JP2000315654A - Method for forming nitride semiconductor quantum dots by position controlled droplet epitaxy, quantum bit device structure and quantum correlation gate device structure in quantum computer - Google Patents

Abstract

(57) [Summary] [PROBLEMS] GaN, InN or AlN or InGaN,
A quantum dot of a nitride semiconductor such as AlGaN can be formed by controlling the position. A method of forming a quantum dot of a nitride semiconductor by position-controlled droplet epitaxy, wherein an external field is applied to a surface of the substrate having a surface energy lower than a surface energy of a metal raw material. A first process for modifying the surface state by modulating the surface state of the substrate, and supplying the metal raw material to the substrate whose surface has been modified by the first process; A second process of forming metal droplets by crystal growth at the place where the metal droplets are formed by supplying a nitrogen source on the substrate on which the metal droplets are formed by the second process, and nitriding the metal droplets A third process for forming quantum dots of a nitride semiconductor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method for forming a quantum dot of a nitride semiconductor by position-controlled droplet epitaxy, a qubit device structure and a quantum correlation gate device structure in a quantum computer, and more particularly, to
For example, a single crystal such as GaN (gallium nitride), InN (indium nitride), or AlN (aluminum nitride), which is required when constructing a Turing-type quantum computer that performs quantum calculations based on the principles of quantum mechanics, A method for forming a quantum dot of a nitride semiconductor by position-controlled droplet epitaxy suitable for use in forming a quantum dot of a group III-V nitride semiconductor using such a mixed crystal (InGaN, AlGaN, etc.) The present invention relates to a quantum bit device structure and a quantum correlation gate device structure in a quantum computer using quantum dots formed by the method.

[0002]

BACKGROUND OF THE INVENTION Conventionally, in the field of semiconductor technology, III-V nitride semiconductors such as GaN, InN and AlN are expected to be extremely useful as optical device materials and electronic device materials.

When the above-mentioned nitride semiconductor is applied to an integrated circuit or the like, the nitride semiconductor has a spherical structure with a diameter of about several tens of nanometers (nm) or less, or a side of one side. However, it is necessary to form minute quantum dots having a cubic shape of about several tens of nanometers (nm) or less.

[0004] However, conventionally, a method of forming gallium arsenide (GaAs) quantum dots by droplet epitaxy has been proposed.
aN, InN or AlN, InGaN, AlGaN
Such a method of forming quantum dots of a nitride semiconductor has not been proposed, and devising a method of forming quantum dots of a nitride semiconductor has been strongly desired.

[0005] In recent years, the concept of a quantum computer that performs quantum computation based on the principle of quantum mechanics has been proposed for an existing digital computer based on classical mechanics.

In order to realize such a quantum computer, a qubit element for realizing a qubit corresponding to the concept of a bit of a digital computer at present and a quantum correlation gate element for operating two qubits are provided. Has been found to be necessary.

Here, in order to facilitate understanding of the following description, a qubit and a quantum correlation gate will be described.

[0008] Existing digital systems based on the principles of classical mechanics
In a computer, arithmetic operations such as addition and Fourier transform can be performed by applying a logic gate such as AND (AND) or OR (OR) to a “bit” formed by “0” and “1”. Circuits have been made to build. As a concept corresponding to such a "bit", the concept of "quantum bit" has been introduced in quantum computers.

According to quantum mechanics that governs microscopic properties of matter, the state of a particle such as an electron (in this specification, an electron is described) is represented by a superposition of various states. That is, in quantum mechanics, when there are only two possible states, the state having the larger energy is represented as “| 1>”, and
If the lower energy state is expressed as “| 0>”, it can be said that the electron state is in a state where | 1> and | 0> are superimposed. These concepts are
The concept of quantum bits is used for conventional bits.

That is, with respect to a conventional bit in which “0” or “1” is definite, in the case of a quantum bit, the state of the quantum bit cannot be said to be either “0” or “1”, and a certain probability exists. Can be said to have a state of "0" and a state of "1" with a certain probability. That is, such a state is called an overlapping state.

Therefore, the physical state of the qubit is | 1
It can be said that this is a two-level system having two quantum levels of> and | 0>.

A quantum correlation gate is a gate that operates a qubit by performing an operation on two qubits as described above. The operation is as shown in FIG.

That is, the quantum correlation gate is commutative, and operates on two qubits in a certain state to obtain two qubits in another state.

Specifically, as conceptually shown in FIG. 1A, the quantum correlation gate is one of the two qubits (two qubits) before being affected by the quantum correlation gate. Is a reference qubit.
This is referred to as a “control bit”. ) Is set to “A” and the other of the two qubits before being affected by the quantum correlation gate (the qubit affected by the “control bit” of the two qubits). , "The target bit".)
Is “B”, the two qubits after the operation of the quantum correlation gate are affected by the quantum correlation gate as conceptually shown in the truth table of FIG. 1B. Exclusive OR "X" of "A", the same state as the previous control bit state, and "A", the control bit state before being affected by the quantum correlation gate, and "B", the target bit state Can be obtained.

As a practical configuration capable of realizing the qubit and the quantum correlation gate as described above, the applicant of the present invention has disclosed a qubit device structure and a quantum correlation device in a quantum computer disclosed in Japanese Patent Application No. 10-232590. Gate element structure ”(filing date: August 1, 1998)
9th).

The principle of the invention according to Japanese Patent Application No. 10-232590 entitled "Quantum Bit Device Structure and Quantum Correlation Gate Device Structure in a Quantum Computer" is based on the assumption that the diameter of a sphere is about several tens of nanometers (nm) or less. ,
By placing two minute quantum dots having a rectangular parallelepiped of about several tens of nanometers (nm) or smaller on one side close to each other, electrons can move between the two quantum dots by the tunnel effect. One electron is moved back and forth between the two quantum dots to be in two states of | 1> and | 0>.

Here, the shorter the distance between the two quantum dots, the more preferable.
When the position at which one quantum dot is to be formed is to be controlled using lithography technology, there is a technical limit in reducing the distance between the two quantum dots.
It has been strongly desired to devise a method of forming quantum dots that enables controlled placement of two quantum dots at extremely close positions.

[0018]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned strong demands for the prior art, and has as its object the purpose of GaN, InN or AlN, InGaN, AlGaN or the like. Allowing the quantum dots of the nitride semiconductor to be formed in a position-controlled manner, thereby making it possible to controllably arrange the two quantum dots of the nitride semiconductor in very close positions; It is another object of the present invention to provide a method for forming a quantum dot of a nitride semiconductor by position-controlled droplet epitaxy capable of realizing a quantum correlation gate.

The present invention also relates to a quantum bit device structure and a quantum correlation gate device structure in a quantum computer using a quantum dot formed by the above-described method of forming a quantum dot of a nitride semiconductor by controlled droplet epitaxy. It is intended to provide.

[0020]

In order to achieve the above object, the present invention provides a method for forming quantum dots of a nitride semiconductor by position-controlled droplet epitaxy, which method has a lower surface energy than a metal material. A first treatment that modifies the surface state of the substrate by applying an external field to the surface of the substrate having surface energy to modify the surface;
A second process of supplying the metal raw material to the substrate whose surface has been modified by the first process and forming metal droplets by crystal growth at a modified location of the surface; Supplying a nitrogen source onto the substrate on which the metal droplets have been formed by the above process, and nitriding the metal droplets to form nitride semiconductor quantum dots. is there.

The present invention provides the above-mentioned invention,
Further, there is provided a fourth treatment for heat-treating the nitride semiconductor quantum dots formed by the third treatment at a predetermined temperature for a predetermined time.

Here, in the third process, a nitrogen source is started to be supplied to the substrate on which the metal droplets are formed at a low temperature, and only the surface of the metal droplets is nitrided. To promote crystallization.

In the third process, a nitrogen source is started to be supplied to the substrate on which the metal droplets are formed at a low temperature to nitride only the surface of the metal droplets. When raising to promote crystallization, an external field can be added to promote crystallization.

In the third process, a nitrogen source is supplied to the substrate on which the metal droplets are formed at a low temperature, and only the surface of the metal droplets is nitrided. The crystallization can be promoted by adding an external field as it is.

In the fourth process, an external field for heat treatment may be added.

The external field may be light, electrons, ions or radicals, or a combination thereof.

Further, the metal raw material may be a group III metal.

The substrate may be a sapphire substrate, a silicon carbide substrate, a quartz substrate, a gallium nitride substrate or a calcium fluoride substrate.

Further, the nitrogen source may be nitrogen, nitrogen radical, ammonia or ammonia radical.

Further, according to the present invention, a first quantum dot having a first quantum level and a second quantum dot different from the first quantum level are provided.
And a second quantum dot having a quantum level of the first quantum dot. The first quantum dot has a quantum level of the first quantum dot so that electrons can freely move between the first quantum dot and the second quantum dot by a tunnel effect. In a quantum bit device structure in a quantum computer in which a quantum dot and the second quantum dot are arranged close to each other and only one electron exists, the first quantum dot and the second quantum dot Claim 1, Claim 2, Claim 4, Claim 5, Claim 6, Claim 7, Claim 8, Claim 9, or Claim 10
The method of forming a quantum dot of a nitride semiconductor by position controlled droplet epitaxy according to any one of the above items.

Further, the present invention has a first quantum dot having a first quantum level and a second quantum dot having a second quantum level lower than the first quantum level. Then, the first quantum dot and the second quantum dot are placed close to each other so that electrons can freely move between the first quantum dot and the second quantum dot by a tunnel effect. Place,
Further, a first quantum bit element structure in which only one electron exists, a third quantum dot having a third quantum level, and a fourth quantum dot below the third quantum level. A fourth quantum dot having a level, wherein the third quantum dot is formed such that electrons can freely move between the third quantum dot and the fourth quantum dot by a tunnel effect. And a second quantum bit structure in which the fourth quantum dot and the fourth quantum dot are arranged in close proximity to each other, and in which only one electron is present. Between the first quantum dot and the third quantum dot.
Are arranged so that the second quantum dot and the fourth quantum dot face each other, and the first quantum dot and the third quantum dot are electrically connected to each other. The second quantum dot and the fourth quantum dot are electrically connected, and further, a level difference between the first quantum level and the second quantum level, and
In the quantum correlation gate device structure in the quantum computer, the quantum level of which is different from that of the fourth quantum level, the first quantum dot and the second quantum level The dot, the third quantum dot, and the fourth quantum dot are referred to as claim 1, claim 2, claim 4, claim 5, claim 6, claim 7, claim 8, claim 9, or claim 9 or claim 9. Item 10 is a method for forming a quantum dot of a nitride semiconductor by position-controlled droplet epitaxy according to any one of Items 10.

Here, the first quantum dot and the third quantum dot
Is connected capacitively via a first variable capacitor, and the second quantum dot and the fourth quantum dot are capacitively connected via a second variable capacitor. You may do so.

Further, the present invention has a first quantum dot having a first quantum level and a second quantum dot having a second quantum level lower than the first quantum level. Then, the first quantum dot and the second quantum dot are placed close to each other so that electrons can freely move between the first quantum dot and the second quantum dot by a tunnel effect. Place,
Further, a first quantum bit element structure in which only one electron exists, a third quantum dot having a third quantum level, and a fourth quantum dot below the third quantum level. A fourth quantum dot having a level, wherein the third quantum dot is formed such that electrons can freely move between the third quantum dot and the fourth quantum dot by a tunnel effect. And a second quantum bit structure in which the fourth quantum dot and the fourth quantum dot are arranged in close proximity to each other, and in which only one electron is present. Between the first quantum dot and the fourth quantum dot.
Are arranged so that the second quantum dot and the third quantum dot face each other, and the first quantum dot and the fourth quantum dot are electrically connected to each other. The second quantum dot and the third quantum dot are electrically connected, and further, a level difference between the first quantum level and the second quantum level, and
In the quantum correlation gate device structure in the quantum computer, the quantum level of which is different from that of the fourth quantum level, the first quantum dot and the second quantum level The dot, the third quantum dot, and the fourth quantum dot are referred to as claim 1, claim 2, claim 4, claim 5, claim 6, claim 7, claim 8, claim 9, or claim 9 or claim 9. Item 10 is a method for forming a quantum dot of a nitride semiconductor by position-controlled droplet epitaxy according to any one of Items 10.

Here, the first quantum dot and the fourth quantum dot
Is connected capacitively via a first variable capacitor, and the second quantum dot and the third quantum dot are capacitively connected via a second variable capacitor. You may do so.

Further, the first qubit element structure has the following structure.
The fourth qubit element structure is connected to the first single-electron transistor via a third variable capacitor,
May be connected to the second single-electron transistor via the variable capacitor.

[0036]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the accompanying drawings, a method of forming a quantum dot of a nitride semiconductor by position-controlled droplet epitaxy, a quantum bit device structure and a quantum correlation gate device structure in a quantum computer according to the present invention will be described below. An example of the embodiment will be described in detail.

FIGS. 2 (a), 2 (b), 2 (c) and 2 (d) show an example of an embodiment of a method for forming quantum dots of a nitride semiconductor by position controlled droplet epitaxy according to the present invention. A conceptual explanatory diagram is shown.

Hereinafter, FIGS. 2 (a), (b), (c), and (d)
An example of an embodiment of the method for forming quantum dots of a nitride semiconductor by position-controlled droplet epitaxy of the present invention will be described in detail with reference to FIG.

(1) Substrate: See FIG. 2A In the method of forming quantum dots of a nitride semiconductor by position-controlled droplet epitaxy according to the present invention, the quantum dots 4 of the nitride semiconductor are formed on a substrate 1 (see FIG. 2A). 2 (c) (d))
Is formed.

Here, the substrate 1 is made of, for example, Ga (gallium), A
III such as l (aluminum) and indium (In)
Group metal (in the present specification, a metal that is a raw material of the nitride semiconductor quantum dots 4 is appropriately referred to as a “metal raw material”) can be three-dimensionally grown on the substrate 1. Thus, it is assumed that the metal material has a lower surface energy than the surface energy of the metal raw material. That is, the surface energy of the metal raw material is higher than that of the substrate 1.

Examples of the substrate 1 having a surface energy lower than the surface energy of such a metal raw material include, for example, the raw material of the substrate 1 (in this specification, the raw material of the substrate 1 is appropriately referred to as “substrate raw material”). A)
l ₂ O ₃ (sapphire), SiO ₂ (quartz), SiC
(Silicon carbide), GaN (gallium nitride), CaF ₂
(Calcium fluoride) and the like.

That is, if the surface energy of the metal to be deposited on the substrate is higher than the surface energy of the substrate, the effect of minimizing the energy of the system occurs. The metal to be grown grows while changing spherically so as to minimize the surface area. In addition, such a growth mode is referred to as Forma-Weber (V
It is referred to as an “olmer-Weber” style (VW style).

In general, metals have a higher surface energy than semiconductors and insulators, and are therefore advantageous in forming a fine three-dimensional structure.
Metals such as n are also used for the above-mentioned substrate raw materials such as Al ₂ O ₃ and S
Surface energy is higher than semiconductors and insulators such as iC, SiO ₂ , GaN, and CaF ₂ .

As the combination of the metal material and the substrate material, for example, when the metal material is Ga, the substrate material may be AlN because of the lattice constant matching between the semiconductor and the substrate to be formed and the confinement of electrons. When the metal raw material is Al, the substrate raw material is preferably CaF _2, and when the metal raw material is In, the substrate raw material is preferably GaN.

As the substrate on which the metal raw material is grown three-dimensionally, the Al ₂ O ₃ substrate, SiO ₂ substrate, Ga
A hetero substrate such as an N substrate or a CaF ₂ substrate can also be used.

When the above-mentioned hetero substrate is used, a sapphire substrate, a quartz substrate, a gallium nitride substrate, a calcium fluoride substrate, or the like is used because it can be integrated with an existing Si integrated circuit or GaAs integrated circuit. More effective than when used.

For example, as the substrate 10, a substrate obtained by epitaxially growing CaF ₂ on a Si (silicon) substrate can be used.

CaF ₂ is a crystalline insulator that can be favorably epitaxially grown on a Si (111) substrate. In particular, since the (111) outermost surface is terminated with fluorine ions, the surface energy is extremely low. It has the feature of.

As the substrate 1 in which CaF ₂ is epitaxially grown on a Si (111) substrate, for example, 20 nm of CaF ₂ is grown on a Si (111) substrate at a growth temperature of 800 ° C. by molecular beam epitaxy (MBE). What was made can be used.

(2) Formation of Metal Droplets: See FIG. 2 (b) (2-1) On the substrate 1 described in the above “(1) Substrate: see FIG. For example, G
By supplying a group III metal such as a, Al, or In by MBE or metal organic chemical vapor deposition (MOCVD), a metal droplet 2 is formed on the substrate 1 by crystal growth.

Here, the surface state of the substrate 1 is arbitrarily modulated by adding an external field such as light, electrons, ions or radicals, or a combination thereof to the surface of the substrate 1, whereby the surface of the substrate 1 is modulated. Is modified, and the nucleus growth in the crystal growth accompanying the supply of the metal raw material is preferentially performed at the lowest potential for the resulting adsorption, and the position where the metal droplet 2 is formed is determined. You will be able to control it.

For example, CaF _{2 is} deposited on the Si (111) substrate described in “(1) Substrate: See FIG.
The surface state of the substrate 1 is modified by arbitrarily modulating the surface state of CaF ₂ using an electron beam, and the potential of the resulting adsorption is lowest. However, nuclear growth takes priority.

This point will be described with reference to FIGS. 3 (a), 3 (b) and 3 (c), which are explanatory views of the principle of the modification of the substrate surface by electron beam irradiation. FIG. 3 (a) shows CaF ₂
The surface structure of CaF ₂ crystal is shown as F
The ions are terminated by ions, the surface energy is lower than that of metals and semiconductors, and dangling bonds do not appear on the surface. Therefore, it is difficult for the deposited material to form nuclei. In FIG. The illustration of the ions is omitted).

When such fluorides as CaF ₂ crystals are irradiated with charged particles such as electrons, F ions are desorbed from the surface. For example, as shown in FIG. 3B, when a CaF ₂ crystal is irradiated with an electron beam in an As (arsenic) atmosphere, F ions are desorbed from the surface due to the desorption phenomenon of F ions accompanying the Auger process by electrons. To detach.

Since the place where the F ion is desorbed is active, the surface is replaced with As and modified as a result of taking in As atoms. That is, in the As atmosphere, the electron beam is
By irradiating on aF ₂ , F ions on the outermost surface can be desorbed and replaced with As of one atomic layer, whereby the surface is modified.

When irradiating the CaF ₂ crystal with an electron beam, it is not always necessary to perform the irradiation in an As atmosphere.
In a (phosphorus) atmosphere, the surface is replaced by P and reformed,
In addition, if in an electron beam exposure apparatus, the surface is replaced by residual carbon and modified.

Then, as shown in FIG. 3C, when Ga is supplied as a metal raw material to the surface of the CaF ₂ crystal whose surface has been modified as described above, the surface of the CaF ₂ crystal is modified. The area where the surface energy increases increases G
a comes to gather selectively. Since Ga has a high surface energy, nucleus growth is performed by agglomeration in a spherical shape, and a Ga metal droplet 2 is formed.

Here, the electron beam irradiation on the CaF ₂ on which the As film shown in FIGS. 4A, 4B, and 4C is deposited and the position control of the Ga metal droplet 2 by the natural formation method are performed. An example of an experiment of the process of forming the metal droplet 2 by the present applicant will be described with reference to the conceptual diagram of FIG.

First, a Si (111) substrate is placed in an MBE apparatus, and CaF is deposited on the Si (111) substrate by MBE.
₂ was grown to 20 nm, followed by deposition of 30 nm As on the surface using an As ₂ molecular beam.

Next, the Si (1) treated as described above was used.
11) The substrate is taken out from the MBE apparatus, and the taken out S
The i (111) substrate was placed in an electron beam exposure system, and spot exposure was performed in a periodic array pattern using the electron beam exposure system to form a surface-modified region (see FIG. 4A).

Then, the Si having the surface modified region
The (111) substrate was taken out of the electron beam exposure system, the taken out Si (111) substrate was subjected to surface cleaning, and then placed again in the MBE apparatus, and the substrate temperature was set to 5 ° C.
Excess As is removed by evaporation at 50 ° C.
At 0 ° C., Ga as a metal raw material is supplied and adsorbed on the surface modified region (FIG. 4B), and this is converted to a film thickness of 1 nm to 2 n.
By depositing m, Ga droplets, which are Ga metal droplets 2, were formed (FIG. 4C).

FIGS. 5A and 5B show the above description.
FIG. 9 is a scanning microscope (SEM) photograph showing the results of the experiment described with reference to FIG.
nm and the irradiation amount of the electron beam is 0.4 pC / dot.

As shown in the SEM photograph of FIG. 5, Ga droplets are formed one by one at the electron beam exposure position.

As shown in FIGS. 4 (a), 4 (b) and 4 (c), the CaF ₂ on which an As film is deposited is used.
When the electron beam is irradiated upward, the electron beam in the metal film is forward-scattered, so that even if the electron beam is narrowed down, it will blur until it reaches the CaF ₂ surface. It is difficult to get.

Therefore, as a method for enabling surface modification without using an As film and obtaining a fine structure, referring to FIGS. 6A, 6B and 6C, FIG. There is a technique to explain.

That is, the concept of the process of irradiating the electron beam onto CaF _{2 in} vacuum and controlling the position of the Ga metal droplet 2 by the natural formation method shown in FIGS. 6 (a), 6 (b) and 6 (c). An example of an experiment of the process of forming the metal droplet 2 by the present applicant will be described with reference to the drawings.

First, a Si (111) substrate is placed in an MBE apparatus, and CaF is placed on the Si (111) substrate by MBE.
₂ was grown to 20 nm.

Next, the Si (1) treated as described above was used.
11) The substrate is taken out from the MBE apparatus, and the taken out S
The i (111) substrate was placed in an electron beam exposure system, and spot exposure was performed in a periodic array pattern using the electron beam exposure system to form a surface-modified region (see FIG. 6A). It is considered that the surface of the CaF ₂ is modified by residual carbon in the electron beam exposure apparatus.

Then, the Si having the surface modified region
The (111) substrate is taken out of the electron beam exposure system, and the taken out Si (111) substrate is placed again in the MBE apparatus, and Ga as a metal source is supplied at a substrate temperature of 500 ° C. to be adsorbed on the surface modified region. (FIG. 6B), this is deposited in a thickness of 1 nm to 2 nm in terms of film thickness, and the Ga metal droplet 2 is deposited.
A barrel Ga droplet was formed (FIG. 6C).

FIGS. 7A, 7B, and 7C are scanning microscope (SEM) photographs showing the results of the experiment described above with reference to FIGS. 6A, 6B, and 6C. The distance between the Ga droplets was 20 nm (FIG. 7A) and 17 nm, respectively.
(FIG. 7B), 14 nm (FIG. 7C), and a case where the electron beam irradiation amount is 5 pC / dot.

As shown in the SEM photographs of FIGS. 7A, 7B and 7C, Ga droplets are formed one by one at the electron beam exposure position.

Next, a two-step Al / Ga deposition method using Al nucleation will be described with reference to FIG.

That is, the formation of the metal droplet 12 can be classified into three processes of “nucleation”, “growth” and “coalescence”, and the metal droplet 12 is thereafter formed by “growth” and “coalescence”. Are repeated, the size increases, the density decreases, and the distance between the metal droplets 12 increases.

By the way, in order to realize a quantum computer, it is desired to control and arrange two quantum dots at extremely close positions as described above. That is, in order to allow electrons to move between the two quantum dots by the tunnel effect, it is preferable that the space between the two quantum dots is extremely narrow, for example, 1 nm to 3 nm.

According to the two-step deposition method described with reference to FIG. 8, the space between the quantum dots is extremely narrow.
1 nm to 3 nm can be obtained.

That is, the two-step deposition method described with reference to FIG. 8 utilizes the fact that the melting point differs depending on the metal. First, a very small amount of Al is deposited at 350 ° C. , The density is inversely proportional to the deposition amount).

After that, Al is fixed by lowering the substrate temperature to 30 ° C., and then Ga is supplied. At this time,
Al acts as a growth nucleus for Ga.

Since the nucleus is hard to move even if the metal droplets adhere to each other due to insufficient control, the interval between the metal droplets can be kept extremely small.

Therefore, this two-stage deposition method is an important method for forming a fine dot array.

As described above, by applying an external field such as light, electrons, ions or radicals, or a combination thereof to the surface of the substrate 1, for example, the surface of the substrate 1 is irradiated with a focused electron beam. This makes it possible to locally modify the surface state by using the modulation of the surface potential, and to arrange the metal droplets at the modified location.

Here, the temperature of the metal raw material is controlled at a predetermined temperature, for example, “600 ° C. to 1500 ° C.”, and the temperature of the substrate 1 is controlled at a predetermined temperature, for example, “−10 ° C. to 1500 ° C.
° C ”and the deposition amount of the metal source is controlled to a predetermined deposition amount, for example,“ 1 × 10 ¹⁷ cm ⁻² or less ”, whereby the principle of crystal growth of atoms of the metal source on the substrate 1 described later. , The size and density of the metal droplet 2 can be controlled.

According to the experiment of the applicant of the present invention, specifically,
For example, when the metal source is Ga and the substrate 1 is CaF ₂ , the temperature of the metal source is 800 ° C., the temperature of the substrate 1 is 30 ° C., and the deposition amount of the metal source is 3 × 10 ¹⁵ c
It was found that by setting it to m ⁻² , the size of the metal droplet can be controlled to 7 nm and the density can be controlled to 1 × 10 ⁶ cm ⁻¹ .

According to the experiment by the applicant of the present invention, for example, when the metal raw material is Al and the substrate 1 is CaF ₂ , the temperature of the metal raw material is set to 1060 ° C. and the temperature of the substrate 1 is set to 350 ° C. And the deposition amount of the metal raw material is 7.3 × 10
By setting it to ¹⁵ cm ⁻² , the size of the metal droplet is reduced to 7 n.
It has been found that the density can be controlled to 9 × 10 ⁵ cm ⁻¹ while controlling to m.

Here, nucleation in the initial stage of crystal growth can be roughly classified into uniform nucleation and heterogeneous nucleation. Hereinafter, uniform nucleation and heterogeneous nucleation will be described.

(2-2) First, when uniform nucleation is used to form the metal droplet 2, the lower the temperature of the metal material to be supplied, the lower the energy of atom migration (diffusion). Therefore, the probability that the atoms coalesce on the substrate 1 is reduced, and nucleation occurs at the place where the atoms reach the substrate 1, so that the metal droplets 2 can be formed on the substrate 1 at high density.

Also, the energy for migrating atoms can be exchanged from the substrate 1.
Lowering the temperature of the substrate 1 allows the metal droplets 2 to be formed on the substrate 1 at high density.

The size of the structure of the metal droplet 2 depends on the deposition amount of the metal material. That is, nucleation occurs at one point on the substrate 1, and the nucleus grows to form a metal droplet 2.
Is formed, the size of the structure of the metal droplet 2 is determined by the deposition amount of the metal raw material.

However, in actuality, since the nuclei on the substrate 1 are united or disappear during crystal growth, the size of the structure of the metal droplet 2 is strictly predicted for each metal raw material. It is not possible.

However, the average tendency of the whole is that when the deposition amount of the metal raw material is increased, the density of the metal droplet 2 is reduced but its size is increased, so that the quantum effect is remarkably exhibited. When a fine structure is formed at a high density, the deposition amount of the metal raw material is reduced (for example, the deposition amount of the metal raw material is set to about 1 × 10 ¹⁵ cm ⁻² ), and the metal raw material and the substrate 1 It is desirable to lower the temperature within a practical range.

[0090] Regarding the area to lower the temperature of the metal source and substrate 1 largely depends on according to the type of metal material, for example, when supplying Ga as a metal raw material CaF ₂ on a substrate, CaF ₂ substrate Is set to “about −10 ° C.”, and the temperature of Ga is set to “about 800 ° C.”. Further, when supplying Al as a metal raw material CaF ₂ substrate, the temperature of the CaF ₂ substrate and "about 350 ° C."
The temperature of Al is set to “about 1100 ° C.”.

(2-3) Next, the case of heterogeneous nucleation will be described. In this heterogeneous nucleation, nucleation different from the above-described uniform nucleation is performed.

That is, in heterogeneous nucleation, crystal growth occurs using defects or impurities on the substrate surface as growth nuclei.

Therefore, if defects and impurities are arranged on the surface of the substrate 1, nucleation can be realized with these defects and impurities as the center under the following conditions.

Here, it is basically known that the rate of nucleation is extremely higher in the homogeneous nucleation and the heterogeneous nucleation than in the heterogeneous nucleation.

By the way, in the case of heterogeneous nucleation, the migration energy of atoms is reduced to some extent between the nuclei arranged on the substrate 1 in order to prevent new growth nuclei from being generated by uniform nucleation. It needs to be raised. Therefore, it is necessary to increase the temperature of the metal raw material and the temperature of the substrate 1.

However, if the temperature of the metal raw material and the temperature of the substrate 1 are too high, nucleation will not occur due to re-evaporation of the metal raw material.

In the case of the above-described heterogeneous nucleation, the nucleus density and the formation location are determined by the number and location of the defects and impurities on the substrate 1, and the size of the structure of the metal droplet 2 is determined by the deposition of the metal raw material. The larger the amount, the larger.

For example, if the adhesion coefficient of the metal raw material to the substrate 1 is “1”, the value obtained by dividing the deposition amount of the metal raw material per unit area by the number of impurity nuclei per unit area is one metal liquid. The number of atoms is equal to the number of droplets 2.

According to the experiment by the applicant of the present invention, for example, when a CaF ₂ substrate is used as the substrate 1 and Ga is used as the metal raw material, nucleation occurs when the substrate temperature is 30 ° C. When the substrate temperature rises to 200 ° C, G
The re-evaporation of a becomes remarkable and nucleation is not performed.

According to the experiment conducted by the present applicant, the substrate 1
In the case where a CaF ₂ substrate is used as the material and Al is used as the metal material, nucleation is performed when the substrate temperature is 350 ° C.
The re-evaporation of 1 becomes remarkable and nucleation is not performed.

According to the experiment conducted by the applicant of the present application, when a surface modified by an electron beam was used as a growth nucleus, a CaF ₂ substrate was used as the substrate 1 and Ga was used as a metal raw material, Nucleation occurs when the temperature is 500 ° C., but it has been found that nucleation is difficult even at higher or lower temperatures.

In each of the experiments by the applicant of the present invention, the temperature of Ga was 800 ° C. and the temperature of Al was 106 ° C.
0 ° C.

As described above, by irradiating the substrate 1 with foreign atoms as impurities before the supply of the metal raw material, the position of the nuclei for forming the metal droplet 2 and the nucleus density can be controlled.

(3) Nitriding (semiconductor): see FIG. 2 (c) The above-mentioned “(2) Formation of metal droplets: see FIG. 2 (b)”
When the processing is completed, the substrate temperature is set to the temperature at which the metal droplets are formed.
While maintaining the temperature as nitrogen source (N ₂),
Element radical (N^*), Ammonia (NH₃) Or a
Monmonia radical (NH₃ ^*) And start irradiating the substrate
The nitriding of the metal droplet 2 formed on 1 is performed.

By nitriding the metal droplet 2 in this manner, a quantum dot 4 of a nitride semiconductor is obtained.

At this time, in order to promote crystallization of the metal droplet 2, the substrate temperature is gradually increased from the temperature at which the metal droplet is formed to about 300 ° C. to 1000 ° C.
An external field such as light, electrons, ions or radicals, or a combination thereof may be added.

The setting range of the temperature needs to be appropriately determined depending on the combination of the substrate and the metal. For example, in the case of GaN on a sapphire substrate, the substrate temperature is set to 300 ° C. to 600 ° C.
Raise to about.

Here, the metal droplet 2 of Ga or the like formed on the substrate 1 by the process of “(2) Formation of metal droplet: see FIG. 2B” is heated in an ultra-high vacuum. When the height is increased, the surface diffusion becomes remarkable, the respective metal droplets 2 are united and become large, and the density of the metal droplets 2 on the substrate 1 is reduced, or the metal droplets 2 that have been formed May become a film.

In order to suppress such a phenomenon,
Nitrogen (N₂), Nitrogen radical (N ^*),ammonia
(NH₃) Or ammonia radical (NH₃ ^*)
It is necessary to perform the nitriding process at the lowest possible temperature.
You.

However, if the above-mentioned nitriding process is performed only at a low temperature, the chemical energy for crystallization of the metal raw material and nitrogen and the energy of diffusion of nitrogen into the metal raw material are insufficient, so that the crystallinity is deteriorated. This is considered to be insufficient and not sufficient for actual use as a light emitting device material or an electronic device material.

Accordingly, the temperature is low (the temperature greatly differs depending on the combination of the metal raw material and the substrate raw material. For example, when the metal raw material is Ga and the substrate raw material is CaF ₂ , the temperature is 30 ° C.) If the raw material is Al and the substrate raw material is CaF ₂ , the temperature is 350 ° C.) and start supplying nitrogen to the substrate 1 on which the metal droplets 2 are formed,
First, only the surface of the metal droplet 2 is nitrided, and thereafter, the temperature is increased during nitridation to promote crystallization, or light, electrons, ions, or radicals are kept at a low or increasing temperature. Alternatively, it is considered effective to promote crystallization by adding an external field such as a combination thereof.

By irradiating the metal droplet 2 with the energy of light, electrons, ions, or radicals, or the energy of a combination thereof, the metal droplet 2 is nitrided, so that the substrate 1
Energy required for crystallization can be provided without increasing the temperature.

Also, light, electrons, ions or radicals,
Another effect expected by adding an external field such as a combination thereof is that in the case of light, the use of an optically transparent substrate 1 enables selective application of energy only to metal. Therefore, in the case of a low substrate temperature, crystallization can be performed with very little change in size by suppressing surface diffusion extremely.

In the case of electrons, if the substrate 1 having a small electron inelastic scattering cross section is used, it is possible to selectively apply energy to almost only metal, as in the case of the light described above. Therefore, in the case of a low substrate temperature, crystallization can be performed with little change in the size by extremely suppressing surface diffusion.

As a nitrogen source for performing nitriding, a nitrogen radical or an ammonia radical having high reactivity with a metal is used instead of a nitrogen gas or an ammonia gas, so that the speed of the chemical reaction can be increased. Therefore, crystallization can be performed in a shorter time and at a lower temperature than when nitrogen gas or ammonia gas is used.

(4) Heat treatment (high quality): see FIG. 2 (d) [3] Nitriding (semiconductor): see FIG. 2 (c)
In order to improve the quality of the quantum dots 4 of the nitride semiconductor obtained by the nitriding process in the above, the pressure of nitrogen (N ₂ ), nitrogen radical (N ^* ), ammonia (NH ₃ ) or ammonia radical (NH ₃ ^* ) is reduced or In an air atmosphere, at a predetermined temperature, for example, 500 ° C. to 1500 ° C.
Heat treatment is performed at a high temperature for about a predetermined time, for example, 10 minutes.

The temperature setting range must be appropriately determined depending on the combination of the substrate and the metal. However, for GaN on a sapphire substrate, heat treatment is performed at a high temperature of about 1000 ° C.

When the above-described heat treatment is performed, the heat treatment may be performed while applying an external field such as light, electrons, ions, or radicals, or a combination thereof. There is an effect that energy can be selectively applied to the quantum dots 4 of the nitride semiconductor.

As described above, the nitride semiconductor quantum dots 4
Is heat-treated at a high temperature of about 500 ° C. to 1500 ° C.,
The crystal quality of the nitride semiconductor quantum dots 4 can be improved.

As described in "(3) Nitriding (semiconductor): see FIG. 2 (c)", when heated in an ultra-high vacuum, the surface diffusion becomes remarkable and the nitride semiconductor Since the fine structure of the quantum dots 4 cannot be realized, it is necessary to perform the heat treatment in the air, under reduced pressure (not in ultra-high vacuum), or under pressure.

As a result of the heat treatment with the increased pressure, collision of metal atoms such as Ga with molecules and atoms such as nitrogen gas and ammonia gas becomes remarkable, and it is necessary to increase the temperature while suppressing surface diffusion. As a result, a high-quality quantum dot structure can be obtained.

Incidentally, light, electrons, ions or radicals,
Alternatively, the reason for using the combination of nitrogen radicals and ammonia radicals is based on the same reason as that described in the nitridation process of “(3) Nitriding (semiconversion): see FIG. 2C”. , And a detailed description thereof will be omitted.

Through this heat treatment, a high quality nitride semiconductor quantum dot 14 can be finally formed.

Next, an experiment conducted by the present applicant,
That is, an experiment of forming GaN quantum dots as the nitride semiconductor quantum dots 4 by droplet epitaxy and the results of the experiment will be described in detail.

The outline of this experiment is as follows.
Al ₂ O ₃ substrate (sapphire substrate) as well as Ga as a metal raw material, and G on the sapphire substrate
After forming the metal droplet 2 of a, ammonia (NH ₃ )
Irradiating gas to nitride the Ga metal droplets 2 to form GaN quantum dots as nitride semiconductor quantum dots 4,
Further, the GaN quantum dots are heat-treated to produce good GaN quantum dots on the sapphire substrate.

(1) Formation of GaN Quantum Dot Structure That is, in experiments conducted by the present applicant, GaN quantum dots were formed on a sapphire (0001) substrate by using a gas source molecular beam epitaxy (GSMBE) method. That is, solid gallium (Ga) is used as a group III raw material.
And ammonia (NH ₃ ) gas was used as a group V raw material.

As the substrate 1, a substrate which was subjected to ultrasonic cleaning in a 10% hydrogen fluoride water for 20 minutes after organic cleaning and dried with nitrogen (N ₂ ) gas was used.

First, after transporting the substrate 1 to the GSMBE apparatus, the surface of the substrate 1 is heated at 800 ° C. in a vacuum until a pattern showing a flat surface is observed by using ultra-high speed electron diffraction (RHEED). Cleaned.

Thereafter, the substrate temperature is lowered to 300 ° C.
A metal Ga molecular beam is supplied to the substrate 1 in an ultra-high vacuum by 1.5 × 10 ¹⁵ cm ⁻² , and a Ga metal droplet 2
Was formed.

Then, an ammonia (NH ₃ ) gas is supplied at a substrate temperature of 300 ° C., only the surface of the metal droplet 2 is nitrided, and the temperature of the substrate is gradually increased. The temperature was raised to 0 ° C., and the Ga metal droplet 2 formed on the substrate 1 was nitrided and crystallization was promoted to obtain GaN quantum dots as the nitride semiconductor quantum dots 4.

Note that the substrate 1 has G
Heated until a ring pattern indicating crystallization of aN appeared.

(2) Heat Treatment of GaN Quantum Dots After the above-mentioned processing of “(1) Formation of GaN quantum dot structure”, substrate 1 is taken out of the GSMBE apparatus and placed in a metal organic chemical vapor deposition (MOCVD) apparatus at 760 To.
Heat treatment was performed at 1000 ° C. for 10 minutes in a mixed gas atmosphere of rr nitrogen (N ₂ ) and ammonia (NH ₃ ) to improve the quality of the crystal.

Thus, high-quality GaN quantum dots were formed on the sapphire (0001) substrate by droplet epitaxy.

(3) Experimental Results (3-1) Confirmation that Metal Droplet 2 Became Quantum Dot of Nitride Semiconductor The RHEED pattern showed a ring pattern having a lattice constant similar to that of GaN. Atomic force microscope (AFM)
In contrast to metal droplets, a structure similar to a hexagonal prism structure of a stabilized GaN structure was shown. Therefore, it is recognized that Ga was nitrided to become GaN.

Further, from the GaN quantum dots, photoluminescence (PL) emitted red light at room temperature (semiconductors emit light, but metals do not).

The smallest GaN quantum dot having a hexagonal prism structure has a diameter of 5 nm and a height of 2 nm.
nm.

The results of these experiments will be described in more detail. FIG. 9A shows that the temperature of
An AFM photograph of the surface of the GaN quantum dot obtained when the temperature was raised to ° C is shown. Also, in FIG. 9B,
FIG. 10 shows a cross-sectional view of the GaN quantum dot shown in FIG.

As shown in FIGS. 9A and 9B,
The diameter of the GaN quantum dots on the surface of the substrate 1 is about 5 n
The height of the GaN quantum dots ranges from about 2 nm to 10 nm.

The hexagonal top region of each GaN quantum dot shown in the same gray scale in the photograph shown in FIG. 9A is a hexagonal prism rather than a hemispherical GaN quantum dot. It indicates that there is.

After heating to 600 ° C., RHE
The ring pattern of the lattice constant of GaN observed in the ED observation indicates that the dots in the AFM are GaN quantum dots.

FIG. 10 shows a PL spectrum of the GaN quantum dot shown in FIG. 9A at room temperature. This spectrum was measured by “Hamamatsu Photonics System 6551”, and the detector senses the red region with high sensitivity. The peak energy of PL is 2.5 eV, and this GaN quantum dot shows bright red light emission.

This is considered to be due to insufficient crystallization of the GaN quantum dots shown in FIG. 9A. That is, it is considered that increasing the temperature to 600 ° C. is not sufficient for crystallization of GaN in droplet epitaxy.

(3-2) Confirmation that good GaN quantum dots could be formed by heat treatment at 1000 ° C. for 10 minutes The PL peak shifted to a higher energy side than the GaN thin film at liquid nitrogen temperature (77 K). . That is, the quantum confinement effect of electrons was confirmed.

That is, FIG. 11A shows that the GaN quantum dots shown in FIG. 9A are not heat-treated at 1000 ° C. (be
Fore) and after heat treatment (after) are shown. These spectra are 77K
Was measured using an ultraviolet-sensitive photomultiplier tube.

A comparison of both spectra shown in FIG. 11A shows that 3e before heat treatment at 1000 ° C.
A broad and low peak around the light energy of V;
On the other hand, after heat treatment at 1000 ° C., 3.5
At 8 eV, a strong peak appears.

This is a result of the improvement in the quality of the crystal of the GaN quantum dots shown in FIG.

FIG. 11B shows a Ga film having a thickness of 300 nm.
The N film and the GaN quantum dots shown in FIG.
With respect to the GaN quantum dots after heat treatment at 0 ° C.,
7 shows a comparison of PL spectra at 7K.

As shown in FIG. 11B,
The GaN film has an inter-band emission peak at 3.45 eV, while the GaN quantum dot has a peak at 3.58 eV, and the GaN quantum dot has a PL higher than the GaN thin film at the liquid nitrogen temperature (77 K). Are shifted.

It should be noted that 130 m
The eV blue shift is considered to be the quantized shift energy due to the formation of quantum dots.

In the above experiment, G was used as a metal raw material.
GaN as quantum dots 14 of nitride semiconductor using a
Quantum dots are obtained, but when Al is used as a metal material, quantum dots 4 of a nitride semiconductor are used.
As an AlN quantum dot, and In as a metal raw material.
Is used as the quantum dot 4 of the nitride semiconductor.
An nN quantum dot is obtained. In addition, G
When a, Al, and In are appropriately mixed and used, a mixed crystal of these is obtained.

As described above, in addition to SiO ₂ and GaN, many other materials can be considered in principle as substrate materials.

As described above, in the nitriding process, nitrogen radicals or ammonia radicals may be used, or the pressure may be changed. In the case of heat treatment at a high temperature, not only the temperature is raised but also the light An external field such as an electron, an ion, a radical, or a combination thereof may be added.

As described in detail above, when the method for forming quantum dots of nitride semiconductor by position-controlled droplet epitaxy of the present invention is used, a plurality of nitride semiconductors having extremely close gaps can be formed. Quantum dots, for example, GaN quantum dots can be formed.

Therefore, when the quantum dots of the nitride semiconductor are formed by using the method for forming the quantum dots of the nitride semiconductor by the position-controlled droplet epitaxy of the present invention, the quantum bit device in the quantum computer is used. The structure and the quantum correlation gate device structure can be realized.

Hereinafter, a quantum bit device structure and a quantum correlation gate device in a quantum computer using a nitride semiconductor quantum dot formed by the method of forming a nitride semiconductor quantum dot by position-controlled droplet epitaxy of the present invention will be described. The structure will be described.

In the following description, the term “quantum dot” refers to a nitride semiconductor quantum dot formed by the method of forming a nitride semiconductor quantum dot by position-controlled droplet epitaxy of the present invention. , For example, Ga
N quantum dots.

FIG. 12 is a conceptual explanatory diagram showing an example of an embodiment of a quantum bit device structure in a quantum computer according to the present invention.

That is, the qubit element structure 10 in the quantum computer according to the present invention can be formed, for example, by two nitride semiconductors formed by the above-described method of forming quantum dots of nitride semiconductor by position-controlled droplet epitaxy of the present invention. It is composed of quantum dots of a semiconductor, for example, two quantum dots 12 and 14 of GaN. In other words, the physical state of a qubit is a two-level system, but in the qubit element structure 10 in the quantum computer according to the present invention, two quantum levels 1 and 2 are formed by two quantum dots 12 and 14.
6, 18 are formed.

More specifically, a semiconductor material such as GaN has a diameter of several tens of nanometers (n
m), when a minute quantum dot having a spherical shape of about or less or a rectangular shape of about several tens of nanometers (nm) or less is formed, such a quantum dot has a discrete quantum level. Is formed.

Accordingly, as a two-level system of qubits, two minute quantum dots having only one quantum level of interest therein are prepared, and these two quantum dots are used in the qubit element structure 10. Quantum dots 12, 1 for constituting
4 is used.

Note that the quantum level 1 of these quantum dots 12 is
6 and the quantum level 18 of the quantum dot 14 are set to be different from each other. In this embodiment, the quantum level 16 of the quantum dot 12 located on the right side in FIG. It is set to be lower than the quantum level 18 of the quantum dot 14 located on the upper left side in FIG.

Specifically, the quantum level 1 of the quantum dot 12
The energy difference E between the level of the quantum dot 6 and the quantum level 18 of the quantum dot 14 can be freely changed by an external voltage. In the present embodiment, the quantum difference located on the right side in FIG. An external voltage is set so that the quantum level 16 of the dot 12 is lower than the quantum level 18 of the quantum dot 14 located on the left side in FIG.

The quantum dot 12 and the quantum dot 14 are arranged such that the interval G is close to, for example, about 10 angstroms, and electrons are generated between the quantum dot 12 and the quantum dot 14 by a tunnel effect. You can move freely between them.

In the above configuration, one electron exists in the qubit element structure 10 by utilizing, for example, the Coulomb blockade effect.
Electrons have a certain probability that the quantum level 16 of the quantum dot 12
(The state of | 0>) or at a certain probability at the quantum level 18 of the quantum dot 14 (the state of | 1>).

The Coulomb blockade effect is a mechanism for storing only one electron in a quantum dot by utilizing Coulomb repulsion between electrons.

Here, the qubit operation of the qubit element structure 10 can be performed by utilizing the principle of Rabi oscillation.

Here, the Rabi oscillation means that when an electromagnetic wave that resonates with the energy difference between the levels in a two-level system is irradiated,
This is a phenomenon in which the probability that an electron exists above or below two levels periodically oscillates.

Therefore, in the quantum bit element structure 10, for example, as an initial state, the probability (P1) that an electron exists at the upper quantum level 18 is 0 (P1 = 0), and the lower quantum level 16 The probability (P0) that an electron exists is 1 (P0
= 1), the probability that an electron exists in the upper quantum level 18 after irradiating an electromagnetic wave that resonates with the energy difference E between the quantum levels 18 and 16 for a half cycle of the rabbi oscillation. (P1) becomes 1 (P1 = 1), and the probability (P0) that an electron exists at the lower quantum level 16 becomes 1 (P0 = 0).

That is, by using the Rabi oscillation, the state of the qubit can be inverted. By appropriately selecting the irradiation time of the electromagnetic wave, the state of the qubit can be arbitrarily controlled.

Next, an example of an embodiment of a quantum correlation gate device structure in a quantum computer according to the present invention will be described with reference to FIGS.

That is, FIG. 13 is a diagram illustrating a conceptual configuration of an example of an embodiment of a quantum correlation gate element structure in a quantum computer according to the present invention.

The quantum correlation gate 100 is configured using two quantum bit device structures according to the above-described embodiment of the present invention.

Specifically, the quantum correlation gate 100
As two qubit device structures having different energy differences between levels, a first qubit device structure 102 having a large energy difference between two levels and a second qubit device structure having a small energy difference between two levels 104. Here, the qubit of the first qubit element structure 102 having the larger energy difference between the two levels is set as the control bit, and the qubit of the second qubit element structure 104 having the smaller energy difference between the two levels is used as the control bit. Is the target bit.

Note that the first qubit element structure 102 is
A quantum dot 108 having an upper quantum level 106 and a quantum dot 112 having a lower quantum level 110 are provided.

The second qubit element structure 104 has
It is composed of a quantum dot 116 having an upper quantum level 114 and a quantum dot 120 having a lower quantum level 118.

In the first qubit element structure 102 and the second qubit element structure 104, for example, as shown in FIG. 13, the quantum dots 108 and the quantum dots 116 face each other, and the quantum dots 112 and The quantum dots 120 are arranged in two upper and lower stages so as to face each other.
In FIG. 13, the first qubit element structure 10
2 are arranged in the upper stage, and the second qubit element structure 104 is arranged in the lower stage.

Then, the quantum dot 108 and the quantum dot 1
16 is connected via a variable capacitor 122, and the quantum dots 112 and 120 are connected via a variable capacitor 124.

Further, in such a quantum correlation gate device structure 100, the quantum dots 112 of the first quantum bit device structure 102 are
A single-electron transistor for detecting the state of the first bit by the first qubit element structure 102 is connected to the quantum dot 120 of the second qubit element structure 104 via a variable capacitor 128. A single-electron transistor for detecting the state of the second bit by the second qubit element structure 104 is connected.

In the embodiment shown in FIG. 13, the single-electron transistor has the first qubit element structure 1
02 is connected to the quantum dot 112 via the variable capacitor 126 and the second quantum bit element structure 104
Is connected to the quantum dot 120 of the first qubit element structure 102 via the variable capacitor 126, but is not limited thereto. And the second
The quantum dot 116 of the quantum bit element structure 104 may be connected via a variable capacitor 128.

In the above configuration, the variable capacitor 12
2 is set to 0 (C1 = 0) and the capacity C2 of the variable capacitor 124 is set to 0 (C2 = 0), the first qubit element structure 102 and the second qubit element structure 104 They become electrically independent from each other.

Therefore, if the above-mentioned rabbi vibration is used,
The state of the control bit of the first qubit element structure 102 and the state of the target bit of the second qubit element structure 104 are set to the states before the operation of the quantum correlation gate shown in the truth table of FIG. can do.

FIG. 14 shows an energy level indicating the total value of the electron energy of the first qubit element structure 102 and the electron energy of the second qubit element structure 104 before the operation of the quantum correlation gate. A state diagram is shown. Note that the quantum level 110 and the quantum level 1
The energy level of the electrons at 18 and 18 is a reference level A.

Therefore, if the state of the control bit and the target bit is | 0>, the energy level becomes the reference level A.

When the state of the control bit is | 0>
And if the state of the target bit is | 1>, the energy level is level B.

Further, when the state of the control bit is | 1
> And the state of the target bit is | 0>, the energy level becomes level C.

Further, if the state of the control bit is | 1> and the state of the target bit is | 1>, the energy level becomes level D.

However, the capacitance C of the variable capacitor 122
1 is set to “C1 ≠ 0” and the capacity C2 of the variable capacitor 124 is set to “C2 ≠ 0”, the first qubit element structure 102 and the second qubit element structure 10
4 are capacitively coupled to each other.

Therefore, “C1 ≠ 0” and “C2 ≠ 0”
In the case of, electrons exist diagonally with respect to the quantum levels 106 and 110 of the first quantum bit element structure 102 and the quantum levels 114 and 118 of the second quantum bit element structure 104 in the state shown in FIG. (When the state of the control bit is | 1> and the state of the target bit is | 0>, the state of the control bit is | 0>, and the state of the target bit is | 1>. "In some cases)," C1 = 0 "and" C2
= 0, the energy hardly changes, but when the electrons do not exist diagonally (when the state of the control bit is | 1> and the state of the target bit is | 1> And when the state of the control bit is | 0> and the state of the target bit is | 0>), "C1 = 0" and "C2
= 0 ". Assuming that the difference is {E}, “C1 ≠ 0” and “C2 ≠”
In the case of "0", the level A rises to the level A ', the level B becomes the level B' almost as it is, the level C becomes the level C 'almost as it is, and the level D rises to the level D'.

Therefore, the target bit is inverted only when the control bit is | 1> by irradiating the quantum correlation gate element structure 100 with an electromagnetic wave having energy of “E2 + ΔE” for a half period of the rabbi oscillation. Thus, the operation of the truth table shown in FIG. 1B can be realized.

When it is necessary to operate the control bit and the target bit independently, set “C1 = 0” and “C2 = 0” as described above, and The interaction between them may be reduced.

To observe the state of the qubit after operation by the quantum correlation gate element structure 100, the capacitance C3 of the variable capacitor 126 is set to “C3 ≠ 0” and the capacitance C4 of the variable capacitor 128 is set to “C3「 0 ”. C4 ≠
By setting to "0", a single-electron transistor is used. During the calculation, the single-electron transistor is not used and “C
3 = 0 ”and“ C4 = 0 ”.

As described above, since only one electron exists in each of the first qubit element structure 102 and the second qubit element structure 104, it is necessary to measure the charge of one electron. Since this is impossible with an existing electrometer, a single-electron transistor is used in this embodiment.

In the present invention, the upper and lower relation of the level of each quantum dot in each quantum bit element constituting the quantum correlation gate element, in other words, the arrangement relation of each quantum dot is limited to the above embodiment. Of course, it is not.

That is, instead of the arrangement shown in FIG. 13, the first qubit element structure 10 shown in FIG.
2 and the second qubit element structure 104
08 and the quantum dots 120 may be opposed to each other, and the quantum dots 112 and the quantum dots 116 may be arranged in two upper and lower tiers. In FIG. 15, the first qubit element structure 102 is arranged in the upper stage,
The second qubit element structure 104 is arranged at the lower stage.

Then, the quantum dot 108 and the quantum dot 1
20 are connected via a variable capacitor 124, and the quantum dots 112 and the quantum dots 116 are connected via a variable capacitor 122.

In the quantum correlation gate device structure 100 shown in FIG. 15, the state of the first bit by the first quantum bit device structure 102 is applied to the quantum dots 108 of the first quantum bit device structure 102 via the variable capacitor 126. A single-electron transistor for detecting
In the quantum dot 120 of the second quantum bit element structure 104,
A single-electron transistor for detecting the state of the second bit by the second qubit element structure 104 is connected via the variable capacitor 128.

Therefore, in the embodiment shown in FIG. 15, the energy level state diagram is as shown in FIG.

That is, in the case of “C1 ≠ 0” and “C2 ≠ 0”, the quantum levels 106 and 110 of the first quantum bit element structure 102 and the quantum levels 106 and 110 of the second quantum bit element structure 104 in the state shown in FIG. Regarding the quantum levels 114 and 118, when electrons do not exist diagonally (when the state of the control bit is | 0> and the state of the target bit is | 0>, and when the state of the control bit is | 1> and the state of the target bit is | 1>), “C1 = 0” and “C2
= 0, the energy is hardly changed, but when the electrons are on diagonal lines (when the state of the control bit is | 0> and the state of the target bit is | 1> And when the state of the control bit is | 1> and the state of the target bit is | 0>), “C1 = 0” and “C2 =
The energy is higher than in the case of "0". Assuming that the difference is ΔE, “C1 ≠ 0” and “C2 ≠ 0”
In the case of (1), level A becomes level A 'almost as it is, level B rises to level B', level C rises to level C ', and level D becomes level D' almost as it is.

Therefore, by irradiating the quantum correlation gate element structure 100 with an electromagnetic wave having an energy of “E2-ΔE” for a half period of the rabbi oscillation, the target bit can be changed only when the control bit is | 1>. The operation of the truth table shown in FIG. 1B can be realized.

That is, the upper and lower relationship of the level of each quantum dot in each quantum bit device constituting the quantum correlation gate device in the present invention, in other words, the arrangement relationship of each quantum dot does not matter. The energy of the electromagnetic wave radiated during the half cycle of the vibration changes according to the vertical relation of the level of each quantum dot in each quantum bit element constituting the quantum correlation gate element in the present invention, in other words, according to the arrangement relation of each quantum dot. Need to be done.

[0201]

Since the present invention is configured as described above, GaN, InN or AlN or InGa
Quantum dots of nitride semiconductors such as N and AlGaN can be formed by controlling the position, thereby enabling the quantum dots of two nitride semiconductors to be controlled and arranged at extremely close positions. Thus, for example, there is an excellent effect that a qubit and a quantum correlation gate can be realized.

Further, since the present invention is constructed as described above, it is possible to provide a quantum bit device structure and a quantum correlation gate device structure in a Turing type quantum computer with a solid-state device. It has the effect.

[Brief description of the drawings]

FIG. 1A is an explanatory view conceptually showing a quantum correlation gate, and FIG. 1B is a conceptual truth table of the quantum correlation gate.

FIGS. 2A and 2B are explanatory diagrams showing a process for forming a quantum dot of a nitride semiconductor by position-controlled droplet epitaxy, wherein FIG. 2A shows a “substrate” and FIG. (C) shows “nitriding (semiconductor conversion)”, and (d) shows “heat treatment (high quality)”.

FIG. 3 is a diagram illustrating the principle of modifying the surface of a substrate by electron beam irradiation.

FIG. 4 is a conceptual diagram of a process of irradiating an electron beam onto CaF ₂ on which an As film is deposited and controlling the position of a Ga metal droplet by a natural formation method.

FIG. 5 is a scanning micrograph of the results of the experiment shown in FIGS. 4 (a), (b), and (c), in which the distance between Ga droplets is 150 nm, and the irradiation amount of the electron beam is 0.4 pC / dot.
The result of two-dimensional spot exposure is shown.

FIG. 6 is a conceptual diagram of a process of irradiating an electron beam onto CaF ₂ in a vacuum and controlling the position of a Ga metal droplet 2 by a spontaneous formation method.

FIGS. 7A and 7B are scanning micrographs of the results of the experiments shown in FIGS. 6A, 6B, and 6C, wherein FIG.
(b) shows the result of one-dimensional spot exposure where the electron beam irradiation amount was 5 pC / dot.
The distance between the droplets is 17 nm, and the irradiation amount of the electron beam is 5 p.
C / dot shows the result of one-dimensional spot exposure, and (c) shows the result of one-dimensional spot exposure with a Ga droplet interval of 14 nm, an electron beam irradiation of 5 pC / dot. .

FIG. 8 is an explanatory view of a two-step deposition method of Al / Ga using nucleation of Al.

FIG. 9 shows GaN quantum dots obtained by the applicant's experiment, wherein (a) shows that the temperature of
It is an AFM photograph of the surface of the GaN quantum dot obtained when the temperature was raised to ℃, (b) is a GaN quantum dot shown in (a)
It is sectional drawing of a quantum dot.

FIG. 10 is a graph showing a PL spectrum of the GaN quantum dots shown in FIG. 9A at room temperature.

11A is a graph showing PL spectra before (before) and after (after) heat treatment of the GaN quantum dot shown in FIG. 9A at 1000 ° C., and FIG. 11B is a graph showing 300 nm. Thickness GaN film and FIG.
It is a graph which shows the PL spectrum at 77K with the GaN quantum dot after heat-treating the GaN quantum dot shown in (a) at 1000 degreeC.

FIG. 12 is a conceptual configuration explanatory view showing an example of an embodiment of a qubit element structure in a quantum computer according to the present invention.

FIG. 13 is a conceptual structural explanatory view of an example of an embodiment of a quantum correlation gate element structure in a quantum computer according to the present invention.

14 is the sum of the energy of the electrons of the first qubit element structure and the energy of the electrons of the second qubit element structure in a state before the operation of the quantum correlation gate with respect to the quantum correlation gate element structure shown in FIG. 13; FIG. 4 is an energy level diagram showing

FIG. 15 is a conceptual structural explanatory view of an example of another embodiment of the quantum correlation gate element structure in the quantum computer according to the present invention.

16 is the sum of the electron energy of the first qubit element structure and the electron energy of the second qubit element structure in a state before the operation of the quantum correlation gate, with respect to the quantum correlation gate element structure shown in FIG. FIG. 4 is an energy level diagram showing

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Substrate 2 Metal droplet 4 Quantum dot of nitride semiconductor 10 Quantum bit element structure 12, 14, 108, 112, 116, 120 Quantum dot 16, 18, 106, 110, 114, 118 Quantum level 100 Quantum correlation gate element Structure 102 First qubit element structure 104 Second qubit element structure 122, 124, 126, 128 Variable capacitor

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kazuo Tsutsui 4259 Nagatsutacho, Midori-ku, Yokohama-shi, Kanagawa Prefecture F-term in Tokyo Institute of Technology 5F053 AA50 DD20 FF10 GG01 HH04 HH05 LL10 PP14 RR20 5F103 AA04 AA05 DD28 HH03 HH04 LL17 PP04 PP20

Claims (16)

[Claims] 1. A method for forming quantum dots of a nitride semiconductor by position-controlled droplet epitaxy, comprising applying an external field to a surface of a substrate having a surface energy lower than that of a metal raw material. A first treatment for modulating the surface state of the substrate to modify the surface, supplying the metal raw material to the substrate having the surface modified by the first treatment, and modifying the surface A second process of forming metal droplets by crystal growth at the set location, supplying a nitrogen source onto the substrate on which the metal droplets have been formed by the second process, and nitriding the metal droplets. Forming a nitride semiconductor quantum dot by position-controlled droplet epitaxy. 2. The method for forming a quantum dot of a nitride semiconductor by position-controlled droplet epitaxy according to claim 1, further comprising the step of: Forming a quantum dot of a nitride semiconductor by position-controlled droplet epitaxy, comprising: performing a heat treatment at a predetermined temperature for a predetermined time. 3. The method for forming a quantum dot of a nitride semiconductor by position-controlled droplet epitaxy according to claim 1, wherein the third treatment is performed at a low temperature on the metal. A position-controlled droplet epitaxy which starts supplying a nitrogen source to the substrate on which the droplets have been formed to nitride only the surface of the metal droplet, and then raises the temperature during nitriding to promote crystallization. Of forming quantum dots of nitride semiconductor by the method described above. 4. The method for forming a quantum dot of a nitride semiconductor by position-controlled droplet epitaxy according to claim 3, wherein the third process includes forming the metal droplet at a low temperature. When a source of nitrogen is supplied to the substrate and only the surface of the metal droplet is nitrided, and then the temperature is increased during nitriding to promote crystallization, an external field is added to promote crystallization. A method for forming a quantum dot of a nitride semiconductor by droplet epitaxy with a controlled position. 5. The method for forming a quantum dot of a nitride semiconductor by position-controlled droplet epitaxy according to claim 1, wherein the third treatment is performed at a low temperature at a low temperature. A position control that starts supplying a nitrogen source to the substrate on which the droplets are formed and nitrifies only the surface of the metal droplets, and then applies an external field at a low temperature during nitriding to promote crystallization. Of forming quantum dots of nitride semiconductor by droplet epitaxy. 6. The method for forming quantum dots of a nitride semiconductor by position-controlled droplet epitaxy according to claim 2, wherein the fourth Is a method for forming a quantum dot of a nitride semiconductor by position-controlled droplet epitaxy in which an external field for heat treatment is added. 7. A quantum dot of a nitride semiconductor by position-controlled droplet epitaxy according to any one of claim 1, claim 2, claim 3, claim 4, claim 5, or claim 6. The method of forming a nitride semiconductor quantum dot by position-controlled droplet epitaxy, wherein the external field is light, electrons, ions or radicals, or a combination thereof. 8. A quantum dot of a nitride semiconductor by position-controlled droplet epitaxy according to any one of claims 1, 2, 4, 5, 6, and 7. The method of forming a quantum dot of a nitride semiconductor by position-controlled droplet epitaxy, wherein the metal source is a Group III metal. 9. A nitride by position-controlled droplet epitaxy according to any one of claims 1, 2, 4, 5, 5, 6, 7 and 8. In the method for forming a semiconductor quantum dot, the substrate is a sapphire substrate, a silicon carbide substrate, a quartz substrate, a gallium nitride substrate, or a calcium fluoride substrate. Formation method. 10. The position-controlled droplet according to any one of claim 1, claim 2, claim 4, claim 5, claim 6, claim 7, claim 8, or claim 9. In the method of forming a quantum dot of a nitride semiconductor by epitaxy, the method of forming a quantum dot of a nitride semiconductor by position-controlled droplet epitaxy, wherein the nitrogen source is nitrogen, nitrogen radical, ammonia or ammonia radical. 11. A semiconductor device comprising: a first quantum dot having a first quantum level; and a second quantum dot having a second quantum level different from the first quantum level, wherein a tunnel effect is provided. The first quantum dot and the second quantum dot are arranged close to each other such that electrons can freely move between the first quantum dot and the second quantum dot, and In a qubit element structure in a quantum computer in which only one electron exists, the first quantum dot and the second quantum dot are:
Claim 1, Claim 2, Claim 4, Claim 5, Claim 6,
A quantum computer formed by the method of forming a quantum dot of a nitride semiconductor by position-controlled droplet epitaxy according to any one of claims 7, 8, 9, and 10. Qubit device structure. 12. A tunnel effect comprising: a first quantum dot having a first quantum level; and a second quantum dot having a second quantum level lower than the first quantum level. The first quantum dot and the second quantum dot are arranged close to each other so that electrons can freely move between the first quantum dot and the second quantum dot, and A first qubit element structure in which only one electron exists, a third quantum dot having a third quantum level, and a fourth quantum level below the third quantum level. A fourth quantum dot having a third quantum dot, and the third quantum dot and the third quantum dot so that electrons can freely move between the third quantum dot and the fourth quantum dot by a tunnel effect. The fourth quantum dot is arranged close to the fourth quantum dot, and furthermore, only one electron exists. A second quantum bit device structure, wherein the first bit device structure and the second bit device structure are configured such that the first quantum dots and the third quantum dots face each other, The second quantum dot and the fourth quantum dot
Are arranged so as to face each other, the first quantum dot and the third quantum dot are electrically connected, and the second quantum dot and the fourth quantum dot are electrically connected to each other. And a level difference between the first quantum level and the second quantum level and a level difference between the third quantum level and the fourth quantum level. In a quantum correlation gate device structure in a quantum computer that is set differently, the first quantum dot, the second quantum dot, the third quantum dot, and the fourth quantum dot are each formed as follows. Any one of claim 1, claim 2, claim 4, claim 5, claim 6, claim 7, claim 8, claim 9, or claim 10
Item 18. A quantum correlation gate device structure in a quantum computer formed by the method for forming a quantum dot of a nitride semiconductor by position-controlled droplet epitaxy according to Item. 13. The quantum correlation gate device structure in a quantum computer according to claim 12, wherein said first quantum dot and said third quantum dot are capacitively connected via a first variable capacitor. The quantum correlation gate device structure in a quantum computer, wherein the second quantum dot and the fourth quantum dot are capacitively connected via a second variable capacitor. 14. A tunnel effect comprising: a first quantum dot having a first quantum level; and a second quantum dot having a second quantum level lower than the first quantum level. The first quantum dot and the second quantum dot are arranged close to each other so that electrons can freely move between the first quantum dot and the second quantum dot, and A first qubit element structure in which only one electron exists, a third quantum dot having a third quantum level, and a fourth quantum level below the third quantum level. A fourth quantum dot having a third quantum dot, and the third quantum dot and the third quantum dot so that electrons can freely move between the third quantum dot and the fourth quantum dot by a tunnel effect. The fourth quantum dot is arranged close to the fourth quantum dot, and furthermore, only one electron exists. A second quantum bit device structure, wherein the first bit device structure and the second bit device structure are configured such that the first quantum dots and the fourth quantum dots face each other, The second quantum dot and the third quantum dot
Are arranged so as to face each other, the first quantum dot and the fourth quantum dot are electrically connected, and the second quantum dot and the third quantum dot are electrically connected to each other. And a level difference between the first quantum level and the second quantum level and a level difference between the third quantum level and the fourth quantum level. In a quantum correlation gate device structure in a quantum computer that is set differently, the first quantum dot, the second quantum dot, the third quantum dot, and the fourth quantum dot are each formed as follows. Any one of claim 1, claim 2, claim 4, claim 5, claim 6, claim 7, claim 8, claim 9, or claim 10
Item 18. A quantum correlation gate device structure in a quantum computer formed by the method for forming a quantum dot of a nitride semiconductor by position-controlled droplet epitaxy according to Item. 15. The quantum correlation gate device structure in a quantum computer according to claim 14, wherein the first quantum dot and the fourth quantum dot are capacitively connected via a first variable capacitor. The quantum correlation gate device structure in a quantum computer, wherein the second quantum dot and the third quantum dot are capacitively connected via a second variable capacitor. 16. The method of claim 12, claim 13, or claim 14.
Or the quantum correlation gate device structure in the quantum computer according to claim 15, wherein the first qubit device structure is connected to a first single-electron transistor via a third variable capacitor; The fourth quantum bit device structure is a quantum correlation gate device structure in a quantum computer connected to a second single-electron transistor via a fourth variable capacitor.