JP3307007B2 - Quantum box assembly and operation method of quantum box assembly - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION This invention, Oyo quantum box set element
And an operation method of the quantum box assembly device .

[0002]

2. Description of the Related Art In recent years, in quantum wave electronics, a micro-box structure having a cross-sectional dimension comparable to the de Broglie wavelength of electrons, that is, a so-called quantum box, has been attracting attention. There is great interest in the quantum effects exhibited by two-dimensional electrons.

[0003] A quantum box assembly element is a combination of a plurality of such quantum boxes, and attempts to perform information processing by causing quantum mechanical tunneling of electrons between these quantum boxes to change the electron distribution. Is what you do.

[0004]

As described above, when information processing is performed by conducting electrons between a plurality of quantum boxes by quantum mechanical tunneling, the intensity of tunnel coupling between these quantum boxes must be modulated. If it is possible, it is possible to perform various information processing.

[0005] The strength of the tunnel coupling is determined by the tunnel transmittance (or tunnel probability) of electrons between quantum boxes. The factors that determine the tunnel transmittance are the relative distance between quantum boxes and the barrier between quantum boxes. Height, effective mass of electrons in the quantum box, etc. However, it is impossible to change the effective mass if the material forming the quantum box is determined, and it is difficult to change the relative distance if the quantum box is formed by a heterojunction. The remaining method is to change the height of the barrier between quantum boxes, but it has been difficult to do this in the past.

Accordingly, an object of the present invention is to provide a quantum box assembly element capable of modulating the intensity of tunnel coupling between quantum boxes by applying an electric field to the quantum boxes using a control electrode.
And an operation method of the quantum box assembly element .

Another object of the present invention is to provide a quantum box assembly element having a simple structure and easy manufacture.

Still another object of the present invention is to provide a quantum box assembly element and a quantum box assembly element capable of inputting and outputting light .
An operation method of the present invention is provided.

[0009]

Means for Solving the Problems In order to achieve the above object, a quantum box assembly according to the present invention comprises a plurality of quantum boxes (QDs) arranged on one surface and a plurality of quantum boxes (QDs). Are provided at intervals and correspond to quantum boxes (QDs).
Having an opening (4a) at the part where
And a forming a control electrode (4), the control electrode (4)
Bias the quantum box (QD) to the first negative potential
With the electric field applied in the direction perpendicular to the above plane, the quantum box
Wavelength that resonates with the electron-hole pair generation energy of (QD)
Light through the aperture (4a) or the control electrode (4).
Transmitting and irradiating the selected quantum box (QD)
And input the control electrode (4) to the quantum box (QD).
On the other hand, to a second negative potential lower than the first negative potential.
And apply an electric field in a direction perpendicular to the above plane.
Increase the strength of the coupling between multiple quantum boxes (QDs)
By conducting electrons between a number of quantum boxes (QDs),
Information processing, and then bias the control electrode (4).
The voltage is substantially removed and the control electrode (4) is placed in the quantum box (Q
D) bias to a positive potential with respect to
Due to electron-hole recombination by applying an electric field
Output is performed by causing light emission . Also, the operation method of the quantum box assembly device according to the present invention
Law, a plurality of quantum boxes arranged in one plane (QD), double
Spaced apart for a number of quantum boxes (QDs)
Whether there is an opening (4a) in the part corresponding to the child box (QD)
Or a control electrode (4) formed of a transparent material.
A method of operating a quantum box set element, the control electrodes
(4) Bypass the quantum box (QD) to the first negative potential.
In a state where an electric field is applied in a direction perpendicular to the above surface,
Resonates with the electron-hole pair generation energy of the quantum box (QD)
Light of different wavelengths through the aperture (4a) or the control electrode
Transmit through (4) and irradiate selected quantum box (QD)
And input the control electrode (4) to the quantum box.
(QD) first negative second negative lower than the potential with respect to
Apply an electric field in a direction perpendicular to the above plane by biasing it to a potential.
To increase the strength of coupling between multiple quantum boxes (QDs)
To conduct electrons between multiple quantum boxes (QDs).
, And then process information for the control electrode (4).
And the control electrode (4) is removed.
Bias to a positive potential with respect to the child box (QD)
Electron-hole recombination by applying electric field in vertical direction
So that light is output by causing
It was done.

[0010]

[0011]

In a preferred embodiment of the quantum box assembly according to the present invention, the quantum box (QD) is formed by a type II heterojunction superlattice. Specifically, the quantum box (QD) has a structure in which, for example, a well layer (3) made of InAs is surrounded by a barrier layer (2) made of AlGaSb.

[0013]

Now, as shown in FIG. 15, a plurality of quantum boxes have x
Consider a case in which they are periodically arranged close to each other in the −y plane. In this case, due to this periodic structure, as shown in FIG. 16A, subbands are formed in the x direction and the y direction. Here, when an electric field is applied in the z-axis direction in FIG.
The quantum confinement of electrons in the z-axis direction in the quantum box becomes stronger, and the ground energy of the electrons in the quantum box increases.
At this time, the effective barrier height between the quantum boxes in the xy plane decreases, so that the tunnel coupling between the quantum boxes in the xy plane increases and the sub-band width increases (FIG. 16B). ). Such modulation of the intensity of the tunnel coupling between a plurality of quantum boxes arranged close to each other is not only performed when the quantum boxes are periodically arranged, but also when the quantum boxes are aperiodically arranged. It is equally possible.

As can be seen from the above, according to the quantum box assembly according to the present invention configured as described above,
By applying an electric field to the plurality of quantum boxes (QDs) using the control electrode (4), the intensity of quantum confinement of electrons in the direction of application of the electric field in the quantum boxes (QD) is modulated, whereby the quantum box (QD) is modulated. By effectively changing the barrier height between the QDs, the strength of the tunnel coupling between the quantum boxes (QDs) can be modulated. Moreover, since this quantum box assembly element uses only one quantum box (QD), its structure is simple, and therefore, its manufacture is easy. Further, this quantum box assembly element can input electrons to the quantum box (QD) by light irradiation, and can perform output by light emission by electron-hole recombination, and can perform light input and light output.

[0015]

An embodiment of the present invention will be described below with reference to the drawings. In this embodiment, a quantum box is called a quantum dot, and an element obtained by combining a plurality of quantum dots is called a quantum dot aggregate element.

FIG. 1 shows a quantum dot assembly according to this embodiment. As shown in FIG. 1, in the quantum dot integrated device according to this embodiment, for example, an i-type AlGaSb layer 2 as a barrier layer is formed on a p-type GaSb substrate 1, and a well layer is formed in the i-type AlGaSb layer 2. Is embedded in a two-dimensional array in the xy plane. Each quantum dot QD is formed by a structure in which the i-type InAs layer 3 serving as a well layer is surrounded by the i-type AlGaSb layer 2 serving as a barrier layer, and these quantum dots QD are formed in an xy plane. It is formed in a dimensional array. In this case, the AlGaSb / InAs heterojunction constituting the quantum dot QD is a type II superlattice.

An electrode 4 made of metal is formed on the i-type AlGaSb layer 2 as a barrier layer. The electrode 4 has openings 4a at portions corresponding to the quantum dots QD. Further, although not shown, p-type GaS
An electrode is in ohmic contact with the back surface of the b substrate 1. Then, an electric field is applied in the vertical direction of FIG. 1, that is, in the z-axis direction due to a potential difference between the electrode formed on the back surface of the p-type GaSb substrate 1 and the electrode 4 formed on the i-type AlGaSb layer 2. You can do it.

The direction along the line α-α and the line β-β in FIG.
2 and FIG. 3 show energy band diagrams in the directions along. 2 and FIG. 3, E _c is the energy, E _v at the lower end of the conduction band at the upper end of the energy of the valence band, E ₀ denotes the ground energy of electrons in the quantum dots QD.

As can be seen from FIG. 2, in this case, the direction along the line α-α in FIG.
The height of the potential barrier in the AlGaSb / InAs heterojunction in the connecting direction is very large, and thus the tunnel coupling between the quantum dots QD in this state is very weak. At this time, electron conduction by tunneling is not allowed between the quantum dots QD. Note that A
The height of the potential barrier in the lGaSb / InAs heterojunction can be adjusted by changing the composition ratio of Al to Ga in AlGaSb, and specifically, can be set to, for example, about 1.5 eV.

Next, the principle of operation of the quantum dot integrated device according to this embodiment configured as described above will be described. Here, it is assumed that the electrode formed on the back surface of the p-type GaSb substrate 1 is grounded (0 V), and the electrode 4 formed on the i-type AlGaSb layer 2 is biased to the potential φ.

First, at the time of input, the electrode 4 is biased to a small negative potential φ. At this time, the energy band in the direction along the line β-β in FIG. 1 is slightly inclined as shown in FIG. Next, in this state, for the quantum dot QD selected according to the information to be input, through the opening 4a of the electrode 4, monochromatic light having a wavelength that resonates with the electron-hole pair generation energy of the quantum dot QD, that is, Irradiate monochromatic light having a frequency ν satisfying hν = E ₀ −H ₀ , thereby generating an electron (e ⁻ ) -hole (h ⁺ ) pair in the quantum dot QD. Here, H ₀ is the energy at the upper end of the valence band of InAs, and h is Planck's constant. Specifically, the irradiation with the monochromatic light can be performed using, for example, a laser beam having a sufficiently small spot diameter.

In this case, for the holes of the electron-hole pairs generated by the light irradiation, the energy outside the quantum dot QD, that is, in the i-type AlGaSb layer 2 is lower, and the electrode 4 Since an electric field due to the potential φ is applied, the holes are quickly drawn toward the electrode 4 and sucked into the electrode 4 as shown in FIG. As a result, only electrons remain in the quantum dot QD.

At this stage, the electrons left in the quantum dot QD remain in the quantum dot QD. This is because the strength of the tunnel coupling between the quantum dots QD is small due to the small potential φ of the electrode 4 at this stage.

In this way, all the quantum dots QD selected in accordance with the information to be input are irradiated with light, and input is performed, while holding the electrons in the irradiated quantum dots QD. Thereby, the initial electron distribution can be input.

When the input of the initial electron distribution to the quantum dots QD arranged in a two-dimensional array as described above is completed, the electrode 4 is biased to a large negative potential φ. As a result, the energy band in the direction along the line β-β in FIG.
As shown in FIG. At this time, the strength of quantum confinement of electrons in the z-axis direction in the quantum dot QD decreases, and the strength of coupling between the quantum dots QD increases, so that the electrons conduct between the quantum dots QD by tunneling. This causes a time-dependent change in the electron distribution in the quantum dots QD arranged in a two-dimensional array. This electron conduction occurs according to the arrangement of the quantum dots QD, and information processing is performed by changing the electron distribution with time.

After the necessary time has elapsed, the potential φ of the electrode 4
To 0. Thereby, the energy band in the direction along the line β-β in FIG. 1 returns to the original state as shown in FIG.
Then, at this time, the coupling between the quantum dots QD is weakened again, so that the conduction of electrons between the quantum dots QD does not occur. At this point, the electron distribution in the quantum dots QD arranged in a two-dimensional array becomes output information.

Next, at the time of output, the electrode 4 is biased to a positive potential φ. At this time, the energy band in the direction along the line β-β in FIG. 1 is inclined in a direction opposite to that at the time of input and at the time of information processing, as shown in FIG. At this time, FIG.
As shown in (1), holes are injected from the electrode 4 into the i-type AlGaSb layer 2 in contact with the electrode 4. Then, the holes recombine with the electrons in the quantum dot QD to emit light (h
ν) occurs. Therefore, the final electron distribution in the quantum dot aggregate element can be known by spatially resolving and detecting this light emission, whereby output information can be obtained.

The operation of the quantum dot integrated device according to this embodiment as described above can be summarized as follows.
That is, if the electron distribution f (x, y) input by irradiation with laser light or the like is changed to g (x, y) with the passage of time, the electron distribution g (x, y) in the final state is read. Therefore, the processing of f (x, y) → g (x, y) can be performed after all.

Next, a method of manufacturing the quantum dot integrated device according to this embodiment will be described. First, as shown in FIG. 10, an i-type AlGaSb layer 2 is formed on a p-type GaSb substrate 1 by, for example, a metal organic chemical vapor deposition (MOCVD) method.
a, the i-type InAs layer 3 and the i-type AlGaSb layer 2b are sequentially epitaxially grown.

Next, for example, an i-type AlGa
After forming the SiO ₂ film 5 on the Sb layer 2b,
_{The two} films 5 are patterned into a shape corresponding to the quantum dots QD by lithography and etching. In addition,
The formation of the resist pattern for patterning the SiO ₂ film 5 is carried out, for example, by using an i-type Al
This is performed by selectively irradiating the GaSb layer 2b with an electron beam having a sufficiently small spot diameter and depositing a decomposition product of a source gas on the irradiated portion.

Next, the SiO ₂ thus formed is formed.
Using the film 5 as a mask, the i-type AlGaSb layer 2b and the i-type InAs layer 3 are sequentially etched in a direction perpendicular to the substrate surface by an anisotropic dry etching method such as a reactive ion etching (RIE) method. This etching is slightly over-etched so that the i-type InAs layers 3 are completely separated from each other. In this way,
As shown in FIG. 11, the i-type InAs layer 3 and the i-type Al
The GaSb layer 2b is patterned into a quadrangular prism shape.

[0032] Next, as shown in FIG. 12, SiO ₂ film 5
Is used as a mask to form an i-type AlGa
The Sb layer 2c is selectively epitaxially grown to fill a portion between the quadrangular prism-shaped i-type InAs layer 3 and the i-type AlGaSb layer 2b. Here, a quadrangular prism-shaped i-type InAs layer 3 is formed.
And the i-type A in the portion between the i-type AlGaSb layer 2b and
The thickness of the lGaSb layer 2c is, for example,
The thickness is selected to be smaller than the total thickness of the As layer 3 and the i-type AlGaSb layer 2b.

Next, as shown in FIG. 13, for example, Al is vacuum-deposited from a direction perpendicular to the substrate surface to form an Al film 6. In this case, by choosing a sufficiently small thickness of the Al film 6 of the thickness of the SiO ₂ film 5 is formed on the surface of the Al film 6 and the SiO ₂ film 5 other than the portion on the SiO ₂ film 5 The Al film 6 is separated from the Al film 6 by a step due to the SiO ₂ film 5.

Thereafter, the SiO ₂ film 5 is wet-etched to remove the Al film 6 on the SiO ₂ film 5 (lift-off). As described above, as shown in FIG. 14, a quantum dot aggregate element having substantially the same structure as the quantum dot aggregate element shown in FIG. 1 is completed.

As described above, according to the quantum dot aggregation device of this embodiment, the quantum dots QD arranged in a two-dimensional array are provided in one stage, and the electrode 4 is provided thereon. By using the electrode 4 to apply an electric field to the quantum dots QD arranged in a two-dimensional array in a direction perpendicular to their arrangement plane, that is, in the z-axis direction, these quantum dots in this arrangement plane QD
The strength of the coupling between them can be modulated. For this reason, according to the quantum dot collective element according to this embodiment, various information processing can be performed using the quantum dot collective element. Further, the quantum dot integrated device according to this embodiment has a simple structure, and thus is easy to manufacture. Further, the quantum dot aggregation device according to this embodiment is capable of optical input and optical output.

As described above, one embodiment of the present invention has been specifically described. However, the present invention is not limited to the above-described embodiment, and various modifications based on the technical idea of the present invention are possible. .

For example, in the above embodiment, since the electrode 4 is formed of a metal which is opaque to light, in order to irradiate the quantum dot QD with light, the quantum dot Q
It is necessary to previously form an opening 4a in the portion of the electrode 4 corresponding to D.
By using a transparent electrode material such as dium-tin oxide, it is not necessary to form the opening 4a in the electrode 4.

The method of manufacturing the quantum dot element described in the above embodiment is merely an example, and it goes without saying that another manufacturing method may be used.

Further, in the above-described embodiment, AlGaSb, InAs and GaSb are used as the material of the quantum dot aggregate element.
More generally, semiconductor materials other than these may be used as the material of the quantum box assembly element.

[0040]

As described above, according to the present invention,
By applying an electric field to a plurality of quantum boxes using a control electrode, the intensity of tunnel coupling between the plurality of quantum boxes can be modulated.Since the structure is simple, manufacturing is easy.
Moreover, it is possible to realize a quantum box assembly element capable of optical input and optical output.

[Brief description of the drawings]

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

FIG. 2 is an energy band diagram in a direction along a line α-α in FIG.

FIG. 3 is an energy band diagram in a direction along a line β-β in FIG. 1;

FIG. 4 is an energy band diagram for explaining an input method of the quantum dot aggregation device shown in FIG.

FIG. 5 is an energy band diagram for explaining an input method of the quantum dot aggregate element shown in FIG.

FIG. 6 is an energy band diagram of the quantum dot integrated device shown in FIG. 1 during information processing.

FIG. 7 is an energy band diagram of the quantum dot aggregate element shown in FIG. 1 after information processing and before output.

FIG. 8 is an energy band diagram for explaining an output method of the quantum dot aggregate element shown in FIG.

FIG. 9 is an energy band diagram for explaining an output method of the quantum dot aggregate element shown in FIG.

FIG. 10 is a perspective view for explaining a method of manufacturing a quantum dot aggregate element having substantially the same structure as the quantum dot aggregate element shown in FIG.

FIG. 11 is a perspective view for explaining a method of manufacturing a quantum dot aggregate element having substantially the same structure as the quantum dot aggregate element shown in FIG.

FIG. 12 is a perspective view for explaining a method of manufacturing a quantum dot aggregate element having substantially the same structure as the quantum dot aggregate element shown in FIG.

FIG. 13 is a perspective view for explaining a method of manufacturing a quantum dot aggregate element having substantially the same structure as the quantum dot aggregate element shown in FIG.

FIG. 14 is a perspective view for explaining a method of manufacturing a quantum dot aggregate element having substantially the same structure as the quantum dot aggregate element shown in FIG.

FIG. 15 is a schematic diagram illustrating a two-dimensional array of quantum boxes in which a plurality of quantum boxes are periodically arranged close to each other.

16 is an energy band diagram for explaining subband modulation in the two-dimensional array of the quantum box shown in FIG.

[Explanation of symbols]

 1 p-type GaSb substrate 2, 2a, 2b, 2ci i-type AlGaSb layer 3 i-type InAs layer 4 electrode 4a opening

Claims (4)

(57) [Claims] 1. A plurality of quantum boxes arranged in one plane, provided at a distance from the said plurality of quantum boxes, the
Opening or transparent material corresponding to quantum box
And a control electrode formed at a first negative potential with respect to the quantum box.
State with an electric field applied in the direction perpendicular to the above plane
Resonates with the electron-hole pair generation energy of the quantum box.
Through the aperture or through the control electrode.
By transmitting and irradiating the selected quantum box
And the control electrode is connected to the first negative potential with respect to the quantum box.
Bias to a second negative potential lower than
By applying an electric field in various directions,
Increase the strength of the bond between
Performs information processing by conducting, and then controls
The bias voltage to the electrode is substantially removed, and the control electrode is biased to a positive potential with respect to the quantum box.
And apply an electric field in a direction perpendicular to the above plane.
Output by emitting light due to electron-hole recombination
Quantum box assembly element that performs 2. The quantum box is a type II heterojunction super-junction.
2. The quantum box assembly according to claim 1, wherein the device is formed by a lattice . 3. The quantum box has a well layer made of InAs.
It has a structure surrounded by a barrier layer made of AlGaSb.
The quantum box assembly device according to claim 1, wherein: 4. A plurality of quantum boxes arranged in one plane and a plurality of quantum boxes are provided at intervals with respect to the plurality of quantum boxes.
Opening or transparent material corresponding to quantum box
Of a quantum box assembly having a control electrode formed by
An operation method, comprising : controlling the control electrode to a first negative potential with respect to the quantum box.
State with an electric field applied in the direction perpendicular to the above plane
Resonates with the electron-hole pair generation energy of the quantum box.
Through the aperture or through the control electrode.
By transmitting and irradiating the selected quantum box
And the control electrode is connected to the first negative potential with respect to the quantum box.
Bias to a second negative potential lower than
By applying an electric field in various directions,
Increase the strength of the bond between
Performs information processing by conducting, and then controls
The bias voltage to the electrode is substantially removed, and the control electrode is biased to a positive potential with respect to the quantum box.
And apply an electric field in a direction perpendicular to the above plane.
Output by emitting light due to electron-hole recombination
The operation method of the quantum box collective element configured to perform the operation.