _0.41 Ga _0.59 As channel layer 24 In _0.40 Al _0.60 As spacer layer 25 Si-doped In _0.40 Al _0.60 As carrier supply layer 26 In _0.40 Al _0.60 As undoped Schottky layer 31 Si-doped In _0.41 Ga _0.59 As to In _0.50 G
a _0.50 As linear contact layer 32 In _0.50 Ga _0.50 As _0.85 contact layer 111 In _0.15 (Ga _0.5 Al _0.5 ) _0.85 As buffer layer 112 In _0.15 Al _0.85 As buffer layer 113 In _0.15 (Ga _0.5 Al) _0.5 ) _0.85 As buffer layer 114 In _0.15 Al _0.85 As buffer layer 121 In _0.23 (Ga _0.3 Al _0.7 ) _0.77 As undoped layer 122 In _0.23 Al _0.77 As undoped layer 123 In _0.23 (Ga _0.3 Al _0.7 ) _0.77 As undoped layer 124 In _0.23 Al _0.77 As undoped layer 131 In0.30 (Ga _0.15 Al _0.85 ) _0.70 As undoped layer 132 In0.30 Al _0.70 As undoped layer 133 In0.30 (Ga _0.15 Al _0.85 ) _0.70 As undoped layer 134 In0.30 Al _0.70 As Undoped layer 141 In _0.35 (Ga _0.15 Al _0.85 ) _0.65 As undoped layer 142 In _0.35 Al _0.65 As undoped layer 143 In _0.35 (Ga _0.15 Al _0.85 ) _0.65 As undoped layer 144 In _0.35 Al _0.65 As undoped layer 151 In _0.40 (Ga _0.15 Al _0.85 ) _0.60 As undoped layer 152 In _0.40 Al _0.60 As undoped layer 153 In _0.40 (Ga _0.15 Al _0.85 ) _0.60 As undoped layer 154 In _0.40 Al _0.60 As undoped layer 200 Strain relaxation buffer layer 212 In _0.40 Ga _0.60 As subcollector layer 222 In _0.40 Ga _0.60 As collector layer 223 p-type In _0.40 Ga _0.60 As base layer 231 In _0.40 Al _0.60 As emitter layer 232 InAlAs cap layer 241 In _0.41 Ga _0.59 As to In _0.50 Ga _0.50 A
Contact layer 242 In _0.50 Ga _0.50 As contact layer whose composition is changed linearly to s

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01L 29/778 29/812 F term (reference) 5F003 BF06 BM03 BP32 5F045 AA04 AB10 AB17 AB18 AD09 AF04 BB07 BB16 CA01 CA07 DA52 DA53 5F102 GB01 GC01 GD01 GJ05 GK05 GK06 GK08 GL04 GM04 GM08 GQ03 HC01

Claims (3)

[Claims] 1. A III-V group compound semiconductor epitaxial wafer having an operating region having a lattice constant different from that of a substrate crystal by 0.15% or more. Al, Ga grown by a MOVPE method in a buffer layer between the substrate and the operating region. Crystal layer having In and Al, In having a lattice constant difference of 30% or less between the crystal layer and In layer
A compound semiconductor epitaxial wafer, characterized in that one or a plurality of sets of crystal layers having the above are provided in a state in which there are many layers. 2. The compound semiconductor epitaxial wafer according to claim 1, wherein the structure of the operation region is a structure of a field effect transistor or a bipolar transistor. 3. A compound semiconductor, comprising the compound semiconductor epitaxial wafer according to claim 2, wherein the compound semiconductor epitaxial wafer is subjected to photolithography, etching, etc., and then provided with electrodes to form a field effect transistor or a bipolar transistor. element.