JPH06216370A - Quantum device - Google Patents

Abstract

PURPOSE:To enable modulating intensity of tunnel coupling between quantum structures. CONSTITUTION:Quantum fine lines QW are formed in an array type, in which fine-line-shaped I-type GaAs layers 1 serve as quantum well layers, and I-type AlGaAs layers 2 serve as barrier layers. An N-type AlGaAs layer 3 is formed on one end surface of the quantum fine lines QW, and a gate electrode G is formed on the layer 3. Electrons supplied from the N-type AlGaAs to the I-type GaAs layer 1 are 3-dimensionally confined in the I-type GaAs layer 1 in the vicinity of a hetero interface of the N-type AlGaAs layer 3 and the I-type GaAs layer 1. The intensity of electron cofinement in the axial direction of the I-type GaAs layer 1 is modulated by a voltage applied to a gate electrode G.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quantum device, and more particularly to a quantum device utilizing quantum mechanical tunneling of electrons between quantum structures.

[0002]

2. Description of the Related Art In recent years, in quantum wave electronics, a quantum structure such as an ultrafine wire or an ultrafine box structure having a cross-sectional dimension about the same as the de Broglie wavelength of electrons has attracted attention. These ultrafine wire and ultrafine box structures are called quantum wires and quantum boxes, respectively, and there is great interest in the quantum effect exhibited by one-dimensional or zero-dimensional electrons confined in the structure.

When a plurality of quantum structures as described above are arranged in close proximity to each other, these quantum structures can be coupled to each other by causing quantum mechanical tunneling of electrons between them. Therefore, it is possible to conduct information processing by conducting electrons by quantum mechanical tunneling between these quantum structures to change the electron distribution.

[0004]

When information processing is performed by conducting electrons by quantum mechanical tunneling among a plurality of quantum structures as described above, it is necessary to modulate the strength of tunnel coupling between these quantum structures. If it is possible, various information processing can be performed.

The strength of this tunnel coupling is determined by the tunnel transmittance (or tunnel probability) of electrons between quantum structures. The factors that determine this tunnel transmittance are:
These include the relative distance between quantum structures, the barrier height between quantum structures, and the effective mass of electrons in quantum structures. However, it is impossible to change the effective mass if the material forming the quantum structure is determined, and it is difficult to change the relative distance if the quantum structure is formed of a heterojunction. The remaining method is to change the barrier height between the quantum structures, but it has been difficult to do this actually.

Therefore, an object of the present invention is to provide a quantum device capable of modulating the strength of tunnel coupling between quantum structures by effectively changing the barrier height between quantum structures by applying a voltage to a control electrode. To provide.

[0007]

In order to achieve the above-mentioned object, the first invention of the present invention provides a plurality of columnar quantum well portions (1) and one end of each quantum well portion (1) with a space. And a control electrode (G) provided therein.

The second invention of the present invention is the first invention of the present invention.
In the quantum device according to the invention, a control electrode (G) is provided at one end of a quantum well portion (1) via an electron supply layer (3) or an insulating layer.

[0009]

According to the quantum element of the first aspect of the invention, by applying a voltage to the control electrode (G) provided at one end of the quantum well portion (1) with a space, the control electrode (G) side Modulates the strength of the axial electron confinement in the quantum well portion (1) of the portion of
Thereby, the strength of the tunnel coupling between the quantum structures can be modulated by effectively changing the barrier height between the quantum wells (1) in the array plane of the quantum wells (1), that is, between the quantum structures. it can.

According to the quantum element of the second invention, the first
Similarly to the quantum device according to the invention of claim 1, by applying a voltage to the control electrode (G) provided at one end of the quantum well portion (1) through the electron supply layer (3) or the insulating layer, a quantum electrode The strength of the tunnel coupling can be modulated. Here, when the control electrode (G) is provided via the electron supply layer (3), electrons are supplied from the electron supply layer (3) to the quantum well portion (1), and the electrons are controlled. Electrode (G)
It is three-dimensionally confined in the quantum well portion (1) of the side portion.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a quantum device according to the first embodiment of the present invention.

As shown in FIG. 1, in the quantum device according to the first embodiment, a plurality of thin linear i-type (intrinsic) GaAs layers 1 extending in the z-axis direction are close to each other in the xy plane. And these i-type GaAs are arranged in parallel with each other.
The portion between the layers 1 is filled with the i-type AlGaAs layer 2. And, by this, these i-type AlGa
An array of quantum wires QW having the As layer 2 and the i-type GaAs layer 1 as a barrier layer and a quantum well layer, respectively, is formed.

An n-type AlGaAs layer 3 as an electron supply layer is formed on one end face of each of the quantum wires QW, and the n-type AlGaAs layer 3 is provided on the n-type AlGaAs layer 3, for example.
A gate electrode G made of a metal forming a Schottky junction with the 1GaAs layer 3 is formed.

Next, a method of manufacturing the quantum device according to the first embodiment constructed as described above will be described.

First, as shown in FIG. 2, i-type GaAs is formed on a substrate (not shown) such as a semi-insulating GaAs substrate by metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). After the layer 1 is epitaxially grown, a mask 4 having the same shape as the cross-sectional shape of the quantum well portion is formed on the portion of the i-type GaAs layer 1 that will be the quantum well portion. This mask 4 is, for example,
A predetermined source gas is introduced into a vacuum chamber of an electron beam irradiation apparatus (not shown), and i-type GaAs is introduced in the source gas atmosphere.
The layer 1 can be formed by selectively irradiating the surface of the layer 1 with a sufficiently narrowed electron beam and depositing a decomposition product of the source gas on the irradiated portion.

Next, the i-type GaAs layer 1 is formed on the substrate by a dry etching method such as a reactive ion etching (RIE) method using a Cl-based etching gas using the mask 4 formed as described above. Anisotropically etched in the direction perpendicular to the surface, and as shown in FIG.
Layer 1 is patterned into a fine line.

Next, after removing the mask 4 by etching,
As shown in FIG. 4, i-type AlG is formed by the same method as described above.
A thin line-shaped i-type G is formed by epitaxially growing the aAs layer 2.
The space between the aAs layers 1 is filled. The surface of the i-type AlGaAs layer 2 is set to have substantially the same height as the upper end surface of the thin-line i-type GaAs layer 1.

Next, as shown in FIG. 1, after the n-type AlGaAs layer 3 is epitaxially grown on the entire surface by the same method as described above, the n-type AlGaAs layer 3 and the Schottky junction are formed on the n-type AlGaAs layer 3. A metal film for forming is formed by, for example, a vacuum vapor deposition method, and the metal film is patterned as needed to form a gate electrode G, thereby completing a target quantum device.

FIG. 5 shows an energy band diagram of the i-type GaAs layer 1, the n-type AlGaAs layer 3 and the gate electrode G in the z-axis direction, and FIG. 6 shows the i-type GaAs layer 1 and the i-type AlGaAs in the xy plane. 3 shows an energy band diagram of Layer 2. FIG. In the quantum device according to the first embodiment, the n-type AlGaAs layer 3 and the i-type GaAs layer 1 serving as the quantum well layer provide a modulation-doping structure.
The electrons in the GaAs layer 3 are supplied to the i-type GaAs layer 1. In this case, from the n-type AlGaAs layer 3 to the i-type Ga
The electrons supplied to the As layer 1 are confined in the x-axis direction and the y-axis direction by the heterojunction composed of the i-type AlGaAs layer 2 and the i-type GaAs layer 1, and the n-type AlGaA
It is also confined in the z-axis direction by the heterojunction composed of the s layer 3 and the i-type GaAs layer 1. That is, n-type AlGa
The electrons supplied from the As layer 3 to the i-type GaAs layer 1 are n
It is three-dimensionally confined in the i-type GaAs layer 1 in the vicinity of the hetero interface between the i-type GaAs layer 3 and the i-type GaAs layer 1. Therefore, in this case, the electrons confined in each quantum wire QW are equivalent to the electrons confined in the quantum box.

As shown in FIGS. 5 and 6, the quantum wire Q
The shift width ΔE of the ground energy level that rises due to the three-dimensional confinement of electrons in W is the confinement in the x-axis direction and the y-axis direction due to the heterojunction composed of the i-type AlGaAs layer 2 and the i-type GaAs layer 1. Is the sum of the energy increase ΔE _xy due to the bias voltage applied to the gate electrode G, that is, the energy increase ΔE _z (V _g ) due to the confinement in the z-axis direction that is a function of the gate voltage V _g .
That is, ΔE (V _g ) = ΔE _xy + ΔE _z (V _g ) (1).

Letting P be the tunnel transmittance of electrons between the quantum wires QW at this time, this is WKB (Wentzel-Kram).
ers-Brillouin) It is expressed as the following equation in the range of approximation. _{P~exp [-2L {2m e (V} 0 -ΔE (V g))} 1/2 / (h / 2π)] (2) However, m _e is the electron effective mass, V ₀ is AlGaAs /
The band discontinuity of the conduction band at the GaAs hetero interface, L is the distance between the quantum wires QW. From the equation (2), it is understood that the tunnel transmittance P can be controlled by the gate voltage V _g .

Now, when the gate voltage is V _g1 and V _g2
Let R be the ratio of the tunnel transmissivity to that when R = exp [2L (2m _e ) ^1/2 {(V ₀ −ΔE (V _g1 )) ^1/2 − (V ₀ −ΔE ( V _g2 )) ^1/2 } / (h / 2π)] (3). Here, as a typical example, i-type A
The 1 GaAs layer 2 and the n-type AlGaAs layer 3 are an i-type Al _0.4 Ga _0.6 As layer and an n-type Al _0.4 Ga layer, respectively.
Considering the case where _0.6 As layer, L~10nm, m _e
~ 0.10 m ₀ (where m ₀ is the rest mass of the electron), V
_{When 0 to} 0.3 eV and ΔE (V _g1 ) to 0.1 eV, Δ
When E (V _g2 ) is modulated, the tunnel transmittance ratio R can be modulated as ΔE (V _g2 ) R 0.15 eV 7.1 0.20 eV 71.7 0.25 eV 1482.9. That is, it is understood that the gate voltage V _g can modulate the tunnel transmittance ratio R between the quantum wires QW within a range of three digits.

As described above, according to this first embodiment,
By applying a gate voltage V _g to a gate electrode G provided on one end surface of each of the plurality of quantum wires QW via an n-type AlGaAs layer 3 as an electron supply layer, the electrons in the quantum wires QW are directed in the z-axis direction. The intensity of the tunnel coupling between the quantum wires QW can be modulated by modulating the energy increase ΔE _z (V _g ) due to the confinement of the quantum wires to modulate the tunnel transmittance P between the quantum wires QW. Since the strength of the tunnel coupling between the quantum wires QW can be modulated in this way, for example, information processing is performed by changing the electron distribution by conducting electrons by quantum mechanical tunneling between the quantum wires QW. In this case, various information processing can be performed.

If the quantum wires QW are arrayed periodically, a subband is formed by this artificial periodic structure. The width of this subband depends on the strength of the tunnel coupling between the quantum wires QW. Proportional. Therefore, by modulating the strength of this tunnel coupling with the gate voltage V _g ,
As shown in FIG. 7, subband modulation is possible. Since the effective mass of electrons and holes also changes due to this sub-band modulation, this sub-band modulation technique can be applied to, for example, a velocity modulation type transistor.

Next, a second embodiment of the present invention will be described. In this second embodiment, Petroff
Quantum having a structure equivalent to that of the quantum device according to the first embodiment using the method for forming a vertical superlattice (Appl. Phys. Lett. 45 (1984) 620) proposed by et al. And confirmed experimentally. The case of manufacturing an element will be described.

That is, in the second embodiment, as shown in FIG. 8, on a semi-insulating GaAs substrate 11 having a main surface in which atomic steps are parallel to each other, which is off by a small angle from a low index surface, For example, the i-type AlGaA is adjusted by adjusting the composition of the source gas to be supplied by MOCVD
s layer 12, i-type GaAs layer 13 and i-type AlGaAs
The layer 14 is repeatedly epitaxially grown by the required number of layers to form a quantum wire QW formed by an AlGaAs / GaAs heterojunction extending in the z-axis direction.

Next, the quantum wires QW thus formed are etched by the RIE method, for example, obliquely with respect to the z-axis direction, as shown in FIG.

Next, as shown in FIG. 10, the n-type AlGaAs layer 1 is formed on at least this obliquely etched surface.
5 is epitaxially grown, then n
A gate electrode G is formed on the AlGaAs layer 15. As a result, a quantum device having a structure substantially equivalent to that of the quantum device according to the first embodiment is completed.

Next explained is a quantum device according to the third embodiment of the invention.

As shown in FIG. 11, in the quantum device according to the third embodiment, for example, an n-type InAs layer 22 used as a gate electrode is formed on a semi-insulating GaSb substrate 21, and this n-type InAs is formed. A p ⁻ -type AlSb layer 23, which is a substantially insulating layer, is formed on the layer 22.
On the p ⁻ -type AlSb layer 23, a plurality of thin-line i-type InAs layers 24 that form the quantum well portion are arranged. Although not shown, these i-type InAs layers 24 are formed.
The portion between the two is filled with, for example, an i-type AlGaAs layer.

In the quantum device according to the third embodiment, for example, the i-type InA selected from the upper side in FIG. 11 is selected.
Input can be performed by making light incident on the s layer 24 to generate electron-hole pairs. In this case, this electron-
Information processing can be performed by causing electrons in the hole pairs to be conducted between the quantum wires QW by quantum mechanical tunneling to change the electron distribution.

The embodiments of the present invention have been specifically described above, but the present invention is not limited to the above-mentioned embodiments, and various modifications can be made based on the technical idea of the present invention.

For example, an i-type AlGaAs layer which is an insulating layer may be used instead of the n-type AlGaAs layer 3 in the above-mentioned first and second embodiments.
Alternatively, the gate electrode G may be provided at one end of the quantum wire QW at a distance without providing the type AlGaAs layer 3 and the i-type AlGaAs layer.

Further, in the above-described first and second embodiments, the quantum wire QW is formed by the AlGaAs (barrier layer) / GaAs (well layer) heterojunction, but this AlGaAs / GaAs heterojunction is formed. Alternatively, the quantum wire QW may be formed by, for example, a GaSb (barrier layer) / InAs (well layer) heterojunction.

[0036]

As described above, according to the present invention, a voltage is applied to a control electrode provided at one end of a plurality of columnar quantum well portions at a distance, and electrons are emitted in the axial direction of the quantum well portion. By modulating the confinement strength of the, the strength of the tunnel coupling between the quantum structures can be modulated.

[Brief description of drawings]

FIG. 1 is a perspective view showing a quantum device according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view for explaining the method of manufacturing a quantum device according to the first embodiment of the present invention.

FIG. 3 is a cross-sectional view illustrating the method of manufacturing the quantum element according to the first embodiment of the present invention.

FIG. 4 is a cross-sectional view illustrating the method of manufacturing the quantum device according to the first embodiment of the present invention.

FIG. 5 is an energy band diagram for explaining the operation of the quantum device according to the first embodiment of the present invention.

FIG. 6 is an energy band diagram for explaining the operation of the quantum device according to the first embodiment of the present invention.

FIG. 7 is an energy band diagram for explaining subband modulation in the quantum device according to the first embodiment of the present invention.

FIG. 8 is a perspective view for explaining a method of manufacturing a quantum device according to the second embodiment of the present invention.

FIG. 9 is a perspective view for explaining the method of manufacturing the quantum device according to the second embodiment of the present invention.

FIG. 10 is a perspective view for explaining the method of manufacturing the quantum device according to the second embodiment of the present invention.

FIG. 11 is a sectional view showing a quantum device according to a third embodiment of the present invention.

[Explanation of symbols]

 1 i-type GaAs layer 2 i-type AlGaAs layer 3 n-type AlGaAs layer QW quantum wire G gate electrode 11 semi-insulating GaAs substrate 12, 14 i-type AlGaAs layer 13 i-type GaAs layer

Claims (2)

[Claims] 1. A quantum device having a plurality of columnar quantum well portions and a control electrode provided at one end of the quantum well portion with a space therebetween. 2. The quantum device according to claim 1, wherein the control electrode is provided at one end of the quantum well portion via an electron supply layer or an insulating layer.