JPH0715003A - Quantum box aggregate element - Google Patents

Abstract

PURPOSE:To realize a quantum box aggregate element wherein the intensity of tunnel coupling between quantum boxes can be modulated, structure is simple, manufacturing is easy, and optical input and optical output are enabled. CONSTITUTION:One stage of two-dimensional array of quantum dots QD is arranged, and thereon an electrode 4 is formed. By using the electrode 4, an electric field is applied to the two-dimensional array of the quantum dots QD. Thereby the intensity of tunnel coupling between the quantum dots QD is modulated. Light is inputted by irradiating the quantum dots QD with light through apertures 4a in the electrode 4. Electrons inputted in the quantum dots QD by light irradiation are conducted by tunneling between the quantum dots QD, and information processing is performed. Holes are injected from the electrode 4 and made to recombine with electrons in the quantum dots QD. Thereby light emission is induced and light is outputted.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art In recent years, in quantum wave electronics, attention has been paid to a so-called quantum box, which is a microbox structure having a cross-sectional dimension similar to the de Broglie wavelength of an electron. There is great interest in the quantum effects exhibited by dimensional electrons.

A quantum box assembly element is a combination of a plurality of such quantum boxes, and an attempt is made to perform information processing by changing the electron distribution by causing quantum mechanical tunneling of electrons between these quantum boxes. To do.

[0004]

When information processing is performed by conducting electrons by quantum mechanical tunneling between a plurality of quantum boxes as described above, it is necessary to modulate the strength of tunnel coupling between these quantum boxes. If it is possible, various information processing can be performed.

The strength of this tunnel coupling is determined by the tunnel transmittance (or tunnel probability) of electrons between quantum boxes. The factors that determine this 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 also difficult to change the relative distance if the quantum box is formed by a heterojunction. The remaining method is to change the barrier height between the quantum boxes, but it was difficult to do this in the past.

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

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

Still another object of the present invention is to provide a quantum box assembly device capable of optical input and optical output.

[0009]

In order to achieve the above object, a quantum box assembly element according to the present invention has a plurality of quantum boxes (QD) arranged in one plane and a plurality of quantum boxes (QD). And a control electrode (4) provided at intervals, and coupling between the plurality of quantum boxes (QD) by applying an electric field to the plurality of quantum boxes (QD) using the control electrode (4). The intensity of is modulated.

In a preferred embodiment of the quantum box assembly device according to the present invention, the control electrode (4) is connected to the quantum box (QD).
In contrast, the bias voltage is applied to the selected quantum box (QD) with a wavelength that resonates with the electron-hole pair production energy of the quantum box (QD) while being biased to the first negative potential. And biasing the control electrode (4) to a second negative potential lower than the first negative potential with respect to the quantum boxes (QDs) to increase the strength of the coupling between the quantum boxes (QDs). Then, information processing is performed by conducting electrons between the plurality of quantum boxes (QD), and then the bias voltage for the control electrode (4) is substantially removed, and the control electrodes (4) are changed to the quantum boxes (QD). On the other hand, output is performed by biasing to a positive potential and causing light emission by electron-hole recombination.

The control electrode (4) has an opening (4a) at a portion corresponding to the quantum box (QD) or is made of a transparent material.

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, for example, a structure in which 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 are x
Consider the case where they are periodically arranged close to each other in the -y plane. In this case, this periodic structure forms subbands in the x direction and the y direction, as shown in FIG. 16A. Here, when an electric field is applied in the z-axis direction of FIG.
The quantum confinement of electrons in the z-axis direction in the quantum box becomes stronger, and the ground energy of the electron in the quantum box rises.
At this time, since the effective barrier height between the quantum boxes in the xy plane is reduced, the tunnel coupling between the quantum boxes in the xy plane is strengthened and the subband width is increased (FIG. 16B). ). Modulation of the strength of the tunnel coupling between a plurality of quantum boxes arranged close to each other is possible not only when the quantum boxes are arranged periodically but also when the quantum boxes are arranged aperiodically. It is possible as well.

As can be seen from the above, according to the quantum box assembly element of the present invention configured as described above,
By applying an electric field to a plurality of quantum boxes (QD) using the control electrode (4), the quantum confinement strength of electrons in the direction of application of this electric field in the quantum boxes (QD) is modulated, and the quantum boxes (QD) are thereby modulated. By effectively changing the barrier height between the QDs, the strength of the tunnel coupling between the quantum boxes (QDs) can be modulated. In addition, this quantum box assembly element has a simple structure because it uses a single-stage quantum box (QD), and is therefore easy to manufacture. Further, this quantum box assembly element can input electrons into a quantum box (QD) by light irradiation and can output by emitting light by electron-hole recombination, and can perform optical input and optical output.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 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 assembly element.

FIG. 1 shows a quantum dot assembly device according to this embodiment. As shown in FIG. 1, in the quantum dot assembly element according to this 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 as a well layer. The box-shaped i-type InAs layer 3 is embedded in a two-dimensional array in the xy plane. The quantum dots QD are formed by the structure in which the i-type InAs layer 3 as the well layer is surrounded by the i-type AlGaSb layer 2 as the barrier layer, and these quantum dots QD are formed in the xy plane. It is formed in a three-dimensional array. In this case, the AlGaSb / InAs heterojunction forming this 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. Each of the electrodes 4 has an opening 4a at a portion corresponding to the quantum dot QD. Further, although not shown, p-type GaS
The electrode is in ohmic contact with the back surface of the substrate 1. Then, due to the 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, an electric field is applied in the vertical direction of FIG. 1, that is, the z-axis direction. Is able to.

The direction along the line α-α in FIG. 1 and the line β-β
2 and 3 are energy band diagrams in the directions along the lines. 2 and 3, E _c is the energy at the lower end of the conduction band, E _v is the energy at the upper end of the valence band, and E ₀ is the ground energy of the electrons of the quantum dot QD.

As can be seen from FIG. 2, in this case, the direction along the line α-α in FIG. 1, that is, the adjacent quantum dots QD
The height of the potential barrier in the AlGaSb / InAs heterojunction in the direction connecting them is very large, and therefore the tunnel coupling between the quantum dots QD in this state is very weak. At this time, conduction of electrons by tunneling is not allowed between the quantum dots QD. In addition, A
The height of the potential barrier in the 1GaSb / InAs heterojunction can be adjusted by changing the composition ratio of Al and Ga of AlGaSb, and specifically, it can be set to, for example, about 1.5 eV.

Next, the operation principle of the quantum dot assembly element according to this embodiment having the above-mentioned structure will be described. Note that, here, 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 resonating with the electron-hole pair generation energy of the quantum dot QD, that is, Irradiation with monochromatic light having a frequency ν satisfying hν = E ₀ −H ₀ produces electron (e ⁻ ) -hole (h ⁺ ) pairs in this quantum dot QD. However, H ₀ is the energy at the upper end of the valence band of InAs, and h is the Planck's constant. This monochromatic light irradiation can be specifically carried out using, for example, laser light having a sufficiently small spot diameter.

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

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

In this manner, while holding electrons in the quantum dots QD that have been irradiated with light, all quantum dots QD selected according to the information to be input are irradiated with light and input. Thus, the initial electron distribution can be input.

When the input of the initial electron distribution to the quantum dots QD arranged in the two-dimensional array is completed as described above, 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. 6, it greatly inclines. At this time, the strength of the quantum confinement of electrons in the z-axis direction inside the quantum dots QD decreases, and the strength of the bond between the quantum dots QD increases, so that the electrons are conducted by tunneling between the quantum dots QD, and Changes the electron distribution over time 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 required time has passed, the potential φ of the electrode 4
To 0. As a result, the energy band in the direction along the line β-β in FIG. 1 returns to the original one as shown in FIG. 7.
Then, at this time, the coupling between the quantum dots QD becomes weak again, so that the conduction of electrons between the quantum dots QD does not occur. The electron distribution in the quantum dots QD arranged in a two-dimensional array at this point becomes output information.

Next, at the time of output, the electrode 4 is biased to the positive potential φ. At this time, the energy band in the direction along the line β-β in FIG. 1 is inclined in the direction opposite to that at the time of input and information processing, as shown in FIG. At this time, FIG.
As shown in, 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, it is possible to know the final electron distribution in the quantum dot assembly element by spatially decomposing and detecting this luminescence, and thereby output information can be obtained.

The operation of the quantum dot assembly element 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 changes to g (x, y) over time, the electron distribution g (x, y) itself in the final state should be read. Therefore, after all, the processing of f (x, y) → g (x, y) can be performed.

Next, a method of manufacturing the quantum dot assembly element 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.
The a, i-type InAs layer 3 and i-type AlGaSb layer 2b are sequentially epitaxially grown.

Next, for example, i-type AlGa is formed by the CVD method.
After the SiO ₂ film 5 is formed on the Sb layer 2b, the SiO ₂ film 5 is formed.
_{2 The} film 5 is patterned into a shape corresponding to the quantum dots QD by lithography and etching. In addition,
The resist pattern for patterning the SiO ₂ film 5 is formed by, for example, i-type Al in a predetermined source gas atmosphere in a vacuum-exhausted sample chamber of an electron beam irradiation apparatus.
This is performed by selectively irradiating the GaSb layer 2b with an electron beam having a sufficiently small spot diameter and depositing decomposition products of the raw material gas on this irradiation portion.

Next, the SiO ₂ thus 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 the direction perpendicular to the substrate surface by anisotropic dry etching such as reactive ion etching (RIE). This etching is performed over etching 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 were formed.
The GaSb layer 2b is patterned into a rectangular columnar shape.

Next, as shown in FIG. 12, a SiO ₂ film 5 is formed.
With i as a mask by, for example, MOCVD, i-type AlGa
The Sb layer 2c is selectively epitaxially grown to fill a portion between the square columnar i-type InAs layer 3 and the i-type AlGaSb layer 2b. Here, the square columnar i-type InAs layer 3 is formed.
And the portion of the i-type A between the i-type AlGaSb layer 2b.
The thickness of the 1GaSb layer 2c is, for example, i-type In.
It 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, an Al film 6 is formed by vacuum-depositing Al, for example, in a direction perpendicular to the substrate surface. 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 and the Al film 6 are separated from each other by the step due to the SiO ₂ film 5.

After that, 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 assembly device having substantially the same structure as the quantum dot assembly device shown in FIG. 1 is completed.

As described above, according to the quantum dot assembly element 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 and applying an electric field to the quantum dots QD arranged in a two-dimensional array in a direction perpendicular to their array plane, that is, the z-axis direction, these quantum dots in the array plane are arranged. QD
The strength of the coupling between can be modulated. Therefore, according to the quantum dot assembly element of this embodiment, various information processing can be performed by utilizing this. Further, the quantum dot assembly element according to this example has a simple structure, and thus is easy to manufacture. Furthermore, the quantum dot assembly device according to this embodiment is capable of light input and light output.

Although one embodiment of the present invention has been specifically described above, the present invention is not limited to the above embodiment, and various modifications can be made based on the technical idea of the present invention. .

For example, in the above-described embodiment, since the electrode 4 is made of a metal opaque to light, the quantum dot QD is irradiated with light in order to irradiate the quantum dot QD.
It is necessary to form the opening 4a in the portion of the electrode 4 corresponding to D in advance.
It is not necessary to form the opening 4a in the electrode 4 by forming the transparent electrode material such as dium-tin oxide.

Further, it goes without saying that the method of manufacturing the quantum dot assembly element described in the above embodiments is merely an example, and other manufacturing methods may be used.

Further, although AlGaSb, InAs and GaSb are used as the material of the quantum dot assembly element in the above-mentioned embodiment, this quantum dot assembly element is
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, it is possible to modulate the strength of tunnel coupling between the plurality of quantum boxes, and the structure is simple, so that the manufacturing is easy,
Moreover, it is possible to realize a quantum box assembly element capable of optical input and optical output.

[Brief description of drawings]

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

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

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

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

5 is an energy band diagram for explaining an input method of the quantum dot assembly device shown in FIG. 1. FIG.

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

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

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

9 is an energy band diagram for explaining an output method of the quantum dot assembly element shown in FIG. 1. FIG.

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

FIG. 11 is a perspective view for explaining a method of manufacturing a quantum dot assembly device having substantially the same structure as the quantum dot assembly device shown in FIG. 1.

FIG. 12 is a perspective view for explaining a method of manufacturing a quantum dot assembly device having substantially the same structure as the quantum dot assembly device shown in FIG. 1.

FIG. 13 is a perspective view for explaining a method of manufacturing a quantum dot assembly device having substantially the same structure as the quantum dot assembly device shown in FIG. 1.

FIG. 14 is a perspective view for explaining a method of manufacturing a quantum dot assembly device having substantially the same structure as the quantum dot assembly device shown in FIG. 1.

FIG. 15 is a schematic diagram showing 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 quantum boxes shown in FIG.

[Explanation of symbols]

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

Claims (5)

[Claims] 1. A plurality of quantum boxes arranged in one plane, and a control electrode provided at a distance from the plurality of quantum boxes, the plurality of quantum boxes using the control electrode. A quantum box assembly element in which the strength of the coupling between the plurality of quantum boxes is modulated by applying an electric field to the quantum box assembly. 2. The control electrode is first with respect to the quantum box.
Of the electron in the above quantum box under the condition that it is biased to the negative potential of
Input is performed by irradiating the selected quantum box with light having a wavelength that resonates with hole pair generation energy, and the control electrode is connected to the quantum box with a second potential lower than the first negative potential. Biasing to a negative potential increases the strength of the coupling between the quantum boxes, and information is processed by conducting electrons between the quantum boxes, after which the bias voltage to the control electrode is substantially changed. 2. The device according to claim 1, wherein the control electrode is biased to a positive potential with respect to the quantum box to cause light emission by electron-hole recombination, and thereby output is performed. Quantum box assembly device. 3. The quantum box assembly element according to claim 1, wherein the control electrode has an opening in a portion corresponding to the quantum box or is made of a transparent material. 4. The quantum box is formed of a type II heterojunction superlattice.
2. The quantum box assembly device according to 2 or 3. 5. The quantum box assembly element according to claim 1, wherein the quantum box has a structure in which a well layer made of InAs is surrounded by a barrier layer made of AlGaSb.