JPH02265251A - Semiconductor device - Google Patents

Abstract

PURPOSE:To control a threshold voltage of a transistor by controlling a thickness of an InAs layer in the middle of a four-layer structure. CONSTITUTION:The following are provided: a p<+> GaAs substrate 1 as a III-V compound semiconductor substrate; a four-layer structure which is composed of an AlSb layer, and InAs layer, an AlSb layer and an InAs layer 2 to 5 which have been formed on the substrate 1 and whose energy level of an electron channel is generated by a quantum effect. Then, a thickness of the InAs layer 3 in the middle of the four-layer structure is controlled. That is to say, while the AlSb/Sb/InAs/AlSb quantum well structure 2 to 4 are used as a channel and the InAs semiconductor 5 on the surface is used as a gate electrode, the thickness of the quantum well layer is controlled. Thereby it is possible to obtain a field-effect transistor whose threshold voltage can be controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a ■-V group compound semiconductor device, and more specifically, to arbitrarily design the threshold voltage of a transistor.

The present invention relates to a controllable III-V compound semiconductor device.

[Conventional technology]

A field effect transistor including a betero junction using a conventional ■-V group compound semiconductor is AJ2GaAs/Ga
Heterojunction field effect transistors or high electron mobility transistors made using As are well known. In these structures, AfGaAs/G a A
Two-dimensional electron gas accumulates at the s-junction and becomes a conduction channel,
By controlling the potential of a metal gate electrode provided on the AffiGaAs surface, the two-dimensional electron gas concentration and, therefore, the resistance between the source and drain are controlled.

[Problem to be Solved by the Invention] The threshold voltage of the transistor in the conventional semiconductor device as described above is AI! , doping of the GaAs layer.

It is determined by the thickness, type of gate metal, etc., but there are problems such as the types of metals that can actually be used are limited and the channel resistance actually changes due to changes in the F-ping. There are not many threshold voltages that can be achieved.

Furthermore, the height of the Schottky barrier formed on AfGaAs is process sensitive, and from this point of view as well, it is difficult to control the threshold voltage.

Furthermore, when considering integrated circuits, a transistor with a threshold voltage of 0 is particularly required, and accurate control of the threshold voltage is desired.

An object of the present invention is to provide a semiconductor device in which the threshold voltage of a transistor can be controlled.

[Means to solve the problem]

The semiconductor device of the present invention includes an m-v group compound semiconductor substrate p"-GaSb, and is formed on the semiconductor substrate.1esb/InAs/A
It includes a four-layer structure consisting of L S b / I n A s in which the energy level of the electron channel is generated by a quantum effect, and the threshold voltage of the transistor can be adjusted by controlling the thickness of InAs in the middle of the four-layer structure. It is characterized by being able to control.

[Effect]

When a second semiconductor with a small forbidden band width is sandwiched between a first semiconductor with a large forbidden band width grown on a ■-■ group compound semiconductor substrate, the allowable energy of the second semiconductor increases due to quantum effects. It is well known that the forbidden band width is larger than that of the original second semiconductor. Furthermore, if a second semiconductor, which is the same as the heavily doped well layer, is grown outside this quantum well structure as a gate, the relationship between the Fermi level of this semiconductor and the allowable energy in the well can be controlled by the width of the well layer. can do.

In reality, depending on the combination of semiconductors, desired characteristics may not always be obtained due to the concentration of electrons accumulated in the channel, conduction band discontinuity, etc. In the present invention, we focused on the fact that the above conditions are well established when /lsb is selected as the first semiconductor and InAs is selected as the second semiconductor.

On the GaAs substrate, which is a ■-■ group compound semiconductor, Al2
Sb and InAs can be grown with near lattice matching, thus resulting in high quality epitaxial layers. Of these, A
l2Sb and InAs have a very large conduction band discontinuity (approximately 1.3 ev), so the carriers emitted from n-type doped A/2Sb are
Regardless of the thickness of TnAs, almost all of it is A I S b /
They accumulate at the T n As interface and contribute as conduction electrons.

On the other hand, when InAs alone is grown as a gate electrode, the interface between InAs and air or vacuum is inverted to n-type.
It functions as a gate electrode that does not require special doping.

Furthermore, the InAs/AffiSb junction on the surface side is produced by normal growth, and is not easily affected by damage caused by microprocessing or deposition of an insulating film for surface stabilization.

Furthermore, when InAs is used as the gate electrode, Al
The band discontinuity for Sb is almost equal between the gate electrode and the two-dimensional electrons, so if the thickness of the InAs well layer is large, it is possible to create a transistor with a threshold voltage of almost 0. , Sb/I
By using quantum well level formation by n A s / A I S b, the threshold voltage of a transistor can be arbitrarily designed.

As described above, according to the present invention, AffiSb/I fabricated on the ■-■ group compound semiconductor substrate p"-GaAs
By using the nA s / A I S b quantum well structure as a channel and the InAs semiconductor on the surface as a gate electrode, it is possible to provide a field effect transistor whose threshold voltage can be controlled by controlling the thickness of the quantum well layer.

〔Example〕

Hereinafter, In
A s / A Q S b / I n A s /
An example of a stacked structure of an AISb/Gasb substrate will be described.

FIG. 1 is a cross-sectional view of this laminated structure. This laminated structure consists of a p''-GaAs substrate 1, an A285 layer 2, an InA
An s layer 3, an AffiSb layer 4, and an InAs layer 5 are fabricated.

The doping concentration and thickness of each layer are as follows.

1! Sb layer 2; 8000 (undoped) t nAsq
3; 300 people (undoped) A/! Sb[4i
100 people (undoped) + 600 people (n-2 x 101
Bc111-'') + 50 people (undoped) InAs layer 5; 1000 people (n = 5 X10X
10l7'') A field effect transistor was fabricated using this structure by a normal process.The threshold voltage of this transistor was approximately O■.

On the other hand, in the above laminated structure, the well layer is InAsA
InAs/A (2S
b / I n A s / A Q S b / G
When a similar transistor was fabricated using an aAs substrate, it was found that the threshold voltage of this transistor changed by ~70 mV compared to the previous transistor.

As described above, the semiconductor device of the present invention includes the ■-■ group compound semiconductor substrate p"-GaSb and the ARSb/InAs/AIS formed on this semiconductor substrate.
The energy level of the electron channel of this four-layer structure is generated by a quantum effect, and therefore the thickness of the middle InAs in the four-layer structure can be controlled to form a transistor. threshold voltage can be controlled.

(Effects of the Invention) As explained above, according to the present invention, a transistor structure in which the threshold voltage is arbitrarily controlled on a ■-■ group compound semiconductor substrate is provided, and its use is expected in IV group compound semiconductor devices. be done.

[Brief explanation of drawings]

Figure 1 shows the T fabricated using molecular beam epitaxy.
n A s / A Q S b / I n A s
FIG. 2 is a cross-sectional view showing an example of a laminated structure of a /A 42 S b /GaSb substrate.

Claims (1)

[Claims] (1) III-V compound semiconductor substrate p^+-GaSb and AlSb/InAs/
It is composed of AlSb/InAs and includes a four-layer structure in which the energy level of the electron channel is generated by a quantum effect, and the threshold voltage of the transistor can be controlled by controlling the thickness of the InAs layer in the middle of the four-layer structure. A semiconductor device characterized by: