JP3415068B2 - 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

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming quantum dots 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 specifically,
For example, a single crystal such as GaN (gallium nitride), InN (indium nitride), or AlN (aluminum nitride), which is required when configuring a Turing-type quantum computer that performs quantum computation based on the principle of quantum mechanics, A method for forming a nitride semiconductor quantum dot by position-controlled droplet epitaxy, which is suitable for use in forming a III-V group nitride semiconductor quantum dot of these mixed crystals (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 In the field of semiconductor technology, III-V group nitride semiconductors such as GaN, InN and AlN have been expected to be extremely useful as optical device materials and electronic device materials.

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

However, although a method of forming gallium arsenide (GaAs) quantum dots by droplet epitaxy has been proposed in the past, up to now G
aN, InN, AlN, InGaN, AlGaN
No method for forming quantum dots of a nitride semiconductor has been proposed, and the devising of a method for forming quantum dots of a nitride semiconductor has been strongly desired.

By the way, in recent years, a concept of a quantum computer for performing quantum calculation 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 quantum bit device for realizing a quantum bit corresponding to the bit concept of the current digital computer and a quantum correlation gate device for performing an operation of two quantum bits. To date, it has been found necessary.

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

Existing digital based on the principle of classical mechanics
In a computer, an arithmetic operation such as addition or Fourier transform can be performed by causing a logical gate such as AND (AND) or OR (OR) to act on a “bit” composed of “0” and “1”. It is designed to build a circuit. As a concept corresponding to such “bit”, the concept of “qubit” is introduced in the quantum computer.

According to the quantum mechanics that governs the microscopic properties of matter, the state of particles such as electrons (in this specification, electrons are explained) is represented by superposition of various states. That is, in quantum mechanics, when there are only two possible states, the state with the larger energy is represented as “| 1>”, and
When the lower energy state is represented as “| 0>”, it can be said that the electron state is in the superposition state of | 1> and | 0>. This concept
The concept of quantum bits is used for conventional bits.

In other words, in the quantum bit, the state of the quantum bit cannot be said to be "0" or "1" as compared with the conventional bit in which "0" or "1" is definite, and there is a certain probability. It can only be said that there is a state of "0" at and a state of "1" with a certain probability. That is, such a state is called a superposed state.

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

The quantum correlation gate is a gate that operates a quantum bit by performing an operation on two quantum bits as described above, and the operation is as shown in FIG.

That is, the quantum correlation gate is commutative so that it can act on two qubits in a certain state to obtain two qubits in another state.

Specifically, as conceptually shown in FIG. 1A, one of two quantum bits (two quantum bits) before being affected by the quantum correlation gate is used for the quantum correlation gate. Is the standard qubit of
It is called a "control bit". ) Is “A” and the other of the two qubits before being affected by the quantum correlation gate (the qubit that is affected by the “control bit” of the two qubits. , Hereinafter referred to as "target bit".)
Is "B", the two quantum bits after being affected by the quantum correlation gate are affected by the quantum correlation gate as conceptually shown in the truth table of FIG. 1 (b). An exclusive OR "X" of "A", which is the same state as the previous control bit, and "A", which is the state of the control bit before being acted on by the quantum correlation gate, and "B", which is the state of the target bit Is what you can get.

The applicant of the present application has disclosed, as a practical structure capable of realizing the above-described quantum bit and quantum correlation gate, Japanese Patent Application No. 10-232590 "Quantum Bit Element Structure and Quantum Correlation in Quantum Computer". Gate device structure "(Filing date: August 1, 1998)
9th) is proposed.

The principle of the invention relating to Japanese Patent Application No. 10-232590 "Quantum bit device structure and quantum correlation gate device structure in a quantum computer" is that the diameter of a sphere is several tens of nanometers (nm) or less, or a spherical shape. ,
Two quantum dots, each of which has a rectangular shape with one side of several tens of nanometers (nm) or less, are arranged close to each other, and electrons can be moved between the two quantum dots by the tunnel effect. One electron is moved back and forth between the two quantum dots to have two states of | 1> and | 0>.

Here, the closer the distance between the two quantum dots is, the more preferable it is.
When it is attempted to control the position where two quantum dots are formed by using a lithography technique, there is a technical limit in bringing the distance between the two quantum dots close to each other.
It has been strongly desired to devise a method for forming quantum dots, which makes it possible to control and arrange 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 its object is to obtain GaN, InN, AlN, InGaN, AlGaN, or the like. A quantum dot of a nitride semiconductor can be formed in a position-controlled manner, whereby two quantum dots of a nitride semiconductor can be controlled and arranged in an extremely close position. Another object of the present invention is to provide a method for forming quantum dots of a nitride semiconductor by position-controlled droplet epitaxy, which can realize 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 position-controlled droplet epitaxy. Is to provide.

[0020]

In order to achieve the above object, the present invention is a method for forming quantum dots of a nitride semiconductor by position-controlled droplet epitaxy, which is lower than the surface energy of a metal raw 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 treatment in which the metal raw material is supplied to the substrate whose surface has been modified by the first treatment, and metal droplets are formed by crystal growth at the modified portion of the surface; By 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 a quantum dot of a nitride semiconductor. is there.

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

Here, in the third treatment, the 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, and then the temperature is increased during the nitriding. Can be raised to promote crystallization.

Further, in the third treatment, a nitrogen source is started to be supplied to the substrate on which the metal droplets are formed at a low temperature to nitrid only the surface of the metal droplets, and then the temperature is changed during nitriding. When raising to promote crystallization, an external field may be added to promote crystallization.

Further, in the third treatment, 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, and thereafter, during the nitriding, a low temperature is applied. An external field can be added to accelerate crystallization.

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

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

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.

The nitrogen source may be nitrogen, nitrogen radicals, ammonia or ammonia radicals.

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, and 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 is present, the first quantum dot and the first quantum dot 2 quantum dots, claim 1, claim 2, claim 3, claim 4, claim 5, claim 6, claim 7, claim 8, claim 9 or claim 10. It is formed by the method for forming quantum dots of a nitride semiconductor by the position-controlled droplet epitaxy described in 1.

Further, the present invention has a first quantum dot having a first quantum level and a second quantum dot having a second quantum level below the first quantum level. 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 the tunnel effect. Place and
Further, the first qubit device structure in which only one electron exists, the third quantum dot having the third quantum level, and the fourth quantum below the third quantum level. A fourth quantum dot having a level, 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. And the fourth quantum dot are arranged in close proximity to each other, and further, a second qubit device structure in which only one electron exists is provided, and the first bit device structure and the second qubit device structure are provided. And a bit element structure of the first quantum dot and the third quantum dot.
And the second quantum dot and the fourth quantum dot are arranged so as to 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 the level difference between the first quantum level and the second quantum level, and the third level
In the quantum correlation gate device structure in a quantum computer in which the level difference between the first quantum dot and the fourth quantum level is set to be different from each other, the first quantum dot, the second quantum The dot, the third quantum dot, and the fourth quantum dot are defined by claim 1, claim 2, claim 3, claim 4, claim 5, claim 6, claim 7, claim 8, and claim 5. It is formed by the method for forming quantum dots of a nitride semiconductor by position-controlled droplet epitaxy according to claim 9 or 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 it.

Further, the present invention has a first quantum dot having a first quantum level and a second quantum dot having a second quantum level below the first quantum level. 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 the tunnel effect. Place and
Further, the first qubit device structure in which only one electron exists, the third quantum dot having the third quantum level, and the fourth quantum below the third quantum level. A fourth quantum dot having a level, 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. And the fourth quantum dot are arranged in close proximity to each other, and further, a second qubit device structure in which only one electron exists is provided, and the first bit device structure and the second qubit device structure are provided. And a bit element structure of the first quantum dot and the fourth quantum dot.
And the second quantum dot and the third quantum dot are arranged to 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 the level difference between the first quantum level and the second quantum level and the third level
In the quantum correlation gate device structure in a quantum computer in which the level difference between the first quantum dot and the fourth quantum level is set to be different from each other, the first quantum dot, the second quantum The dot, the third quantum dot, and the fourth quantum dot are defined by claim 1, claim 2, claim 3, claim 4, claim 5, claim 6, claim 7, claim 8, and claim 5. It is formed by the method for forming quantum dots of a nitride semiconductor by position-controlled droplet epitaxy according to claim 9 or 10.

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

Further, the first qubit device structure is
The fourth qubit device structure, which is connected to the first single-electron transistor through the third variable capacitor, has a fourth
It may be connected to the second single-electron transistor via the variable capacitor.

[0036]

BEST MODE FOR CARRYING OUT THE INVENTION A method for forming a quantum dot of a nitride semiconductor by position-controlled droplet epitaxy of the present invention, a quantum bit device structure in a quantum computer, and a quantum correlation gate device structure will be described below with reference to the accompanying drawings. An example of the embodiment will be described in detail.

Here, FIGS. 2A, 2B, 2C and 2D 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 illustration is shown.

Hereinafter, FIG. 2 (a) (b) (c) (d)
An example of an embodiment of a method for forming a quantum dot 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. 2 (a) 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 a nitride semiconductor are formed on the substrate 1 (see FIG. 2 (c) (d))
Is formed.

Here, the substrate 1 serves as a raw material for the quantum dots 14 of a nitride semiconductor, such as Ga (gallium) or A.
III such as l (aluminum) and indium (In)
A group 3 metal (herein, a metal as a raw material of the quantum dots 4 of the nitride semiconductor will be appropriately referred to as a “metal raw material”) can be three-dimensionally grown on the substrate 1. As described above, the surface energy is lower than the surface energy of these metal raw materials. That is, the surface energy of the metal raw material is higher than that of the substrate 1.

As the substrate 1 having a surface energy lower than that of the metal raw material, 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) as
l ₂ O ₃ (sapphire), SiO ₂ (quartz), SiC
(Silicon carbide), GaN (gallium nitride), CaF ₂
An example is one using a fluoride such as (calcium fluoride).

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 action of minimizing the energy of the system occurs, so that the metal is deposited on the substrate. The metal to be grown grows in a spherical shape to minimize the surface area. It should be noted that this growth pattern is
It is referred to as an olmer-Weber style (VW style).

In general, metal has a higher surface energy than semiconductors and insulators, and is therefore advantageous in forming a fine three-dimensional structure, and Ga, Al, and I, which are the metal raw materials described above, are advantageous.
Metals such as n are also Al ₂ O ₃ and S which are the above-mentioned substrate materials.
Surface energy is higher than that of semiconductors and insulators such as iC, SiO ₂ , GaN, and CaF ₂ .

As a combination of the metal raw material and the substrate raw material, for example, when the metal raw material is Ga, the substrate raw material is AlN because of the lattice constant matching between the semiconductor to be formed and the substrate and the electron confinement. It is preferable that the substrate material is CaF ₂ when the metal material is Al, and GaN is the substrate material when the metal material is In.

As the substrate for three-dimensionally growing the metal raw material, the above-mentioned Al ₂ O ₃ substrate, SiO ₂ substrate, Ga are used.
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, etc. can be used because they can be integrated with existing Si integrated circuits and GaAs integrated circuits. It is 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 which can be epitaxially grown well on a Si (111) substrate. Especially, since the (111) outermost surface is terminated with fluorine ions, its surface energy is extremely low. It has the characteristics 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 a molecular beam epitaxy (MBE) method. What was made to use can be used.

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

Here, by applying an external field such as light, electrons, ions or radicals, or a combination thereof to the surface of the substrate 1, the surface state of the substrate 1 is arbitrarily modulated, whereby the surface of the substrate 1 is changed. Is reformed, and as a result, the nucleus growth in the crystal growth accompanying the supply of the metal raw material is preferentially performed at the place where the potential for adsorption formed is the lowest, and the position where the metal droplet 2 is formed is changed. Be able to control.

For example, CaF _{2 is formed} on the Si (111) substrate described in the above "(1) Substrate: see FIG. 2 (a)".
The substrate 1 epitaxially grown will be described. By arbitrarily modulating the surface state of CaF ₂ using an electron beam, the surface of the substrate 1 is modified, and as a result, the lowest potential for adsorption is formed. However, nuclear growth is prioritized.

[0053] In this respect, FIG. 3 (a) (b) will be described with reference to the illustration of the principles of the modification of the substrate surface by electron beam irradiation shown in (c), CaF ₂ in FIGS. 3 (a)
The surface structure of CaF ₂ crystal is
It is terminated with ions, its surface energy is lower than that of metals and semiconductors, and dangling bonds do not appear on the surface, so it is difficult for the deposited material to nucleate (in Fig. 3 (a), Ca is used for simplicity). Ions are not shown in the figure.).

When such a fluoride such as a CaF ₂ crystal is 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, the F ion is desorbed from the surface due to the desorption phenomenon of the F ion accompanied by the Auger process by the electron. Desorb.

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

It is not always necessary to irradiate the CaF ₂ crystal with the electron beam in an As atmosphere.
In a (phosphorus) atmosphere, the surface is replaced with P and modified,
Further, in the electron beam exposure apparatus, the surface is replaced by the 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 surface area increases as a result of increasing G
a will be selectively gathered. Since Ga has a high surface energy, it aggregates into a spherical shape to grow nuclei and form a metallic droplet 2 of Ga.

Here, the electron beam irradiation onto 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 forming process of the metal droplet 2 by the applicant of the present application will be described with reference to the conceptual diagram of FIG.

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

Then, Si (1
11) Remove the substrate from the MBE device, and remove the 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 on which the surface modified region was formed was formed.
The (111) substrate was taken out of the electron beam exposure system, the Si (111) substrate taken out was subjected to surface cleaning, and then placed again in the MBE apparatus to obtain a substrate temperature of 5
Excess As is evaporated and removed at 50 ° C, and finally the substrate temperature is 50
Ga, which is a metal raw material, was supplied at 0 ° C. to be adsorbed on the surface modification region (FIG. 4B), and this was converted to a film thickness of 1 nm to 2 n.
m was deposited to form Ga droplets, which are metallic droplets 2 of Ga (FIG. 4C).

FIG. 5 shows the above-mentioned FIG. 4 (a) (b).
It is a scanning microscope (SEM) photograph showing the result of the experiment described with reference to (c), and the Ga droplet spacing is 150
and the irradiation amount of the electron beam is 0.4 pC / dot.

As shown in the SEM photograph of FIG. 5, one Ga droplet is formed at each electron beam exposure position.

Incidentally, as in the method described with reference to FIGS. 4A, 4B and 4C, CaF ₂ on which an As film is deposited is deposited.
When the electron beam is radiated upward, the electrons in the metal film are scattered forward, so no matter how finely focused the electron beam is, it will be blurred by the time it reaches the CaF ₂ surface, and in principle a fine structure will be formed. Hard to get.

Therefore, as a method of enabling surface modification without using an As film and obtaining a fine structure, referring to FIGS. 6 (a) (b) (c), There is a method to explain.

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

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

Next, the Si (1
11) Remove the substrate from the MBE device, and remove the 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 CaF ₂ surface is surface-modified by residual carbon in the electron beam exposure apparatus.

Then, the Si on which the surface modified region was formed was formed.
The (111) substrate was taken out from the electron beam exposure system, the taken-out Si (111) substrate was placed again in the MBE apparatus, and Ga as a metal raw material was supplied at a substrate temperature of 500 ° C. to be adsorbed to the surface modification region. (FIG. 6 (b)), which is deposited to a thickness of 1 nm to 2 nm to form a Ga metal droplet 2
A barrel Ga droplet was formed (FIG. 6C).

FIGS. 7 (a), (b) and (c) are scanning microscope (SEM) photographs showing the results of the experiment described above with reference to FIGS. 6 (a), (b) and (c), Ga droplet intervals are 20 nm (FIG. 7 (a)) and 17 nm, respectively.
(FIG. 7B), 14 nm (FIG. 7C), and the irradiation amount of the electron beam is 5 pC / dot.

As shown in the SEM photographs of FIGS. 7A, 7B and 7C, one Ga droplet is formed at each electron beam exposure position.

Next, the Al / Ga two-step 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 then "grown" and "coalescent". By repeating the above, the size becomes large, the density becomes low, and the interval between the metal droplets 12 becomes wide.

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 distance 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, for example,
It becomes possible to set it to 1 nm to 3 nm.

That is, the two-step deposition method described with reference to FIG. 8 makes use of the fact that the melting points of different metals are different. First, a small amount of Al is deposited at 350 ° C. , Density is inversely proportional to the amount deposited.) To form growth nuclei.

After that, the substrate temperature is lowered to 30 ° C. to fix Al, and then Ga is supplied. At this time,
Al acts as a growth nucleus of Ga.

Even if the metal droplets adhere to each other due to insufficient control, the nuclei do not move easily, so that the interval between the metal droplets can be kept extremely narrow.

Therefore, this two-step 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, irradiating the surface of the substrate 1 with a focused electron beam. By this, it becomes possible to locally modify the surface state by using the modulation of the surface potential and to dispose the metal droplet at the modified place.

Here, the temperature of the metal raw material is controlled to a predetermined temperature, for example, "600 ° C. to 1500 ° C.", and the temperature of the substrate 1 is set to a predetermined temperature, for example, "-10 ° C. to 1500 ° C."
C. "and the deposition amount of the metal raw material 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 raw material on the substrate 1 described later. The size and density of the metal droplet 2 can be controlled based on

According to the experiment by the applicant, specifically,
For example, when the metal raw material is Ga and the substrate 1 is CaF ₂ , the temperature of the metal raw material is 800 ° C., the temperature of the substrate 1 is 30 ° C., and the deposition amount of the metal raw material is 3 × 10 ¹⁵ c
It was found that by setting 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 .

Further, according to the experiment by the applicant of the present application, for example, when the metal raw material is Al and the substrate 1 is CaF ₂ , the temperature of the metal raw material is 1060 ° C. and the temperature of the substrate 1 is 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 7 n.
It has been found that the density can be controlled to 9 × 10 ⁵ cm ⁻¹ while controlling to m.

Here, nucleation at the initial stage of crystal growth can be roughly classified into homogeneous nucleation and heterogeneous nucleation. Less than,
Homogeneous nucleation and heterogeneous nucleation will be described.

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

Further, since energy for atom migration can be exchanged from the substrate 1,
When the temperature of the substrate 1 is lowered, the metal droplets 2 can be formed on the substrate 1 with high density.

The size of the structure of the metal droplet 2 depends on the amount of metal raw material deposited. That is, nucleation occurs at a certain point on the substrate 1, and the nuclei grow into crystals to cause metal droplets 2
In the case of the formation, the size of the structure of the metal droplet 2 is determined by the deposition amount of the metal raw material.

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

However, as an average tendency of the whole, when the deposition amount of the metal raw material is increased, the density of the metal droplets 2 is decreased but the size thereof is increased, so that the quantum effect appears remarkably. When forming a fine structure with 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 are separated. It is desirable to reduce the temperature within a realistic 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 The temperature of Ga is about "-10 ° C" and the temperature of Ga is "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 “about 1100 ° C.”.

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

That is, the heterogeneous nucleation is that crystal growth occurs by 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 conditions described later.

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

By the way, in the case of heterogeneous nucleation, in order to prevent new growth nuclei from being generated by homogeneous nucleation between nuclei arranged on the substrate 1, the atomic migration energy is set to some extent. Need to raise. 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 does not occur due to re-evaporation of the metal raw material.

In the case of the above-mentioned non-uniform nucleation, the nucleus density and formation location are determined by the number of defects and impurities on the substrate 1 and the location thereof, 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 amount of the metal raw material deposited per unit area divided by the number of impurity nuclei per unit area is one metal liquid. It becomes the number of atoms that drop 2 fills.

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

Further, according to the experiment by the applicant of the present application, the substrate 1
When a CaF ₂ substrate is used as a substrate and Al is used as a metal raw material, nucleation is performed when the substrate temperature is 350 ° C., but when the substrate temperature is raised to 500 ° C.
The re-evaporation of 1 becomes remarkable and nucleation is stopped.

Further, according to the experiments by the applicant of the present application, when a region surface-modified by an electron beam is used as a growth nucleus, a CaF ₂ substrate is used as the substrate 1, and Ga is used as a metal raw material, the substrate is Although nucleation occurs at a temperature of 500 ° C., it has been revealed that it is difficult to perform nucleation above or below the temperature.

In each of the experiments by the applicant, the Ga temperature was 800 ° C. and the Al temperature was 106 ° C.
It was set to 0 ° C.

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

(3) Nitriding (semiconductor): See FIG. 2 (c) In the above-mentioned “(2) Formation of metal droplets: see FIG. 2 (b)”
When the process is completed, the substrate temperature is set to the temperature at which the metal droplets are formed.
Nitrogen (N _Two),
Elementary radical (N^*), Ammonia (NH_Three) Or
Nmonia radical (NH_Three ^*) Etc. start irradiating the substrate
Nitriding of the metal droplet 2 formed on 1 is performed.

By nitriding the metal droplets 2 in this manner, the quantum dots 4 of the nitride semiconductor are obtained.

At this time, in order to promote crystallization of the metal droplets 2, the substrate temperature is gradually raised from the temperature at which the metal droplets are 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 temperature setting range must be appropriately determined depending on the combination of the substrate and the metal. For example, for GaN on a sapphire substrate, the substrate temperature is 300 ° C to 600 ° C.
Raise to a degree.

Here, the metal droplets 2 of Ga or the like formed on the substrate 1 by the above-mentioned process “(2) Formation of metal droplets: see FIG. 2B” are heated in an ultrahigh vacuum. When the temperature is raised, the surface diffusion becomes remarkable, and the respective metal droplets 2 coalesce and become large, so that the density of the metal droplets 2 on the substrate 1 is lowered, or the metal droplets 2 formed with care. Becomes a film.

In order to suppress such a phenomenon,
Nitrogen (N_Two), Nitrogen radicals (N ^*),ammonia
(NH_Three) Or ammonia radical (NH_Three ^*)
The nitriding process should be carried out at the lowest possible temperature.
It

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

Therefore, the low temperature (the temperature varies greatly depending on the combination of the metal raw material and the substrate raw material, but for example, when the metal raw material is Ga and the substrate raw material is CaF ₂ , the temperature is 30 ° C. When the raw material is Al and the substrate raw material is CaF ₂ , the temperature is 350 ° C.) and nitrogen is started to be supplied to the substrate 1 on which the metal droplets 2 are formed,
First, only the surface of the metal droplet 2 is nitrided, and then the temperature is raised during the nitriding to promote crystallization, or the temperature is kept low, or the temperature is raised, light, electrons, ions or radicals, Alternatively, it is considered effective to add an external field such as a combination thereof to promote crystallization.

By irradiating the metal droplets 2 with energy possessed by light, electrons, ions or radicals, or a combination thereof, the metal droplets 2 are nitrided so that the substrate 1
It is possible to apply the energy required for crystallization without raising the temperature of the.

Also, light, electrons, ions or radicals,
Alternatively, as another effect expected by adding an external field such as a combination thereof, in the case of light, it is possible to selectively apply energy only to metal by using the optically transparent substrate 1. Therefore, when the substrate temperature is low, crystallization can be performed with extremely small surface diffusion and almost no change in size.

Further, 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 light described above. Therefore, when the substrate temperature is low, surface diffusion is extremely suppressed, and crystallization is possible with almost no change in size.

As the nitrogen source for nitriding, it is possible to increase the rate of chemical reaction by using nitrogen radicals or ammonia radicals having a high reactivity with the metal, instead of nitrogen gas or ammonia gas. Therefore, as compared with the case of using nitrogen gas or ammonia gas, crystallization can be performed in a short time and at low temperature.

(4) Heat treatment (improvement of quality): See FIG. 2 (d). Above-mentioned "(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 1., decompression of nitrogen (N ₂ ), nitrogen radical (N ^* ), ammonia (NH ₃ ) or ammonia radical (NH ₃ ^* ) or In the air atmosphere, a predetermined temperature, for example, 500 ° C to 1500 ° C
Heat treatment is performed at a high temperature of about 10 minutes for a predetermined time, for example, 10 minutes.

The temperature setting range needs to be appropriately determined depending on the combination of the substrate and the metal, but GaN on the sapphire substrate is heat-treated at a high temperature of about 1000 ° C.

When the above heat treatment is performed, an external field such as light, electrons, ions or radicals, or a combination thereof may be added. In that case, the process temperature may be lowered or the heat treatment may be performed. There is an effect that energy can be selectively applied to the quantum dots 4 of the nitride semiconductor.

Thus, the nitride semiconductor quantum dots 4
When heat-treated at a high temperature of 500 ° C to 1500 ° C,
The crystal quality of the quantum dots 4 of the nitride semiconductor can be improved.

As described in "(3) Nitriding (semiconductorization): FIG. 2 (c)", surface diffusion becomes remarkable when heated in an ultrahigh vacuum, 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 atmosphere, under reduced pressure (not in ultra-high vacuum) or under pressure.

As a result of increasing the pressure and performing the heat treatment in this way, collision of metal atoms such as Ga with molecules and atoms such as nitrogen gas and ammonia gas becomes remarkable, and the temperature can be increased while suppressing surface diffusion. As a result, a good quality quantum dot structure can be obtained.

Incidentally, light, electrons, ions or radicals,
Alternatively, the reason for using the combination thereof or the nitrogen radical or the ammonia radical is the same as that explained in the nitriding process of “(3) Nitriding (semiconductorization): See FIG. 2C” above. , Its detailed description is omitted.

After this heat treatment, the quantum dots 14 of a good quality nitride semiconductor can be finally formed.

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

The outline of this experiment will be described below.
Is used as an Al ₂ O ₃ substrate (sapphire substrate), and Ga is used as a metal raw material.
After forming the metal droplet 2 of a, ammonia (NH ₃ )
Gas is irradiated to nitride the Ga metal droplets 2 to form GaN quantum dots as nitride semiconductor quantum dots 4.
Furthermore, this GaN quantum dot is heat-treated to produce a good GaN quantum dot on a sapphire substrate.

(1) Formation of GaN Quantum Dot Structure That is, in the experiment by the applicant of the present application, 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.
Was used, and ammonia (NH ₃ ) gas was used as a group V raw material.

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

First, after the substrate 1 was transferred to the GSMBE apparatus, the surface of the substrate 1 was heated at 800 ° C. in vacuum until a pattern showing a flat surface was observed by ultra-high speed electron diffraction (RHEED) method. I cleaned it.

After that, the substrate temperature is lowered to 300 ° C.,
A metallic Ga molecular beam of 1.5 × 10 ¹⁵ cm ⁻² is supplied to the substrate 1 in an ultrahigh vacuum, and a metallic droplet 2 of Ga is deposited on the substrate 1.
Was formed.

Then, ammonia (NH ₃ ) gas is started to be 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 raised until finally 600 The temperature was raised to 0 ° C. to nitrid the Ga metal droplets 2 formed on the substrate 1 and promote crystallization to obtain GaN quantum dots as the nitride semiconductor quantum dots 4.

The substrate 1 is G-colored by RHEED observation.
Heated until a ring pattern was observed showing aN crystallization.

(2) Heat Treatment of GaN Quantum Dots After the above-mentioned “(1) Formation of GaN quantum dot structure”, the substrate 1 is taken out from the GSMBE apparatus and placed in a metal organic chemical vapor deposition (MOCVD) apparatus at 760To.
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 crystal quality.

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

(3) Experimental Results (3-1) Confirmation that Metal Droplets 2 Become Quantum Dots of Nitride Semiconductor The RHEED pattern showed a ring pattern with a lattice constant similar to that of GaN. Atomic force microscope (AFM)
However, unlike the metal droplet, the structure was more similar to the hexagonal columnar structure of the stabilized structure of GaN. Therefore, it is recognized that Ga was nitrided to become GaN.

Further, photoluminescence (PL) emitted red light from the GaN quantum dots at room temperature (the semiconductor emits light, but the metal does not).

The size of the smallest hexagonal GaN quantum dot is 5 nm in diameter and 2 in height.
was nm.

The results of such an experiment will be described in more detail. In FIG. 9A, the temperature of the substrate 1 is finally set to 600.
An AFM photograph of the surface of the GaN quantum dot obtained when the temperature was raised to 0 ° C is shown. In addition, in FIG.
A cross-sectional view of the GaN quantum dots shown in FIG. 9A is shown.

As shown in FIGS. 9A and 9B,
The diameter of the GaN quantum dots on the surface of the substrate 1 is about 5n.
It is in the range of m to 20 nm, and the height of the GaN quantum dots is about 2 nm to 10 nm.

The hexagonal apex 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 shape. It indicates that there is.

Then, after raising the temperature to 600 ° C., RHE
The ring pattern of GaN lattice constants observed in the ED shows that the dots in the AFM are GaN quantum dots.

FIG. 10 shows the PL spectrum of the GaN quantum dots shown in FIG. 9A at room temperature. This spectrum is measured by "Hamamatsu Photonics System 6551", and the detector is sensitive to the red region. The peak energy of PL is 2.5 eV, and this GaN quantum dot shows bright red emission.

This is considered to be due to insufficient crystallization of the GaN quantum dots shown in FIG. 9 (a). That is, it is considered that the heating up to 600 ° C. is not sufficient for crystallization of GaN in the 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 the higher energy side than the GaN thin film at the liquid nitrogen temperature (77 K). . That is, the quantum confinement effect of electrons was confirmed.

That is, in FIG. 11A, before the GaN quantum dots shown in FIG. 9A are heat-treated at 1000 ° C. (be).
PL spectra are shown for before and after heat treatment. These spectra are 77K
In a UV sensitive photomultiplier.

Comparing both spectra shown in FIG. 11 (a), 3e before the heat treatment at 1000.degree.
There is a wide and low peak around the V light energy,
On the other hand, after heat treatment at 1000 ° C., 3.5
A strong peak appears at 8 eV.

This is a result of the crystal quality of the GaN quantum dots shown in FIG. 11A being improved by heat treatment at 1000 ° C.

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

As shown in FIG. 11 (b),
The GaN film has a peak of band-to-band emission at 3.45 eV, while the GaN quantum dot has a peak at 3.58 eV, and the GaN quantum dot has a PL on the higher energy side than the GaN thin film at the liquid nitrogen temperature (77 K). The peak of is shifted.

The GaN quantum dot has a length of 130 m.
The blue shift of eV is considered to be the quantized shift energy due to the formation of quantum dots.

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

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

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

As described in detail above, by using the method for forming quantum dots of a nitride semiconductor by position-controlled droplet epitaxy according to the present invention, a plurality of nitride semiconductors arranged with extremely close gaps can be used. A quantum dot, for example, a GaN quantum dot can be formed.

Therefore, when the nitride semiconductor quantum dots are formed by using the method of forming the nitride semiconductor quantum dots by the position-controlled droplet epitaxy of the present invention, the quantum bit device in the quantum computer is used. Structures and quantum correlation gate device structures 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 for forming a nitride semiconductor quantum dot by position-controlled droplet epitaxy according to the present invention. The structure will be described.

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

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

That is, the qubit device structure 10 in the quantum computer according to the present invention is, for example, two nitrides formed by the method for forming quantum dots of a nitride semiconductor by the position controlled droplet epitaxy of the present invention. It is composed of a quantum dot of a semiconductor, for example, two GaN quantum dots 12 and 14. In other words, the physical reality of the quantum bit is a two-level system, but in the quantum bit device structure 10 in the quantum computer according to the present invention, two quantum levels 1 from two quantum dots 12 and 14.
6 and 18 are formed.

More specifically, for example, a semiconductor material such as GaN has a diameter of several tens of nanometers (n
When a minute quantum dot with a spherical shape of about m) or less or a rectangular shape with one side of several tens of nanometers (nm) or less is constructed, such quantum dots have discrete quantum levels. Will be formed.

Therefore, as a two-level system of quantum bits, two minute quantum dots having only one quantum level of interest are prepared, and these two quantum dots are connected to the quantum bit device structure 10. Quantum dots 12, 1 for constructing
4 is used.

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

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

The quantum dots 12 and the quantum dots 14 are arranged close to each other with a gap G of, for example, about 10 angstroms, and electrons are tunneled by the quantum dots 12 and the quantum dots 14. It is designed so that you can move freely between them.

In the above structure, one electron exists in the qubit device structure 10 by utilizing, for example, the Coulomb blockade effect.
Each electron has a certain probability that the quantum level of the quantum dot 12 is 16
Or in the quantum level 18 of the quantum dot 14 (state of | 1>) with a certain probability.

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

Here, the qubit of the qubit device structure 10 can be operated by utilizing the principle of Rabi oscillation.

Here, the Rabi oscillation means that when an electromagnetic wave resonating with an energy difference between 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 oscillates periodically.

Therefore, in the qubit device structure 10, for example, as an initial state, the probability (P1) that an electron exists in the upper quantum level 18 is 0 (P1 = 0), and in the lower quantum level 16, The probability that an electron exists (P0) 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 level 18 and the quantum level 16 for a half period of the Rabi oscillation. (P1) becomes 1 (P1 = 1), and the probability (P0) that electrons exist in the lower quantum level 16 becomes 1 (P0 = 0).

That is, the qubit state can be inverted by utilizing the Rabi oscillation. Then, by appropriately selecting the irradiation time of the electromagnetic wave described above, the state of the qubit can be arbitrarily controlled.

Next, an example of an embodiment of the quantum correlation gate device structure in the quantum computer according to the present invention will be described with reference to FIGS. 13 and 14.

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

The quantum correlation gate 100 is constructed by using two qubit element structures according to the above-described embodiments of the present invention.

Specifically, the quantum correlation gate 100 has 2
As two qubit device structures having different energy levels between the two levels, a first qubit device structure 102 having a large energy difference between the two levels and a second qubit device structure having a small energy difference between the two levels. And 104. Here, the qubit of the first qubit element structure 102 having a larger energy difference between the two levels is used as a control bit, and the qubit of the second qubit element structure 104 having a smaller energy difference between the two levels is set as a control bit. Is the target bit.

The first qubit device structure 102 is
It is composed of a quantum dot 108 having an upper quantum level 106 and a quantum dot 112 having a lower quantum level 110.

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

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

Further, in such a quantum correlation gate device structure 100, the quantum dot 112 of the first qubit device structure 102 is connected to the quantum dot 112 via the variable capacitor 126.
A single-electron transistor for detecting the state of the first bit by the first qubit device structure 102 is connected, and the quantum dot 120 of the second qubit device structure 104 is connected via a variable capacitor 128. A single-electron transistor for detecting the state of the second bit by the second qubit device structure 104 is connected.

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

With the above structure, the variable capacitor 12
When the capacitance C1 of 2 is set to 0 (C1 = 0) and the capacitance 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 are different from each other. They are electrically independent of each other.

Therefore, using the above-mentioned rabbi vibration,
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 state before the action of the quantum correlation gate shown in the truth table of FIG. 1B. can do.

FIG. 14 is an energy level showing the total value of the energy of electrons of the first qubit element structure 102 and the energy of electrons of the second qubit element structure 104 in the state before the action of the quantum correlation gate. A state diagram is shown. Quantum level 110 and quantum level 1
The energy level of electrons at 18 and 18 is defined as a reference level A.

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

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

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

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

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

Therefore, "C1 ≠ 0" and "C2 ≠ 0"
In the case of, with respect to the quantum levels 106 and 110 of the first qubit element structure 102 and the quantum levels 114 and 118 of the second qubit element structure 104 in the state shown in FIG. 13, mutual electrons exist on a diagonal line. When the state of the control bit is | 1> and the state of the target bit is | 0> and the state of the control bit is | 0> and the state of the target bit is | 1> (If present) then "C1 = 0" and "C2
The energy does not change much as compared with the case of "= 0", but when the electrons of each other do not exist on the diagonal line (when the state of the control bit is | 1> and the state of the target bit is | 1>). And the control bit state is | 0> and the target bit state is | 0>), "C1 = 0" and "C2"
The energy will be higher than in the case of "= 0". If the difference is ΔE, “C1 ≠ 0” and “C2 ≠
In the case of "0", level A goes up to level A ', level B goes up almost to level B', level C goes up to level C ', level D goes up to level D'.

Therefore, the target bit is inverted only when the control bit is | 1> by irradiating the quantum correlation gate device structure 100 with the electromagnetic wave having the energy of “E2 + ΔE” for the half cycle of the Rabi oscillation. 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 set the control bit and the target bit to the same value. The interaction between them should be small.

Then, in order to observe the state of the qubit after the calculation by the quantum correlation gate device 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 "4." C4 ≠
Set to "0" to use a single electron transistor. In addition, the single electron transistor is not used during calculation, and “C
It is assumed that “3 = 0” and “C4 = 0” are set.

As described above, since only one electron exists in each of the first qubit device structure 102 and the second qubit device structure 104, it is necessary to measure the charge of one electron. Since this is not possible with the existing electrometer, a single electron transistor is used in this embodiment.

The vertical relation of the levels of the quantum dots in each quantum bit device constituting the quantum correlation gate device in the present invention, in other words, the arrangement relation of each quantum dot is limited to the above-mentioned embodiment. Of course, it is not something.

That is, instead of the arrangement relationship shown in FIG. 13, as shown in FIG. 15, the first qubit device structure 10 is formed.
2 and the second qubit device structure 104, the quantum dot 1
08 and the quantum dots 120 may face each other, and the quantum dots 112 and the quantum dots 116 may face each other in two rows. In FIG. 15, the first qubit device structure 102 is arranged in the upper stage,
The second qubit device structure 104 is arranged in the lower stage.

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

In the quantum correlation gate device structure 100 shown in FIG. 15, the state of the first bit by the first qubit device structure 102 is connected to the quantum dot 108 of the first qubit device structure 102 via the variable capacitor 126. Is connected to a single-electron transistor for detecting
In the quantum dot 120 of the second qubit device structure 104,
A single-electron transistor for detecting the state of the second bit by the second qubit device 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, when “C1 ≠ 0” and “C2 ≠ 0”, the quantum levels 106 and 110 of the first qubit element structure 102 and the second qubit element structure 104 in the state shown in FIG. Regarding the quantum levels 114 and 118, when electrons of each other do not exist on the diagonal line (when the control bit state is | 0> and the target bit state is | 0> and the control bit state is | 1> and the state of the target bit is | 1>), “C1 = 0” and “C2
The energy does not change much as compared with the case of "= 0", but when the electrons of each other are present on the diagonal line (when the control bit state is | 0> and the target bit state is | 1>). And the control bit state is | 1> and the target bit state is | 0>), "C1 = 0" and "C2 =
The energy will be higher than in the case of "0". If the difference is ΔE, “C1 ≠ 0” and “C2 ≠ 0”
In the case of, the level A is almost unchanged to the level A ′, the level B is increased to the level B ′, the level C is increased to the level C ′, and the level D is almost unchanged to the level D ′.

Therefore, by irradiating the quantum correlation gate device structure 100 with an electromagnetic wave having an energy of "E2-.DELTA.E" for a half cycle of the Rabi oscillation, the target bit is set only when the control bit is | 1>. It can be inverted, and the operation of the truth table shown in FIG. 1B can be realized.

That is, 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, the arrangement relation of each quantum dot does not matter. The energy of the electromagnetic wave irradiated during the half cycle of the vibration changes depending on the upper and lower relations of the levels of each quantum dot in each quantum bit element constituting the quantum correlation gate element in the present invention, in other words, the arrangement relationship of each quantum dot. Need to let.

[0201]

Since the present invention is configured as described above, GaN, InN, 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 in extremely close positions. Therefore, for example, it has an excellent effect that a qubit and a quantum correlation gate can be realized.

Since the present invention is configured as described above, it is possible to provide a qubit device structure and a quantum correlation gate device structure in a Turing type quantum computer as a solid-state device. Produce the effect.

[Brief description of drawings]

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

FIG. 2 is an explanatory view showing a process for forming a quantum dot of a nitride semiconductor by position-controlled droplet epitaxy, in which (a) shows a “substrate” and (b) shows “metal droplets”. "Formation", (c) indicates "nitriding (semiconductorization)", and (d) indicates "heat treatment (high quality)".

FIG. 3 is an explanatory diagram of a principle of modifying a substrate surface 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 has been deposited and a position control of a Ga metal droplet by a natural formation method.

5A and 5B are scanning micrographs of the results of the experiments shown in FIGS. 4A, 4B, and 4C, in which the Ga droplet interval is 150 nm, the electron beam irradiation amount is 0.4 pC / dot, and FIG.
The result of two-dimensional spot exposure is shown.

FIG. 6 is a conceptual diagram of a process of irradiating an electron beam on CaF ₂ in a vacuum and a position control of a Ga metal droplet 2 by a natural forming method.

7A and 7B are scanning micrographs of the results of the experiment shown in FIGS. 6A, 6B, and 6C, in which FIG.
and the electron beam irradiation amount is 5 pC / dot and the result of one-dimensional spot exposure is shown.
Droplet spacing is 17 nm and electron beam irradiation dose is 5 p
The result of one-dimensional spot exposure is shown as C / dot, and (c) shows the result of one-dimensional spot exposure with a Ga droplet interval of 14 nm and an electron beam irradiation amount of 5 pC / dot. .

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

FIG. 9 shows a GaN quantum dot obtained by the applicant's experiment, (a) shows the temperature of the substrate at 600 finally.
It is a photograph of the AFM of the surface of the GaN quantum dot obtained when it heated up to 0 degreeC, (b) is the GaN shown by (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. 9 (a) at room temperature.

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

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

FIG. 13 is a conceptual configuration explanatory diagram of an example of an embodiment of a quantum correlation gate device structure in a quantum computer according to the present invention.

14 is a total value of energy of electrons of the first qubit device structure and energy of electrons of the second qubit device structure in a state before the action of the quantum correlation gate in the quantum correlation gate device structure shown in FIG. 13; It is an energy level state diagram showing.

FIG. 15 is a conceptual configuration explanatory diagram of an example of another embodiment of the quantum correlation gate device structure in the quantum computer according to the present invention.

16 is a total value of electron energy of the first qubit element structure and electron energy of the second qubit element structure in the state before the action of the quantum correlation gate in the quantum correlation gate element structure shown in FIG. It is an energy level state diagram showing.

[Explanation of symbols]

1 substrate 2 metal droplet 4 nitride semiconductor quantum dot 10 quantum bit device structure 12, 14, 108, 112, 116, 120 quantum dot 16, 18, 106, 110, 114, 118 quantum level 100 quantum correlation gate device Structure 102 First qubit device structure 104 Second qubit device structure 122, 124, 126, 128 Variable capacitor

─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-5-63305 (JP, A) JP-A-4-179220 (JP, A) JP-A-4-245620 (JP, A) JP-A 11- 330551 (JP, A) International Publication 97/11518 (WO, A1) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 21/203 H01L 21/205 H01L 29/06 H01S 5/00-5 / 50

Claims (16)

(57) [Claims] 1. A method for forming a quantum dot of a nitride semiconductor by position-controlled droplet epitaxy, which comprises applying an external field to the surface of the substrate having a surface energy lower than that of a metal raw material. A first treatment for modifying the surface state of the substrate to modify the surface; and the metal raw material supplied to the substrate whose surface has been modified by the first treatment to modify the surface. A second treatment for forming metal droplets by crystal growth at a designated location, and a nitrogen source is supplied onto the substrate on which the metal droplets have been formed by the second treatment to nitride the metal droplets. Forming a nitride semiconductor quantum dot by means of a third process, and a method of forming a nitride semiconductor quantum dot by position controlled droplet epitaxy. 2. The method for forming a nitride semiconductor quantum dot by position-controlled droplet epitaxy according to claim 1, further comprising a nitride semiconductor quantum dot formed by the third process, Forming a nitride semiconductor quantum dot by position-controlled droplet epitaxy, including a fourth treatment in which the heat treatment is performed at a temperature of a predetermined time. 3. The method for forming a quantum dot of a nitride semiconductor by position-controlled droplet epitaxy according to claim 1 or 2, wherein the third treatment is performed at a low temperature with the metal. Position controlled droplet epitaxy, which starts supplying a nitrogen source to the substrate on which droplets are formed to nitrid only the surface of the metal droplets, and then raises the temperature during nitriding to promote crystallization. Of forming nitride semiconductor quantum dots according to. 4. The method for forming a quantum dot of a nitride semiconductor by position-controlled droplet epitaxy according to claim 3, wherein the third treatment forms the metal droplet at a low temperature. In addition, when a nitrogen source is started to be supplied to the substrate and only the surface of the metal droplets is nitrided, and then the temperature is raised during nitriding to promote crystallization, an external field is added to promote crystallization. Method for forming quantum dots in nitride semiconductors by position-controlled droplet epitaxy. 5. The method for forming quantum dots of a nitride semiconductor by position-controlled droplet epitaxy according to claim 1, wherein the third treatment is performed at a low temperature with the metal. Position control for promoting crystallization by starting to supply a nitrogen source to the substrate on which droplets have been formed, nitriding only the surface of the metal droplets, and then adding an external field at low temperature during nitriding. For forming nitride semiconductor quantum dots by controlled droplet epitaxy. 6. The method for forming a quantum dot of a nitride semiconductor by position-controlled droplet epitaxy according to claim 2, claim 3, claim 4, or claim 5, Is a method of forming nitride semiconductor quantum dots by position-controlled droplet epitaxy, in which an external field for heat treatment is applied. 7. Nitride semiconductor quantum dots by position-controlled droplet epitaxy according to 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 nitride by position-controlled droplet epitaxy according to claim 1, claim 2, claim 3, claim 4, claim 5, claim 6 or claim 7. In the method for forming a semiconductor quantum dot, the metal raw material is a group III metal, and a method for forming a quantum semiconductor nitride dot by position-controlled droplet epitaxy. 9. The position-controlled droplet according to claim 1, claim 2, claim 3, claim 4, claim 5, claim 6, claim 7, or claim 8. In the method for forming a quantum dot of a nitride semiconductor by epitaxy, the substrate is a sapphire substrate, a silicon carbide substrate, a quartz substrate, a gallium nitride substrate or a calcium fluoride substrate, and the nitride by position controlled droplet epitaxy Method for forming semiconductor quantum dots. 10. The position control according to claim 1, claim 2, claim 3, claim 4, claim 5, claim 6, claim 7, claim 8 or claim 9. In the method for forming a nitride semiconductor quantum dot by droplet epitaxy, the nitrogen source is nitrogen, a nitrogen radical, ammonia, or an ammonia radical. Forming method. 11. A tunnel effect, 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. The first quantum dot and the second quantum dot are arranged in close proximity to each other so that electrons can freely move between the first quantum dot and the second quantum dot. In a quantum bit device 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 3, Claim 4, Claim 5,
It is formed in the method for forming quantum dots of a nitride semiconductor by position-controlled droplet epitaxy according to claim 6, claim 7, claim 8, claim 9, or claim 10. Qubit device structure in a quantum computer. 12. A tunnel effect having a first quantum dot having a first quantum level and a second quantum dot having a second quantum level below the first quantum level. The first quantum dot and the second quantum dot are arranged in close proximity to each other so that electrons can freely move between the first quantum dot and the second quantum dot. , A first qubit device structure in which only one electron is present, 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 position, 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 and the fourth quantum dot are arranged in close proximity to each other so that only one electron exists. A second qubit element structure, the first bit element structure and the second bit element structure, the first quantum dot and the third quantum dot are opposed to each other, and The second quantum dot and the fourth
The first quantum dot and the third quantum dot are electrically connected to each other, 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. A quantum correlation gate device structure in a quantum computer that is set differently, wherein the first quantum dot, the second quantum dot, the third quantum dot, and the fourth quantum dot are: The position-controlled liquid according to claim 1, claim 2, claim 3, claim 4, claim 5, claim 6, claim 7, claim 8, claim 9, or claim 10. In the formation method of nitride semiconductor quantum dots by droplet epitaxy Quantum correlation gate device structure in the formed quantum computer. 13. The quantum correlation gate device structure in the quantum computer according to claim 12, wherein the first quantum dot and the third quantum dot are capacitively connected via a first variable capacitor. A quantum correlation gate device structure in a quantum computer in which the second quantum dot and the fourth quantum dot are capacitively connected via a second variable capacitor. 14. A tunnel effect having a first quantum dot having a first quantum level and a second quantum dot having a second quantum level below the first quantum level. The first quantum dot and the second quantum dot are arranged in close proximity to each other so that electrons can freely move between the first quantum dot and the second quantum dot. , A first qubit device structure in which only one electron is present, 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 position, 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 and the fourth quantum dot are arranged in close proximity to each other so that only one electron exists. A second qubit element structure, wherein the first bit element structure and the second bit element structure face the first quantum dot and the fourth quantum dot, and The second quantum dot and the third
The first quantum dot and the fourth quantum dot are electrically connected to each other, 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. A quantum correlation gate device structure in a quantum computer that is set differently, wherein the first quantum dot, the second quantum dot, the third quantum dot, and the fourth quantum dot are: The position-controlled liquid according to claim 1, claim 2, claim 3, claim 4, claim 5, claim 6, claim 7, claim 8, claim 9, or claim 10. In the formation method of nitride semiconductor quantum dots by droplet epitaxy Quantum correlation gate device structure in the formed quantum computer. 15. The quantum correlation gate device structure in the quantum computer according to claim 14, wherein the first quantum dot and the fourth quantum dot are capacitively connected via a first variable capacitor. A quantum correlation gate device structure in a quantum computer in which the second quantum dot and the third quantum dot are capacitively connected via a second variable capacitor. 16. Claims 12, 13, and 14
Alternatively, in the quantum correlation gate device structure in the quantum computer according to claim 15, the first qubit device structure is connected to the first single-electron transistor via a third variable capacitor, The quantum correlation gate device structure in a quantum computer, wherein the fourth qubit device structure is connected to a second single-electron transistor via a fourth variable capacitor.