JPS62219967A - Semiconductor device - Google Patents

Abstract

PURPOSE:To avoid degradation of the mobility and speed of carriers of a two-dimensional carrier gas layer in a carrier traveling semiconductor layer caused by LO (longitudinal optical) phonon scattering and improve sheet density by a method wherein one of two hetero-junction planes of which the two-dimensional carrier gas layer is composed is formed by laminating compound semiconductor layers which have no overlapping of oscillation frequency in the LO phonon branch. CONSTITUTION:1st and 2nd carrier supply layers 1 and 2, which supply carriers to a carrier traveling semiconductor layer 3 in which carriers exist locally and which are made of semiconductors with wider gaps compared to the gap of the carrier traveling semiconductor layer 3 as shown in an energy band model of a conduction band side, are provided on both sides of the layer 3 holding the layer 3 between them and 1st and 2nd hetero-junction planes J1 and J2 are formed. The two junction planes J1 and J2 are, or the one junction plane J1 is, composed of 1st and 2nd wide gap semiconductor thin film layers 11 and 12 which have wide band gaps. The thickness (a) of the carrier traveling semiconductor layer 3 in which carriers exist locally conforms to the relation a<=pi/q, wherein (q) is the momentum of the carrier, for instance electron, in the layer 3.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a semiconductor device, particularly a semiconductor device using a double heterojunction surface, such as a two-dimensional electron gas layer type field effect transistor (FIT) using a double heterojunction surface. ,
Or it relates to semiconductor devices such as speed modulation transistors VMT'.

[Summary of the invention]

The present invention provides a semiconductor device having a double heterojunction surface, in which at least one of the two heterojunction surfaces forming a two-dimensional carrier gas layer of each of the carrier (carrier)' traveling semiconductor layers is provided. The surface is constructed by superimposing a compound semiconductor layer on an LO (vertical optical) phonon branch with no frequency overlap, and 2
dimensional carrier mobility reduction in the carrier gas layer;
Avoiding a decrease in speed and further improving the sheet density of the carrier.

[Conventional technology]

FETs that use a two-dimensional carrier gas layer as a carrier transport channel have the advantage that by utilizing the two-dimensional carrier gas layer, carrier mobility due to impurity scattering can be ignored and high mobility can be expected. The problem is that the sheet density is low. To deal with this, we formed two heterojunction surfaces with wide-gap semiconductor layers that serve as electron supply layers on both sides of a common carrier transport layer, thereby forming two two-dimensional carrier gas layers. , an FET using a two-dimensional carrier gas layer with a double heterojunction surface was proposed, thereby doubling the carrier density.

However, even in a FEET using such a double heterojunction type two-dimensional carrier gas layer, especially 100
At temperatures above K, problems arise in that carrier mobility and velocity decrease due to LO phonon scattering in the two-dimensional carrier gas.

This means that a double heterojunction type VMT has two heterojunction surfaces, each forming a channel of a two-dimensional carrier gas layer with a different carrier mobility, and speed modulation is performed by switching and utilizing these channels. For example, even in the channel that should originally be formed with sufficiently high mobility and speed, the above-mentioned L
There is a problem in that sufficiently high mobility and velocity cannot be obtained due to the problem of O phonon scattering.

[Problem that the invention seeks to solve]

The present invention avoids the problem of the influence of LO phonon scattering in at least one two-dimensional carrier gas layer in the double heterojunction type two-dimensional carrier gas layer type semiconductor device described above, and achieves high carrier density and high mobility. Forming a carrier traveling channel with.

[Means for solving problems]

In the present invention, for example, as shown in FIG. 1 or FIG. 3, the carrier transport semiconductor layer (3) that localizes carriers is sandwiched between the two surfaces thereof, and the conduction layer as shown in FIGS. 2 and 4, respectively. As shown in the energy band model on the band side, the first and second carrier supplies are made of a semiconductor with a wider gap than the carrier traveling semiconductor layer (3) and supply carriers to the carrier traveling semiconductor layer (3). layer(
11 and (2), and the first and second heterojunction surfaces J
The structure shall have a construction and a J2. In this structure, especially in the present invention, for example, the rejoining surfaces J1 and J2 as shown in FIG. 1, or one junction J□ as shown in FIG. However, it is constituted by first and second wide-gap semiconductor thin film layers (11) and (12) having a wide band gap.

These wide gap semiconductor layers (11) and (12) and the carrier traveling semiconductor layer (3) have a momentum-frequency dispersion diagram whose 0 phonon branch is, for example, the curve (5) in FIG.
As shown in 1A) and (51B''), they are made of compound semiconductors that do not overlap in frequency with each other. That is, for example, each semiconductor (3) and thin film layers (11) and (12) are composed of A, B, and C, respectively. Compound semiconductors (A
In the case of B) and (CD), a material is selected that has a large difference in atomic weight between the elements with smaller atomic weights among the constituent elements of each compound semiconductor. For example, as (AB), GaAs , as (CD) All
As can be used. In such a system,
GaAs-like and A1^S-like LO phonons cannot penetrate into other layers and are confined in each layer.

And wide gap semiconductor thin film Ji! In (11) and (12), the thickness is set to 1 to 3 atomic layers so that LO phonons are sufficiently localized and electrons are allowed to tunnel. The carrier traveling semiconductor layer (3) that localizes carriers has a thickness a such that a≦□
...(1), q is the momentum of this carrier, for example, a carrier in the semiconductor layer (3) that localizes electrons, and this q is q''mvS ...(2), mI
' is the effective mass of carriers, and VS is the saturation velocity of carriers in the bulk of the constituent material of this semiconductor layer (3).

Then, the confined momentum π/a is -2 for q
Fulfills 9 relationships.

On the other hand, means for applying an electric field to the Peter junction surfaces J1 and J2 in the plane direction, that is, each source and drain electrode (4
s) and (4d) are provided.

And source and drain electrodes (4s) and (4d)
A gate electrode (5G) or first and second gate electrodes (5Gs) and (5G2) are provided in between.

In such a configuration, each gate electrode (5G).

By applying a required voltage to (5G) and (5G2), carrier transport channels C1 and C2 are generated by a two-dimensional carrier gas layer on the respective heterojunction surfaces J and J2 of the carrier transport semiconductor layer (3), It can be controlled such as disappearing.

[Effect]

According to the configuration of the present invention described above, the carrier sheet density ns is increased by localizing the carriers on at least one heterojunction surface, and the LO phonons are localized at this junction surface, thereby increasing the carrier sheet density ns. The carrier mobility of the two-dimensional carrier gas layer related to the surface can be increased.

Incidentally, the carrier mobility μ is μ侃□ ... (3) (W is the scattering probability between the carrier and the LO phonon), and W is Woc 5M"4' r d" P ...
...(41 (M is a matrix element)) Now, in the device of the present invention, a matrix with a superlattice structure is formed by laminating the carrier traveling semiconductor layer (3) and the wide gap semiconductor thin film layer (11) or (12). Regarding the ratio of element yI LFT SL to that of M2O of a compound semiconductor bulk that does not depend on superlattice structure, for example, Workbook on International
Conference on Electronic Properties on 2-Dimensional System (N, S
awaki, Workbook of Intern
ational conference on el
electronic properties of
2-dimension system, Kyoto
+ 1985+ P639), qJ2+(
qzi )' (5). Here, Qz is the momentum of the carrier in the direction perpendicular to the junction surface of the superlattice structure, and q is the momentum in the direction perpendicular to it. In the above-described configuration of the present invention, the traveling direction of the carrier is selected to be in the plane direction of the heterojunction surface J1 or J2 of the semiconductor rfi (3) and the wide gear semiconductor iFJ layer (11) or (12).
z~0. According to this, from equation (5), q↓2 M uT! EL/M30 = □qJ2+()
2...(5)'.

In the present invention, a is defined as π in equation (1). From equations (3) and (4), it can be seen that the mobility μ is sufficiently large.

〔Example〕

An example of a double heterojunction type two-dimensional electron gas layer channel type FET will be described with reference to FIG. In this case, for example, on a Cr-doped semi-insulating GaAs compound semiconductor substrate (21), a second carrier supply semiconductor layer (2), a second wide gap semiconductor thin film layer (12), and a carrier, that is, an electron transport semiconductor are sequentially formed. Layer (3) and first wide gap semiconductor thin film layer (11)
and the first carrier supplying semiconductor layer (2) are continuously epitaxied by MOCVD (metal organic chemical vapor deposition) or MBR (molecular beam epitaxy), with the carrier traveling layer (3) in between. Then, first and second heterojunction surfaces J1 and J2 are formed on both surfaces thereof.

Then, source and drain electrodes (4S) and (4d
) is formed by alloying the layer from above the first carrier supplying semiconductor layer (1) to a depth reaching the first and second heterojunction surfaces J1 and J2, and between both electrodes (4S) and (4d). For example, a Schottky gate electrode (5G) is formed.

First and second carrier supply semiconductor layers +1) and (2)
is composed of an n-type compound semiconductor layer made of, for example, 8Ilo, 3Gao, yAs, the carrier transport semiconductor Jii (3) is composed of GaAs, and the first and second wide gap semiconductor thin film layers (11) and (12)
is constituted by, for example, a diatomic layer of an IAs compound semiconductor layer.

According to such a configuration, the carrier traveling semiconductor layer (3)
A double heterojunction two-dimensional electron gas layer type FET is constructed in which channels C1 and C2 of first and second two-dimensional electron gas layers are formed on both sides of the conduction band side. is as shown in Figure 2.

FIG. 3 shows an example of a speed modulation transistor according to the present invention. In this case, an n-type buried layer serving as the second gate electrode (5G2) is provided on the substrate (21), and the first channel C1 The first heterojunction surface J1 forming
This is a case where, for example, a binary compound semiconductor thin film layer (11) having a first wide gap is provided only in the first channel C1 to obtain high electron mobility for the first channel C1. FIG. 4 shows an energy band model in this case. still,
In FIG. 3, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and redundant explanation will be omitted. In this case, the first and second channels C1 and C2 are switched by voltages applied to the first and second gate electrodes (5G1) and (5G2).

〔Effect of the invention〕

According to the apparatus of the present invention, for example, for both channels C1 and C2 in the example of FIG. 1, and for one channel in the example of FIG. 3, the sheet density ns of the carrier in the channel can be increased by the two-dimensional carrier gas layer. By being able to do this, the gra can be improved. Also, L.O.
10 by confining phonons.
High carrier mobility can be obtained even at temperatures as high as 0 or higher, and high speeds can be achieved. Furthermore, it is expected that an increase in the saturation speed vg will also be brought about. For example, if we look at the temperature dependence of electron mobility in a high-purity n-GaAs crystal,
As shown in Figure 6, the overall electron mobility is the curve (61
), it rapidly decreases above about 100K. In the figure, the curve (62) is due to ionized impurities;
(64) is due to LO phonons, (63) is due to neutral impurities, (65) is due to deformation potential, and (66) is due to piezoelectric scattering.

The decrease in electron mobility of about 100 or more is largely dependent on LO phonons. However, according to the present invention, L
By confining O phonons, it is possible to effectively improve the drop in mobility, especially at high temperatures of 100 or higher, and in this two-dimensional carrier gas channel, it is possible to reduce the mobility near room temperature while maintaining high speed. It offers many benefits such as allowing its use in

[Brief explanation of drawings]

1 and 3 are respectively enlarged linear cross-sectional views of the semiconductor device according to the present invention, FIGS. 2 and 4 are band model diagrams thereof, FIG. 5 is a momentum-frequency molecule diagram, and FIG. is a diagram showing the temperature dependence of electron mobility. (21) is the substrate, (1) and (2) are the first and second carrier supply layers, (3) is the carrier transit layer, and (11) and (12) are the first and second wide gap semiconductor layers. It is.

Claims (1)

[Scope of Claims] A carrier traveling semiconductor layer that localizes carriers, and a wide gap carrier supply layer sandwiching the carrier traveling semiconductor layer and forming a heterojunction surface on both sides thereof are provided, and the carrier traveling semiconductor layer In a double heterojunction type semiconductor device in which first and second carrier traveling channels are formed by two-dimensional carrier gas layers on both sides of the semiconductor device, at least one of the first and second heterojunction surfaces is dispersed. In the relationship, the LO phonon branch is constituted by a heterojunction between the LO phonon branch of the carrier traveling semiconductor layer and a wide gap semiconductor thin film layer in which the frequencies do not overlap, and the carrier traveling semiconductor layer has a thickness a of a ≦π/
q (However, q is the carrier momentum q=m^*vs in the carrier traveling semiconductor layer, m^* is the effective mass of the carrier, and vs is the saturation velocity of the carrier in the bulk of the constituent material of the semiconductor layer. ), and further comprising an electric field applying means for selecting a traveling direction of the carrier in a direction along the heterojunction surface.