JPS61203683A - Hetero junction field effect transistor - Google Patents

Abstract

PURPOSE:To enable the arbitrary control of the transmission characteristic of transistor characteristics by arranging an N-type region at least in a part of thickness direction of the first semiconductor layer and contriving that the electrons existing said N-type region and the two-dimensional electron gas layer contribute to the operation of the transistor. CONSTITUTION:In the adjacent part to a hetero junction 9 in a GaAs layer 2, an N<-> layer 2a in which an impurity concentration is constant in depth direction is formed in such a manner that it involves a two-dimensional electron gas layer 10. A distribution profile for the distance (x) from the hetero junction in depth direction of the carrier concentration in the N<-> layer 2a except the two-dimensional electron gas layer 10 is constant. The distribution profile of electron concentration (Ce) in the layer 10 is steep, having the peak in the vicinity of the hetero junction 9. The electrons existing in the N<-> layer 2a are added to the two-dimensional electron gas layer 10 so that the number of electrons which contribute the operation of HEMT is enhanced by corresponding to that. Consequently the ohmic contact resistance between the two-dimensional electron gas layer 10 and a source region and a drain region 8, accordingly a source electrode 5 and a drain electrode 6 can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a heterojunction field effect transistor, and more particularly, to a high electron mobility transistor (high electron mobility transistor).
ectron mobility transistor
r, HE MT).

[Summary of the invention]

The present invention provides a heterojunction field effect transistor comprising:
By providing an n-type region in at least a portion in the thickness direction of the first semiconductor layer in which the two-dimensional electron gas layer is formed,
This makes it possible to arbitrarily control the transmission characteristics of the transistor.

[Conventional technology]

Hitherto, a HEMT as shown in FIG. 6 has been known. In the HEMT shown in FIG. 6, semi-insulating GaAs
Undoped GaAs layer 2 and n-AlXG on substrate 1
a, -XAs layer 3 (electron supply layer) is epitaxially grown in sequence, and this n-81. A Schottky gate electrode 4 made of, for example, Ti/Pt/Au, and a source electrode 5 and a drain electrode 6 made of, for example, AuGe/Au are formed on Ga, -XAsAs. Also, n below these source electrodes 5 and drain electrodes 6
In the AIX Ga+-x As layer 3 and the GaAs layer 2, a source region 7 and a drain region 8 are formed which are made of an alloy layer of these semiconductors and a source electrode 5 and a drain electrode 6. In the HEMT shown in FIG. 6, a heterojunction 9 is formed between the GaAs layer 2 and the n-AlXGa, -XAs layer 3, and a heterojunction 9 is formed in a portion of the GaAs layer 2 adjacent to this heterojunction 9. The concentration of the two-dimensional electron gas layer 10 is modulated by the gate voltage.

Most of the two-dimensional electron gas layer 10 described above is localized in an extremely narrow area within about 100 points from the heterojunction 9, and this two-dimensional electron gas layer 10 is localized in an extremely narrow area within about 100 nm from the heterojunction 9, and this two-dimensional electron gas layer 10 is located in n-A1, which is the source of electrons. ．． The Ga+-g As layer is spatially separated from the ionized donor impurities in the layer. Therefore, the degree to which electrons undergo Coulomb scattering due to these ionized donor impurities is extremely small, so the electron mobility of the two-dimensional electron gas layer 10 is extremely high. Therefore, H.E.M.
Generally, T has the advantage of being able to obtain a high transconductance.

[Problem that the invention seeks to solve]

However, when the HEMT is used as a switching element, the entire two-dimensional electron gas layer 10 is used, so the gs
Although it can certainly be said that a high g.g.

A high value is not necessarily a feature.

In addition, the characteristics of HEMT are as follows: GaAs layer 2 and n AIX
Since it is determined in principle by the heterostructure with the Ga+-xAs layer 3 and the purity of the GaAs layer 2,
It is difficult to control the characteristics arbitrarily.

Furthermore, the above-mentioned HEMT has the feature that the electron mobility is extremely high in the low temperature region where scattering by ionized impurities is the dominant scattering factor for electrons, but if you look at it from another perspective, the characteristics have a large temperature dependence. This means that if the HEMT is limited to use at room temperature, it may actually be a disadvantage.

Furthermore, it is currently not easy to grow the undoped GaAs layer 2 epitaxially using the MBE method or the like with good reproducibility, and there is a drawback that it may become n-type or p-type depending on the growth conditions.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a heterojunction field effect transistor that corrects the various drawbacks of conventional heterojunction field effect transistors such as HEMTs.

Means for Solving Problem C] The heterojunction field effect transistor according to the present invention has a first
a semiconductor layer (for example, an undoped GaAs layer 2i2), and a second semiconductor layer (for example, an n AIX Gat-xAs layer 3),
a two-dimensional electron gas layer formed in a portion of the first semiconductor layer adjacent to the heterojunction (for example, a forward HE
MT), an n-type region is provided in at least a portion of the first semiconductor layer in the thickness direction.

[Effect]

With this configuration, the two-dimensional electron gas layer and the electrons present in the n-type region can contribute to the transistor operation.

〔Example〕

Hereinafter, a heterojunction field effect transistor according to the present invention will be described.
An embodiment applied to EMT will be described with reference to the drawings. In the following FIGS. 1 and 3, the same parts as in FIG. 6 are denoted by the same reference numerals, and the explanation thereof will be omitted as necessary.

First, a first embodiment of the present invention will be described.

As shown in FIG. 1, in the HEMT according to the first embodiment, the two-dimensional electron gas layer 10 is included in the portion of the GaAs layer 2 adjacent to the heterojunction 9, for example, at a depth of about 1000 layers. The structure is similar to that of the conventional HEMT shown in FIG. 6, except that an n layer 2a having a constant impurity concentration in the horizontal direction is formed. Note that this n layer 2a is made of GaAs by, for example, the MB2 method or the MOCVD method.
It can be formed by doping an n-type impurity such as Si when epitaxially growing layer 2.

The carrier concentration in the above-mentioned n-layer 2a excluding the two-dimensional electron gas layer 10, that is, the electron concentration N(in) (however,
(distance in the depth direction from the heterojunction 9) has a rectangular distribution profile as shown in FIG. 2, corresponding to the fact that the impurity concentration in the n layer 2a is constant in the depth direction. ing. That is, N (x) is constant regardless of X. The value of this N (x) is, for example, 5 X I Q
"cs-" can be selected, and this can be set as surface concentration N,
Expressing this, the depth of n layer 2a is 1000 people-10-'c
If m, N, = 5x I Q"X I O-'
=5X 10"elm-". FIG. 2 also shows the profile of the electron concentration distribution in the two-dimensional electron gas layer 10, and as mentioned above, most of the two-dimensional electron gas layer 10 is located in an extremely narrow region within about 100 points from the heterojunction 9. It can be seen that there is a steep profile with a peak near the peterojunction 10, corresponding to the fact that it is localized at . In the HEMT according to the first embodiment, the two-dimensional electron gas layer 10 and the electrons in the n layer 2a represented by N (x) contribute to the operation, and the former is different from the conventional HEMT.
Similar operation as in M T, the latter is GaAs F
Since the operation is similar to that in ET, the result is an operation that is like adding GaAs FET operation to HEMT operation.

In this way, according to the first embodiment described above, the GaAs layer 2
Since the n-layer 2a is formed in the portion adjacent to the heterojunction 9, the electrons present in the n-layer 2a are added to the two-dimensional electron gas layer 10, and therefore the number of electrons contributing to the operation of the HEMT is reduced. can be increased by this amount.

Moreover, for this reason, the ohmic contact resistance between the source region 7 and the drain region 8, and therefore between the source electrode 5 and the drain electrode 6, and the two-dimensional electron gas layer 10 can be reduced.

Furthermore, since the n layer 2a is provided between the source region 7 and the drain region 8, the parasitic resistances, that is, the source resistance R3 and the drain resistance R4 can be reduced.

Further, according to the HEMT according to the first embodiment described above, as a result of adding the GaAs FET operation by electrons generated from the n layer 2a to the HEMT operation by the two-dimensional electron gas layer 10, the Vcs-In characteristic (where Vas is the gate voltage ,
(2) is the drain current), so-called remote cutoff characteristics can be obtained.

When the HEMT according to the first embodiment is used in a linear circuit, the operation can be controlled by designing the impurity concentration, depth, etc. of the n-layer 2a so that the two-dimensional electron gas layer 10 operates dominantly at the operating point. A decrease in g at the point can be substantially prevented.

Furthermore, since the part of the GaAs layer 2 that determines the characteristics of the HEMT is the n'' layer 2a, epitaxial growth of GaAs can be performed with good reproducibility, and therefore HEMTs can be manufactured with good reproducibility. Not only that, but especially when limited to use at room temperature, the first
The HEMT according to the embodiment not only has less deterioration in characteristics such as go than the conventional HEMT shown in FIG. 6, but also has less temperature dependence of the characteristics.

The HEMT according to the first embodiment described above is called a forward HEMT, and next, a GaAs layer and an n-AlXGa
, -H in which the stacking order with the XAs layer is reversed from that of the forward HEMT.
A second embodiment in which the present invention is applied to EMT, that is, reverse HEMT, will be described.

As shown in FIG. 3, in the HEMT according to the second embodiment, undoped A1.
Ga, -, to S layer 11, n -A1. Ga1-,
An As layer 3, an n--GaAs layer 12, and an n"-GaAs layer 13 are epitaxially grown in sequence by MB2 method or MOCVD method, and a Schottky gate electrode 4, a source electrode 5, and a drain electrode are formed on this n"-GaAs layer 13. 6 is formed. Furthermore, below the source electrode 5 and drain electrode 6, a source region 7 and a drain region 8 are formed that reach the AIX Ga+-x As layer 11. And n AIX Ga+-, As
A heterojunction 9 is formed between the layer 3 and the n''-GaAs layer 12, and a two-dimensional electron gas layer 10 is formed in a portion of the n''-GaAs layer 12 adjacent to the heterojunction 9.

Here, semi-insulating GaAs substrate 1 and n-AlXGa1-
An undoped A1. Ga, -XA
The reason why the s-layer 11 was formed is to prevent the two-dimensional electron gas layer 10 from being formed also in the semi-insulating GaAs substrate 1. Note that X in the HEMT according to this second embodiment
FIG. 4 shows the distribution of the electron concentration N (x) in the direction.

The reverse HEMT according to the second embodiment described above has the following advantages in addition to various advantages similar to those of the HEMT according to the first embodiment. That is, in this reverse HEMT, by selecting the operating point, that is, ■. By increasing forward AGC (automatic gain
Therefore, even with large input signals, the output has little distortion and is resistant to cross-modulation.

Although the present invention has been described above with reference to embodiments, the present invention is not limited to the above-described first and second embodiments, and various modifications can be made based on the technical idea of the present invention. For example, the electron concentration N (x) of the n layer 2a in the first embodiment
The distribution profile of the electron concentration N (x) of the n--GaAsJil 12 in the second embodiment is not limited to the profiles shown in FIGS. 2 and 4, and can be changed as necessary. For example, instead of the profile shown in FIG. 2, it is possible to use a profile represented by N+(x) or Nz(x) as shown in FIG. Further, the surface concentration N of electrons in the n layer 2a or the n--GaAs layer 12 can be set to various values as necessary,
It is preferable to set the value within the range of n-''.

Furthermore, in the above two embodiments, GaAs-A
Although the present invention is applied to an IGaAs heterostructure, it can be applied to other types of heterostructures, such as Ga1nAs.
The present invention can also be applied to -AIInAs heterostructures.

〔Effect of the invention〕

According to the heterojunction field effect transistor according to the present invention, since the n-type region is provided in at least a portion in the thickness direction of the first semiconductor layer in which the two-dimensional electron gas layer is formed,
It is possible to make the two-dimensional electron gas layer and the electrons present in this n-type region contribute to the operation of the transistor, and therefore, by changing the impurity concentration distribution of this n-type region as necessary, the transmission characteristics of the transistor characteristics can be arbitrarily changed. It is possible to control the Furthermore, not only is the temperature dependence of transistor characteristics small, especially near room temperature, but it is also possible to manufacture transistors with better reproducibility than in the past. Furthermore, the ohmic contact resistance and parasitic resistance between the source and drain and the two-dimensional electron gas layer can be made smaller than in the past.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the HEMT according to the first embodiment of the present invention, FIG. 2 is a graph showing the electron concentration distribution in the X direction in the HEMT shown in FIG. 1, and FIG. 3 is the second embodiment of the present invention. FIG. 4 is a cross-sectional view showing the HEMT according to FIG.
FIG. 5 is a graph showing the electron concentration distribution in the X direction in the EMT. FIG. 5 is a graph similar to FIG. 2 showing the electron concentration distribution according to a modification of the present invention. FIG. 6 is a cross-sectional view showing the conventional HEMT.゛In addition, in the symbols used in the drawings,
aAs substrate 2--1------------
GaAs layer'l a -------------
n 1 layer 3------------=-n A
IX Ga1-x As layer 4-・-・--・-・-...
...Schottky gate electrode 5・---------
−−・−・−Source electrode 6・−・−・・−・・−・−−
−−1・Drain electrode 9・−−−−−−−−−−−−
・−・−・Heterojunction 10・・−・−・−−−−
−・−・Two-dimensional electron gas layer 12 −・−==−−−−−−
-----n --GaAs layer.

Claims (1)

[Scope of Claims] A first semiconductor layer; a second semiconductor layer provided substantially in contact with the first semiconductor layer and forming a heterojunction with the first semiconductor layer; and a two-dimensional electron gas layer formed in a portion of the first semiconductor layer adjacent to the heterojunction, at least a portion of the first semiconductor layer in the thickness direction. ni n
A heterojunction field effect transistor characterized by providing a type region.