JPH01183163A - High electron mobility field effect transistor - Google Patents

Abstract

PURPOSE:To prevent a time-wise reduction of a drain current at the time of operating at a low temperature by providing a GaAs channel layer and an electron supply layer made of strained superlattice of group II-VI compound. CONSTITUTION:ZnTe is selected as first group II-VI compound having smaller electron affinity than that of gallium arsenide single crystal, and ZnSe is selected as second group II-VI compound having larger electron affinity than that of the group II-VI compound having substantially equal lattice constant to that of the GaAs single crystal, a thin layer having 100Angstrom or less of thickness made of nondoped ZnTe and a thin layer having 100Angstrom or less of thickness made of ZnSe added with an N-type impurity are alternately repeatedly epitaxially grown on a high purity GaAs channel layer 2 thereby to form a superlattice structure, and which is used as an electron supply layer 10. Thus, the time-wise reduction of a drain current is eliminated at the time of operating it at a low temperature.

Description

[Detailed Description of the Invention] [Summary] This invention relates to a high electron mobility field effect transistor called HEMT.

HE that does not cause a temporal decrease in drain current during low temperature operation
The purpose is to provide MT.

A channel layer consisting of a high-purity gallium arsenide single crystal, a plurality of thin layers of non-doped zinc telluride single crystals each having a thickness of 100 angstroms or less and deposited alternately on the channel layer, and an n-type impurity. and an electron supply layer having a multilayer structure consisting of a thin layer of zinc selenide single crystal containing.

[Industrial application field]

The present invention is applicable to HEMT (formerly known as gh Electron Mobili), which is being put into practical use as a high-speed semiconductor device.
ty Transis-tor (high electron mobility transistor).

[Conventional technology]

H [! A semiconductor device structure called MT has been proposed. (Unexamined Japanese Patent Publication No. 57-007165.
(January 14, 1982) HEMTs are expected to be one of the high-speed elements that make up high-performance semiconductor integrated circuits, and various improvements have been made to improve their characteristics. The principle structure of the HEMT, which is the premise of the present invention, is shown in the sectional view of FIG.

For example, on a substrate 1 made of semi-insulating gallium arsenide (GaAs) single crystal, a channel layer 2 made of substantially no impurities, that is, made of undoped GaAs single crystal, and silicon (si) added as an impurity. n-type aluminum gallium arsenide (AIXGa, 4 As,
However, X = 0.2 to 0.3) Electron supply layer 3 made of single crystal
is formed. On the surface of the electron supply layer 3, AI
The gate electrode 4 consists of gold and gold on both sides of the gate electrode 4.
A source electrode 5 and a drain electrode 6 made of germanium (AuGe) are formed. A contact layer 8 made of n-type GaAs single crystal is provided under each of the source electrode 5 and drain electrode 6 to reduce contact resistance. Note that in the regions where such sources and drains are formed, there is Au that constitutes these electrodes.
There is an alloy region 7 formed by partially diffusing -Ge to reach part of the electron supply layer 3 and channel layer 2. In this way, an ohmic connection is established between the source electrode 5 and drain electrode 6 and the two-dimensional electron gas layer 9 generated within the channel layer 2 as described below.

Since the electron affinity of AlXGa+-x As constituting the electron supply layer 3 is smaller than that of GaAs constituting the channel layer 2, electrons flow into the channel layer 2 from the donors present in the electron supply layer 3. , these electrons are accumulated in the channel layer 2 near the hetero interface, forming a two-dimensional electron gas layer 9. - As a result of controlling the concentration of the two-dimensional electron gas layer 9 by changing the potential of the gate electrode 4, a function as a field effect transistor is obtained.

H[! of the above structure In the MT, carriers of the current flowing between the source electrode 5 and the drain electrode 6 are made of high-purity Ga.
Since it is a two-dimensional electron gas in the channel layer 2 made of As, it is not scattered by impurities.

As a result, current carriers in HEMTs exhibit higher mobility than in conventional field-effect transistors. Utilizing this high mobility, it becomes possible to form ultrahigh-speed transistors.

[Problem that the invention seeks to solve]

When the HEMT having the structure shown in FIG. 2 is operated at a low temperature such as the temperature of liquid nitrogen, a phenomenon occurs in which the drain current decreases with time. This phenomenon is called collapse, and the 8lx Gar-x that constitutes the electron supply layer 3
This is thought to be due to the DX center that As has in the composition region where X≧0.15. (A, Ka
stalsky et al., IEEE, HD-
33 (1986) p, 414) In other words, the DX center is AIX Gar-x As
The ionized DX centers in Alx Gar-x As near the above-mentioned heterointerface are due to the donor atoms inside.

When the two-dimensional electron gas accelerated by the voltage applied between the source electrode 5 and the drain electrode 6 overcomes the potential barrier at the hetero interface and enters the electron supply layer 3, it is captured and re-emitted at low temperatures. It is explained that this is because it is difficult to do.

In the AJX Gar-x As electron supply layer, X<0.
In the case of 15, the above DX center does not occur. therefore.

n-type AI. , +5Gao, and asAs as the electron supply layer, and a highly purified Ino, zGao, and aAs strained nine layer as the channel layer.

That is, n-Alo, +5Ga6. esAs/
Ino, zGaa, aAs/GaAs structure (GaAs
is the buffer layer) (A, Ketterson et a
l.

IEEE trans, electron dev
ices, EDL6+ No, 12+1985.
p, 628), or a superlattice (superdoped structure) in which AlAs thin layers and n-GaAs thin layers whose lattice constants are similar to those of GaAs are alternately laminated as an electron supply layer,
A structure in which this is lattice-matched with a high-purity GaAs channel layer (Baba et al., Jap, Jour
, Appl, Phys, +23+1984, P
L654) has been proposed.

However, in the former case, +Alo, +5Gao
, ΔEc between the 5sAs electron supply layer and the GaAs channel layer
(Conduction band discontinuity value) is as small as about 0.25 eV, so a high two-dimensional electron gas concentration cannot be obtained.On the other hand, in the latter case, the heat resistance during manufacturing is insufficient.

Since the AlAs layer is used, the source resistance is high.

There are other problems.

It is also conceivable to form the electron supply layer using a material in which the DX center does not occur. For example, n
System of type AlInAs electron supply layer and InGaAs channel layer (Ohata et al., IEICE Microwave M1185-124 (1)
986), n-type InP electron supply layer and InGaAs
An example is a channel layer system. However, in these systems, GaAs cannot be used as the buffer layer, so it must be formed on an InP substrate. This makes it expensive, and in order to achieve lattice matching with the InP substrate, + InGaAs or AlInAs is used.
It is necessary to precisely control the composition of the material, which poses difficulties in mass production technology.

The present invention solves the above-mentioned conventional problems and provides an H
The purpose is to make it possible to provide EMT.

[Means for solving problems]

The above object is to provide an electron supply layer formed on a channel layer made of a high-purity gallium arsenide single crystal, which has an electron affinity smaller than that of a gallium arsenide single crystal, and which is made of a non-doped first n-Vl group compound. a first thin layer having a thickness of less than 100 angstroms and consisting of a single crystal;
A second n--VI group compound that has a lattice constant similar to that of a gallium arsenide single crystal, has an electron affinity larger than that of the first II-VI group compound, and contains an n-type impurity. 100mm thick made of single crystal
Achieved by the high electron mobility field effect transistor of the HEMT structure according to the present invention, characterized in that it is composed of a multilayer structure in which second thin layers of angstrom or less are alternately deposited on the channel layer. be done.

[For production]

ZnTe is used as the first n-VI group compound having an electron affinity smaller than that of gallium arsenide single crystal.
Zn5e is selected as a second n-VI group compound having a lattice constant approximately equal to that of the GaAs single crystal and a larger electron affinity than the n-Vl group compound, and a non-doped layer is formed on the high purity GaAs channel layer. ZnTe
A superlattice structure is formed by epitaxially growing a thin layer with a thickness of 100 Å or less consisting of Zn5e doped with n-type impurities and a thin layer with a thickness of 100 Å or less consisting of Zn5e doped with n-type impurities, and this is used as an electron supply layer. By this, the HEMT does not cause the collapse of the drain current.
can be manufactured.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 (al) is a sectional view of a main part showing the structure of a HEMT according to the present invention, and the same parts as in FIG. 2 are given the same reference numerals.

As in the past, a substrate 1 made of semi-insulating GaAs single crystal has a thickness of 1 μm made of high purity GaAs single crystal.
A channel layer 2 of about 100 mL is formed.

On the channel layer 2, non-doped ZnTe (i-Zn
Te: thickness 10~2 consisting of electron affinity 3.53eV)
A thin layer of about 20 layers consisting of Zn5e containing n-type impurities (electron affinity 4.09 eV) and several to several tens of layers alternately deposited in ZnTe/
An electron supply layer 10 made of an n-Zn5e superlattice is formed.

In this case, the difference between the electron affinity of 1-ZnTe and the electron affinity of GaAs (4.07 eV) is 0.54 eV, so in terms of energy, the difference between the n-ZnTe electron supply layer and the non-doped GaAs channel layer is This is a suitable combination for selectively doped heterostructures. However, Zn
The lattice constant of Te is 6.104, which is about 8% larger than that of GaAs, and the lattice mismatch is much larger. On the other hand, the lattice constant of Zn5e is 5.66
9, and the difference from the lattice constant of +GaAs, which has a lattice constant of 5.642, is 0.4%, which is small.

Therefore, as mentioned above, each 1-ZnTe thin layer and n-Zn
If the thickness of the 5e thin layer is 100 Å or less, 1-ZnT
The e thin layer and n-Zn5e have a so-called strained superlattice structure, and can be epitaxially grown on the GaAs substrate l in good condition. Moreover, this superlattice structure is n-
Only the Zn5e thin layer was doped with impurities. This is a so-called super-doped structure.

The above 1-ZnTe/n-Zn5e superlattice is a well-known MB
It can be formed by the E (molecular beam epitaxy) method or the MOCVD (metal organic chemical vapor deposition) method. Note that aluminum (AI), gallium (Ga), or indium (In) is used as the n-type impurity.

On the electron supply layer lo consisting of the 1-ZnTe/n-Zn5e superlattice, a gate electrode 4. is formed in the same manner as in the conventional structure. Source electrode5. A drain electrode 6 and an alloy region 7° contact layer 8 are provided.

As described above, GaAs channel layer 2 and 1-Zn
It consists of a Te/n-Zn5e superlattice electron supply layer 10. The L (EMT structure) without the DX center is completed. The energy band diagram in this structure is shown in FIG.
indicates the Fermi level.

As shown in FIG. 1 (bl), a GaAs channel layer 2 and a 1-ZnTe/n-Zn5e superlattice electron supply layer 10
An energy barrier of about 0.6 eV is formed between the GaAs channel layer 2 and the 1-ZnTe thin layer 11 at the hetero-interface between the GaAs channel layer 2 and the 1-ZnTe thin layer 11. -X As electron supply layer (X
~0.2), which is larger than the energy barrier of about 0.2 eV. Therefore, seepage of the two-dimensional electron gas from the GaAs channel layer 2 to the electron supply layer 10 is suppressed, and high mobility of the two-dimensional electron gas is maintained. In addition, in the above structure, as shown in FIG.
-ZnTe) 31 layer 11 must be formed so as to be in contact with the GaAs channel layer.

On the other hand, the n-Zn5e thin layer 1 near the hetero interface
The bottom of the conduction band of GaAs layer 2 is located at the same level as that of GaAs layer 2, but in the superlattice structure, the donor order is formed at a higher position (T, Baba et al.
1) + n-Zn5e thin layer 12 to G
Electrons flow into the aAs channel layer 2, forming a two-dimensional electron gas layer 9. Therefore, 1-ZnTe/n-
The electron supply layer 10 made of Zn5e superlattice has 9 ordinary 81
! It functions similarly to the n-type AIX Ga+-)+As electron supply layer in MT.

Moreover, since the DX center is not formed in this electron supply layer IO, no collapse of drain current occurs.

As mentioned above, in the HEMT structure of the present invention,
The electron supply layer is formed using a superlattice of an n-VI group compound without DX centers, which ensures a sufficiently high energy barrier with the GaAs channel layer and a high quality layer with low defect density. A heterojunction is formed. This is an n-Alo using a strained superlattice, +
5Gao, asAs/Ino, zGao, aAs
/GaAs structure (,GaAs structure)
This is based on a different concept from those in which a thin layer of Ink, zGao, eAs, etc. is introduced into the As channel layer.

Note that in the present invention, the electron supply layer composed of a strained superlattice is made of 1-ZnTe used in the above embodiments.
Needless to say, the structure is not limited to the /n-Zn5e superlattice, but can be constructed using an appropriate combination of other ■-■ group compounds.

〔Effect of the invention〕

According to the present invention, by providing an electron supply layer consisting of a GaAs channel layer and a strained superlattice of an n-VI group compound, it is possible to prevent the drain current from decreasing over time during low-temperature operation of the HEMT, and the HEMT can be used. This has the effect of promoting the practical application of high-performance semiconductor integrated circuits.

[Brief explanation of the drawing]

Figure 1 (al) and Figure 1 (bl) are a cross-sectional view of a main part showing the structure of a HEMT according to the present invention and an energy band diagram, respectively. Figure 2 is a cross-sectional view of a main part showing the structure of a conventional IBMT. In the figure. 1 is the substrate. 2 is the channel layer. 3 is the electron supply layer. 4 is the gate electrode. 5 is the source electrode. 6 is the drain electrode. 7 is the alloy region. 8 is the contact layer. 9 is the two-dimensional structure. Electron gas layer. 10 is 1-ZnTe/n-Zn5e superlattice electron supply layer 1
1 is 1-ZnTe) 3 layers. 12 is an n-Zn5e thin layer. 13 is n-type doping

Claims (2)

[Claims] (1) A channel layer made of high-purity gallium arsenide single crystal, an electron supply layer formed on the channel layer, a control electrode provided on a part of the surface of the electron supply layer, and the electron supply layer. A high electron mobility field effect transistor having two electrodes provided in regions facing each other with the control electrode in between and ohmically connected to the channel layer on a part of the surface of the electron supply layer. a first thin layer consisting of an undoped first II-VI compound single crystal having an electron affinity smaller than that of the gallium arsenide single crystal and having a thickness of 100 angstroms or less; a second group II-VI compound single crystal having a lattice constant similar to that of the first group II-VI compound, having an electron affinity larger than that of the first group II-VI compound, and containing an n-type impurity; A high electron mobility field effect transistor having a multilayer structure in which second thin layers having a thickness of angstroms or less are alternately deposited on the channel layer. (2) the first Group II-VI compound is zinc telluride;
2. The high electron mobility field effect transistor according to claim 1, wherein said second group II-VI compound is zinc selenide.