JP2001168353A - Optical element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical element which can convert signal of electro-magnetic wave of light, etc., to electric signal effectively. SOLUTION: A three-level system is formed on a semiconductor substrate via an insulation film by using a bonded quantized dot and an EIT layer. Since much electron is coherently activated in the system, a feeble signal inputted from an outside can be absorbed effectively all over an element. When electron is distributed to quantum level of |1> or |2>, the system forms an electric dipole. Electrical capacitance to a substrate, etc., change according to the state of the electric dipole, thus changing the value of current flowing in a substrate. Furthermore, since three-level system is in its same coherent state in the region of molecule or quantized dot, current flowing in a substrate can be detected effectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical device, and more particularly, to an optical device capable of converting an electromagnetic wave such as light into an electric signal by utilizing a unique transition of an electronic state through three energy levels. To an optical element.

[0002]

2. Description of the Related Art A novel optical device can be realized by utilizing a quantum level formed in a quantum well.

FIG. 17 is a conceptual diagram showing a state where a ground state and an excited state are formed in a quantum well. That is, as shown in FIG. 2A, in a state where no electric field is applied, a ground state | 1> and an excited state | 2> are formed in the quantum well, and electrons take one of the states. Can be.

In such a quantum well, if the energy of light incident from the outside corresponds to the energy difference between the ground state and the excited state, electrons move from the ground state | 1> to the excited state | 2>. Can transition. Moreover, as illustrated in FIG. 2B, this energy difference can be adjusted by applying an electric field to the quantum well. An optical device using such a quantum well is disclosed by A. Barenco et al. (A. Barenco et al, Phys. Rev. Lett. Vol. 74, p408).
3 (1994)).

[0005]

However, when the two states in the quantum well are used as described above, the electrons in the excited state may easily emit light and fall to the ground state. There is. For this reason, it has been difficult to maintain the distribution of electrons for a long period of time, especially in the excited state.

Further, in the case of the above-mentioned optical element, since the signal output of the electron distribution is emitted as light, it has been difficult to couple with the electronic element.

On the other hand, an optical device using a three-level system has been proposed by A. Imamogle et al.
nd RJRam, Opt, Lett. Vol. 19, 1744 (1994)).

FIG. 18 is a conceptual diagram showing the configuration of a three-level optical device. That is, the source 113 and the drain 114
Between them, a quantum well W1 having a small size and a quantum well W2 having a large size are provided. In the quantum well W1,
A ground state quantum level | 2> is formed, and a ground state quantum level | 1> and an excited state | 3> are formed in the quantum well W2.

In such a three-level optical device, by utilizing the state in which the quantum levels | 2> and | 3> are coupled across the wells, electrons can be transferred to the ground state | 1> or the ground state | 1>. State | 2>.
However, in this conventional example, electrons flow constantly to the drain side, which is not preferable from the viewpoint of power consumption.

On the other hand, a method has been proposed in which a material system having three levels is confined in a cavity having a surface having a high reflectivity so as to function as a quantum computer (T. Pellizzari et al., Phys. Rev. Lett. Vol. 75,
p3788 (1995)). In a three-level system, by confining light having a wavelength corresponding to the ground state and the first excited state or between the ground state and the second excited state in the cavity, electromagnetic waves such as light are reflected at the interface between the materials. As a result, only a standing wave having a specific frequency and wavelength can be present.
By utilizing this, the electronic states of the three-level system can be coupled electromagnetically. This standing wave is called "cavity mode". A proposal has been made to realize a three-level quantum computer using a cavity mode using semiconductor quantum dots (MS Sherwin et al., Phys. Rev. A,
Vol. 60, p3508 (1999), A. Imamoglu et a1., Phys. Re.
v. Lett. Vol. 83, p4204 (1999)).

FIG. 19 is a conceptual diagram showing the principle of this proposal. That is, the quantum dots 2 are formed on a predetermined substrate 200.
10 are provided, and are appropriately buried by a burying layer 220 using materials having different physical properties. When an electronic transition occurs inside such a quantum dot, an electromagnetic wave such as light is emitted. In this proposal, this electromagnetic wave is detected by the probe 230. As the probe 230, for example, an optical fiber having a light collecting means at the tip can be used. The wavelengths of the detected electromagnetic waves (ωa, ωb ...
Etc.) can be determined.

However, this quantum computer has the following problems.

First, since the reading of the result of the quantum calculation uses an electromagnetic wave such as light emitted from the quantum dot system, the signal detection efficiency is low.

Second, since it is necessary to form reading and reading electrodes for each quantum dot, a technique such as the use of near-field light is required, which is difficult to realize from the viewpoint of production technology. In addition to the structure, there is a problem that calculation errors and reading errors are likely to occur.

The present invention has been made based on the recognition of the above-mentioned problems, and an object of the present invention is to provide an optical element capable of efficiently converting an electromagnetic wave signal such as light into an electric signal. .

Another object of the present invention is to provide a quantum computer capable of effectively transmitting a weak signal from a quantum dot to an ordinary electronic device and capable of being manufactured by the current fine processing technology. An object of the present invention is to provide an optical element that can be realized.

[0017]

To achieve the above object, an optical device according to the present invention comprises a semiconductor substrate, a high resistance layer provided on the semiconductor substrate, and a high resistance layer provided on the high resistance layer. A detection unit having at least an energy level α, an energy level β, and an energy level γ, and a first electromagnetic wave having energy corresponding to a transition from the energy level α to the energy level β. A change in an electronic state in the detection unit due to irradiation of the detection unit with a second electromagnetic wave having an energy corresponding to the transition from the energy level γ to the energy level β is described below the high resistance layer. Wherein a change in a current flowing through the semiconductor substrate can be detected.

Here, the “high resistance layer” is a concept including a so-called insulator.

Here, the detection section has a plurality of coupled quantum dots, and each of the plurality of coupled quantum dots is
A first quantum dot on which the energy level α is formed;
The second quantum dot on which the energy level γ is formed can be configured as being separated by a barrier capable of tunneling charges.

Further, the first quantum dot and the second quantum dot
The quantum dot can have a different volume of space in which electrons are confined.

Alternatively, the detection section may be made of a material that causes an electromagnetic wave-induced transparency phenomenon.

Alternatively, the detection section has a plurality of quantum dots, and each of the plurality of quantum dots is a second and a second quantum dot different from the first substance in the quantum dots composed of the first substance. 3, the energy level α, the energy level β, and the energy level γ
And may have the following.

On the other hand, the optical element according to the present invention is characterized in that an electric field is applied to the detecting section having at least the energy level α, the energy level β, and the energy level γ, so that the energy levels α, β And γ may be further provided.

Further, different materials are provided so that a difference in refractive index occurs in at least a part of the periphery of the detecting section having at least the energy level α, the energy level β, and the energy level γ. You can also.

In the specification of the present application, “quantum dot” means
It refers to a minute material body in which charged particles are confined in a certain space to generate a discrete energy level due to a quantum size effect. Its shape is approximately spherical, hemispherical,
Examples include various shapes such as a rectangular parallelepiped shape, a pyramid shape, other polyhedral shapes, and irregular shapes.

The term “coupled quantum dot” refers to a combination of two or more quantum dots arranged close to each other,
It means that energy level coupling occurs between these quantum dots. Therefore, in a coupled quantum dot, electron transition may occur between quantum dots.

In each of the configurations described above, a signal of light input as light or electromagnetic waves can be converted as a change in electron current by utilizing the nature of the distribution of electrons in a quantum state of three or more levels.

As will be described later in detail with reference to FIG. 4, by adjusting the intensity of light A and light B in a three-level system, electrons can be freely distributed to | 1> or | 2>. The states of the electrons | 1> and | 2> have the property that they are not affected by the “variation” of the energy levels of the electrons | 3> or more.

In the state of the three-level system, since many electrons take the same state coherently, it becomes possible to effectively absorb a weak signal input from the outside over the entire device. This system forms an electric dipole when the electrons are distributed at the quantum levels | 1> or | 2>.

When such a three-level system is formed on a semiconductor substrate via an insulating film or a substance having a high resistance, the electric capacitance with the substrate changes according to the state of the electric dipole and flows through the substrate. The current value can be changed. Moreover, as described above, since the three-level system coherently takes the same state across molecules or quantum dots, the current flowing through the substrate can be efficiently detected.

[0031]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) First, the first embodiment of the present invention will be described.
As an embodiment of the present invention, an optical element that functions as a light receiving element using “coupled quantum dots” will be described.

FIG. 1 is a perspective view conceptually showing the configuration of an optical device according to the first embodiment of the present invention. That is, the light receiving element 10A of the present invention is formed on a substrate 11 such as silicon (Si),
4 and a channel portion 15 provided therebetween.

An insulating film 16 as a “high resistance layer” is provided on the channel portion 15, and a coupling quantum dot 18 is formed thereon.

FIG. 2 is a conceptual view of the coupled quantum dot 18 as viewed in plan. That is, the coupled quantum dots 18
This is a quantum dot in which a large quantum dot 18A and a small quantum dot 18B are combined. Many such quantum dot pairs are formed on the insulating film 16.

By arranging the large quantum dots 18A and the small quantum dots 18B close to each other, a three-level system can be formed.

FIG. 3 is a conceptual diagram showing a three-level system formed by the coupled quantum dots 18. That is, due to the quantum effect, an energy level | 1> and an energy level | 3> are formed in the large quantum dot 18A as shown in FIG. >
Is formed. The energy level | 1> is the energy level |
2> in terms of energy. This is because the base discrete level of the large quantum dot 18A is smaller than the base discrete level of the small quantum dot 18B.

When the large quantum dots 18A and the small quantum dots 18B are arranged close to each other as shown in FIG. 4B, the wave functions existing at these levels seep out. Coupling between the quantum wells. The result is a transition of electrons across the quantum well.

FIG. 4 is an explanatory diagram conceptually showing this transition. That is, as illustrated in the figure, in the coupled quantum dot 18, the excitation level | 3> formed in the large quantum dot is coupled to the small quantum dot 18B to form a three-level system.

In such a three-level system, light A having energy (ie, wavelength) corresponding to the energy difference between energy level | 2> and energy level | 3>, and energy level | 1> When light B having an energy (ie, wavelength) corresponding to the energy difference with the energy level | 3> is incident, electrons need to be distributed in the state | 3> due to the interference effect of the transition process between the light A and the light B. , It is possible to make a transition between the two states | 1> and | 2>.

As a result, in such a three-level system, by adjusting the intensity of light A and light B, electrons can freely move to the ground level | 1> and the first excitation level | 2>. Can be distributed. Further, the electron states of the ground level | 1> and the first excitation level | 2> are changed to the combined excitation level | 3>.
Alternatively, it is characterized in that it is not affected by a variation in electron energy level higher than that. Details of this mechanism are reported in the literature disclosed by the present inventors (K. Ichimura et al. Phys. Rev. A58, 4116 (199
8), K. Yamamoto et al., Phys. Rev. A58, P2460 (1998)
).

In this three-level system, many electrons take the same state coherently.
It becomes possible to effectively absorb a weak signal input from the outside. When electrons are distributed at the quantum levels | 1> or | 2>, the three-level system forms an electric dipole. Therefore, when the three-level system, that is, the coupled quantum dot 18 is formed on the semiconductor substrate via the insulating film 16, the electric capacitance with the substrate 11 changes depending on the state of the electric dipole, and the current flowing through the substrate is reduced. Can be changed. Moreover, as described above, since the three-level system coherently takes the same state across the quantum dots, the current flowing through the substrate is efficiently detected.

The specific example illustrated in FIG. 1 will be described. When the light A is irradiated, the electrons return to the ground level | 1>.
To the quantum dot 18 where the electron is large.
A. Therefore, the capacitance formed between the substrate 11 and the substrate 11 increases. On the contrary,
Upon irradiation with light B, the electrons are localized in the first excitation level | 2>, that is, in the small quantum dots, and as a result, the substrate 11
And the capacitance formed between them becomes smaller.

As a result of the change in the capacitance formed in the channel section 15 of the substrate 11, the current flowing between the source section 13 and the drain section 14 changes. That is, the intensity components of the irradiated light A and light B can be detected as a change in the channel current. Specifically, for example, the element illustrated in FIG. 1 is configured as a normally-off type MOSFET (Metal Oxide Semiconductor FET), and light A or light B is incident on the coupled quantum dot 18 without providing a gate electrode. Thus, a switching operation can be performed.

In the optical device illustrated in FIG. 1, electrons can be freely transferred to two levels of an energy level | 1> and a slightly higher energy level | 2> in a three-level system. It can be distributed. In this three-level system, if the energy level | 1> and the energy level | 2> are formed uniformly over the entire quantum dot, the second or more excited states, which are relatively variable, are uniformly formed. It is possible to maintain coherence over the entire quantum dot system without distribution.

The outline of the method of manufacturing the optical element 10A of the present embodiment is as follows.

First, S is formed on the substrate 11 by a thermal oxidation method.
An iO ₂ insulating film 16 is formed to a thickness of about 8 nm. next,
The insulating film 16 is selectively removed by etching in the source portion 13 and the drain portion 14 and impurities are diffused to form the source portion 13 and the drain portion 14.

Next, LPCVD (Low Pressure Chemical Vapor Deposition) is formed on the insulating film 16 left on the channel portion 15.
r Deposition: A 6 nm diameter quantum dot 18A made of silicon (Si) is formed by a reduced pressure chemical vapor deposition method. Once the substrate 11 is taken out of the LPCVD apparatus, a natural oxide film having a thickness of about 1 nm is formed on the surface of the quantum dot 18A, and a silicon quantum dot 18B having a diameter of about 4 nm is formed again by the LPCVD method. At this time, the two quantum dots 18A and 18B can be electrically coupled depending on the distance between the first formed quantum dot 18A. In this specific example, a natural oxide film having a thickness of about 1 nm formed on the surface of the quantum dot 18A has an energy level |
3> acts as a barrier that can be tunneled. Therefore, if the quantum dots 18A and 18B are adjacent to each other via the natural oxide film, they are stably coupled to each other, and the three-level system described above can be formed.

Next, a modified example of this embodiment will be described. FIG. 5 is a conceptual diagram illustrating a cross-sectional configuration of an optical element according to a modification of the present embodiment. In this figure, the same portions as those described above with reference to FIGS. 1 to 4 are denoted by the same reference numerals, and detailed description thereof will be omitted.

The optical device 10 B according to the present modification has a configuration in which an insulating film 19 and a gate electrode 20 are stacked on a coupling quantum dot 18 formed on a channel portion 15. Further, a back gate electrode 30 is formed on the back side of the substrate 11 so that a bias 32 can be applied.

The upper gate electrode structure is composed of the coupled quantum dot 1
8 is formed, an insulating film 19 made of SiO ₂ or the like is formed by a CVD method or the like.
(Indium tin oxide), tin oxide,
The translucent gate electrode 20 using indium oxide or the like is formed.

Such an optical element 20B has the gate electrode 2
By appropriately applying a voltage to 0 or 30, it is possible to adjust the amount of channel current for detecting information relating to charges localized in the coupled quantum dots. Here, in order to adjust the channel current, the upper gate electrode 20
Alternatively, only one of the gate electrodes 30 on the back side may be provided and a bias may be applied as appropriate.

In the specific examples shown in FIG. 1, FIG. 2, and FIG. 5, a configuration in which two quantum dots are arranged in a substrate plane as coupled quantum dots is exemplified, but the present invention is not limited to this. It is not something to be done. In addition, for example, quantum dots may be arranged and coupled in the vertical direction with respect to the substrate surface. Further, three or more quantum dots may be combined, and two of them may form three levels.

(Second Embodiment) Next, a second embodiment of the present invention will be described.
As an embodiment of the invention, the electromagnetic wave induced transparency phenomenon (Electric
An optical element using ally induced transparency (EIT) will be described.

FIG. 6 is a conceptual diagram showing a cross-sectional configuration of an optical device according to the present embodiment. In this figure, the same portions as those described above with reference to FIGS. 1 to 5 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In the optical device 10 C of this embodiment, an EIT layer 40 made of a material that generates EIT is formed on the insulating film 16 of the channel portion 15. Here, "EI
As illustrated in FIG. 4, “T” refers to the effect of the interference between the transition process due to light A and the transition process due to light B in a three-level system, where the electron transitions are at levels | 1> and | 2>. Is a phenomenon that occurs between For details of “EIT”, see the literatures disclosed by the present inventors (Ichihara, Yamamoto, Genma: Applied Physics Vol. 68, No. 9, (1999) p. 1021, Ichihara, Yamamoto, Genmaki:
Solid State Physics, Vol. 34, No. 8, (1999), p. 715).

Materials in which EIT occurs include Ce, Pr, Nd, P having an incomplete 4f shell among rare earth ions.
m, Sm, Eu, Gd, Tb, Dy, Ho, Er, T
The ions of elements such as m and Yb are converted to Y ₂ SiO ₅ , YAG
(Yttrium Aluminrm Garnet), YAlO ₃ , LaF _{3, and the} like.

In such a crystal, a three-level system illustrated in FIG. 4 is formed. Therefore, such an EIT
Providing layer 40 on the FET structure causes a varying FET structure capacitance effect on the charge distribution within the crystal and reduces the electron levels in EIT layer 40, as described above with respect to the first embodiment. Can be detected. In a solid-state EIT crystal, since coherence in the crystal is maintained, electrons are distributed to either the energy level | 1> or the energy level | 2> throughout the crystal. Therefore, even a weak signal can be observed as a change applied to the channel current of the entire EIT layer 40 using only each dipole.

Also in this embodiment, the gate electrode 20 or the back gate electrode 30 as illustrated in FIG.
Can be provided in the same manner to obtain the same effect.

(Third Embodiment) Next, a third embodiment of the present invention will be described.
As an embodiment of the present invention, a description will be given of an optical device in which the operating wavelength is changed by applying an electric field to the coupled quantum dots.

FIG. 7 is a conceptual diagram showing an optical device according to this embodiment. That is, FIG. 1A is a conceptual diagram showing the plane configuration, FIG. 2B is a conceptual diagram showing a part of the AA line cross-sectional configuration, and FIG. 1C is a conceptual diagram showing the equivalent circuit of the quantum dot. is there.

In the optical element 10D of the present embodiment, control electrodes 42 are formed at predetermined intervals on the surface of the channel portion of the substrate 41. Then, a coupling quantum dot 44 is formed on the substrate, an insulating layer 46 is formed so as to cover this, and a transparent gate electrode 48 is further laminated on the surface thereof. A source region 53 and a drain region 54 are formed on both sides of the channel portion. The source region 53 and the drain region 54 may be formed separately from each other as shown in the figure, and may be commonly connected by wiring.

The substrate 41 has a structure in which a conductive region 41A is buried with an insulating burying layer 41B. Such a structure is, for example, SOI (silicon on insulator)
It can be formed by adding a predetermined buried insulating region to a wafer or the like. The electrode 42 is formed by depositing Al (aluminum) or Cu (copper) on the substrate,
It can be formed by patterning by dry etching or the like. Further, the coupling quantum dots 44 can be, for example, Si quantum dots formed by an LPCVD method or the like.

In this embodiment, a plurality of control electrodes 4
By applying a voltage between the two, the coupled quantum dots 44
An electric field can be applied. That is, by dividing the formation region of the quantum dots 44 into several parts and forming the control electrodes 42 between these divided regions, the potential profile of the quantum dots 44 is changed by the electric field applied between these electrodes 42. Can be changed.

FIG. 8 is a conceptual diagram showing a change in potential of a coupled quantum dot due to application of an electric field. FIG.
When an electric field is applied to the coupled quantum dots as shown in FIG. 4B, the potential between the quantum dots changes according to the intensity as compared to the state where no electric field is applied as shown in FIG. In the figure, it is illustrated that the energy interval between the states | 2> and | 3> changes depending on the application of an electric field.
In this case, the application direction of the electric field and the coupling quantum dots 44A,
The orientation of the 44B array must match. That is, as illustrated in FIG.
The control electrode 42 is formed so that an electric field is applied along the arrangement direction of A and 44B.

As shown in FIG. 7C, the capacitance between the quantum dots 44A, 44B and the channel portion 41A through which the current flows differs depending on the size of the quantum dots. This is because the electric field effect varies depending on the state of the charges spatially distributed in the quantum dot depending on the size of the quantum dot. Then, as described above with respect to the first embodiment, the substrate 41A
The current flowing through changes.

FIG. 8 illustrates three levels in the quantum well formed in the conduction band. Such three levels may be three levels formed in the valence band. It may straddle the body and the valence band. Further, any impurity level formed in a semiconductor such as a band gap or an interface may be used.

FIG. 7 (a) shows an example in which eight sets of coupled quantum dots 44 are provided in one divided area. However, the present invention is not limited to this. The number can be determined as appropriate. In addition, these quantum dots may be Ge (germanium) or SiGe.

Further, in addition to the specific example shown in FIG. 7, the positional relationship between the control electrode 42 and the substrate 41 may be formed in the same oxide film 46 as the quantum dots.
6 may be formed. Further, the substrate 41 may be embedded and formed.

FIG. 7 shows a case where two quantum dots are combined in the horizontal direction. However, a combination quantum dot in which three or more quantum dots are combined may be used.

FIG. 9 is a conceptual diagram showing such a combined quantum dot composed of three quantum dots. As shown in FIG. 3A, when three quantum dots 44A to 44C having different sizes from each other are formed close to each other, they act as coupled quantum dots. Then, as shown in FIG. 3B, electrons can be transferred between the quantum dots, and can be used as a three-level coupled quantum dot.

Next, a modified example of this embodiment will be described. FIG. 10 is a conceptual diagram illustrating a more generalized configuration of the optical element illustrated in FIG. That is, FIG. 10 shows an optical element 10E in which quantum dots are formed more randomly while maintaining the idea of the present embodiment that the potential profile of the quantum dots is changed by the control electrode.

Si oxide film 41B formed on Si substrate
On top of that, when quantum dots of silicon are formed at random by a method such as LPCVD, when the density of the formed quantum dots is high, or when the quantum dots are formed several times with several different materials, In such a case, only a quantum dot system having an energy level difference corresponding to the frequency of an electromagnetic wave such as incident light can be reacted.

The control electrodes 42A and 42B illustrated in FIG.
Since the directions of the quantum dots to be coupled are different, by installing the quantum dots vertically and horizontally with respect to the substrate surface, it becomes possible to control more quantum dots with an electric field. In the same figure, the dotted line indicates that the control electrode is buried under the quantum dot via an oxide film.

As described above, even when the quantum dots have a random arrangement or size, it is possible to change the transition energy between the levels in a predetermined coupled quantum dot system according to the direction of application of the electric field.

(Fourth Embodiment) Next, a fourth embodiment of the present invention will be described.
As an embodiment of the present invention, an optical element for forming a cavity mode by stacking quantum dots will be described.

FIG. 11 is a conceptual diagram showing a cross-sectional configuration of a main part of an optical device according to the present embodiment. That is, the optical element 10F of the present embodiment has a Si-doped GaAs layer 62, a non-doped GaAs layer 63, an AlGa
An As layer 64 is stacked in this order, and Ga layer is further formed thereon.
A layer in which InAs quantum dots 65A embedded in the As layer 66 are arranged is provided, and a layer in which InAs quantum dots 65B embedded in the GaAs layer 66 are arranged is provided thereon. In the figure, the quantum dots 65
The case where the size of A is larger than the quantum dot 65B has been illustrated.

On the stack of quantum dots 65A and 65B, a Si-doped GaAs layer 67 and an AlGaAs layer 68 are further stacked, and confinement regions 69 are formed at both ends of these stacks. Then, electrodes 70 and 71 are provided on the element.

The GaAs layer 62 on the GaAs substrate 61, A
The lGaAs layer 63 and the like are, for example, MBE (molecular be
am epitaxy) method and MOCVD (metal-organic chemical)
It can be formed by a vapor deposition method or the like. Then, quantum dots 65 of InAs are formed using a growth mode called SK (Stranski-Kranstanov) mode. Further, these quantum dots are embedded in the GaAs layer 66, and an upper quantum dot 65 is formed thereon.
The GaAs layer 66 is buried.

In this specific example, the quantum dots 65A and 65B are stacked in the stacking direction of the quantum dots, that is, vertically.
Between them form coupled quantum dots. The assembly of quantum dots coupled in the vertical direction in this way is divided into a plurality of regions in a plane, and electrodes (for example, 70, 71, etc.) are respectively provided.
Is provided. Further, the Si-doped GaAs layer 67 functions as a layer for supplying charges to these coupled quantum dots.

The optical device shown in FIG. 11 further separates the quantum dot system from the material system containing the quantum dot system, and uses the electronic state of the quantum dot system as a cavity corresponding to the energy level difference in the quantum dot. In order to confine the device with probability, the devices are separated by a confinement region 69 made of a material having a different refractive index from the material surrounding the quantum dots (here, the GaAs layer 66). Thereby, a cavity mode can be formed between the quantum dots. As a material of the confinement region 69, for example, a metal such as Nb (niobium), Al (aluminum), Hf (hafnium), SiN (silicon nitride), Ti (titanium) oxide, or the like can be used.

The medium surrounding the quantum dot system 65 may be a gas such as air or a vacuum instead of the GaAs layer 66. Further, the lower quantum dots 65A may have a smaller size than the upper quantum dots 65B.

FIG. 12 is a conceptual sectional view showing a first modified example of the optical device of this embodiment. FIG.
The same reference numerals are given to the same elements as those described in (1), and the detailed description thereof will be omitted.

In the optical device 10G of this modified example, three or more quantum dots 65A, 65B, 65C... Are laminated, and the coupling quantum dots 65 are formed in the laminating direction. Then, any one of the three or more quantum dots formed in the valence band or the conduction band in the three or more quantum dots thus combined.
Use transitions between two levels. The sizes of the coupled quantum dots coupled in the stacking direction may be the same or different. When the sizes are different from each other, a transition between levels different from each other can be used for each dot.
On the other hand, when the sizes of the coupled quantum dots are the same, the energy level is split into a plurality of levels according to the number of coupled quantum dots. The transition between levels due to this fine structure can be used.

As in the case of the optical device shown in FIG. 11, the devices are separated by a confinement region 69 made of a material having a different refractive index from the material surrounding the quantum dots (here, the GaAs layer 66). Can form a cavity mode. As described above, the material surrounding the quantum dots may be air.

FIG. 13 is a conceptual sectional view showing a second modified example of the optical device of the present embodiment. FIG.
The same reference numerals are given to the same elements as those described in (1), and the detailed description thereof will be omitted.

In the optical device 10H of this modified example, a DBR (Dist) having a high reflectivity corresponds to the confinement region 69 in the optical devices 10F and 10G described above.
A ributed Bragg reflector structure 75 is provided.

When the energy level difference in the coupled quantum dot 65 is on the order of eV (electron volt), the wavelength as the cavity mode is shortened, and a series of quantum dots distributed in a range of about several microns is divided into GaAs.
It is possible to form a DBR structure 75 having a total of about 20 pairs of stacks by using the s layer 75A and the AlGaAs layer 75B as one pair.

The same DBR can be applied to the optical device shown in FIG.

FIG. 14 shows an optical device in which three or more quantum dots are coupled in the vertical direction as shown in FIG.
It is a conceptual sectional view showing the example provided with 75. DBR7
By forming 5, it is possible to confine the cavity mode in the coupled quantum dot 65 with high reflectance.

As the DBR described above, Ga
In addition to the stacked structure of the As layer and the AlGaAs layer, various configurations in which two or more layers having different refractive indexes are repeatedly stacked can be used.

On the other hand, the combination of the quantum dot and the base for forming the quantum dot in the present invention is GaN.
(Quantum dot) / AlGaN, InGaN (quantum dot) / GaN, AlInAs (quantum dot) / AlGa
As, InAs (quantum dot) / GaN, InAs (quantum dot) / AlGaAs, InAs (quantum dot) /
AlAs, GaAs (quantum dot) / AlGaAs, G
aAs (quantum dot) / AlAs, GaSb (quantum dot) / AlGaAs, InSb (quantum dot) / AlG
aAs, AlSb (quantum dot) / AlGaAs, Pb
Se (quantum dot) / PbEuTe and the like can be mentioned. In these chemical formulas, detailed component ratios of each element are omitted.

Further, various other III-V group systems, II-V
Group I material, IV-VI group material, group IV material and the like quantum dots,
It can be used as appropriate for one or both of the bases. For example, ZnS, ZnSe, ZnTe, CdS, CdSe, Cd on a GaAs substrate or a Si substrate
Te, HgCdTe, HgS, HgSe, HgTe, etc. may be used as the quantum dots.

On the other hand, the combinations of the material systems listed above can be applied to the DBR. That is, the DBR can be formed by stacking the above combinations as a pair for a predetermined period.

(Fifth Embodiment) Next, a fifth embodiment of the present invention will be described.
As an embodiment of the present invention, a specific configuration of a coupled quantum dot that can be used in the present invention will be described.

FIG. 15 is a conceptual diagram showing a method of forming coupled quantum dots. First, as shown in FIG. 2A, the first quantum dots 80 are formed of, for example, silicon (Si).
For example, it is formed on a substrate such as SiO _{2 (} not shown). Then, boron (B) or phosphorus (P) is ion-implanted or the like.
A second impurity such as 80A is implanted.

Further, as shown in FIG.
Is implanted. At this time, the first impurity 8
0A and the second impurity 80B, the first impurity
A three-level system can be formed in combination with the levels formed by the second and third impurities in the quantum dot 80.

Here, the material of the first quantum dot is, for example, GaN, InGaN, AlInAs, In, in addition to Si (silicon) and germanium (Ge).
As, GaAs, GaSb, InSb, AlSb, etc.
Various compounds such as III-V compounds and other II-VI compounds can be used.

The second and third impurities to be implanted include C, Si, Ge, Sn, Pb, Be, Ca, Sr,
Ba, Ra, Zn, Cd, Hg, Mg, C, Se, T
Various elements such as e and Po can be used.

Also, ZnS, ZnSe, ZnTe, Cd
S, CdSe, CdTe, HgCdTe, HgS, Hg
N (nitrogen), Cl, etc. are added to quantum dots such as Se and HgTe.
(Chlorine), As (arsenic) or the like may be appropriately doped.

FIG. 16 is a conceptual diagram showing the cross-sectional structure of another coupled quantum dot of the present invention. In the coupled quantum dot shown in the figure, a layer 92 made of a second material is provided around a first quantum dot 90 made of a first material, and a layer 94 made of a third material is provided therearound. I have.

The forming process is as follows. That is, first, the first quantum dots 90 are formed on the substrate S made of, for example, SiO2. As a material of the quantum dots 90, for example, silicon or the like can be used, and as a formation method thereof, for example, LPCVD or the like can be used.

Next, a second layer 92 is formed by forming a natural oxide film or the like on the surface of the quantum dot 90.
Further, concentric coupling quantum dots can be formed by forming the layer 94 made of the same material as the first material, such as silicon or another material, such as germanium.

The first to third materials can be appropriately selected from the aforementioned III-V group, II-VI group or other various materials and combined.

The material of the quantum dots may be a π-electron organic compound. For example, a high molecular compound such as polyacetylene or polyaniline, a carbon fiber or a pyrene-based compound, or a dye such as a triphenylamine derivative or Alq3 can be used.

The embodiments of the present invention have been described with reference to the examples. However, the present invention is not limited to these specific examples.

For example, in the specific example described above, the portion of the field effect element is formed by using silicon (Si), but other than this, for example, germanium (Ge),
The field effect element portion can be formed using various materials such as a III-V compound semiconductor such as GaAs, a II-IV compound semiconductor, or other various compound semiconductors.

In the above-described specific example, only three levels have been described for the sake of convenience. However, a high energy level including an auxiliary excitation level and an energy level having a small transition probability are formed. May be. That is, it is only necessary that three or more of three or more levels cause transition of electrons or holes.

Further, in each of the above-described embodiments, an external electric field, an external magnetic field, an external stress field or other various external fields are applied to the coupled quantum dot system or the EIT crystal material to change the energy difference between the levels. You can also. In this way, the wavelength of the light to be detected can be adjusted.

In each of the specific examples described above, the case where a source electrode, a drain electrode, or a gate electrode is provided as an electrode has been described. Another electrode for controlling the energy interval of three levels may be provided on the upper or side surface of the level system or on the back surface of the substrate. This makes it possible to adjust the wavelength of the light to be detected.

Further, in the above-described specific example, only a single element having one source / drain is illustrated. However, a plurality of such elements are arranged, and an electrode or the like connected to a word line and a bit line is provided. Alternatively, they may be integrated by being combined with.

The planar shape of the optical element as exemplified in FIGS. 7A and 10 is not limited to a rectangular shape, but may be various shapes such as a polygonal shape, a circular shape, and an elliptical shape.

Further, regarding the fourth embodiment, in order to form a cavity mode that couples the coupled quantum dot system in an electromagnetic field, FIGS. 11 and 12 show a metal such as Nb or Al, or an oxide of SiN or Ti. Although a material having a different refractive index from the material surrounding the quantum dots such as hafnium, or air, and a configuration in which a DBR structure is formed in FIGS. 13 and 14 are illustrated, the same applies to the first to third embodiments. The cavity mode can be formed by the method described above.

In the third embodiment, the configuration using quantum dots of silicon (Si) is illustrated, and in the fourth embodiment, a configuration using a material system other than Si is illustrated. It can be appropriately selected from various types. In addition, the electrode may be placed on the quantum dot with respect to the substrate in the Si quantum dot system, or the electrode structure may be placed in the same material as the quantum dot or in a place closer to the substrate in a material system other than Si. It does not matter. Further, quantum dots of Si and Ge may be formed on an amorphous film.

Further, in the optical device of the present invention, when quantum computation is performed, a stationary magnetic field and an electric field or a time-varying magnetic field and an electric field may be applied from electrodes other than the electrodes exemplified in each embodiment. .

[0116]

As described in detail above, according to the present invention,
By constructing two quantum states forming an electric dipole from three or more quantum states, it is possible to realize two stable quantum states, which were conventionally impossible, with good controllability.

Further, according to the present invention, the charge distribution state in the two separate quantum states can be converted into an electric signal flowing through the substrate as a field effect. That is, since the electric charge at the quantum level forming the electric dipole can be controlled by electromagnetic waves such as light, it is possible to provide an element that can effectively convert an incident signal of light or electromagnetic waves into an electric signal.

[Brief description of the drawings]

FIG. 1 is a perspective view conceptually showing a configuration of an optical element according to a first embodiment of the present invention.

FIG. 2 is a conceptual view of a coupled quantum dot 18 as viewed in a plane.

FIG. 3 is a conceptual diagram showing a three-level system formed by coupled quantum dots 18;

FIG. 4 is an explanatory diagram conceptually showing an electron transition in a three-level system.

FIG. 5 is a conceptual diagram illustrating a cross-sectional configuration of an optical element according to a modification of the first embodiment of the present invention.

FIG. 6 is a conceptual diagram illustrating a cross-sectional configuration of an optical device according to a second embodiment of the present invention.

FIG. 7 is a conceptual diagram illustrating an optical device according to a third embodiment of the present invention. More specifically, FIG.
FIG. 2B is a conceptual diagram showing a part of the cross-sectional configuration along the line AA, and FIG. 2C is a conceptual diagram showing an equivalent circuit of the quantum dot.

FIG. 8 is a conceptual diagram illustrating a change in potential of a coupled quantum dot due to application of an electric field.

FIG. 9 is a conceptual diagram illustrating a combined quantum dot including three quantum dots.

10 is a conceptual diagram illustrating a more generalized configuration of the optical device illustrated in FIG. 7;

FIG. 11 is a conceptual diagram illustrating a cross-sectional configuration of a main part of an optical element according to a fourth embodiment of the present invention.

FIG. 12 is a conceptual sectional view illustrating a first modified example of the optical element according to the fourth embodiment of the present invention.

FIG. 13 is a conceptual sectional view showing a second modified example of the optical device according to the fourth embodiment of the present invention. same

14 is a conceptual cross-sectional view illustrating a specific example in which a DBR 75 is provided in an optical element in which three or more quantum dots are coupled in a vertical direction as illustrated in FIG.

FIG. 15 is a conceptual diagram illustrating a method for forming a coupled quantum dot of the present invention.

FIG. 16 is a conceptual diagram illustrating a cross-sectional structure of another coupled quantum dot of the present invention.

FIG. 17 is a conceptual diagram showing a state where a ground state and an excited state are formed in a quantum well.

FIG. 18 is a conceptual diagram illustrating a configuration of a conventional three-level FET type device.

FIG. 19 is a conceptual diagram showing a conventional quantum dot detection system.

[Explanation of symbols]

 10A to 10I Optical element 11, 41 Substrate 13, 53 Source part 14, 54 Drain part 15 Channel part 16 Insulating film 18, 44 Coupling quantum dot 18A, 18B, 44A, 44B, 44C Quantum dot 19 Insulating film 20 Gate electrode 30 Back surface Gate electrode 32 Bias 40 EIT layer 42, 42A, 42B Control electrode 46 Oxide film 48 Transparent thin film electrode 61 GaAs substrate 62 Si-doped GaAs layer 63 Non-doped GaAs layer 64 AlGaAs layer 65 Quantum dot 66 GaAs layer 67 Charge supply layer 68 AlGaAs layer 70 , 71 electrode 75 DBR 80, 90 quantum dot

Claims (5)

[Claims] 1. A detection device comprising: a semiconductor substrate; a high-resistance layer provided on the semiconductor substrate; and at least an energy level α, an energy level β, and an energy level γ provided on the high-resistance layer. A first electromagnetic wave having energy corresponding to the transition from the energy level α to the energy level β and energy corresponding to the transition from the energy level γ to the energy level β. A change in the electronic state of the detection unit due to the irradiation of the detection unit with the second electromagnetic wave having the second electromagnetic wave can be detected as a change in a current flowing through the semiconductor substrate below the high-resistance layer. Optical element. 2. The detection section has a plurality of coupled quantum dots, each of the plurality of coupled quantum dots is a first quantum dot on which the energy level α is formed, and the energy level γ. 2. The optical device according to claim 1, wherein the second quantum dot on which the is formed is separated from each other by a barrier capable of tunneling charges. 3. The detection section has a plurality of quantum dots, and each of the plurality of quantum dots is a second and a third quantum dot made of a first substance, which are different from the first substance. 2. The optical device according to claim 1, wherein the energy level α, the energy level β, and the energy level γ are provided by respectively containing the three substances. 4. A relative relationship among the energy levels α, β, and γ by applying an electric field to the detection unit having at least the energy levels α, β, and γ. The optical element according to any one of claims 1 to 3, further comprising an electrode for changing the value. 5. A method according to claim 1, wherein a different material is provided so as to cause a difference in refractive index in at least a part of a periphery of said detecting section having at least said energy level α, said energy level β and said energy level γ. The optical device according to any one of claims 1 to 4, wherein the optical device is an optical device.