JPH0794806A - Quantum box aggregation element and light beam input/ output method - Google Patents

Abstract

PURPOSE:To provide a quantum box aggregation element using IV group element having activity for light beam and a method of inputting and outputting a light beam utilizing such quantum box aggregation element. CONSTITUTION:A quantum box aggregation element is composed of a mixed crystal layer 20 consisting of a mixed crystal of two kinds of IV group elements and a quantum box 30 consisting of the IV group element and a type II heterojunction super lattice is formed between the mixed crystal layer 20 and quantum box 30. The mixed crystal layer 30 can be formed of SiGe, the quantum box 30 can be formed of Si formed on the mixed crystal layer and a wall layer 40 for covering the quantum box 30 and an electrode 42 provided in separation from the quantum box to form the electric field can further be provided. A light beam inputting and outputting method comprises steps for (A) irradiating the mixed crystal layer 20 with a light beam under the condition that the electric field is formed and the electrons generated thereby are trapp in the quantum box 30 and (B) generating a light beam by forming an opposite electric field and recoupling the electrons trapp by the quantum box 30 with the holes supplied externally.

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 element composed of a group IV element and an optical input / output method using the quantum box assembly element.

[0002]

2. Description of the Related Art In recent years, in quantum wave electronics, attention has been paid to a hyperfine structure having a cross-sectional dimension similar to the de Broglie wavelength of electrons, that is, a so-called quantum box or a quantum box assembly element which is a collection of a plurality of quantum boxes. Therefore, there is great interest in the quantum effect exhibited by the zero-dimensional electrons confined in this quantum box. Above all, the technique of trapping electron or hole carriers generated by photoexcitation in the quantum box is highly expected to be applied to the field of electron-optical devices in the future. For applications in such fields,
It is necessary that the material forming the quantum box assembly element be active with respect to light.

Silicon is widely used in VLSI and the like, and is a material of high purity and good crystallinity. However,
Silicon is an indirect transition type semiconductor material and is inactive to light. Therefore, conventionally, it has been considered that a compound semiconductor, which is a direct transition type semiconductor material, is indispensable as a material for forming the quantum box assembly element. Also, from the viewpoint of the degree of freedom in selecting the material forming the barrier layer in the quantum box assembly element, it was considered that the compound semiconductor is suitable for the material forming the quantum box assembly element.

However, recent studies have revealed that SiGe, which is a mixed crystal of two kinds of Group IV elements, is photoactive. In general, in group IV elements, direct transition is prohibited due to the symmetry of the perfect crystal. On the other hand, I
The group V element mixed crystal becomes active against light because the translational symmetry of the crystal is broken by the randomness and the direct transition prohibition rule is broken. Further, research on hetero-epitaxial growth of Si / SiGe is also progressing.

[0005]

The present applicant has proposed a technique for generating carriers inside a quantum box by photoexcitation.
It was proposed in Japanese Patent Application No. 4-360263 filed on Dec. 28, 2012. This quantum box is composed of a compound semiconductor heterojunction superlattice. In general, compound semiconductor materials have a problem that they are less stable than silicon. Further, when the quantum box and the barrier layer are formed from the compound semiconductor material, there is a problem that the barrier layer has a low barrier and it is difficult to confine electrons in the quantum box. Further, in the case of configuring the entire system, integration with a conventional silicon device such as MOS can be considered, and in this case, it is desirable to configure the quantum box from silicon.

The present invention aims to solve these problems of a quantum box assembly element made of a compound semiconductor material, and is a quantum box assembly element using a group IV element having activity to light, and An optical input / output method using such a quantum box assembly element is provided.

[0007]

A quantum box assembly element according to a first aspect of the present invention comprises a mixed crystal layer composed of two kinds of group IV element mixed crystals and a quantum box composed of group IV elements.
A type II heterojunction superlattice is formed between the mixed crystal layer and the quantum box. The mixed crystal layer can be made of SiGe, and the quantum box can be made of Si or Ge formed on the mixed crystal layer. The quantum box assembly element may further include a barrier layer covering the quantum box, and an electrode provided apart from the quantum box to form an electric field.

The quantum box assembly element according to the second aspect of the present invention comprises a mixed crystal layer composed of two kinds of group IV element mixed crystals,
And a quantum box composed of two kinds of group IV element mixed crystals having a mixed crystal ratio different from the mixed crystal ratio of the group IV element mixed crystal forming the mixed crystal layer. Is characterized in that a type II heterojunction superlattice is formed. The mixed crystal layer can be made of SiGe, and the quantum box can be made of SiGe formed on the mixed crystal layer. The quantum box assembly element may further include a barrier layer covering the quantum box, and an electrode provided apart from the quantum box to form an electric field.

The barrier layer in these quantum box assembly devices can be made of SiO ₂ . The electrode is an upper electrode made of a transparent electrode material provided on the barrier layer,
Alternatively, it is desirable to use an upper electrode having a kind of window above the quantum box.

In the light input / output method for the quantum box assembly according to the present invention, a mixed crystal layer composed of two kinds of group IV element mixed crystals and I
IV forming a quantum box or mixed crystal layer composed of group V elements
Having a mixed crystal ratio different from the mixed crystal ratio in the mixed crystal of group elements 2
A quantum box assembly element is used which is composed of a quantum box made of a mixed crystal of a group IV element of a seed, and in which a type II heterojunction superlattice is formed between the mixed crystal layer and the quantum box. Then, the light input / output method in the quantum box assembly element according to the first aspect includes (a) a step of irradiating the mixed crystal layer with light in a state where an electric field is formed, and trapping the electrons generated thereby in the quantum box. And (b) forming an opposite electric field to cause the electrons trapped in the quantum box to recombine with holes supplied from the outside to emit light.

In the optical input / output method for the quantum box assembly element of the present invention, the mixed crystal layer is made of SiGe, and the quantum box is made of Si, Ge or SiGe formed on the mixed crystal layer,
It is desirable that the quantum box assembly element further includes a barrier layer that covers the quantum box. The barrier layer can be made of SiO ₂ .

In the present invention, the quantum boxes may be arranged in a two-dimensional array periodically or aperiodically. The size of the quantum box is 2 nm to 50 nm. Usually, there are one to several electrons in the quantum box. The quantum box may be called a quantum dot.

[0013]

[Function] For example, Si which is a group IV element and two kinds of IV
In the heterojunction superlattice composed of SiGe, which is a mixed crystal composed of a group element mixed crystal, strain is generated due to the difference in the lattice constants, and the band structure is largely changed depending on how the strain enters. When SiGe is grown on bulk Si, SiGe is arranged with the Si lattice constant, and a type I heterojunction superlattice having a band structure as shown in FIG. 9B is formed. On the other hand, when Si is epitaxially grown on bulk SiGe to form a Si thin film, a type II heterojunction superlattice having a band structure as shown in FIG. 9A is formed. The present invention utilizes this type II heterojunction superlattice.

The mixed crystal layer is active with respect to light. On the other hand, the quantum box is inactive to light. Therefore, electron-hole pairs are generated in the mixed crystal layer by the light incident on the mixed crystal layer. If a predetermined electric field is formed in the quantum box assembly element,
Since the type II heterojunction superlattice is formed between the mixed crystal layer and the quantum box, the generated electrons are trapped in the quantum box.

If an electric field opposite to that trapped in the quantum box is formed in the quantum box assembly element, the electrons trapped in the quantum box are recombined with holes supplied from the outside. as a result,
Since light is emitted and light is emitted from the quantum box assembly element,
By detecting this light, the distribution of electrons and the like in the quantum box assembly element can be known.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described based on embodiments with reference to the drawings.

(Structure of Quantum Box Assembly Element of the Present Invention) FIG. 1 is a schematic sectional view of the quantum box assembly element of the present invention. This quantum box assembly element is composed of a mixed crystal layer 20 made of two kinds of group IV element mixed crystals and a quantum box 30 made of group IV elements, and between the mixed crystal layer 20 and the quantum box 30. Forms the type II heterojunction superlattice shown in FIG. 9 (A). More specifically, the mixed crystal layer 20 composed of two kinds of group IV element mixed crystals is composed of i-type SiGe, and I
The quantum box 30 made of a group V element is made of Si. The quantum boxes 30 are also formed in the direction perpendicular to the paper surface of FIG. 1, and are arranged in a two-dimensional array.

The quantum box assembly element of the present invention further comprises a barrier layer 40 made of SiO ₂ and covering the quantum box 30. Further, an upper electrode 42 made of, for example, a transparent ITO film is provided on the top surface of the barrier layer 40. Furthermore, Si
A high-concentration impurity region 14 functioning as a lower electrode is formed below the mixed crystal layer 20 made of Ge. The mixed crystal ratio of the mixed crystal layer 20 is Si: 50 atom%, Ge: 50 atom.
%.

Two kinds of quantum box assembly elements are used, which have a mixed crystal layer composed of two kinds of group IV element mixed crystals and a mixed crystal ratio different from the mixed crystal ratio of the group IV element mixed crystals forming the mixed crystal layer. IV
It may be composed of a quantum box made of a mixed crystal of group elements. A type II heterojunction superlattice is formed between the mixed crystal layer and the quantum box. In this case, the mixed crystal layer is composed of, for example, a mixed crystal of Si and Ge, and the mixed crystal ratio is, for example,
Si: 40 atom%, Ge: 60 atom%. The quantum box is also composed of a mixed crystal of Si and Ge, and the mixed crystal ratio is, for example, Si: 90 atom% and Ge: 10 atom%. still,
Generally, the atomic percentage of Si in the mixed crystal layer may be lower than the atomic percentage of Si in the quantum box. still,
Even in the quantum box assembly device having such a configuration, the quantum box 3
A high concentration impurity region 14 functioning as a lower electrode formed below the mixed crystal layer 20 and a barrier layer 40 covering 0, an upper electrode 42 made of, for example, a transparent ITO film formed on the top surface of the barrier layer 40. Form.

(Manufacturing Method of Quantum Box Assembly Element of the Present Invention) A manufacturing method of the quantum box assembly element shown in FIG. 1 will be described below with reference to FIG.

First, using a molecular beam epitaxy (MBE) technique on a substrate 10 made of, for example, a silicon wafer,
A buffer layer 12 made of SiGe is formed, and then a bulk SiGe crystal is grown on the buffer layer 12 to form a SiGe layer having a sufficient thickness. After that, a necessary region of the SiGe layer is doped with a p-type impurity by using, for example, an ion implantation technique to form a high concentration impurity region 14. Then, a mixed crystal layer 20 of i-type SiGe having a sufficient thickness is further formed thereon by using the MBE technique (see FIG. 2A).

Next, using the MBE technique, a Si layer 30 having a thickness of, for example, 10 nm is formed on the mixed crystal layer 20 made of SiGe.
A is epitaxially grown (see FIG. 2B).
As a result, a type II heterojunction superlattice is formed between the Si layer 30A and the underlying mixed crystal layer 20. Then, the Si layer 30A is patterned to form a plurality of quantum boxes 30 made of Si (see FIG. 2C). During patterning, the resist material is formed on the Si layer 30A by, for example, using an electron beam with a spot diameter narrowed sufficiently in a predetermined resist source gas atmosphere in a sample chamber of the electron beam irradiation apparatus that is evacuated. This can be performed by selectively irradiating the upper part and depositing a decomposition product of the resist source gas on the portion of the Si layer 30A irradiated with the electron beam. The etching of the Si layer 30A during patterning can be performed by an anisotropic dry etching method such as the RIE method. The planar shape of the quantum box 30 may be rectangular, for example.

Then, a SiO ₂ layer is deposited on the entire surface including the quantum box 30 by, for example, a CVD method to form the quantum box 30 into S.
coated with a barrier layer 40 made of iO _2. After that, using the sputtering method, lithography technology and etching technology,
An upper electrode 42 made of, for example, an ITO film is formed on the barrier layer 40 to complete the quantum box assembly element shown in FIG.

When the upper electrode is not composed of the transparent electrode material, the quantum box 30 is covered with the barrier layer 40 made of SiO ₂ and then the barrier layer 40 is patterned to form the barrier layer 40.
Then, a protrusion 40A having a shape corresponding to the quantum box 30 is formed (see FIG. 3A). When patterning, the barrier layer 40
The above resist material is formed by, for example, selectively irradiating the barrier layer 40 with an electron beam with a spot diameter sufficiently narrowed in a predetermined resist source gas atmosphere in a vacuumed sample chamber of an electron beam irradiation apparatus. Then, the decomposition product of the resist source gas is deposited on the portion of the barrier layer 40 irradiated with the electron beam. The etching of the barrier layer 40 for forming the protrusion 40A can be performed by an anisotropic dry etching method such as the RIE method.

Next, an electrode material layer made of, for example, aluminum is formed on the entire surface of the barrier layer 40 by a vacuum deposition method or the like (see FIG. 3B). In this case, by making the thickness of the electrode material layer sufficiently smaller than the height of the protrusion 40A of the barrier layer 40, the electrode material layer on the protrusion 40A of the barrier layer 40 and the electrode material layer of the other portion They are separated from each other by the step. Then, as shown in FIG.
Of the barrier layer 40 by wet etching
A and the electrode material layer on the protrusion 40A are removed (lift-off). Thus, the upper electrode 42 having a kind of window is formed above the quantum box 30. Light can be incident on the mixed crystal layer 20 through this window.

(Operation of Quantum Box Assembly Device of the Present Invention) The operation principle of the quantum box assembly device shown in FIG. 1, that is, the principle of the optical input / output method of the present invention will be described below with reference to FIGS. Explain.

Energy band diagrams along line AA of FIG. 1 are shown in FIGS. Incidentally, in FIGS. 5 to 7, E _C
Is the energy at the bottom of the conduction band, and E _V is the energy at the top of the valence band. In the state shown in FIG. 5, no electric field is formed in the quantum box assembly element.

First, an electric field is formed in the quantum box assembly element via the high-concentration impurity region 14 and the upper electrode 42. For example, the high concentration impurity region 14 is grounded and a positive potential is applied to the upper electrode 42. The potential may be about 3V. At this time, as shown in FIG. 6, the energy band is inclined.
In this state, the i-type S is passed through the upper electrode 42 (or the window formed in the upper electrode), the barrier layer 40, and the quantum box 30.
The mixed crystal layer 20 made of iGe is irradiated with light. The wavelength of light may correspond to the band gap of i-type SiGe, and for example, laser light having a wavelength in the visible region can be used. The irradiated light is absorbed by the mixed crystal layer 20, and electrons and holes are generated in the mixed crystal layer 20. Since the quantum box 30 is made of indirect transition Si, the quantum box 30 does not absorb light.

As shown in the energy band diagram of FIG.
A type II heterojunction superlattice is formed between the mixed crystal layer 20 and the quantum box 30. As a result, the electrons approach the quantum box 30 made of Si by the formed electric field and are trapped in the quantum box 30 having a low potential. On the other hand, the holes move in a direction away from the quantum box, reach the high concentration impurity region 14, and are absorbed in the high concentration impurity region 14. In this way, the electrons are absorbed by the high barrier of Si / SiO ₂ and Si / i.
Trapped by the SiGe barrier and confined within the quantum box 30. Although the Si / i-type SiGe barrier is relatively low, the electrons are reliably confined in the quantum box 30 by the electric field formed in the quantum box assembly element.

In this way, light is irradiated to all selected mixed crystal layer regions while trapping and holding electrons in the quantum boxes corresponding to the light-irradiated mixed crystal layer regions. . Thereby, the electron distribution based on the pattern of incident light can be input to the quantum box assembly element.

In order to detect the distribution of the electrons trapped in the quantum box assembly 30 in the quantum box assembly element, an electric field opposite to the above is formed in the quantum box assembly element. That is, a negative potential is applied to the upper electrode 42.
The potential may be about 3V. As shown in FIG. 7, the energy band tilts in the direction opposite to the direction shown in FIG. At this time, holes are injected into the mixed crystal layer 20 from the high concentration impurity region 14. Then, as shown in the energy band diagram of FIG. 7, the injected holes are recombined with the electrons trapped in the quantum box 30 to emit light.
The light thus obtained is emitted from the quantum box assembly element.
By detecting this light with an external photodetector and spatially resolving it, the electron distribution in the quantum box assembly element can be known.

In the quantum box assembly device of the present invention which operates in this way, for example, if the spacing between the quantum boxes is narrow (for example, about 5 nm), the electrons are conducted between the plurality of quantum boxes by quantum mechanical tunneling, The electron distribution input to the quantum box assembly element changes with time. After the elapse of a predetermined time,
Various information processing can be performed by detecting the electron distribution.

Alternatively, the quantum box assembly element of the present invention which operates as described above can be used as a photodetector. That is, as shown in the schematic cross-sectional view of FIG. 8, the electrodes 50A and 50A are formed on the mixed crystal layer 20 other than the region where the quantum boxes 30 are formed.
50B is provided and a bias is applied between these electrodes 50A and 50B. When light is incident on the region between the electrodes 50A and 50B, the electrons generated in the mixed crystal layer 20 reach the electrode 50A or 50B via the quantum box 30 and are observed as a current. That is, whether the quantum box assembly element is irradiated with light, or whether a specific area of the quantum box assembly element is irradiated with light, and also how many quantum boxes are exposed to light. Whether or not it is irradiated can be detected by the presence or absence of a current flowing between the electrodes 50A and 50B or the value of the current.

[0034]

According to the present invention, it is possible to provide a quantum box assembly element composed of a group IV element. Since the group IV element is stable in material, it is possible to stably form the mixed crystal layer and the quantum box, and the manufactured quantum box assembly element has high reliability. In addition, electrons and the like in the quantum box are effectively confined by the high barrier of the group IV element and the barrier layer that make up the quantum box. Since SiO ₂ has a low dielectric constant,
By forming the barrier layer from SiO ₂ , a large electron interaction can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a quantum box assembly element of the present invention.

FIG. 2 is a schematic cross-sectional view for explaining a manufacturing process of the quantum box assembly device of the present invention.

FIG. 3 is a schematic cross-sectional view for explaining a part of the manufacturing process of the quantum box assembly device of the present invention which is different from the part in FIG. 2 in part of the process.

FIG. 4 is a schematic cross-sectional view for explaining a part of the manufacturing process of the quantum box assembly device of the present invention, following FIG. 3.

FIG. 5 is an energy band diagram of the quantum box assembly device of the present invention in a state where no electric field is formed.

FIG. 6 is an energy band diagram of the quantum box assembly element of the present invention when light is incident.

FIG. 7 is an energy band diagram of the quantum box assembly element of the present invention when light is emitted.

FIG. 8 is a schematic cross-sectional view of a quantum box assembly element of the present invention when used as a photodetector.

FIG. 9 is a diagram for explaining band structures of type I and type II heterojunction superlattices.

[Explanation of symbols]

 10 substrate 12 buffer layer 14 high concentration impurity region 20 mixed crystal layer 30 quantum box 30A Si layer 40 barrier layer 42 upper electrode 50A, 50B electrode

Claims (8)

[Claims] 1. A mixed crystal layer comprising two kinds of group IV element mixed crystals,
A quantum box assembly element comprising a quantum box made of a group IV element, and a type II heterojunction superlattice formed between the mixed crystal layer and the quantum box. 2. The mixed crystal layer is made of SiGe, the quantum box is made of Si and is formed on the mixed crystal layer, and a barrier layer for covering the quantum box and a quantum box for forming an electric field are formed. The quantum box assembly element according to claim 1, further comprising: an electrode provided apart from the quantum box assembly. 3. A mixed crystal layer composed of two kinds of group IV element mixed crystals,
And a quantum box composed of two kinds of group IV element mixed crystals having a mixed crystal ratio different from the mixed crystal ratio of the group IV element mixed crystal forming the mixed crystal layer. Type I
A quantum box assembly device, wherein an I heterojunction superlattice is formed. 4. The mixed crystal layer is made of SiGe, the quantum box is made of SiGe and is formed on the mixed crystal layer, and a barrier layer for covering the quantum box and a quantum box for forming an electric field are formed. The quantum box assembly element according to claim 3, further comprising an electrode provided apart from each other. 5. The quantum box assembly element according to claim _2, wherein the barrier layer is made of SiO ₂ . 6. A mixed crystal layer comprising two kinds of group IV element mixed crystals,
I constituting a quantum box or mixed crystal layer composed of a group IV element
And a quantum box composed of two kinds of group IV element mixed crystals having a mixed crystal ratio different from the mixed crystal ratio in the group V element mixed crystal,
In a quantum box assembly device in which a type II heterojunction superlattice is formed between a mixed crystal layer and a quantum box, (a) electrons are generated by irradiating the mixed crystal layer with light in a state where an electric field is formed. Are trapped in the quantum box, and (b) a reverse electric field is formed so that the electron trapped in the quantum box is recombined with a hole supplied from the outside to emit light. Optical input / output method for the characterized quantum box assembly. 7. The mixed crystal layer is made of SiGe, the quantum box is made of Si or SiGe and is formed on the mixed crystal layer, and the quantum box assembly element further comprises a barrier layer covering the quantum box. The optical input / output method in a quantum box assembly element according to claim 6, wherein. 8. The light input / output method in a quantum box assembly element according to claim 7, wherein the barrier layer is made of SiO ₂ .