JPH02254731A - Hetero-junction type field effect transistor - Google Patents

Abstract

PURPOSE:To enable a novel hetero-junction structure lightening the restriction on the lattice alignment to be manufactured by a method wherein InGaAs, InAlAs in larger lattice constant than that of an InP substrate are used in the region in film thickness exceeding the film thickness. CONSTITUTION:A non-doted InyAl1-yAs layer 11 in larger lattice constant than that of an InP substrate 1, another non-doped InxGa1-xAs layer 12, the other non-doped InyAl1-yAs thin film 13 and an N type InyAl1-yAs layer 14 respectively in the same lattice constant as that of the the said layer 11 are successively formed on the semiinsulating InP substrate 1. Then, the whole thickness of the layers formed on the InP substrate 1 is set up thicker than the film thickness determined by the difference from the lattice constant of the semiinsulating InP substrate 1. Through these procedures, the restriction on the crystal deposition such as the lattice alignment with the InP substrate 1 can be lightened so as to attain the simplification, the mass production and the price cut down of the crystal deposition process.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an improvement in a field effect transistor using a heterojunction structure.

Conventional technology In a heterojunction structure in which an N-type AeGaAs layer is formed on a non-doped GaAs layer, a two-dimensional electron gas with high mobility is formed on the GaAs side of the heterojunction interface, and this is used to generate high electron mobility. A heterojunction field effect transistor called a transistor (HEMT) was invented. This H
In order to improve the characteristics of EMT, many studies have been conducted from the material and structural aspects.In terms of materials, INO, s3cAO, lattice matched to InP instead of GaAs,
47A s, and InAeA instead of AeGaAs.
The one using s is At! GaAs/GaAs HEM
It exhibits higher electron mobility, higher electron saturation velocity, and higher two-dimensional electron gas concentration than T, and is considered promising as a high-speed device. However, InP formed on an InP substrate
GaAs/InAf! In As-based HEMT, InGaA
Since the lattice constant of each layer of S and InAeAs differs depending on the InAs composition, InA is lattice-matched to the InP substrate.
There was a major constraint that the composition of s had to be precisely controlled. In order to alleviate this constraint and increase the InAs composition to improve electron mobility and further improve device characteristics, InGaAs/InAeA,
InGaAs which becomes the channel layer in s-based HEMT
The InAs composition of the layer is increased to about 0.6, and the InGaA
In recent years, methods have been used to reduce the thickness of the s-layer so that lattice defects are not introduced. InGaAs/InAe using such an InGaAs strained layer
FIG. 3 shows a cross-sectional view of the layer structure of the As-based HEMT.

In Fig. 3, 1 is a semi-insulating InP substrate, 2 is an InP substrate, and 2 is an InP substrate.
Non-doped Ino, 52A (0,48A S buffer layer, 3
is undoped I no, s3G lattice matched to InP
ao, +7A s layer, 4 is non-doped InGaAs with X of 0.53 or more (approximately lattice matched at 0.53), 5 is non-doped I
no, 52Ae 0.411A S spacer layer, 6 is N
Type I no, 5zAe 0.4eA 8 layers, 7 is a non-doped I no, 52Ae0.48A s layer. However, even with the structure of Shinakarako, I nxG a 1-, A s
For each of the 2°3.5 and 6.7 layers other than strained layer 4, InAs compositions are selected to lattice match the InP substrate, and the problem of lattice matching remains a major constraint on crystal growth. There is.

Problems to be Solved by the Invention As described above, in an InGaAs/InAeAs HEMT with a conventional structure, it is necessary to lattice match each layer of crystal growth with the InP substrate except for the channel layer, and it is necessary to accurately adjust the InAs composition during crystal growth. There were major constraints that had to be controlled. This restriction can be alleviated to some extent by reducing the thickness of the crystal growth film, but buffer layer 2 and the like are usually formed to a thickness of 200 nm or more in order to suppress adverse effects from the substrate, such as impurity contamination from the InP substrate. , it is unrealistic to make the crystal growth layer extremely thin.

The present invention is based on the conventional structure of InGaAs/I nAe A.
The present invention provides a novel heterojunction structure in which the above-mentioned lattice matching constraints in the heterostructure of an s-based HEMT are significantly reduced.

Conventionally, InGaAs/I crystals were grown on InP substrates.
In the nAeAs heterostructure, it was considered necessary to match the lattice constant of InGaAs or InAeAs with that of the InP substrate in order to obtain good electrical characteristics. Furthermore, when the lattice constant of the crystal-grown film is shifted from that of the substrate, the grown film with good electrical properties must be limited to a critical film thickness that corresponds to the shift in the lattice constant. It was thought that it could not be obtained.

The present inventors have developed an InGaAs/InAe film on an InP substrate.
As a result of fabricating As-based HEMT heterostructures in a wide range of InAs composition ratios and comparing their electrical properties, it was found that good electrical properties can be obtained even in a region where the thickness exceeds the critical film thickness.

Means for Solving the Problems The present invention is based on such discoveries, and is based on InP.
InGaAs has a larger lattice constant than the substrate.

InAeAs is actively used in a film thickness region exceeding the critical film thickness. At this time, InGa becomes the channel layer.
It is important to have a structure in which the lattice constants of the As layer and the InAeAs layer provided directly below are almost matched, and by using such a structure, the lattice constants of the As layer and the InAeAs layer provided directly below are higher than when lattice-matched to the InP substrate. l nGa with electron mobility
An As/I nAe As-based HEMT structure can be obtained.

In addition, when the lattice constant of the InGaAs layer serving as the channel layer is larger than the lattice constant of the InGaAs layer provided directly below it, the layer thickness of the InGaAs layer is determined from the critical film thickness determined from the lattice constant difference between the two layers. Experiments have also revealed that good electrical characteristics can be obtained by making the film thinner than the above.

The present invention is based on the above experimental results.

InGaAs/I has a lattice constant significantly different from that of the working InP substrate.
It is not clear why the nAl2s heterostructure exhibits good electrical properties. I has a smaller lattice constant than the InP substrate
In the nGaAs/I nAe As heterostructure, the electrical properties are significantly degraded, so in the InGaAs/fnAeAs heterostructure, which has a larger lattice constant than the InP substrate, defects depending on the crystal do not have much of a negative effect on electrical conduction. it is conceivable that. Although it is a guess, InP
InGaAs/InAe with a larger lattice constant than the substrate
In the As heterostructure, defects are mainly confined near the interface between the InP substrate and this heterostructure, and are thought to extend toward the surface.

As will be explained in more detail by way of examples, InAs of the InGaAs/InAl2As heterostructure according to the present invention
The range of values that the composition and film thickness can take is extremely wide, and the present invention can be applied to InGaA, which was previously thought to be difficult.
This facilitates crystal growth of the s/I nA+2 As heterostructure and greatly contributes to mass production and low cost of growth of this system.

Embodiment A first embodiment of the present invention will be described with reference to FIG. 1st
Figure (a) shows an InGaAs/InAgAs-based HEM grown on an InP substrate 1 using molecular beam epitaxy.
It shows a cross-sectional structural diagram of T Tachibana-zukuri. semi-insulating InP
A non-doped I nyAe +-yAs layer 1 is provided on the substrate 1.
1 to a film thickness of W, and then InxG a 1-
The XA 8 layer 12 is formed to a thickness of W2. On top of that, a non-doped I nyAf21-y As spacer layer 1
3 is formed, for example, 30A, and on top of that, N type 1 ny A
Q 1-y, As layer 14 was formed with a thickness of 300A. I
a Ga-x As layer 12 is I ny Ae l-
y It is almost lattice matched to the As layer 11. In other words, X
zy state. 15 is a cap layer for forming a Schottky electrode, and a thin film of GaAs, AeGaAS, or the like is used. At this time, 0, which lattice matches y to the InP substrate 1,
At the same time as changing from 52 to 0.72, W, and W2
The characteristics of the heterostructure were investigated by varying the sum of the film thicknesses. Figure 1(b) shows the results, and in the shaded area, the mobility at room temperature is 10'cli? /V,S showed a value well in excess of S. The dashed line in Figure 1(b)1 shows the critical film thickness calculated from the difference in lattice constant with the InP substrate, but the region with good electrical properties actually obtained from experiments is much wider. It can be seen that the range is wide.

Moreover, even when y=0.72, it shows a high mobility of 10'cj/V,S up to a film thickness of about 1 μm, and in practice, even with a composition of 0.72, it is possible to form a sufficiently thick film. It can be seen that formation is possible.

In this example, InxG a 1-xA S layer thickness (W
2) typically used 0.1 μm. The feature of this example is that InGaAs/InA which is not lattice matched to the InP substrate
The entire film thickness of the l2s heterostructure is the layer 11 to 1 on the substrate 1.
5) exceeds the critical thickness determined by the lattice constant difference with InP, and the I
The nGaAs layer and the InAs composition layer are lattice matched to each other.

A second embodiment of the present invention has a semi-insulating InP substrate 1 with a cross-sectional structure shown in FIG. 1(a) and a non-doped I ny/l
Non-doped Ino, 5zAeo, 4aA lattice-matched to the InP substrate 1 between 1-yA, 9N11
s buffer layer is inserted. Normally, InP substrates do not have sufficient crystal quality (unnecessary impurities, etc. are introduced from the substrate into the crystal-grown layer. It is desirable to introduce a buffer layer to remove this, but in this example, the film thickness is 100OA-5000A non-doped I no,s
A 2G ao, 4eA s layer was inserted between InP substrate 1 and layer 11. The results showed that a good HEMT structure could still be obtained in the shaded area in FIG. 1(b). Therefore, it can be seen that there is no change even if a buffer layer lattice-matched to the substrate is introduced between the semi-insulating InP substrate 1 and the non-doped InyAel-yAs layer 110 in FIG. 1(a). It goes without saying that this buffer layer may have a somewhat larger lattice constant than the InP substrate as long as it is within the critical thickness range.

A third embodiment of the present invention will be described using FIG. 2. Second
In the figure, 21 is a non-doped I with a layer thickness of about 3000A.
no, 52A90.48A S buffer layer,
As explained in the second embodiment, this is not particularly necessary in the present invention. 11 is an InyAel-yAs layer with y>0. ! 52 and the layer thickness was greater than the critical film thickness determined by the lattice constant difference with the InP substrate. 22 is In,
Ae 1-yA 9 layers I n with larger lattice constant than 11
, G'a 1-, A s layer, In, Ael-, A
In order to make the conduction band discontinuity value thicker with layer 9 and layer 11,
InAs composition is thickened (i.e. y<z
It is said that Such I nzG a 1-, A s
In the case of using a layer 22, the electrical characteristics become thick (changed depending on the InAs composition 2 of the layer 22, and
Experiments have shown that the s-layer thickness cannot be made too large. In this case, it is necessary to form the In, Ga1-, and As layers thinner than the critical thickness determined by y and 2.

Usually, the thickness of the channel layer is about 150A to 300A, so the upper limit of the value of Z is 0.8 when y is 0.65.
It will be about.

In addition, I nyAf! of the cross-sectional structure shown in FIG. 1-yAs
Between 1 nzG a +− on the As layer and the As layer 22,
I nx with single-child matching on I nVAel-yAsAs layer
It can be easily inferred that a structure in which a Ga + -xA s layer is inserted may also be used.

Effects of the Invention The present invention provides an InP substrate with a lattice-mismatched InP substrate.
GaAs/InA1! It forms an As heterojunction structure, and is characterized in that the layer thickness of the heterostructure exceeds the critical film thickness at which lattice defects are introduced. The constraints on crystal growth are significantly reduced, and InGaAs/I
The present invention greatly contributes to the simplification, mass production, and cost reduction of the crystal growth process of nAeAs-based HEMT structures.

[Brief explanation of drawings]

FIG. 1(a) is a cross-sectional view of a field-effect transistor according to a first embodiment of the present invention, FIG. 1(b) is a diagram showing the relationship between InAs composition and layer thickness in the same transistor, and FIG. A cross-sectional view of the field-effect transistor of the second embodiment, and FIG. 3 is a cross-sectional view of a conventional field-effect transistor. 1... Semi-insulating InP substrate, 11...
Non-doped InyA eI-yA sil, 12.
...Non-doped InxGal-xAs layer,
13...Non-doped InyAel-, As
Spacer layer, 14...N type I nyAe +-
yAs layer, 15... Schottky electrode formation cap layer, 16... gate electrode, 17...
... Source electrode, 18 ... Drain electrode, 21
・・・・・・Non-doped I no, 52Aeo4aAs
Batsuhua, 22...Non-doped InzG
a I-zA s layer. Name of agent: Patent attorney Shigetaka Awano and one other person θ, s2 ρ57 σ32

Claims (2)

[Claims] (1) A non-doped In_yAl_1_-_yAs layer with a larger lattice constant than this InP substrate on a semi-insulating InP substrate and this In_yAl_
A non-doped In_xGa_1_-_xAs layer whose lattice constant is almost the same as that of the 1_-_yAs layer, and a non-doped In_xGa_1_-_xAs layer.
_yAl_1_-_yAs thin layer and N-type In_yA
l_1_-_yAs layers are sequentially formed, and the total thickness of the layers formed on the InP substrate is set to be thicker than a critical film thickness determined from a lattice constant difference with the semi-insulating InP substrate. A heterojunction field effect transistor having a heterojunction structure. (2) Non-doped In_yAl_1_-_yAs having a larger lattice constant than the InP substrate and thicker than the critical film thickness determined from the difference in lattice constant with the InP substrate on a semi-insulating InP substrate. layer and this In_yAl
A thin layer of non-doped In_zGa_1_-_zAs with a larger lattice constant than the _1_-_yAs layer, a thin layer of non-doped In_yAl_1_-_yAs and an N-type In_
A heterojunction field effect transistor having a heterojunction structure in which yAl_1__yAs layers are sequentially formed.