JP3245907B2 - Quantum dot coupling device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quantum dot coupling device in which quantum dots in which electrons are spatially confined are two-dimensionally arranged and required information processing is performed by tunnel transition between the quantum dots. The present invention relates to an information processing method using a coupling element.

[0002]

2. Description of the Related Art Wiring technology is indispensable in the current VLSI and ULSI technologies, and as the degree of integration increases, the occupancy of wiring in the entire circuit increases. In the case where a wiring is formed using a metal film or a conductive film, there are problems such as limitations on processing speed due to resistance of the wiring itself, transmission loss, interference between wirings, and the like.

There is optical transmission as a signal transmission method without using a metal film or a conductive film. For example, as a three-dimensional optoelectronic integrated circuit device (OEIC), there is also known a device for transmitting a signal between substrates three-dimensionally by light.

However, even when an opto-electronic integrated circuit is used, its processing speed is limited, and its function is sufficiently sufficient for the near future information processing which is required to be faster and more complicated. It is hard to say that it can fulfill.

[0005] The applicant of the present application has previously proposed a device having the processing speed and accuracy of innovative information processing as disclosed in Japanese Patent Application No. Hei.
The quantum dot coupling device described in the specification and the drawing of -150446 is proposed. The quantum dot coupling element arranges quantum dots having a size of about an electron wavelength for confining electrons, and the arrangement method corresponds to information processing to be processed. The coupling between quantum dots, that is, the spatial movement of electrons is governed by the tunnel transition probability determined by the wave function of the electrons, and is an element whose information processing result is indicated by the spatial distribution of electrons.

[0006] The use of such a quantum dot coupling element makes it possible to perform an ultra-high-speed operation with high accuracy.

[0007]

The data input to the quantum dot coupling device is performed by partially irradiating light from outside. When this external light is applied, electron-hole pairs are generated.

However, when the generated electrons and holes are recombined or undergo a tunnel transition between quantum dots, sufficient data cannot be input. Also, even an electron or hole once conducted to another quantum dot may recombine with another excited electron or hole. After all, unless the electron distribution at the time of data input is fixed to a certain fixed arrangement, an ultra-high-speed operation based on the tunnel transition probability cannot be used.

In view of the above technical problems, an object of the present invention is to provide a quantum dot coupling element improved so as to enable reliable data input and an information processing method using the quantum dot coupling element. I do.

[0010]

In order to solve the above-mentioned technical problems, a quantum dot coupling device according to the present invention has a tunnel transition probability of electrons between quantum dots corresponding to a required information processing algorithm. A plurality of quantum dots arranged and arranged with the distance between the quantum dots as described above, in the quantum dot coupling element that performs the information processing by the spatial distribution of electrons of the quantum dots, each quantum dot, It has a two-stage stacked structure, in which the tunnel transition probability between the first-stage quantum dots is lower than the tunnel transition probability between the second-stage quantum dots.

Here, the quantum dot is a region having a size capable of spatially confining electrons, and the tunnel transition probability between the quantum dots is determined according to the position and shape of both. Layers with different forbidden bandwidths can be used to confine electrons and to provide different tunnel transition probabilities. In particular, when providing a difference in the tunnel transition probability, a material having a wide bandgap can have a lower tunnel transition probability than a material having a narrow bandgap. What is necessary is just to use for the material between dots.

Further, in the quantum dot coupling device of the present invention,
Electrons are transferred from the first stage quantum dots to the second stage quantum dots, but can be transferred by applying an electric field. Furthermore, the present invention provides a plurality of quantum dots arranged and arranged with the distance between the quantum dots such that the tunnel transition probability of electrons between the quantum dots having the two-stage stacked structure corresponds to the required information processing algorithm. an information processing method using a quantum dot, a step of generating electrons to at least a portion of the quantum dots of the first stage low tunnel transition probability of the plurality of quantum dots, a two-stage stacked structure
Transfer bias is applied to the quantum dots of
Is the first stage quantum dot with low tunnel transition probability
From the second stage with a high tunnel transition probability
Transfer to quantum dots and high tunnel transition probability
Tunneling of electrons between quantum dots in the second stage
And a step of performing an arithmetic process using the coupling relationship of the quantum dots .

[0013]

The quantum dot has a two-stage structure with different tunnel transition probabilities, so that data is input to the first stage quantum dot having a lower tunnel transition probability to generate electrons. It can be transferred to the second stage quantum dot having a high transition probability. That is, in the first-stage quantum dot having a low tunnel transition probability, the spatial portion of electrons and holes is suppressed, and data can be sufficiently input. In the second stage quantum dot having a high tunnel transition probability, a spatial distribution of electrons based on sufficiently input data is transferred, and a high-speed operation is performed according to the high tunnel transition probability.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic perspective view of a quantum dot coupling device 1 of the present embodiment. Each quantum dot has its first
Stage quantum dot QD _11, QD ₁₂ of, ..., and QD _17, the quantum dots QD ₂₁ of the second stage, QD _22, ..., consists QD ₂₇ Prefecture,
The upper side is the first quantum dot, and the lower side is the second quantum dot. The positions of the upper-stage first-stage quantum dots and the lower-stage second-stage quantum dots are two-dimensionally coincident with each other, and are in a stacked relationship via a thin film. Each quantum dot Q
D _{11 to} QD ₂₇ each have a size about the wavelength of an electron, and can confine electrons. Moreover, each quantum dot QD ₁₁ ~QD ₂₇ is respectively a cylindrical shape, but may be another rectangular shape or other shapes. Although the device is composed of seven quantum dots in FIG. 1, the number, arrangement, dimensions and the like are determined according to the information processing system to be processed.

Each quantum dot is made of a compound semiconductor, and a region between the quantum dots is also made of a compound semiconductor. Specifically, the first-stage quantum dots QD ₁₁ , QD
D _12, ..., QD ₁₇ consists GaAs, the quantum dots QD ₂₁ of the second stage, QD _22, ..., QD ₂₇ also consists of GaAs. The region between the first-stage quantum dots is made of a flat AlAs substrate 2, and the region between the second-stage quantum dots is an AlGaAs substrate bonded to the back surface of the AlAs substrate 2.
s substrate 3. Each first stage quantum dot QD ₁₁ , QD
_12, ..., QD ₁₇ is embedded in the AlAs substrate 2, the surface 2a and the back 4 of the AlAs substrate 2 is not face the quantum dots of the first stage. Each second stage quantum dot QD ₂₁ ,
QD _22, ..., QD ₂₇ is the two-dimensional disposed at a position corresponding to the first stage respectively, AlAs of AlGaAs substrate 3
It is formed facing the back surface 4 of the AlAs substrate 2 which is the interface with the substrate 2.

Each quantum dot is arranged in proximity to one or more other quantum dots. The distance at which these quantum dots are closely arranged is a distance at which the wave functions overlap, and is a distance at which a tunnel transition probability exists. For example, an entire array may be configured such that one quantum dot is located in close proximity to a plurality of other quantum dots, while another certain quantum dot is located only in close proximity to one other quantum dot. Since the distance between the quantum dots follows the tunnel transition probability, if the coupling between the quantum dots, that is, the tunnel transition probability is set in accordance with the algorithm of the information processing system, the required information processing can be performed by the quantum dot coupling device. Will be advanced.

FIG. 2 is a sectional view of a part of the quantum dot coupling device of the present embodiment. An AlAs substrate 2 is laminated on an AlGaAs substrate 3 and a plurality of first
Step quantum dots QD ₁ are formed, and the AlGaAs substrate 3
Reflecting the position of the quantum dots QD ₁ and the first stage faces the surface of which the quantum dots QD ₂ of the plurality of second stage are formed.

In this structure, each quantum dot QD ₁ ,
QD ₂ functions as a potential well because it is composed of GaAs, and its surrounding AlAs
The substrate 2 and the AlGaAs substrate 3 function as a potential barrier.

FIG. 3 is a potential diagram along the line III-III in FIG. On this III-III line, GaAs of quantum dots becomes a potential well,
The surrounding area becomes a potential barrier made of AlAs.
Since AlAs has a wide band gap and a high potential barrier, the tunneling transition probability of electrons is as follows.
It is lower than that of aAs.

FIG. 4 is a potential diagram along the line IV-IV in FIG. On this IV-IV line, the GaAs of the quantum dot becomes a potential well, and the periphery thereof becomes a potential barrier made of AlGaAs. Al
Since GaAs has a narrower forbidden band width than AlAs, the potential barrier does not increase as much as the AlAs substrate 2 side. Therefore, the tunnel transition probability of electrons is higher than that of AlAs, and a spatial distribution by high-speed conduction of electrons can be easily realized.

FIG. 5 is a potential diagram along the line VV in FIG. As shown in FIG. 5, the quantum dots made of GaAs have the same conduction band bottom at the first stage and the second stage because they have the same forbidden band width, but the height of the potential barrier around the conduction band is different. Therefore, towards the quantum dot QD ₂ of the second stage is higher tunnel transition probability.

Next, a method of inputting data to the quantum dot coupling device 1 of the present embodiment will be described with reference to FIG. 1 and FIGS.

First, a potential as shown in FIG. 6 is obtained by applying an initial bias Vi such that the front surface 2a of the AlAs substrate 2 is on the minus side and the back surface 5 of the AlGaAs substrate 3 is on the plus side. become. FIG. 6 shows the potential along the line VV in FIG.

With the initial bias Vi applied,
Light (hv) is irradiated from a light irradiation means 6 such as a laser or an electron beam shown in FIG. The irradiated light is AlAs
The quantum dots QD _{11 to} QD ₁₇ in the first stage in the substrate 2 absorb the light. Irradiation of light is not necessarily performed for the first stage of the quantum dot QD ₁₁ ~QD ₁₇ total, it is determined according to be the input data.

Electron-hole pairs are generated by the absorption of light energy in the first stage quantum dots. As shown in FIG. 7, the electrons are stored in the initial bias Vi potential well W ₁ of the quantum dots of the first stage which is inclined by, accumulated holes in the potential well w ₁ of the quantum dots of the first stage at the same time. This potential well W
₁ is surrounded by the AlAs substrate 2 having a wide forbidden band, so that the probability of tunnel transition between quantum dots is reduced, and tunnel transition to other quantum dots cannot be easily performed.
Thus electrons are accumulated reliably in the potential well W ₁ data input by light irradiation are effectively performed. Also, by the initial bias Vi applied to the quantum dot,
Each of the potential wells W ₁ and w ₁ is inclined. Therefore, holes are accumulated on the front side of the first stage quantum dots, and electrons are accumulated on the rear surface side of the first stage quantum dots. Therefore, electrons and holes are spatially separated in the same first-stage quantum dot, and the probability of recombination of electrons and holes can be sufficiently suppressed.

At the point of time when the entire data input is completed, the bias to be applied is increased to the transfer bias Vt. When the transfer bias Vt is applied, a steep potential gradient is formed in the quantum dot coupling device 1 as shown in FIG. The electrons accumulated in the quantum dots by light irradiation is moved from the potential well W ₁ of the quantum dots of the first stage in accordance with the steep potential in the potential well W ₂ of the quantum dots of the second stage.

Finally, the distribution of electrons and holes is as shown in FIG. That is, the second-stage quantum dot QD ₂₁
ＱQD _27, and after the movement, the quantum dots in the second stage undergo tunnel transition between the quantum dots via the AlGaAs substrate 3 having a low potential barrier, and the tunnel transition probability is high. Dot QD _21- Q
High-speed operation processing using the binding relationship between D ₂₇ operation is performed. At this time, holes are quantum dots QD ₁₁ to Q of the first stage
For trapped in the potential well w ₁ of D _17, electron - recombination between the holes is suppressed.

For the application of the above-mentioned bias, for example, a spatial electric field may be formed between the external electrodes, and the spatial electric field may be used, and a region serving as an electrode may be formed on the front surface 2a or the back surface 5 of each substrate. Then, a voltage may be applied thereto. Further, in this embodiment, the material constituting the quantum dot coupling device is made of AlAs, AlGaAs, and GaAs. However, the material is not limited to this, and epitaxial growth can be performed and three different band gaps can be realized. Any combination of semiconductors may be used.

[0030]

According to the quantum dot coupling device of the present invention, the quantum dots have a two-stage laminated structure having different tunnel transition probabilities.
For this reason, data is input to the first stage quantum dot side with a low transition probability to generate electrons, and after sufficient data input,
It can be transferred to the second-stage quantum dot having a high tunnel transition probability. Therefore, reliable data input is realized,
Ultra-high-speed information processing is performed, and recombination of electrons and holes at the time of input is also prevented by the electric field.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view of an example of a quantum dot coupling device of the present invention.

FIG. 2 is a partial cross-sectional view of an example of the quantum dot coupling device of the present invention.

FIG. 3 is a potential energy diagram along an III-III line in FIG. 2 in one example of the quantum dot coupling device of the present invention.

FIG. 4 is a potential energy diagram along an IV-IV line of FIG. 2 in one example of the quantum dot coupling device of the present invention.

FIG. 5 is a potential energy diagram taken along the line VV in FIG. 2 in an example of the quantum dot coupling device of the present invention.

FIG. 6 is a potential energy diagram along the line VV of FIG. 2 in one example of the quantum dot coupling device of the present invention, showing potential in an initial bias state.

FIG. 7 is a potential energy diagram along the line VV of FIG. 2 in one example of the quantum dot coupling device of the present invention, showing a state at the time of light irradiation.

FIG. 8 is a potential energy diagram along the line VV of FIG. 2 in one example of the quantum dot coupling device of the present invention, showing a transfer state from the first stage quantum dots to the second stage quantum dots. FIG.

FIG. 9 is a potential energy diagram along the line VV of FIG. 2 in one example of the quantum dot coupling device of the present invention, showing a required information processing state.

[Explanation of symbols]

QD ₁₁ ~QD ₁₇ ... first stage of quantum dots QD ₂₁ ~QD ₂₇ ... second stage of the quantum dots 1 ... quantum dot coupling element 2 ... AlAs substrate 3 ... AlGaAs substrate 6 ... light irradiation means

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 29/66 H01L 29/06 G06G 7/00

Claims (3)

(57) [Claims] A plurality of quantum dots arranged and arranged at a distance between the quantum dots such that a tunnel transition probability of electrons between the quantum dots corresponds to a required information processing algorithm; In the quantum dot coupling device that performs the information processing by the spatial distribution of the electrons of the quantum dots, each quantum dot has a two-stage stacked structure, and the tunnel transition probability between the first stage quantum dots is the second stage quantum dot. A quantum dot coupling device characterized by a tunnel transition probability lower than a tunnel transition probability between the quantum dots. 2. The quantum dot coupling device according to claim 1, wherein electrons are transferred from the first stage quantum dots to the second stage quantum dots by an electric field. 3. A plurality of quantum dots arranged and arranged with a distance between the quantum dots such that the electron tunnel transition probability between the quantum dots having the two-stage stacked structure corresponds to a required information processing algorithm. an information processing method using a dot, at least part of the step of generating electrons in the quantum dots of the first stage low tunnel transition probability, the transfer bias to the quantum dot two-stage stacked structure of a plurality of quantum dots And apply
The generated electrons are transferred to the first stage having a low tunnel transition probability.
From the child dot, the corresponding high tunnel transition probability
Transferring the electrons to the second stage quantum dots, and transferring electrons between the second stage quantum dots having a high tunnel transition probability.
Tunnel transitions use quantum dot coupling
Performing an arithmetic process .