JPH02132864A - Quantum interference type semiconductor device - Google Patents

Abstract

PURPOSE:To make carriers, which are induced into an element, the same in speed by a method wherein a resonant tunnel barrier is provided to a contact section through which the carriers are introduced into a channel. CONSTITUTION:A side face of a formed epitaxial crystal is obliquely etched to form a slope where a resonant tunnel barrier structure is formed, the resonant tunnel barrier composed of a first barrier layer 8, a well layer 9, and a second barrier layer 10 and a source contact layer 11 are formed, and furthermore a source electrode 13, a drain electrode 14, and a gate electrode 15 are provided. As mentioned above, a resonant tunnel barrier is provided, whereby all injected electrons are made to have the same energy, so that the variability of the phase difference of an electron wave function which occurs when a control voltage is applied is eliminated and the range of a conductance change of an element is almost equal to a theoretical value.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to a quantum interference semiconductor device, and an object of the present invention is to keep the speed of carriers introduced into the device constant. It relates to a quantum interference type semiconductor device that controls the conductance of an element by controlling the phase difference of the wave function of carriers traveling through a provided channel.

In recent years, with advances in processing technology related to the formation of semiconductor devices, such as lithography and crystal growth, semiconductor elements with various structures and functions have been put into practical use. Datt
The quantum interference device proposed by et al. For details of the device, see (1) S. Datta e
t at. Phys. Rev. Lett. ．． 54.
p. 2344(2) S. Datta et al.
Appl. Phys. Lett. , ia. p. 4
87(3) Bandyopadhyay et al.
．． IEDM-'86. Tech. Dig. , p. 7
6, and its structure and operation can be roughly understood as follows.

[Conventional technology]

FIG. 6 is a schematic diagram of the quantum interference device shown in the above-mentioned document (1). The paper surface of the figure is an X-Z plane, and it can be considered that the semiconductor substrate surface on which elements are actually formed is an X-Y plane, and a vertical cross section thereof is shown. A channel 102 formed of semiconductor materials with different band gaps inside a bulk semiconductor 101 that is a base body is divided into two paths 102' at the part involved in changing the conductance, and furthermore, there are two paths 102' at both ends of the channel. It has a structure in which contacts 103 are provided.

When a voltage is applied between both contacts of the element as shown in the figure, electrons sent from the left contact travel to the right through the channel, but in the part where the channel is divided into two paths, the wave functions of the electrons are It divides into two paths, and then overlaps again by merging channels.

At that time, if an electric or magnetic field is applied to the channel, a phase difference will occur in the wave functions traveling on each of the two paths, and when they are superimposed again, they will interfere with each other, so the effective current value in the channel will be The effect is increased or decreased.

Looking at this effect from the perspective of electron transmittance, the conductance G of the element is G = Go (1 + < co sφ>) −−−−−−
(1) becomes. Here, φ is a phase shift caused by an electric field or a magnetic field, and <Cosφ> is an ensemble average of electrons passing through the element.

The phase difference φ (e Iec tro
static Ahavonov-Bohm effe
ct) as a function of the applied electric field ε2, φ=eεz L d / 'K V x '
'−'−”−” is given by (2). Here, e is the electron equivalent, L is the length of the divided channel in the electric field, d is the distance between the respective axes of the divided channel, 5 is the blank constant, and 8 is the traveling speed of the electron in the channel axis direction. be.

Above (1). From equation (2), if the electric field applied in the Z direction is changed to change the phase difference φ, the conductance G
It can be seen that the changes. That is, the conductance C of the element oscillates as shown in FIG. 7 as the phase difference φ changes.

The above is an overview of the quantum interference device, but when the operation of the device is examined in detail, it is found that there are the following problems.

(Problem to be Solved by the Invention) According to equation (2) above, the phase difference φ is not only a function of the electric field ε2, but also a function of the velocity vX of the injected electrons, so the rapid release of the electric hand In other words, if there are variations in the energy of electrons, there will be variations in the phase difference φ, and the width of change ΔG in the conductance of the element will become small.If ΔG/G is not large enough, it will not function as an active element. Therefore, it is desirable that the energy of the injected electrons be constant.

Means for Solving Problem C] In order to eliminate the variation in VX that causes a reduction in ΔG/G of the device, in the quantum interference device of the present invention, only electrons with a specific energy are injected into the electron injection part of the device. The structure is equipped with a resonant tunnel barrier as a structure that allows electrons to pass through, so that only electrons at a specific energy level are injected.

[For production]

FIG. 3 is an energy band diagram illustrating the function of the resonant tunnel barrier used in the present invention. Figure (a) shows a state in which no voltage is applied in the father direction, and when a semiconductor region B with a narrower forbidden band exists sandwiched by a semiconductor region A with a wider forbidden band, Focusing on the conduction band,
A standing wave of electrons will form in a quantum well that is sandwiched by barriers on both sides.

As shown in Figure 3(b), when an electric field is applied in the X direction, the energy band deforms, and when the energy level of the standing wave and the lower end of the conduction band match, the electron The tunneling probability of electrons becomes close to 1, and the tunneling probability of electrons with other energies becomes close to O.

In other words, the resonant tunnel barrier functions as an extremely high-Q bandpass filter that allows only electrons that resonate with the quantum well to pass through, and has a thermal spread as depicted on the left side of the figure (b). Among the electron group, only electrons with energy at the resonance level pass through this barrier, as shown on the right side of the figure.

In principle, the same effect can be obtained by using a material other than a resonant tunnel barrier that exhibits a similar filter effect or has the function of aligning the phase of the electron wave function. By aligning the speeds of the electrons, variations in phase difference can be eliminated.

According to a report by Tsuchiya et al., the relationship between the thickness of the barrier constituting a quantum well and the half-width ΔE of the energy level of the lowest order standing wave is as shown in Figure 4 (M.Tsuchiya et al.
a et al, Applied Electronics Physics Subcommittee Research Report, No.
410. p. 25). In the figure, a + b + C +
d is the value when the width of the well is different.

The value of ΔE=several tens of μeV achieved by providing a resonant tunnel barrier is of course sufficiently small compared to the thermal energy of 26 meV at room temperature, and the thermal energy of 4.2 K is 0.
．． Since it is about one order of magnitude smaller than 36 m e V, the blur in the implanted energy due to the thermal blur of the Fermi surface is reduced to a negligible level.

Furthermore, the standing waves in quantum wells are not only of first order, but also of higher order, and the relationship between electron energy and barrier transmission coefficient in these waves is as shown in FIG. The peak at 65 meV in the figure is due to the first-order resonance level, and the peak at 260 meV is due to the second-order resonance level.

The ratio of the respective velocities V,, V2 of the electrons injected by these energy levels is V+/Vz=(26 0 meV/6 5 meV)""=
2, so by equation (2) above, the same control voltage ε2
The phase difference caused by this becomes 1/2, and the period in which the conductance G changes is doubled.

If the resonant tunnel barrier is provided in the electron injection part in this manner, even if the dimensions and shape of the elements are the same, the characteristics of the elements can be made different by selecting the usage conditions.

〔Example〕

FIG. 1 is a schematic diagram showing the cross-sectional structure of an element according to an example of the present invention. A GaAs buffer layer 2, a first
n-GaAs layer 3, first i-GaAs layer 4, second n-CraAs layer 5, second i-CyaAs layer 6, third
It has a structure in which n-GaAs layers 7 are sequentially stacked, and a first barrier N8, a well layer 9,
A second barrier layer 10 and a source contact layer 11 are provided.

Furthermore, a source electrode 13 and a drain electrode 1 necessary for the element
4. Although the gate electrode 15 is provided, the drain Ul
Alloy region 12 for making i an ohmic contact
are also formed by impurity diffusion.

The device of the above embodiment is formed using an epitaxial crystal prepared as follows. First, GaAs or S
A GaAs buffer N2 is grown on a single crystal substrate 1 of i,
On top of that, n
Type GaAs layer 3.5.7 and i-type Cy without adding impurities
The aAs layers 4.6 are epitaxially grown alternately.

These two layers of i-GaAs are the current path and correspond to the two-split channel in the device shown in FIG. 6, but in the device shown in FIG. However, in this example, the structure exhibits conductivity by being supplied with electrons from the n-GaAs layers sandwiching i-GaAsJi. Note that the thickness and path length of these i-CraAs layers are determined at the time of device design.

The sides of the epitaxial crystal formed as described above are etched diagonally to create slopes on which resonant tunneling structures are formed. The reason why this surface is an inclined surface is because the wafer-shaped epitaxial crystal is to be processed, and when a processing method that allows a specified crystal growth on a vertical surface is adopted, it is necessary to use a vertical surface instead of an inclined surface. I don't mind.

The etching method is performed while irradiating ultraviolet light of about 250 nm, for example. Two gas etching is used.

Since this processing method exhibits anisotropy depending on the plane orientation, it is suitable for forming slopes, and does not cause mechanical damage to the element forming region.

A resonant tunnel barrier layer is formed on this slope. This is Af
A barrier layer several nm thick made of a material with a wider band gap than GaAs, such as GaAs, is sandwiched between a well layer made of a CyaAs layer of similar thickness.
As shown, it is composed of a first barrier layer 8, a well layer 9, and a second barrier layer JILO.

The resonant tunnel barrier structure having a superlattice structure is suitably formed by atomic layer epitaxy, which is performed by repeatedly supplying a material exhibiting a self-limiting effect for a predetermined period of time. The number of atomic layers to grow in each layer is determined at the time of device design.

After forming the resonant tunnel barrier, a contact layer l1 made of n'-GaAs is epitaxially grown to form C r /
A source contact electrode 13 of Au is formed by a method such as sputtering.

On the other hand, on the drain side of the element, an alloy region 12 is formed by impurity diffusion, and an AuGe/Au drain electrode 14 is provided in that region. Furthermore, a gate electrode 15 is deposited for applying a control voltage to the divided electron paths.
This forms a Schottky barrier with respect to the GaAs layer 7, and Al is used, for example. In the operation of the device, the phase difference between the two divided channels is controlled by the voltage applied to the gate.

The above is an example of the structure and formation method of the device of the present invention having a superlattice-structured resonant tunnel barrier. However, the resonant tunnel barrier can also be created by partially applying a voltage. The element of the present invention can also be configured with a structure in which a resonant tunnel electrode is provided on the wafer.

An example of the planar shape of the element in that case is shown in FIG. The shape of the channel provided inside the host crystal and the structure of the drain and gate are the same as those of the device shown in FIG. u G e /
A source electrode 23 of Au is provided, and two Schottky barrier type resonant tunnel electrodes 28 and 29 are further provided on the host crystal surface between the source side alloy region and the gate electrode. There is.

By applying a bias voltage to the resonant tunnel electrode, the N of the channel below the electrode changes and an effective resonant tunnel is formed, so that the speed of the injected electrons can be made uniform.

〔Effect of the invention〕

As explained above, in the quantum interference device of the present invention, the energy of the injected electrons is made constant by using a special source structure, so that the phase difference in the wave function of the electrons that occurs when a control voltage is applied is There is no variation in
The range of change in conductance of the element becomes close to the theoretical value.

[Brief explanation of the drawing]

Fig. 1 is a schematic cross-sectional diagram showing the structure of an element of an example, Fig. 2 is a schematic diagram showing the structure of an element of another example, Fig. 3 is an energy band diagram of a resonant tunnel barrier, and Fig. 4 is a barrier diagram. Figure 5 is a diagram showing the relationship between structure and energy level half width, Figure 5 is a diagram showing the relationship between electron energy and transmission coefficient, Figure 6 is a cross-sectional schematic diagram showing the structure of a known quantum interference device, and Figure 7 is a diagram showing the relationship between electron energy and transmission coefficient. It is a diagram showing the relationship between conductance and phase difference of an element, in which 1 is the substrate, 2 is the buffer layer, and 3, 5.7 is n-Aj! GaAs, 4 and 6 are i-GaAs, 8.10 is a barrier layer, 9 is a well layer, 11 is a contact layer, 12.22 is an alloy region, 13.23 is a source electrode, 14 is a drain electrode, 15 is a gate electrode , 28 and 29 are resonant tunnel electrodes, 101 is a semiconductor matrix, 102 is a channel, 102' is a divided path, and 103 is a contact. (, L) No-bias state (b) Bias applied state Energy band diagram of resonant tunnel barrier Figure 3 1.0 2.0 3.0 Thickness (nm) Figure 4: Schematic cross-sectional diagram showing the structure of an element in one substrate embodiment Figure 1: Resonance tunnel electrode Schematic diagram showing the structure of an element in another embodiment Figure 2: Electron energy (meV) Electron energy 11-L-12 101 Semiconductor matrix A schematic cross-sectional diagram showing the structure of a known quantum interference element FIG. 6

Claims (1)

[Claims] A wave function of electrons traveling in a channel consisting of two parallel paths provided in a semiconductor matrix causes a phase difference between the paths due to an electric field or a magnetic field applied to the channel. 1. A quantum interference semiconductor device that uses quantum interference to change conductance, characterized in that a resonant tunnel barrier is provided in a contact portion for introducing carriers into the channel.