JPH06125074A - Quantum element - Google Patents

Abstract

PURPOSE:To realize a quantum box set element or a quantum fine wire set element in which a strength of coupling between quantum boxes or quantum fine wires can be controlled at each box or fine wire. CONSTITUTION:After an array of quantum dots 4 is formed, the dot 4 selected in a raw material gas atmosphere is irradiated with an electron beam to form a GaAs layer 8 having selected thickness and shape, and a strength of coupling between the adjacent dots 4 is controlled. Or, a barrier layer having selected composition or selected thickness is formed in a region between the selected dots 4. In the fine wire set element, the array of the fine wires is formed, and then the above treatment is executed on a part in which the selected fine wire is selected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quantum device using a quantum box or a quantum wire.

[0002]

2. Description of the Related Art In recent years, in quantum wave electronics, a so-called quantum box structure, ie, a so-called quantum box structure having a cross-sectional dimension about the same as the de Broglie wavelength of an electron, has been attracting attention, and it is confined within this quantum box. There is great interest in the quantum effects exhibited by dimensional electrons.

As one of the quantum elements using such a quantum box, a quantum box assembly element (also called a quantum box coupling element) is considered, and research has been started toward its realization. This quantum box assembly element intends to perform information processing by arranging a plurality of quantum boxes and changing the electron distribution by causing transition of electrons by quantum mechanical tunneling between these quantum boxes.

[0004]

In order to realize the above quantum box assembly element, the following conditions must be satisfied.

The size of each quantum box is sufficiently small (for example, the length of one side of the quantum box is 10 nm). this is,
This is because the spacing between the energy levels of the electrons in the quantum box must be sufficiently larger than the thermal energy at room temperature k _B T (k _B : Boltzmann constant, T: absolute temperature) to 26 meV.

The distance between adjacent quantum boxes is about 10 nm or less. This is a condition for increasing the coupling strength between the quantum boxes and allowing the electrons to move between the quantum boxes by tunneling.

Controlling the strength of coupling between quantum boxes for each quantum box. This is a necessary condition for controlling the electron distribution change according to the purpose of use of the quantum box assembly element.

The above-mentioned condition, that is, formation of a quantum box having a sufficiently small size, has already been possible by a method such as electron beam lithography. Further, it has been difficult in the past to satisfy the condition (1), that is, to set the distance between the quantum boxes to about 10 nm or less. A method has been proposed in which an interval between quantum boxes is effectively reduced by forming an epitaxial layer which becomes a part of the quantum boxes on the side wall.

However, at present, no proposal has been made so far regarding the condition (1), that is, the method of controlling the coupling strength between quantum boxes for each quantum box. This problem also applies to quantum devices using quantum wires instead of quantum boxes, that is, quantum wire assembly devices.

Therefore, an object of the present invention is to provide a quantum device capable of realizing a quantum box assembly device capable of controlling the coupling strength between quantum boxes for each quantum box.

Another object of the present invention is to provide a quantum wire element capable of realizing a quantum wire assembly element capable of controlling the coupling strength between quantum wires for each quantum wire.

[0012]

In order to achieve the above object, a first invention of the present invention has a plurality of quantum boxes (4) arranged adjacent to each other, and a selected quantum box ( 4)
This is a quantum device in which the shape and / or size of the selected quantum box (4) is changed by providing an epitaxial layer (8) on the quantum element.

A second aspect of the present invention has a plurality of quantum boxes (4) arranged adjacent to each other, and the selected quantum boxes (4) are formed by etching the selected quantum boxes (4). ) Is a quantum device whose shape and / or size are changed.

A third invention of the present invention has a plurality of quantum boxes (4) arranged adjacent to each other, and a composition selected in a region between the selected adjacent quantum boxes (4). It is a quantum device in which barrier layers (10, 11, 12, 13) having are provided.

A fourth invention of the present invention has a plurality of quantum boxes (4) arranged adjacent to each other, and a selected thickness in a region between the selected adjacent quantum boxes (4). It is a quantum device in which barrier layers (15, 16, 17, 18) having a thickness are provided.

A fifth aspect of the present invention has a plurality of quantum wires (18) arranged adjacent to each other, and an epitaxial layer (8) is provided on a selected portion of the selected quantum wires (18). ) Is provided to change the shape and / or size of the selected portion.

A sixth aspect of the present invention comprises a plurality of quantum wires (18) arranged adjacent to each other and is selected by etching selected portions of the selected quantum wires (18). It is a quantum device in which the shape and / or the size of the broken portion is changed.

A seventh aspect of the present invention has a plurality of quantum wires (18) arranged adjacent to each other, and an area between selected portions of the selected adjacent quantum wires (18). A barrier layer (10, 11,
12, 13), and is a quantum device.

The eighth invention of the present invention has a plurality of quantum wires (18) arranged adjacent to each other, and an area between selected portions of the selected adjacent quantum wires (18). Barrier layers (15, 16,
17 and 18), and is a quantum device.

[0020]

According to the quantum device according to the first and second aspects of the invention configured as described above, the selected quantum box (4)
Since the epitaxial layer (8) is provided on the above or the selected quantum box (4) is etched, the shape and / or the size of the selected quantum box (4) is changed. The strength of the coupling between the quantum boxes (4) can be controlled for each quantum box (4). As a result, it is possible to realize a quantum box assembly element capable of controlling the change in electron distribution according to its intended use.

According to the quantum device according to the third and fourth aspects of the invention configured as described above, the barrier layer having the selected composition is provided in the region between the selected adjacent quantum boxes (4). (10, 11, 12, 13) is provided, or a barrier layer (15, 16, 17,) having a selected thickness is formed in a region between the selected adjacent quantum boxes (4).
18), the quantum box (4)
The strength of the coupling between the quantum boxes (4) can be controlled. As a result, it is possible to realize a quantum box assembly element capable of controlling the change in electron distribution according to its intended use.

According to the quantum device according to the fifth and sixth aspects of the invention configured as described above, the epitaxial layer (8) is provided on the selected portion of the selected quantum wire (18), Alternatively, selected quantum wires (18)
Since the shape and / or size of the selected portion is changed by etching the selected portion of the quantum wire (18), the strength of the coupling between the selected portions of the quantum wires (18) adjacent to each other is increased. Can be controlled for each quantum wire (18). As a result, it is possible to realize a quantum wire assembly element capable of controlling the change in electron distribution according to its purpose of use.

According to the quantum element according to the seventh invention and the eighth invention constructed as described above, the selected quantum wire (18) is selected in a region between the selected portions of the adjacent quantum wires (18). A barrier layer having a composition (10, 11, 12, 1
3) or providing a barrier layer (15, 16, 17, 18) having a selected thickness in the region between the selected portions of the selected adjacent quantum wires (18). Therefore, the selected quantum wire (1
The strength of the coupling between the selected parts of 8) can be controlled for each quantum wire (18). As a result, it is possible to realize a quantum wire assembly element capable of controlling the change in electron distribution according to its purpose of use.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing the embodiments of the present invention, a physical quantity called transfer energy, which is a measure of the strength of coupling between quantum boxes, will be described.

Here, in general, a quantum box that can store only one electron among quantum boxes that can generally store one or more electrons is called a quantum dot, and an element formed by combining a plurality of quantum dots. Is called a quantum dot assembly element. Then, the following description will be given for this quantum dot assembly element.

The quantum dots are three-dimensionally surrounded by a barrier layer around a dot-shaped well portion, and the potential well of a single quantum dot and the wave function of the ground state of electrons in this potential well are conceptual. It is represented as shown in FIG.

Now, consider a quantum dot coupling system composed of two quantum dots as shown in FIG. Then, the dynamics of electrons in this quantum dot coupled system can be determined from the exact solution of the electronic state of the isolated hydrogen atom to the hydrogen molecular ion (H
LCAO (Linear Combination of AtomicOr), which is known as an effective approximation method when considering the electronic state of ₂ ⁺ ).
Consider based on the (bitals) approximation.

Considering this LCAO approximation, when the initially isolated quantum dots 1 and quantum dots 2 approach each other, the ground state | 1> of the electron of the quantum dot 1 and the ground state | of the electron of the quantum dot 2 | Splitting with a width 2ΔE occurs in the energy level E ₀ of 2>, and two states of a bound state and an anti-bound state are obtained. The energy and wave function of these bound and anti-bound states are expressed as follows.

[0029]

[Equation 1]

[Equation 2] Where ΔE is called transfer energy,
As will be described later, it is a measure of the tunneling time τ of electrons between quantum dots, and thus the strength of the bond between quantum dots.

The Hamiltonian of this quantum dot coupled system is

[Equation 3] Is written,

[Equation 4] Is an eigenstate of this Hamiltonian as shown in the following equation.

[Equation 5]

Now, assuming that electrons are localized in the quantum dot 1, for example, this state is

[Equation 6] Can be written. When this state is time-developed by the Schrodinger equation, the state at time t is

[Equation 7] Becomes

From this,

[Equation 8] It can be seen that at time t that satisfies, the electrons localized in the quantum dot 1 reach the quantum dot 2. Therefore, within this LCAO approximation range, the electron tunneling time τ from quantum dot 1 to quantum dot 2 is

[Equation 9] Can be considered.

More generally, this tunnel time τ is

[Equation 10] Can be written.

From the above, if the dynamics of electrons in the quantum dot coupled system are simplified most, the electrons will move by tunneling depending on the magnitude of the transfer energy ΔE between the quantum dots.

Next, the expression of the transfer energy ΔE in the range of LCAO approximation will be obtained.

Now, considering a single square quantum dot having a side length of 2d, its potential energy is

[Equation 11] Is. Therefore, if we write the kinetic energy as K, the Hamiltonian of this system is

[Equation 12] Is. This Hamiltonian ground state

[Equation 13] And its energy is E ₀ ,

[Equation 14] Holds.

On the other hand, the Hamiltonian of the quantum dot coupled system (see FIG. 20) consisting of two square quantum dots can be written as the following equation.

[0038]

[Equation 15] However, when the center coordinates of one quantum dot and the center coordinates of the other quantum dot are written as shown in FIG. 20,

[Equation 16] Is.

On the other hand, the wave function of the ground state of the Hamiltonian of the single square quantum dot expressed by the equation (10) is

[Equation 17] In Although,

[Equation 18] Respectively

[Formula 19] Meets

When the above preparation is completed, the energy eigenvalue of the Hamiltonian of the quantum dot coupled system expressed by the equation (12) is calculated on the two-dimensional subspace where the eigenstates of the single square quantum dot expressed by the equation (15) extend. Ask in. Since the two eigenstates shown in Eq. (15) are not orthogonal, if an orthogonal basis is first constructed, this will be as follows, for example.

[0041]

[Equation 20]

When the Hamiltonian matrix elements are calculated with this orthogonal basis,

[Equation 21]

[Equation 22]

[Equation 23]

[Equation 24] Becomes However, in the calculation of these matrix elements,
Equation (16) and the following equation were used.

[0043]

[Equation 25]

As can be seen from the equations (20) and (21), since the non-diagonal elements of the Hamiltonian matrix are 0, this Hamiltonian matrix is actually diagonalized. Therefore, the energy eigenvalue is

[Equation 26] And their eigenvectors are

[Equation 27] Has become.

In equations (18) and (19), from the localization of the wave function,

[Equation 28] As energy,

[Equation 29] Can be thought of as.

FIG. 22 shows the result of precise calculation of the transfer energy ΔE for the two-dimensional square quantum dot coupling system as shown in FIG. 21 based on the theory described above. However, in this calculation, a quantum dot having a GaSb (barrier) / InAs (well) heterostructure is assumed, and the length of one side of the quantum dot is 2d = 10 nm. , M _InAs = 0.027 m _e (m _e : mass of electrons in vacuum), and the effective mass of electrons in the barrier part composed of GaSb outside the quantum dot is m _GaSb = 0.049 m
_e , the height of the potential barrier at the GaSb / InAs hetero interface was set to V ₀ = 0.8 eV.

From FIG. 22, for example, the distance 2 between quantum dots is
When r = 15 nm and the relative angle θ = 0, the tunnel time τ is about several tens of ns, and 2r = 17.5n.
In the case of m and θ = 0, τ is on the order of ms. If the tunneling of electrons between the quantum dots, which is only an elementary process for the quantum dot assembly device, requires such a long time, the operating speed of the entire quantum dot assembly device must be very slow. From this, it will be understood that the distance between the quantum dots needs to be about 10 nm or less.

From FIG. 22, the distance between quantum dots is 2
Even if r is fixed, the change in relative angle θ causes ΔE
It can be seen that is greatly changed. For example, 2r = 1
In the case of 7.5 nm, ΔE changes by 8 digits or more as θ changes in the range of 0 to π / 4. As a result, the tunneling time τ of electrons between quantum dots is 8
Change by more than one digit.

As described above, the transfer energy ΔE serves as a measure of the strength of coupling between quantum dots, but if the electron energy of a single quantum dot differs between adjacent quantum dots, Generally, the transfer energy ΔE becomes small, and therefore the time required for the electrons to move between the adjacent quantum dots by tunneling becomes long. That is, as shown in FIG. 23A, the transfer energy Δ when the electron energies are equal between the adjacent quantum dots 1 and 2
As shown in FIG. 23B, the transfer energy ΔE ₂ when the electron energy is different between the adjacent quantum dots 1 and ₂ becomes smaller than E ₁ ,
Therefore, the tunnel time τ _{2 in} the case of FIG. 23B becomes longer than the tunnel time τ ₁ in the case of FIG. 23A.

Embodiments of the present invention will be described below with reference to the drawings. In all the drawings of the embodiments, the same or corresponding parts are designated by the same reference numerals.

First, the first embodiment of the present invention will be described.

In the first embodiment, first, an array of quantum dots having sufficiently small intervals is formed as follows.

That is, as shown in FIG. 1, for example, AlGa
On the As substrate 1, for example, metal organic chemical vapor deposition (MOCV)
D) method or molecular beam epitaxy (MBE) method is used to epitaxially grow, for example, a GaAs layer 2 as a material for forming quantum dots. The GaAs layer 2 is selected to have a thickness corresponding to the height of quantum dots to be formed, and specifically, the thickness is selected to be, for example, about 10 nm. AlGaAs substrate 1
For example, an AlGaAs layer epitaxially grown on a GaAs substrate is used. Next, this GaAs layer 2
A resist pattern 3 having a planar shape corresponding to the quantum dots to be formed is formed thereon. This resist pattern 3
Is, for example, selectively irradiating the GaAs layer 2 with an electron beam whose beam diameter is sufficiently narrowed in a predetermined source gas atmosphere,
It is formed by depositing decomposition products by irradiation on this irradiation part.

Next, using the resist pattern 3 thus formed as a mask, the GaAs layer 2 is etched in a direction perpendicular to the substrate surface by a dry etching method such as a reactive ion etching (RIE) method. In this dry etching, for example, chlorine (Cl) based etching gas is used. This etching is performed until the AlGaAs substrate 1 is exposed. As a result, as shown in FIG. 2, a plurality of square pillar-shaped quantum dots 4 made of GaAs are formed adjacent to each other in an array. In this case, these quantum dots 4 are periodically formed at regular intervals.

Next, after removing the resist pattern 3,
As shown in FIG. 3, for example, a GaAs layer 5 is epitaxially grown on the entire surface by MOCVD or MBE, for example.

Next, the GaAs layer 5 is etched in the direction perpendicular to the substrate surface by a dry etching method such as the RIE method. This etching is the quantum dot 4
Until the top surface of is exposed. This leaves the GaAs layer 5 only on the sidewalls of the quantum dots 4, as shown in FIG. The GaAs layer 5 constitutes a part of the quantum dot 4.

Now, as shown in FIG. 4, assuming that the interval between the quantum dots 4 before forming the GaAs layer 5 is l and the width (thickness) of the GaAs layer 5 is s, this GaAs layer 5 is formed. The interval l ′ of the quantum dots 4 after that is l ′ = 1−2s. That is, by forming the GaAs layer 5 on the sidewalls of the quantum dots 4, the distance between the quantum dots 4 can be effectively reduced by a distance corresponding to twice the width of the GaAs layer 5.

The reduction of the interval between the quantum dots 4 by forming the GaAs layer 5 on the side wall of the quantum dots 4 may be repeated a plurality of times as necessary.

FIG. 5 shows an array of quantum dots 4 formed by the above method and having sufficiently small intervals.

In this first embodiment, the AlGaAs substrate 1 on which an array of quantum dots 4 having sufficiently small intervals is formed, as shown in FIG. 5, is placed in a vacuumed sample chamber of a predetermined electron beam irradiation apparatus. In this sample chamber, for example, (C
A gas such as H ₃ ) ₃ Ga or (CH ₃ ) ₃ As is introduced. Then, the molecules of these source gases are changed to the quantum dots 4 and AlGa.
As Adsorbed on the surface of the substrate 1. The state at this time is shown in FIG. In FIG. 6, reference numeral 6 indicates an adsorbed molecule.

Next, the electron beam 7 is selectively applied to the quantum dots 4 selected according to the purpose of use of the quantum dot assembly element. As a result, the adsorbed molecule 6 in the portion irradiated with the electron beam 7 is decomposed, and the decomposition product epitaxially grows in the irradiated portion. That is, as shown in FIG. 7, the GaAs layer 8 is selectively epitaxially grown on the quantum dots 4 in the portion irradiated with the electron beam 7.
This GaAs layer 8 becomes a part of the quantum dot 4. in this case,
The growth amount (thickness and the like) and growth shape of the GaAs layer 8 can be controlled by the irradiation time of the electron beam 7 and the beam intensity. In this case, since the irradiation amount (exposure amount) of the electron beam 7 is generally small, the influence of backscattering of electrons is small, and therefore the electron beam 7 is selectively irradiated only to the target quantum dot 4. It is possible to Further, if the influence of electron backscattering becomes a problem, the influence can be minimized by back-etching the AlGaAs substrate 1 to reduce its thickness.

By irradiating all the selected quantum dots 4 with the electron beam 7 as described above, as shown in FIG.
As shown in, a GaAs layer 8 having a desired thickness and shape is selectively epitaxially grown on all the selected quantum dots 4. In this way, by changing the thickness and shape of the GaAs layer 8 for each quantum dot 4 according to the purpose, it is possible to change the energy level of the electrons in each quantum dot 4 and thereby adjacent to each other. It is possible to control the tunneling time of electrons between the quantum dots 4, and hence the strength of the bond between the quantum dots 4, via the transfer energy ΔE.

After that, as shown in FIG. 9, for example, an AlGaAs layer 9 is epitaxially grown as a barrier layer on the entire surface by MOCVD or MBE to complete the desired quantum dot assembly element. In this case, the quantum dots 4 are AlGa
The structure is surrounded by the As layer 9 and the AlGaAs substrate 1.

As described above, according to the first embodiment,
On the quantum dots 4 selected according to the purpose of use of the quantum dot assembly element, the GaAs layer 8 which is a part of the quantum dots 4 is selectively grown by selective epitaxial growth of the GaAs layer 8 by irradiation of the electron beam 7. Since the quantum dots 4 are formed in the amount and the growth shape, the strength of the coupling between the quantum dots 4 can be controlled for each quantum dot 4. And thereby, the quantum dot assembly element which can control the electron distribution change according to the use purpose can be realized.

Next, a second embodiment of the present invention will be described.

In the second embodiment, as shown in FIG. 5, an array of quantum dots 4 is formed in advance at sufficiently small intervals, and then the AlGaAs substrate 1 on which the array of quantum dots 4 is formed is subjected to predetermined electrons. The beam irradiation apparatus is placed in a vacuum-exhausted sample chamber, a predetermined etching gas is introduced into the sample chamber, and molecules of this etching gas are adsorbed on the quantum dots 4 and the surface of the AlGaAs substrate 1. The state at this time is similar to that shown in FIG.

Next, similarly to the first embodiment, the electron beam 7 is selectively irradiated to the quantum dots 4 selected according to the purpose of use of the quantum dot assembly element. by this,
Energy is applied to the adsorbed molecules 6 in the portion irradiated with the electron beam 7, and the quantum dots 4 irradiated with the electron beam 7 are chemically etched. In this case, the depth and etching shape of this chemical etching can be controlled by the irradiation time of the electron beam 7, the beam intensity, and the like.

By irradiating all the selected quantum dots 4 with the electron beam 7 as described above, as shown in FIG.
As shown at 0, all selected quantum dots 4 are etched to their desired height. By changing the height of the quantum dots 4 selected in this way according to the purpose, the energy levels of the electrons in these quantum dots 4 can be changed, whereby the quantum dots 4 adjacent to each other can be changed. It is possible to control the tunneling time of electrons between the quantum dots 4 and thus the strength of the bond between the quantum dots 4 via the transfer energy ΔE.

Thereafter, as shown in FIG. 11, MOCVD is performed.
Method or MBE method is used to epitaxially grow the AlGaAs layer 9 as a barrier layer on the entire surface to complete the target quantum dot assembly element. In this case, the quantum dots 4 are AlGa
Similar to the first embodiment, the structure is surrounded by the As layer 9 and the AlGaAs substrate 1.

As described above, according to this second embodiment,
Since the quantum dots 4 selected according to the purpose of use of the quantum dot assembly element are made to have the height selected by the chemical etching by irradiation of the electron beam 7, the strength of the bond between the quantum dots 4 is increased. It can be controlled for each quantum dot 4. As a result, similarly to the first embodiment, it is possible to realize the quantum dot assembly element capable of controlling the change of the electron distribution according to the purpose of use.

Next, a third embodiment of the present invention will be described.

In the third embodiment, as shown in FIG. 5, an array of quantum dots 4 is formed in advance at sufficiently small intervals, and then the AlGaAs substrate 1 on which the array of quantum dots 4 is formed is subjected to predetermined electron emission. The beam irradiation apparatus is placed in a vacuum-exhausted sample chamber, and a source gas necessary for epitaxial growth of AlGaAs, for example, is introduced into the sample chamber. Then, the molecules of these source gases become
Adsorb to the surface of the substrate 1. The state at this time is shown in FIG.

Next, the electron beam 7 is selectively irradiated to the region between the adjacent quantum dots 4 selected according to the purpose of use of the quantum dot assembly element. As a result, the adsorbed molecule 6 in the portion irradiated with the electron beam 7 is decomposed, and the decomposition product epitaxially grows in the irradiated portion. That is, as shown in FIG.
Al _x1 Ga _1-x1 As layer 1 having a selected Al composition ratio x1 in the region between adjacent quantum dots 4 irradiated with
0 selectively grows epitaxially.

By repeating the irradiation of the electron beam 7 as described above a necessary number of times while changing the composition of the raw material gas introduced into the sample chamber according to the purpose, as shown in FIG. In the region between the quantum dots 4 to be selected, the Al composition ratios x1, x2, x3 respectively selected
And an Al _x1 Ga _1-x1 As layer 10, an Al _x2 Ga _1-x2 As layer 11, an Al _x3 Ga _1-x3 As layer 12 and an Al _x3 Ga _1-x3 As layer 13 are epitaxially grown as barrier layers. Similarly, an AlGaAs layer having the selected Al composition ratio is also epitaxially grown in a region between the other selected adjacent quantum dots 4 not shown. In this case, these Al _x1 Ga _1-x1 As layers 10, Al _x2 Ga _1-x2 As layers 11, Al _x3 Ga as barrier layers are used.
_1-x3 As layer _{12, Al x4 Ga 1-x4} As layer 13, ... barrier height by its Al composition ratio x1, x2, x3, x4, since it depends ..., these Al _x1 Ga _1-x1 As Layer 10, Al _x2 Ga _1-x2 As Layer 1
1. Ease of electron tunneling between the quantum dots 4 adjacent to each other through the Al _x3 Ga _1-x3 As layer 12, the Al _x4 Ga _1-x4 As layer 13, ... The strength of the bond depends on the Al composition ratios x1, x2, x3, x4, ....

Thereafter, as shown in FIG. 15, MOCVD is performed.
Method or MBE method is used to epitaxially grow a semiconductor layer having a wider gap than the AlGaAs layer, for example, the AlAs layer 14 as a barrier layer on the entire surface to complete the desired quantum dot assembly device. In this case, the quantum dots 4 and the AlAs layer 14
The structure is surrounded by the AlGaAs substrate 1 and the Al _x1 Ga _1-x1 As layers 10 ,.

As described above, according to the third embodiment,
Al _x1 Ga _1-x1 As layers 10 and Al _x2 as a barrier layer having a selected Al composition ratio in a region between the adjacent quantum dots 4 selected according to the purpose of use of the quantum dot assembly device.
By providing the Ga _1-x2 As layer 11, the Al _x3 Ga _1-x3 As layer 12, the Al _x4 Ga _1-x4 As layer 13, ... It is possible to realize a quantum dot assembly device that can be controlled for each of the devices and that can control the change in electron distribution according to the purpose of use.

Next explained is the fourth embodiment of the invention.

In the fourth embodiment, as shown in FIG. 5, an array of quantum dots 4 is formed in advance at sufficiently small intervals, and then the AlGaAs substrate 1 on which the array of quantum dots 4 is formed is subjected to predetermined electrons. The beam irradiation apparatus is placed in a vacuum-exhausted sample chamber, and a source gas necessary for epitaxial growth of AlGaAs, for example, is introduced into the sample chamber. Then, in the same manner as shown in FIGS. 6 and 12, the molecules of these source gases are adsorbed on the surfaces of the quantum dots 4 and the AlGaAs substrate 1.

Next, the electron beam 7 is selectively irradiated to the region between the adjacent quantum dots 4 selected according to the purpose of use of the quantum dot assembly element. As a result, the adsorbed molecule 6 in the portion irradiated with the electron beam 7 is decomposed, and the decomposition product epitaxially grows in the irradiated portion. That is, as shown in FIG.
Al having a thickness corresponding to the irradiation time and the beam intensity in the region between the adjacent quantum dots 4 irradiated with
The GaAs layer 15 is selectively epitaxially grown.

By irradiating the electron beam 7 as described above with respect to the region between all the selected quantum dots 4 adjacent to each other while changing the irradiation time and the beam intensity according to the purpose, FIG. As shown in FIG. 3, AlGaAs layers 15, 16, 17, and 18 each having a selected thickness are epitaxially grown in the region between all the selected quantum dots 4 as a barrier layer. Similarly, an AlGaAs layer having a selected thickness is also epitaxially grown in a region between other selected adjacent quantum dots 4 not shown. In this case, the Al composition ratio of the AlGaAs layer formed in the region between the quantum dots 4 is constant. In this case, these AlGaAs layers 15, 16, 1 as barrier layers
Depending on the thickness of 7, 18, ...
It is possible to control the ease of tunneling of electrons between the quantum dots 4 adjacent to each other via 16, 17, 18, ..., Therefore, the strength of the coupling between the quantum dots 4.

After this, as in the third embodiment, as shown in FIG. 17, the entire surface is, for example, formed by MOCVD or MBE.
Epitaxially grow the AlAs layer 14 as a barrier layer,
Complete the target quantum dot assembly device.

As described above, according to the fourth embodiment,
AlGaAs layers 15 and 16 as barrier layers each having a selected thickness in a region between the adjacent quantum dots 4 selected according to the purpose of use of the quantum dot assembly element,
By providing 17, 18, ...
The strength of the coupling between the quantum dots 4 can be controlled for each quantum dot 4, and thus a quantum dot assembly element capable of controlling the change in electron distribution according to the purpose of use can be realized.

Next explained is the fifth embodiment of the invention.

In the fifth embodiment, as shown in FIG. 18, a plurality of quantum wires 18 made of, for example, GaAs are formed on an AlGaAs substrate 1 in parallel at regular intervals. Here, these quantum wires 18 are the quantum dots 4 shown in FIG.
It can be considered that the distance between the quantum dots 4 arranged in one direction in the array of is set to zero.

In the fifth embodiment, the array of the quantum wires 18 is subjected to the same processing as that of the above-mentioned first embodiment, second embodiment, third embodiment or fourth embodiment.

That is, when the same method as that of the first embodiment is used, by providing a GaAs layer on the selected portion of the selected quantum wire 18 by the selective epitaxial growth by irradiation of the electron beam, this portion is formed. Locally change the shape and size of.

When the same method as in the second embodiment is used, the selected portion of the selected quantum wire 18 is etched by irradiation with an electron beam so that the shape or size of this portion is locally changed. Change.

When the same method as that of the third embodiment is used, Al having the selected Al composition ratio is formed in the region between the selected portions of the selected quantum wires 18 adjacent to each other.
A GaAs layer is provided as a barrier layer.

Further, when the same method as in the fourth embodiment is used, AlGa having a selected thickness is formed in the region between the selected portions of the selected quantum wires 18 adjacent to each other.
The As layer is provided as a barrier layer.

By using any of the above methods, it is possible to control the strength of the coupling between the selected portions of the quantum wires 18 that are adjacent to each other to a strength suitable for the purpose. As a result, according to the fifth embodiment, it is possible to realize the quantum wire assembly element capable of controlling the change of the electron distribution according to the purpose of use.

Although the embodiments of the present invention have been specifically described above, 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, the strength of the coupling between the quantum dots 4 can be increased by arbitrarily combining the methods according to the first, second, third, and fourth embodiments described above, if necessary. You may make it control for each quantum dot 4. By doing so, the number of controllable parameters in the quantum dot assembly element can be increased. As an example, by combining the method according to the third embodiment and the method according to the fourth embodiment, Al of the AlGaAs layer as a barrier layer formed in the region between the selected adjacent quantum dots 4 is formed.
The composition ratio and the thickness may be changed for each quantum dot.

Further, in the above-mentioned first embodiment, second embodiment, third embodiment and fourth embodiment, the square pillar-shaped quantum dots 4 are used, but various shapes other than the square pillar shape are used. The present invention can also be applied to a quantum dot assembly element using the quantum dots of.

Further, as shown in FIG. 22, the transfer angle ΔE greatly changes depending on the relative angle θ between the quantum dots. It is also possible to change according to.

Furthermore, the above-mentioned first embodiment, second embodiment,
In the third, fourth and fifth embodiments, the quantum dots 4 and the quantum wires 18 are formed by AlGaAs / GaAs heterojunctions, but other semiconductor heterojunctions such as GaSb / InAs heterojunctions are used. Thus, the quantum dots 4 and the quantum wires 18 may be formed.

[0096]

As described above, according to the present invention,
It is possible to realize a quantum box assembly element capable of controlling the coupling strength between the quantum boxes for each quantum box, and thus controlling the electron distribution change according to the purpose of use. Further, according to the present invention, a quantum wire assembly element capable of controlling the coupling strength between quantum wires for each quantum wire and thus controlling the electron distribution change according to the purpose of use thereof. Can be realized.

[Brief description of drawings]

FIG. 1 is a perspective view for explaining a method of manufacturing a quantum dot assembly device according to a first embodiment of the present invention.

FIG. 2 is a perspective view for explaining a method of manufacturing a quantum dot assembly device according to the first embodiment of the present invention.

FIG. 3 is a perspective view for explaining a method of manufacturing a quantum dot assembly device according to the first embodiment of the present invention.

FIG. 4 is a perspective view for explaining a method of manufacturing a quantum dot assembly device according to the first embodiment of the present invention.

FIG. 5 is a perspective view for explaining the method of manufacturing the quantum dot aggregate device according to the first embodiment of the present invention.

FIG. 6 is a cross-sectional view for explaining the method of manufacturing a quantum dot assembly device according to the first embodiment of the present invention.

FIG. 7 is a cross-sectional view for explaining the method of manufacturing a quantum dot assembly device according to the first embodiment of the present invention.

FIG. 8 is a cross-sectional view illustrating the method of manufacturing the quantum dot aggregate device according to the first embodiment of the present invention.

FIG. 9 is a cross-sectional view for explaining the method of manufacturing a quantum dot assembly device according to the first embodiment of the present invention.

FIG. 10 is a cross-sectional view for explaining the method of manufacturing a quantum dot assembly device according to the second embodiment of the present invention.

FIG. 11 is a cross-sectional view for explaining the method of manufacturing a quantum dot assembly device according to the second embodiment of the present invention.

FIG. 12 is a cross-sectional view for explaining the method of manufacturing a quantum dot assembly device according to the third embodiment of the present invention.

FIG. 13 is a cross-sectional view for explaining the method of manufacturing a quantum dot assembly device according to the third embodiment of the present invention.

FIG. 14 is a cross-sectional view for explaining the method of manufacturing a quantum dot assembly device according to the third embodiment of the present invention.

FIG. 15 is a cross-sectional view for explaining the method of manufacturing a quantum dot assembly device according to the third embodiment of the present invention.

FIG. 16 is a cross-sectional view for explaining the method of manufacturing a quantum dot assembly device according to the fourth embodiment of the present invention.

FIG. 17 is a cross-sectional view for explaining the method of manufacturing a quantum dot aggregate device according to the fourth embodiment of the present invention.

FIG. 18 is a perspective view for explaining a quantum wire assembly element according to a fifth embodiment of the present invention.

FIG. 19 is a schematic diagram conceptually showing a potential well of a single quantum dot and a ground-state wave function of electrons in the potential well.

FIG. 20 is a schematic diagram showing a quantum dot coupling system composed of two quantum dots.

FIG. 21 is a schematic diagram showing a relative distance and a relative angle between quantum dots in a two-dimensional square quantum dot coupled system.

22 is a graph showing changes in transfer energy ΔE and tunnel time τ according to the relative angle θ in the square quantum dot coupled system shown in FIG. 21.

FIG. 23 is an energy level diagram for explaining a change in transfer energy due to a difference in electron energy level between adjacent quantum dots.

[Explanation of symbols]

1 AlGaAs substrate 2, 5, 8 GaAs layer 3 Resist pattern 4 Quantum dot 6 Adsorbed molecule 7 Electron beam 9, 15, 16, 17, 18 AlGaAs layer 10 Al _x1 Ga _1-x1 As layer 11 Al _x2 Ga _1-x2 As Layer 12 Al _x3 Ga _1-x3 As layer 13 Al _x4 Ga _1-x4 As layer 14 AlAs layer

Claims (8)

[Claims] 1. A plurality of quantum boxes arranged adjacent to each other, wherein the shape and / or size of the selected quantum box is changed by providing an epitaxial layer on the selected quantum box. The quantum device. 2. A plurality of quantum boxes arranged adjacent to each other, wherein the shape and / or size of the selected quantum box is changed by etching the selected quantum box. Quantum element. 3. A quantum device having a plurality of quantum boxes arranged adjacent to each other, wherein a barrier layer having a selected composition is provided in a region between the selected adjacent quantum boxes. 4. A quantum device having a plurality of quantum boxes arranged adjacent to each other, wherein a barrier layer having a selected thickness is provided in a region between the selected adjacent quantum boxes. . 5. A plurality of quantum wires arranged adjacent to each other, the shape and / or the shape of the selected parts being provided by providing an epitaxial layer on the selected parts of the selected quantum wires. A quantum device whose size is changed. 6. A plurality of quantum wires arranged adjacent to each other, wherein the shape and / or size of the selected portions is changed by etching selected portions of the selected quantum wires. Quantum element that was made to do. 7. A barrier layer having a plurality of quantum wires disposed adjacent to each other, the barrier layer having a selected composition in a region between selected portions of the selected quantum wires adjacent to each other. Quantum device. 8. A barrier layer having a plurality of quantum wires disposed adjacent to each other, the barrier layer having a selected thickness in a region between selected portions of the selected quantum wires adjacent to each other. The quantum device.