JPH01225175A - field effect transistor - Google Patents

Abstract

PURPOSE:To obtain a field effect transistor having good high speed performance by employing a structure in which optical phonon scattering is localized in a two-dimensional direction as a channel. CONSTITUTION:Two types of semiconductors A, B having different phonon dispersing relations are employed. Then, a source 3, a drain 4 and a gate 5 are formed on a substrate having a structure in which electrons are regularly aligned at a sufficiently shorter interval than one side of a fine line with one- dimensional quantum fine line having approximately de Broglie wavelength of electron in the length of the sectional direction of a layer 1 made of the semiconductor A and the interval is buried with a layer 2 of the semiconductor B to obtain a field effect transistor. Accordingly, phonon vibrations 8-11 are localized in two-dimensional direction, thereby largely increasing the mobility in the channel. Thus, the high speed characteristic of a transistor is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a field effect transistor, and particularly to a high mobility field effect transistor that utilizes the phonon localization effect in a superlattice structure.

[Conventional technology]

The operating principle of a field effect transistor is, for example, Tse (S
ze), “Physics of Semiconductor Devices J”
Johns Wiley & Sump, 1981
ley and Sons).

One method of improving the characteristics of this transistor is to increase the mobility of electrons in the channel, as described in the above-mentioned document. This reduces the transit time of electrons from source to drain, improving high-speed performance.

Optical phonon scattering is one of the factors that reduce the mobility of semiconductors. In order to reduce this optical phonon scattering, conventionally, two types of semiconductors are used to create a superlattice with an alternating layer structure, and phonon vibrations are localized in one layer, reducing scattering and moving. A method has been proposed to increase the degree of

Translated literature “Journal of Physics C:
Solid State Physics (Journal
of Physics C:5olid 5tate
According to a paper published in ``Physics'', 1986, volume 19, page 4956, gallium arsenide (GaAs) and aluminum gallium arsenide (
A superlattice with an alternating layer structure of Aj7GaAs) is created and AJ? If the thickness of the GaAs layer is made sufficiently shorter than the electron de Broglie wavelength (several tens of people), the electrons will spread throughout the superlattice. On the other hand, optical phonon vibration is caused by GaAs and ^j
7 Vibration nodes are formed at the heterointerface made of GaAs, and A
e It cannot penetrate into GaAs and is localized in GaAs. That is, long wavelength optical phonon oscillations are prohibited.

FIG. 3 is a schematic cross-sectional view for explaining the localization of optical phonon vibrations in a conventional superlattice structure.

GaAs layer 12 and a layer thickness Aj? sufficiently thinner than the de Broglie wavelength of electrons. GaAs layers 13 are alternately stacked to form a superlattice. Optical phonon vibrations A whose wavelength is shorter than the thickness of the GaAs layer occur similarly to the case of bulk GaAs. The optical phonon vibration B, whose half wavelength is equal to that of the GaAs layer, is the vibration with the longest wavelength that can be realized. The optical phonon vibration C is caused by the GaAs layer 12 and the AeGaAs
This is prohibited because there are no vibration nodes at the heterointerface consisting of layer 13.

As is clear from the above explanation, in the superlattice with the above structure, restrictions are placed on the vibrational mode of optical phonons that can be realized, so optical phonon scattering is suppressed and high-mobility electron transport is achieved compared to bulk GaAs. happen. By employing this structure in the channel of a field effect transistor, high-speed performance is improved.

[Problem to be solved by the invention]

However, in this structure, among the optical phonon vibration modes realized in three-dimensional directions, only the one-dimensional direction perpendicular to the hetero-interface is modulated, so the effect of localization of the vibration modes of free and non-contact is small.

An object of the present invention is to localize phonon vibration in two-dimensional directions, obtain a channel with higher mobility, and provide a field effect transistor that operates at high speed.

[Means to solve the problem]

In the field effect transistor of the present invention, two types of semiconductors A and B having different dispersion relationships of phonon oscillations are prepared, and semiconductor A
The one-dimensional quantum wires, whose length in the cross-sectional direction is about the de Broglie wavelength of an electron, are regularly arranged in two cross-sectional directions at intervals sufficiently shorter than one side of the wire, and the layers of semiconductor B It is characterized by having channels arranged so as to fill each other.

[Effect]

In the present invention, by localizing phonon vibration in two-dimensional directions and reducing phonon scattering using two types of semiconductors with different dispersion relationships of phonon vibration, a structure with high mobility is obtained, and the channel of a field effect transistor is It is used to realize transistors with good high-speed performance.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a perspective view showing an embodiment of the present invention.

Using two types of semiconductors A and B with different phonon dispersion relationships, a one-dimensional quantum wire whose length in the cross-sectional direction of the layer 1 made of semiconductor A is about the de Broglie wavelength of an electron is sufficiently shorter than one side of the thin wire in the two cross-sectional directions. A conventional process is applied to a substrate having a structure in which the semiconductor B layers 2 are arranged regularly at intervals, and the layers 2 of the semiconductor B are arranged so as to fill the intervals, and the sources 3. A drain 4 and a gate 5 are formed to obtain a field effect transistor.

With this structure, optical phonon vibrations are localized in two-dimensional directions,
The improvement in mobility will be explained using the drawings.

FIG. 2 is a schematic cross-sectional view for explaining that phonon vibrations in two-dimensional directions are localized.

In the figure, 8.9 represents the short and long wavelength optical phonon vibrations in the longitudinal direction, and 10.11 represents the short and long wavelength optical phonon vibrations in the transverse direction, respectively, as described in the above-mentioned translation. , the heterointerface must be a node of phonon vibration. Due to this lick, short wavelength phonon vibrations 8 and 10 are realized, but long wavelength phonon vibrations 9 and 11 are not realized. In other words, phonon vibrations are localized in two-dimensional directions. On the other hand, the semiconductor B layer 2 is sufficiently thinner than the electron de Broglie wavelength, and the electrons are spread over the entire substrate.

Therefore, the two-dimensional localization of phonon vibrations significantly increases the mobility in the channel and improves the high-speed characteristics of the transistor.

In this example, the source and drain are provided in the length direction of the thin wire, but as shown in the above-mentioned literature, only the conduction in the direction perpendicular to the direction in which phonons are localized is improved. The source train may be provided in the cross-sectional direction of the thin wire, since it also improves other directions.

〔Effect of the invention〕

As explained above, the present invention employs a structure in which optical phonon scattering is localized in two-dimensional directions for the channel, so that it has the effect of providing a field effect transistor with good high-speed performance.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing an embodiment of the present invention, Fig. 2 is a cross-sectional view to explain that optical phonon vibration is localized in two-dimensional directions, and Fig. 3 is an optical diagram of a conventional superlattice structure. FIG. 3 is a schematic cross-sectional diagram for explaining localization of phonon vibrations. DESCRIPTION OF SYMBOLS 1... Semiconductor A layer, 2... Semiconductor B layer, 3... Source, 4... Drain, 5... Gate, 8-11.
・・Optical phonon vibration, l 2−・−GaAs layer, 13
-ke GaAs layer. Agent Patent Attorney Oto Uchihara M57 Zuzuki Z Zusei J Dia

Claims (1)

[Claims] Two types of semiconductors A with different dispersion relationships of phonon vibrations,
B is prepared, one-dimensional quantum wires whose length in the cross-sectional direction of a layer made of semiconductor A is about the de Broglie wavelength of an electron are regularly arranged in two directions of the cross-section with an interval sufficiently shorter than one side of the wire; A field effect transistor characterized in that it has a channel arranged so that a layer of semiconductor B fills the gap.