JP2014049661A - Semiconductor quantum device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor exciton system which is available as a semiconductor quantum device for a quantum computer and in which Bose-Einstein condensate is performed within a macro region.SOLUTION: A semiconductor quantum device 1 comprises a semiconductor hetero interface which is constituted in the order of a semiconductor I2, a semiconductor II3, a semiconductor III4, and a semiconductor IV05, and an exciton comprised of quantum levels of electrons and positive holes in a triangular potential formed by applying an electric field is used for a semiconductor hetero structure including a staggered hetero interface, thereby reducing influences of hetero interface roughness upon the exciton. Further, by using a substrate for which an orientation of a GaAs substrate where AlGaAs/AlAs staggered hetero interface is grown is made off from (100) to 23.8°, the staggered hetero interface grown thereon is made into super flat surface and decoherence of the exciton in which Bose-Einstein condensate is performed is reduced, thereby obtaining a semiconductor quantum device 1 of which the computing time is long.

Description

  The present invention relates to a semiconductor quantum device using a macroscopic quantum effect caused by Bose Einstein (B-E) condensation of Bose particles. More specifically, the present invention relates to a semiconductor quantum device in which excitons in a triangular potential generated by applying an electric field to a semiconductor heterostructure are B-E condensed.

  Neumann computers have dramatically improved their computing capabilities as semiconductor processing miniaturization technology has progressed according to Moore's Law for a long time. However, miniaturization is approaching the limit, and the individual elements forming the VLSI start to be affected by quantum fluctuations, and the power consumed when many computers are parallelized in order to increase computing power. Due to the enormous volume, further capacity building is approaching its limits.

  On the other hand, the newly proposed quantum computer uses a superposition (quantum entanglement) between quantum states as a calculation method based on a completely new algorithm, which makes it difficult for a Neumann computer to solve. Can be solved instantly, and many researchers have proposed and experimented with a system that realizes it.

In the BE condensed state of the Bose particle, the thermal de Broglie wavelength of the particle becomes longer as the temperature becomes lower, and the waves overlap each other, so that the entire system becomes a coherent state. Since the thermal de Broglie wavelength is inversely proportional to the half power of the product of the mass and temperature of the Bose particle, it is necessary to cool the heavy mass to the nano Kelvin order.
The BE condensation of Rb atoms, which was awarded the Nobel Prize in Physics, required a cryogenic temperature of 170 nK because the atoms were heavy (see Non-Patent Document 1). In order to obtain such an extremely low temperature, cooling by a laser and cooling by a magnetic field are necessary. To realize a large number of bits like the quantum computer described in Patent Document 1, the apparatus is too large and practical. Is difficult.

  On the other hand, excitons in semiconductors are quasiparticles in which electrons and holes are attracted to each other by Coulomb force, become like hydrogen atoms, and can move freely around the semiconductor, and recombine with a finite lifetime. Bose particles that emit light and disappear, and their mass is about 1 / 1,000,000 lighter than atoms. Therefore, the temperature required for condensation is one million times higher than that of atoms.

  Therefore, since Keldysh theoretically showed the possibility of B-E condensation of excitons in 1965, many researchers have been working on the world's first “observation of B-E condensation”. However, many of the exciton systems that have been studied in the past often have short lifetimes of recombination luminescence, and are extinguished before being cooled to the lattice temperature from a state of being optically excited and having a high electron temperature, Exciton BE condensation could not be realized for many reasons, such as the disappearance of the Bose particle system and formation of exciton molecules because electrons and holes are in droplets by high-density excitation.

  In addition, a cuprous oxide bulk crystal with a long exciton lifetime has poor cooling efficiency, and the exciton cannot be cooled sufficiently, or the exciton diffuses spatially to obtain the concentration required for BE condensation. I could not. In 2011, it was reported that BE condensate was achieved by spatially confining excitons in a cuprous oxide bulk crystal using laser light and cooling to 287 mK (see Non-Patent Document 2). ). However, in this system, the condensate is only a part of light confinement, and it is industrially difficult to realize a large number of qubits necessary for a quantum computer.

As a solution to overcome these difficulties related to exciton BE condensation, Fukuzawa, one of the inventors of this application, announced in 1989 that "exciton system consisting of electrons and holes separated in space in a double quantum well". Proposed (see Non-Patent Document 3).
FIG. 21 is a conceptual diagram of an exciton electronic state of an exciton system composed of electrons and holes separated in space in this double quantum well. In FIG. 21, reference numeral 303 denotes an electron wave function of the exciton system, and 304 denotes a hole wave function, both of which are obtained by numerical analysis, and are obtained by applying an electric field to tilt the conduction band 301 and the valence band. 302 is displayed in an overlapping manner. This double quantum well uses 5 nm thick GaAs as the quantum well and 4 nm thick Al _0.3 Ga _0.7 As as the barrier between the quantum wells. When photoexcitation is performed in the state where an electric field is applied to a double quantum well constituting this system, electrons are excited from a value electron band 302 to a conduction band 301 in each of the two quantum wells, and electrons and holes are respectively However, since the barrier between the two quantum wells is sufficiently thin as 4 nm, electrons and holes are tunneled to the lower quantum well by the electric field, resulting in the electrons 303 and the holes. 304 are separated into separate quantum wells.

As a result, the overlap integral of the wave function of electrons and holes is reduced, the emission lifetime of the exciton is increased by about 100 times, and the exciton can be sufficiently cooled to the lattice temperature. As a result, for the first time, the behavior of cryogenic excitons can be experimentally observed (see Non-Patent Document 4).
FIG. 24 is a plot of the electric field that applies the temperature dependence of the half width of the photoluminescence spectrum of this double quantum well exciton system as a parameter. In FIG. 24, the temperature dependence 305 when the electric field is not applied increases the half-value width as the temperature decreases, but the temperature dependence 306 when the electric field is applied to extend the exciton lifetime is 7K. A sharp decrease in the half-width was observed at lower temperatures. The interpretation of the temperature dependence of the half width in the photoluminescence spectrum shown in FIG. 24 will be described later.

  In this system, the quantum well in which electrons and holes are separated is uniquely determined by the direction of the electric field, so that the directions of the electric dipoles of all excitons are aligned. For this reason, the interaction between Bose particles is an interaction between dipoles, and unlike the Coulomb interaction between electrons, until the Bose particle is closest, it is a repulsive force close to neutral, so BE condensation is likely to occur. I can say that. In addition, since the electric dipoles are aligned, they are unlikely to form exciton molecules or electron / hole droplets, and this is also a suitable system for BE condensation.

  However, this system has four interfaces between GaAs, which is two quantum wells, and AlGaAs, which is a barrier layer. Al composition fluctuation is inevitable. In the two-dimensional plane, the combination of the thickness of each quantum well and the thickness of the intermediate barrier layer due to fluctuation is different from the place where the excitons exist, and the different combinations give different exciton energies. As a result, different exciton energy distribution in the two-dimensional plane is observed as the non-uniform width of the emission spectrum up to 20 meV. FIG. 25 is an example in which the two-dimensional in-plane roughness 307 of exciton energy is modeled by calculation in accordance with the experimentally obtained non-uniform width.

  Therefore, the minimum exciton energy differs depending on where the excitons of the double quantum well system exist in the two-dimensional space. Even if the lattice temperature is cooled to a temperature much lower than the temperature at which BE condensation can be expected in a small region, the exciton energy differs in other places.・ Independent local condensation occurs at many local minimums caused by roughness.

Fukuzawa, one of the inventors of the present application, conducted an experiment after predicting that the double quantum well excitons proposed in Non-Patent Document 3 have such problems by theoretical calculation. 4 clarified the situation evidence that the double quantum well excitons cause BE condensation.
The temperature dependence of the photoluminescence half-width of the double quantum well excitons indicated by 306 in FIG. 24 is as follows: “The sites where each BE condensate exists due to induction cooling of the BE condensate generated in each local minimum. Continued to move to a site with a lower exciton energy than the energy of, and eventually all excitons present in the system were filled in order from the lowest of the sites present in the system. The result was able to be interpreted as “a state.”
Here, induction cooling is the state of a classical Bose particle that has not undergone BE condensation, and the exciton trapped in the potential barrier due to low thermal energy becomes a BE condensate when the temperature is lowered. This is the phenomenon that BE condensate moves to a lower energy site as if it were over the potential barrier despite the lack of thermal energy.

  If the temperature is higher than the temperature at which B-E condensation occurs, it is in the state of a classical Bose particle, and as the thermal kinetic energy of excitons decreases, it becomes impossible to overcome the local minimum barrier. This increases the proportion of high energy local minimums while leaving lower energy sites vacant, thus increasing the average energy of the entire exciton, which is opposite to the previous result of inductive cooling. This is shown (see 305 in FIG. 24). From the above results, it is considered that the proof of the situation that double-well excitons caused BE condensation was obtained.

LVButov, who has continued to study this system since 1992, is that Fukuzawa's double quantum well exciton system, one of the inventors of this application, is the most suitable system for observing the BE condensation of excitons. Many papers have been reported on various physical phenomena of double quantum well excitons at low temperatures. In 2012, LVButov published a result showing BE condensation of double quantum well excitons (see Non-Patent Document 5).
FIG. 26 shows the temperature dependence of the spatial distribution of double quantum well excitons obtained from the emission intensity measured two-dimensionally. Like Fukuzawa, one of the inventors of the present application, electrons and holes are separated by an electric field to extend the lifetime of recombination emission of excitons, and the lattice temperature is cooled to a sufficiently low temperature.
In FIG. 26, when the temperature of the double quantum well system is 7K, the excitons have a spatial expansion as shown at 308, but at 4K, the excitons start to gather at the center as 309, and at 50 mK, as 310. More concentrated on the center.

  FIG. 27 is a diagram illustrating the spatial dependence of the degree of first-order coherence of exciton emission. The lattice temperature is used as a parameter. This shows that the state of high first-order coherence of exciton emission spreads spatially with decreasing temperature. First-order coherence is known to increase as the proportion of B-E condensation increases, and the results shown in FIG. 27 strongly suggest that excitons are causing B-E condensation. As proposed by Fukuzawa, one of the inventors of the present application, after 20 years, it was proved that the double quantum well exciton system undergoes B-E condensation. However, as described above, the roughness of the exciton energy based on the four heterointerfaces exists, so that only BE condensation in a very narrow region that happens to be flat can be realized, which is necessary for a quantum computer. The BE condensation in the region has not been realized even in this known example.

FIG. 28 is a diagram reported in Non-Patent Document 6 and is a conceptual diagram of exciton energy levels due to X-Γ indirect transition in a GaAs / AlAs quantum well structure.
After Fukuzawa proposed a double quantum well exciton system, LVButov et al. Proposed a GaAs / AlAs quantum well system as another system that can separate electrons and holes and extend the recombination emission lifetime of excitons. We have reported the exciton of Γ-X indirect transition in.
This is a system having a structure in which a GaAs quantum well 403 having a thickness of 3 nm and an AlAs quantum well 404 having a thickness of 4 nm are sandwiched between AlGaAs, as shown in FIG.
In the figure, a solid line 400 is a conduction band representing the Γ band of the AlGaAs / GaAs / AlAs / AlGaAs heterostructure, and a dotted line 401 is a conduction band representing the X band of the AlGaAs / GaAs / AlAs / AlGaAs heterostructure. The solid line 402 is the Γ band valence band of the AlGaAs / GaAs / AlAs / AlGaAs heterostructure.

In FIG. 28, since the Γ band and the X band are written in an overlapping manner, the Γ band and the X band are separately displayed in FIGS. 29 and 30 for easier understanding.
FIG. 29 shows a conduction band by the Γ band of the AlGaAs / GaAs / AlAs / AlGaAs heterostructure of FIG. In the figure, 410 is an AlGaAs layer, 411 is a GaAs layer, 412 is an AlAs layer, and 413 is an AlGaAs layer. Since the GaAs layer 411 becomes a quantum well, a quantum level 406 is provided by a well-type potential.

  FIG. 30 shows the conduction band by the X band of the AlGaAs / GaAs / AlAs / AlGaAs heterostructure of FIG. In the figure, 410 is an AlGaAs layer, 411 is a GaAs layer, 412 is an AlAs layer, and 413 is an AlGaAs layer. Since the AlAs layer 412 becomes a quantum well, a quantum level 407 is provided by a well-type potential.

It is well known that when the width of the quantum well is narrowed, the electron level due to the well-type potential shifts to the high energy side, but in the heterostructure shown in FIG. 28, the thickness of the GaAs quantum well is narrowed to 3 nm. By doing so, the quantum level 406 in the Γ band 400 of GaAs can be made higher than the quantum level 407 in the X band 401 of AlAs.
Therefore, when this structure is photoexcited, only electrons out of the electron-hole pairs generated by light absorption in the GaAs quantum well (Γ-Γ transition) from the quantum level 406 of GaAs to the quantum level in the X band of AlAs. Move to 407. As a result, holes in GaAs and electrons in AlAs can be spatially separated. In the figure, reference numeral 405 denotes exciton emission based on an indirect transition between the electron level 407 in the X band of AlAs and the hole level in the X band of GaAs. Since this transition has a small overlap integral between electrons and holes, the emission lifetime is increased, and the exciton temperature can be sufficiently lowered.

In addition, a hole is formed in the electrode to which an electric field is applied in the same system as in Non-Patent Document 6 above, and a relatively weak portion is formed in the two-dimensional plane with respect to the electric field strength felt by the exciton, and the exciton is electrically connected there. A method of trapping is described (see Non-Patent Document 7). This method is suitable for making excitons with light.
However, in both systems of Non-Patent Document 6 and Non-Patent Document 7, in order to make the energy of the quantum level 406 in the Γ band of GaAs higher than the quantum level 407 in the X band of AlAs, The well width needs to be as narrow as 3 nm. Also, the X band level of AlAs is based on a quantum well as narrow as 4 nm. Therefore, as in the case of double quantum well excitons, the excitons feel strongly the influence of fluctuations at the heterointerface, and the breakdown of BE condensation due to potential roughness is inevitable.

The BE condensation of excitons and polaritons in a semiconductor optical resonator has been studied as a Bose particle system that is not easily affected by the potential and roughness of excitons. Excitons and polaritons are light in a semiconductor, and the mass as a Bose particle is about 1 / 1,000,000 that of an exciton. For this reason, although it is theoretically possible to condense at a temperature one million times higher than that of excitons, the reported BE condensation temperature of excitons and polaritons is currently 10 K (see Non-Patent Document 8). The BE condensation of excitons and polaritons is very advantageous in that it is not affected by potential and roughness and the condensation temperature is high, and research is currently being conducted as an element for quantum computers (see Patent Document 2).
However, excitons and polaritons have a very short lifetime, on the order of picoseconds, and are difficult to use as quantum computers.

JP 2006-59277 A Special table 2012-508990 gazette

M.H. Anderson, J.R.Ensher, M.R.Matthews, C.E.Wieman, and E.A.Cornell, "Observation of Bose-Einstein Condensation in a Dilute Atomic Vapor", Science, 269, no 5221, pp. 198-201, 1995 K. Yoshioka, E. Chae and M. Kuwata-Gonokami, "Transition to a Bose-Einstein condensate and relaxation explosion of excitons at sub-Kelvin temperatures", Nature Comm., 2, Article numB-Er: 328, 31 May 2011 T. Fukuzawa, S.S. Kano, T.K.Gustafson and T. Ogawa, "Possibility of Coherent Light Emission from Bose Condenced States of SEHP", Proc. Of International Conference on Modulated Semicomductor Structures, Michigan, Illinois, 1989 T. Fukuzawa, E. E. Mendez, and J. M. Hong, "Phase Transition of an Exciton System in GaAs Coupled Quantum Wells", Phys. Rev. Letts, 64, 3066, 1990 A.A.High, J.R.Leonard, M. Remeika, L.V.Butov, M. Hanson, and A.C.Gossard, "Condensation of Excitons in a Trap", Nano Lett., 12, pp.2605-2609, 2012 L.V.Butov & A.I.Filin, "Anomalous transport and luminescence of indirect excitons in AlAs / GaAs coupled quantum Wells as evidence for exciton condensation", Phys. Rev., B58, 1980, 1998 A.T.Hammack, N.A.Gippius, Sen Yang, G.O.Andreev, and L.V.Butov, "Excitons in electrostatic traps", J. of Appl.Phys., 99, 066104, 2006 D. N. Krizhanovskii, M. S. Skolnick, C. Tejedor and L. Vina, "Collective fluid dynamics of a polariton condensate in a semiconductor microcavity", Nature Letters, doi: 10.1038 / nature 07640, pp.291-295, 2009

The BE condensation in the conventional Bose particle system has the following problems when used for quantum computers.
(1) The equipment is large and not suitable for practical use.
(2) It is difficult to control the condensate,
(3) Due to the potential roughness felt by excitons, a sufficiently large BE condensation cannot be obtained.
(4) Condensate has a lifetime of about picoseconds and is not suitable for quantum computation.
However, this is a big wall when the conventional Bose particle system is used as an element of a quantum computer.

  In view of the above problems, the present invention is a novel exciton Bose particle system using a semiconductor heterointerface, which is (1) extremely compact and can be integrated, and (2) sufficient calculation time due to a long exciton lifetime. (3) Coherence of BE condensation is less likely to be scattered because there is little potential / roughness influence, (4) BE condensation can be expected in the macro region necessary for device realization, and (5) Controllability of excitons An object of the present invention is to provide a semiconductor quantum device comprising a novel exciton Bose particle system using a semiconductor heterointerface having good features.

  In order to achieve the above object, the semiconductor quantum device of the present invention includes a semiconductor heterointerface configured in the order of semiconductor I, semiconductor II, semiconductor III, and semiconductor IV, and the conduction band of semiconductor II is the conduction band of semiconductor III. By having higher energy for electrons, the conduction band at the heterointerface forms a step, and at the same time the valence band of semiconductor II is energetically lower for holes than the valence band of semiconductor III Thus, the semiconductor II and the semiconductor III are selected so that the valence band of the hetero interface forms a step, and an electric field is applied perpendicularly to the hetero interface, and the semiconductor II and the semiconductor III are excited by photoexcitation. Electrons and holes are generated at the heterointerface, electrons and holes are supplied to the heterointerface electrically, or both photoexcitation and electrical excitation are performed. Semiconductor III, half In the heterostructure formed by the body IV, the ground state of the electrons is not an energy level determined by the quantum well type potential due to the heterostructure formed by the semiconductor II, semiconductor III, or semiconductor IV, but a gradient due to the conduction band step and the electric field. In the heterostructure formed by the three semiconductors I, II and II, the semiconductor III is thickened so that it has the energy level of the triangular potential formed by the conduction band of the semiconductor III. The ground state of is not the energy level determined by the quantum well-type potential due to the heterostructure formed by the semiconductor I, the semiconductor II, and the semiconductor III, but the valence band of the semiconductor II having a gradient due to the valence band step and the electric field. The semiconductor II is made thicker so that it becomes the energy level of the triangular potential formed in (1).

In the above configuration, the electrons of the electron-hole pair are preferably X band electrons of the semiconductor III, and the holes are Γ band holes of the semiconductor II.
Preferably, the semiconductor II is Al _0.4 Ga _0.6 As having a thickness of 20 nm or more, the semiconductor III is AlAs having a thickness of 20 nm or more, and the electric field applied to the heterointerface between the semiconductor II and the semiconductor III is 10 kV / cm. That's it.
The plane orientation of the crystal growth substrate is preferably a GaAs substrate with 23.8 ° off from the (100) direction.
The substrate temperature during molecular beam epitaxy crystal growth is preferably 580 ° C. to 640 ° C.
Preferably, the semiconductor II is Si and the semiconductor III is Si _0.7 Ge _0.3 .
Preferably, the intensity of the in-plane distribution of the electric field strength at the surface where the electron and hole are opposed to each other gives the strength to the two-dimensional in-plane distribution of the gradient of the triangular potential for the electron and hole, and a region with a steep gradient By forming a region with a gentle gradient surrounded by, electrons and hole pairs are trapped in the region with a gentle gradient.
The in-plane distribution of the electric field strength is preferably a two-dimensional electrode shape, or a three-dimensional shape of a conductive region formed by ion implantation into a semiconductor undoped layer, thermal diffusion or etching of a semiconductor crystal, or By applying different voltages to the divided electrodes, electron-hole pairs are trapped.

  The semiconductor quantum arithmetic device of the present invention is characterized by using any of the semiconductor quantum elements described above and provided with a cooling means.

  In the above configuration, the cooling temperature by the cooling means is preferably 13K or lower or 4K or lower.

  The excitons in the semiconductor quantum device provided by the present invention have a sufficiently long recombination luminescence lifetime, and all the dipole moments are aligned in one direction. In the device, a macro number of two-dimensional excitons can be trapped in an arbitrary shape, and there is no disturbance of exciton potential energy due to interface roughness in the trap. By cooling the semiconductor quantum device from several hundred mK to several K or about 15K, exciton BE condensation in the macro region can be realized and can be used as an arithmetic element for a quantum computer. Since the excitons in the semiconductor quantum device according to the present invention are generated at the interface of staggered portions in the semiconductor heterostructure, the excitons are called staggered heterointerface excitons.

It is a conceptual diagram of a staggered hetero interface exciton when an electric field is applied to the semiconductor quantum device according to the present invention. FIG. 6 is a diagram showing a basic concept of staggered heterointerface excitons in a semiconductor quantum device according to the present invention, and the semiconductor I and the semiconductor IV in FIG. 1 are omitted for comparison with FIG. It is a conceptual diagram showing the exciton in the comparative example which made the semiconductor quantum element similar to FIG. 1 the thickness of the semiconductor II and the semiconductor III thinly. It is an energy level conceptual diagram of a staggered heterostructure when no electric field is applied to the semiconductor quantum device of the present invention. In the semiconductor quantum device concerning the present invention, it is a conceptual diagram explaining that a staggered heterointerface exciton in an electric field is not easily influenced by heterointerface roughness. FIG. 4 shows calculation results of wave functions of electrons and holes when the electric field is 1 kV / cm with staggered heterointerface excitons in the semiconductor quantum device according to the present invention. FIG. 3 shows the calculation results of the wave functions of electrons and holes when the electric field is 20 kV / cm with staggered heterointerface excitons in the semiconductor quantum device according to the present invention. 3 shows the calculation results of the wave functions of electrons and holes when the electric field is 40 kV / cm with staggered heterointerface excitons in the semiconductor quantum device according to the present invention. It is a calculation example of the electric field dependence of staggered hetero interface exciton and binding energy in the semiconductor quantum device according to the present invention. It is a calculation example showing the electric field dependence of the staggered hetero interface exciton Bohr radius in the semiconductor quantum device concerning the present invention. It is a calculation example showing the electric field dependence of the recombination probability of the staggered hetero interface exciton in the semiconductor quantum device according to the present invention. It is a calculation example showing the electric field dependence of the staggered hetero interface exciton energy in the semiconductor quantum device according to the present invention. It is sectional drawing showing the structure of the AlGaAs / AlAs type | system | group semiconductor crystal in the semiconductor quantum element based on this invention. It is a figure of the atomic force microscope image of the crystal | crystallization surface at the time of growing a staggered hetero interface with the surface orientation of a board | substrate as (100) with the semiconductor crystal used for the semiconductor quantum element concerning this invention. FIG. 4 is an atomic force microscope image of a crystal surface when a semiconductor crystal having a staggered hetero interface in a semiconductor quantum device according to the present invention is grown with a substrate orientation of 23.8 ° off. It is a conceptual diagram showing the method to generate a staggered hetero interface exciton in an AlGaAs / AlAs type semiconductor crystal in a semiconductor quantum device concerning the present invention. 4 represents the plane orientation dependence of the growth substrate of the photoluminescence spectrum of a semiconductor crystal having a staggered hetero interface according to the present invention. The photoluminescence spectrum in the case of a semiconductor crystal having a staggered hetero interface according to the present invention when the plane orientation of the substrate is (100) and the growth temperature is changed is shown. 2 shows a photoluminescence spectrum of a semiconductor crystal having a staggered hetero interface according to the present invention when the plane orientation of the substrate is off by 23.8 ° and the growth temperature is changed. In the semiconductor quantum device according to the present invention, a low temperature photoluminescence spectrum at 4K is shown when a crystal is grown with the plane orientation of the substrate as (100) and an electric field of 40 kV / cm is applied in the crystal growth direction. It is sectional drawing of a crystal | crystallization in case SiGe / Si type semiconductor crystal is used for the semiconductor quantum element concerning this invention. It is a conceptual diagram showing the method of generating a staggered hetero interface exciton in a SiGe / Si based semiconductor crystal in the semiconductor quantum device according to the present invention. It is a conceptual diagram of the exciton electronic state of the exciton system which consists of the space-separated electron and the hole in a double quantum well. It is a figure showing the temperature dependence of the half value width of the photoluminescence spectrum of a double quantum well exciton system. It is a figure which shows the two-dimensional in-plane roughness calculation example of the exciton energy based on the photoluminescence spectrum nonuniform width of a double quantum well exciton system. This is the temperature dependence of the exciton spatial distribution in a known example in which B-E condensation is observed in a double quantum well exciton. This is the spatial dependence of the first-order coherence of doublet-well exciton emission in a known example in which B-E condensation is observed. It is the conceptual diagram of the energy level of the exciton by the X-Γ indirect transition in the GaAs / AlAs quantum well structure. It is a conceptual diagram of an electron level in a Γ conduction band in a GaAs / AlAs quantum well structure. It is a conceptual diagram of the electron level in the X conduction band in a GaAs / AlAs quantum well structure.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a conceptual diagram of a staggered heterointerface exciton when an electric field is applied to the semiconductor quantum device 1 according to the present invention, and FIG. 2 is an illustration of staggered heterointerface excitation in the semiconductor quantum device according to the present invention. FIG. 4 is a diagram showing a basic concept of a child, in which the semiconductor I2 and the semiconductor IV5 of FIG. 1 are omitted for comparison with FIG.
As shown in FIG. 1, the semiconductor quantum device 1 has a continuous semiconductor layer composed of at least a semiconductor I2, a semiconductor II3, a semiconductor III4, and a semiconductor IV5 as a heterostructure in the device. The band alignment between the semiconductor layers is conceptually shown as a conduction band 8 of the entire heterostructure of the semiconductor quantum device 1 and a valence band 9 of the entire heterostructure. In FIG. 1, the electron ground level and the hole ground level in the triangular potential are indicated by symbols 6 and 7, respectively.

  An important staggered hetero interface in the present invention is that an electric field is applied to a heterostructure composed of a semiconductor II3 having a conduction band 22 and a valence band 26 and a semiconductor III4 having a conduction band 21 and a valence band 25. It is characterized by having a conduction band step 23 and a valence band step 27. A heterojunction that gives such a step difference in the conduction band (staggered) is called a staggered heterointerface in this specification, and an exciton as shown in FIG. 1 is called a staggered heterointerface exciton. The reason why excitons are formed in this state will be shown later by theoretical calculation.

In the conduction band, the triangular potential formed by the conduction band step 23 and the conduction band 21 tilted by the electric field generates an electron ground level 6 (electron ground level in the triangle potential). The electron wave function 24 with respect to is shown.
In the valence band, the triangular potential formed by the valence band step 27 and the valence band 26 tilted by the electric field has the hole ground level 7 (the hole ground level in the triangle potential). The hole wave function 28 produced and its level is shown.
These electrons and holes are stabilized by the amount of binding energy generated by attracting each other by Coulomb force, and become Bose particles like a hydrogen atom. The energy of the exciton can be obtained by subtracting the exciton binding energy from the energy difference 29 between the electron level 6 and the hole level 7. As shown in FIGS. 1 and 2, the exciton system of the semiconductor quantum device 1 used in the present invention is a new exciton system in which electrons and holes are spatially separated.

  In the crystal forming the semiconductor quantum device 1 of the present invention, as shown in FIG. 1, the semiconductor I2 and the semiconductor IV5 are provided on both sides of the semiconductor II3 and the semiconductor III4, and a heterostructure exists at each junction surface. If the thickness of II3 and semiconductor III4 is made sufficiently thicker than the position where the tail of the wave function on the side opposite to the interface of electrons and holes reaches, as shown in FIG. The ground level is not a quantum level due to the quantum well type potential but a quantum level determined only by the triangular potential.

FIG. 3 shows a comparative example in which the thickness of the semiconductor II3 and the semiconductor III4 is not sufficiently thicker than the position where the “tail of the wave function on the side opposite to the interface” reaches. It is a conceptual diagram in case the ground level of a hole is the well type potential of a quantum well.
As shown in FIG. 3, the constituent semiconductor layers are the same as those in FIG. 1, but only the thicknesses of the semiconductors II3 and III4 are reduced. As is clear from the figure, the wave function 10 of the electrons in the electric field and the wave function 11 of the holes in the electric field are soaked in the barrier layers on both sides of the quantum well, and the thickness of the quantum well changes, The ground level of electrons and holes changes sensitively.
Accordingly, the exciton energy fluctuates in the plane due to the fluctuation of the semiconductor heterointerface, and the influence of the coherence reduction of the BE condensed state due to the potential roughness occurring in the double quantum well excitons cannot be avoided.

An object of the present invention is to provide a system that is not affected by potential roughness due to interface fluctuations. The thickness of the semiconductor II3 and the semiconductor III4 required for this is applied if the semiconductor II3 is Al _0.4 Ga _0.6 As and the semiconductor III4 is AlAs if the thickness of each semiconductor layer is about 20 nm. It can be considered that when the electric field strength is 20 kV / cm to 40 kV / cm, the energy levels of electrons and holes are determined by the triangular potential. The reason will be described later with reference to FIGS.

FIG. 4 shows a combination example of semiconductors that realize a band structure having a heterostructure “staggered heterointerface” in the semiconductor quantum device 1 shown in FIG.
FIG. 4 is a conceptual diagram of energy levels of the staggered heterostructure when no electric field is applied to the semiconductor quantum device 1 of the present invention.
In FIG. 4, the Al _0.4 Ga _0.6 As layer 31 is the semiconductor layer II3, and the AlAs layer 30 is used as the semiconductor layer III4. The semiconductor layer I2 and the semiconductor layer IV5 will be described in Examples. The Γ-Γ transition 13 of Al _0.4 Ga _0.6 As is 2064 meV, and the Γ-Γ transition 12 of AlAs is 3109 meV.

However, the X band of AlAs is lower than the adjacent Al _0.4 Ga _0.6 As, and the electron of the electron-hole pair generated in the Γ-Γ transition 33 of Al _0.4 Ga _0.6 As is transferred to the X band electron 34 of AlAs. Moving. The hole 35 in the Γ band of Al _0.4 Ga _0.6 As is blocked by the AlAs valence band step and remains in Al _0.4 Ga _0.6 As as it is.

  The spatially separated electrons and holes attract each other by Coulomb interaction and become excitons. This is an X-Γ exciton denoted by reference numeral 36 in FIG. 4 and its energy is 1821 meV. FIG. 4 shows a state in which no electric field is applied. By applying an appropriate electric field thereto, a staggered heterointerface exciter as shown in FIGS. 1 and 2 is obtained.

  In this way, electrons and holes at the hetero interface are closely opposed to each other, and an exciton is formed by Coulomb interaction, but the energy is the conduction band step 23 or value electron caused by one hetero interface. It is determined by the band step 27 and the triangular potential generated by the electric field. The advantages of using this triangular potential will be described below.

  In general, even if the semiconductor heterointerface is crystal-grown with care by the molecular beam epitaxy (MBE) method or the like, fluctuation of one atom in the growth plane is inevitable. As a result, in the doublet-well exciton system, thickness fluctuations corresponding to single atoms occurred at each of the four heterointerfaces, and when combined, the exciton energy produced a large roughness in the plane.

The GaAs / AlAs quantum well exciton system closest to the exciton system of the present invention shown in FIG. 23 uses two narrow quantum wells having a width of 3 nm and 4 nm. The energy level due to is not the lowest energy level, and the exciton is governed by the energy level of each quantum well and is strongly influenced by fluctuations of a single atom.
This means that the coherent state is scattered immediately to realize BE condensation, and BE condensation in a macro region is impossible.

FIG. 5 is a conceptual diagram showing the disturbance of the staggered hetero interface of the semiconductor quantum device 1 according to the present invention. Hereinafter, it will be described with reference to FIG. 5 that the exciton system of the present invention is significantly different from the above-described known examples and comparative examples, and the influence of interface fluctuation of exciton energy is extremely small.
It is assumed that the heterojunction interface 37 is a position in the direction perpendicular to the substrate of the heterointerface at a “certain location” of the two-dimensional exciton system shown in FIG. It is assumed that a fluctuation of about a monoatomic layer occurs in “another place” in the plane, and the position of the heterojunction interface moves to the heterojunction interface 38. The energy of electrons due to the triangular potential increases from the energy level 39 in a place where there is no fluctuation to the energy level 40 in the case of fluctuation.
However, with respect to the movement of the heterojunction interface, the hole energy level corresponds to the hole level 41 corresponding to the heterojunction interface 37 with respect to the movement from the heterojunction interface 37 to the heterojunction interface 38, respectively. To the hole level 42 corresponding to the heterojunction interface 38, and the increase in the electron level is offset. Therefore, the exciton energy 43 at the heterojunction interface 37 and the exciton energy 44 at the heterojunction interface 38 are substantially equal.

  In order to satisfy this condition, the relationship between the thicknesses of the semiconductor layers II3 and III4 in the staggered heterostructure and the voltage applied to the staggered heterointerface is important. As described with reference to FIG. 1B, if the semiconductor layer II3 or the semiconductor layer III4 is thin and is not a triangular potential even when an electric field is applied, but the energy level of the quantum well becomes dominant, the interface The fluctuation of the monoatomic layer thickness greatly affects the exciton energy and is severely affected by the potential roughness. In the semiconductor quantum device 1 of the present invention, an electric field is applied perpendicular to the heterointerface. In the semiconductor quantum device 1, electrons and holes are generated at the heterointerface between the semiconductor II and the semiconductor III by photoexcitation, or electrons and holes are electrically supplied to the heterointerface, or photoexcitation and electrical excitation are performed. Either of both is done.

The dependence of applied physical strength on various physical quantities of Al _0.4 Ga _0.6 As / AlAs staggered heterointerface excitons in the semiconductor quantum device 1 according to the present invention will be described.
First, the features of the exciton system of the present invention will be described, and then the relationship between the thickness of the semiconductor layer II3 and the semiconductor layer III4 to become a triangular potential and the applied electric field strength will be described.
First, a method for calculating the applied voltage intensity dependence of various physical quantities of the staggered heterointerface excitons by calculation will be described.
Equation (1) shows the exciton wave function at the triangular potential generated at the applied staggered hetero interface.

In Equation (1), Ψ (x ₁ , x ₂ , r) is the exciton wave function, φ _e (x ₁ ) is the electron wave function 24, φ _h (x ₂ ) is the hole wave function 28, f (r) is an envelope function generated by the Coulomb interaction between electrons and holes. The exciton wave function ψ (x ₁ , x ₂ , r) satisfies the Schroedinger equation shown in equation (2).

In equation (2), r ₁ is the space coordinate of the electron, r ₂ is the space coordinate of the hole, _me is the effective mass of the electron, m _h is the effective mass of the hole, ε is the dielectric constant of the semiconductor, and μ is converted The mass M is the sum of the masses of electrons and holes, and is an amount related to the translational motion of excitons. V (x ₁ , x ₂ ) is calculated on the assumption that a hetero barrier in a conduction band or a valence band is superimposed on a potential gradient due to an electric field.
Equation (3) shows the Coulomb interaction P (r) between electrons and holes in the triangular potential generated at the staggered hetero interface to which an electric field is applied.

  In the Schroedinger equation of Equation (2), the second term is a term related to the translational motion of the exciton and can be neglected as compared with the relative motion of electrons and holes. The simplified Schroedinger equation is shown in Equation (4).

By numerically solving the Schroedinger equation in the form of equation (4), φ _e (x ₁ ), φ _h (x ₂ ), f (r), and E can be obtained.
Furthermore, the electric field dependence of the recombination probability of electrons and holes is expressed by the equation for the overlap integral S of the wave functions of electrons and holes, with φ _e (x ₁ ) and φ _h (x ₂ ) obtained in equation (4). It can be calculated by putting in (5).

FIG. 6 shows an electron wave function 51 and a hole wave function 52 at the Al _0.4 Ga _0.6 As / AlAs staggered hetero interface when the electric field is weak (1 kV / cm) in the semiconductor quantum device 1 of the present invention. Is a calculation example obtained from Equation (4). The wave function of the holes is shown upside down compared to the case of FIG.
In all of the following calculation examples including this example, the thickness of Al _0.4 Ga _0.6 As which is the semiconductor II3 is 20 nm, and the thickness of AlAs which is the semiconductor III4 is 20 nm.
In the calculation example of FIG. 4, the tails (tails) of the electron wave function 51 and the hole wave function 52 ooze out slightly at the heterointerface between the semiconductor layer I2 and the semiconductor layer IV5. Therefore, not only the triangular potential but also the influence of the well-type potential occurs, and if there is a fluctuation of a thickness of about a monoatomic layer at the heterointerface, a slight fluctuation occurs in the exciton energy.

FIG. 7 is a calculation example in which the electron wave function 53 and the hole wave function 54 at the Al _0.4 Ga _0.6 As / AlAs staggered hetero interface are obtained from Equation (4) when the electric field is 20 kV / cm. is there.
Since the electric field is stronger than in the case of FIG. 6, the inclination of the triangular potential is increased, and electrons and holes are closer to each other than in the case of 1 kV / cm. As a result, the tail of the wave function is reduced to a negligible level at the heterointerface (distance 20 nm) with the semiconductor I2 or the semiconductor IV5.
Therefore, it can be said that the electric field strength satisfies the condition defined by the present invention, that is, “the potential sensed by electrons and holes is determined by the triangular potential rather than the quantum well level”.

FIG. 8 is a calculation example of the electron wave function 55 and the hole wave function 56 at the Al _0.4 Ga _0.6 As / AlAs staggered hetero interface when the electric field is 40 kV / cm.
As shown in FIG. 8, it can be seen that the wave function is pressed further toward the heterointerface than when the electric field of FIG. 7 is 20 kV / cm. The tail of the wave function is also zero before the heterointerface (distance 20 nm), and it is clear that the electron level is determined only by the triangular potential. In such a state, even if there is a fluctuation of about a monoatomic layer at the staggered hetero interface, the exciton energy is not affected, and the realization of BE condensation in the macro region can be expected.

FIG. 9 is a diagram showing the electric field strength dependence 57 of the exciton binding energy formed at the Al _0.4 Ga _0.6 As / AlAs staggered hetero interface. As shown in FIG. 9, the exciton binding energy increases as the electric field strength increases and the wave functions of electrons and holes approach each other. If the binding energy is large, it can exist as an exciton without being decomposed into electrons and holes even at such a high temperature.

FIG. 10 is a diagram showing the electric field strength dependence 58 of the exciton Bohr radius formed at the Al _0.4 Ga _0.6 As / AlAs staggered hetero interface. As shown in FIG. 10, as the electric field strength increases, the wave functions of electrons and holes approach each other, thereby strengthening the connection and reducing the Bohr radius.

FIG. 11 shows the electric field strength dependence of the recombination probability of the Al _0.4 Ga _0.6 As / AlAs staggered heterointerface excitons obtained from the overlap integral S of Equation (5). As shown in FIG. 11, the recombination probability of the Al _0.4 Ga _0.6 As / AlAs staggered heterointerface excitons is not an absolute value, but a relative value obtained by comparing the recombination probabilities at respective electric field strengths. The probability of recombination increases as the electric field strength increases, but since this transition is an indirect transition, the reference emission lifetime is several orders of magnitude longer than in the case of direct transition.

FIG. 12 shows an example in which the shift amount 60 due to the electric field of exciton energy formed at the Al _0.4 Ga _0.6 As / AlAs staggered hetero interface is calculated.
As shown in FIG. 12, as the electric field increases, the triangular potential becomes an acute angle. As a result, the electron energy level and the hole energy level increase, and the exciton energy shifts to a higher energy side. .
When this is utilized, the region where the exciton is to be trapped in the semiconductor quantum device 1 according to the present invention is surrounded by a region having an applied voltage that is about 10 kV / cm higher than the trap region, so that it is lateral to the exciton. A potential barrier of about 5 meV to 10 meV can be formed, and excitons can be trapped two-dimensionally. Various experiments on excitons are possible by making this shape a circle or a waveguide.

So far, Al _0.4 Ga _0.6 As / AlAs staggered heterointerface excitons have been described as examples. However, the combination of semiconductors is not limited to Al _0.4 Ga _0.6 As / AlAs, and a staggered structure as shown in FIG. It is clear that any combination that provides a guard heterostructure has the characteristics of the staggered heterointerface excitons described above.
As an example, by selecting Si as the semiconductor II3 and Si _0.7 Ge _0.3 as the semiconductor III4, a staggered hetero interface similar to that shown in FIG. 1 can be obtained, and excitons that are not easily affected by the interface roughness can be obtained.

Further, by selecting Al _x Ga _1-x As as the semiconductor II3 and In _0.5 Ga _0.5 P as the semiconductor III4, the staggered heterointerface excitons similar to those in FIG. 1 can be obtained.
Al _0.4 Ga _0.6 As / AlAs staggered hetero interface, Si / Si _0.7 Ge _0.3 staggered hetero interface, Al _x Ga _1-x As / In _0.5 Ga _0.5 P staggered hetero interface Can be produced by a widely used semiconductor epitaxy method such as a normal molecular beam epitaxy method or MOCVD method. At that time, only the flatness of the interface is required, and the accuracy with respect to the film thickness of the growth layer is characterized by far greater tolerance than the case of using the quantum well.
For example, if the thickness of the semiconductor layer II3 and the semiconductor layer III4 exceeds a thickness of 20 nm to become a triangular potential, it will be 30 nm or 40 nm, but there is no change in characteristics. is there. Furthermore, the semiconductor quantum device may be configured by further including a layer for adjusting the electric field strength of the semiconductor quantum device 1 in addition to the semiconductor I2, the semiconductor II3, the semiconductor III4, and the semiconductor IVI5.

  As described above, the staggered heterointerface excitons used in the semiconductor quantum device 1 of the present invention are not easily affected by the interface roughness and have a long exciton recombination emission lifetime. By cooling, high-concentration excitons that are sufficiently cooled to the lattice temperature can be obtained, and the BE condensation condition can be satisfied. The exciton can be easily supplied by a conventional optical device excitation method such as photoexcitation or carrier injection, and is extremely advantageous for industrialization as compared with the case of performing B-E condensation of atoms.

A semiconductor quantum arithmetic device using the semiconductor quantum element 1 of the present invention is configured to include a cooling means. The cooling temperature by the cooling means may be about 13K or less or about 4K or less.
The semiconductor quantum device 1 of the present invention will be described more specifically in the following examples.

In order to obtain the semiconductor quantum device 1 of the present invention, a semiconductor crystal having an Al _0.4 Ga _0.6 As / AlAs staggered hetero interface having the structure shown in FIG. 13 was produced by a molecular beam epitaxy (MBE) method. In order to prevent contamination by impurities, the ion pump and titanium sublimation pump were operated during the growth. Further, the growth rate was suppressed to 0.1 to 1 μm or less per hour, and the growth film was flattened.
FIG. 13 is a sectional view showing the structure of an AlGaAs / AlAs semiconductor crystal in the semiconductor quantum device according to the present invention. As shown in FIG. 13, an n-GaAs buffer layer 101, an Al _0.4 Ga _0.6 As layer 102 (thickness 20 nm), an AlAs layer 103 (thickness 20 nm), on an n-GaAs substrate 100 having a plane orientation (100), Al _0.4 Ga _0.6 As layer 104 (thickness 20 nm), AlAs layer 105 (thickness 20 nm), Al _0.4 Ga _0.6 As layer 106 (thickness 20 nm), AlAs layer 107 (thickness 60 nm), n-AlGaAs layer 108 ( The n-GaAs layer 109 (thickness 20 nm) was grown by MBE at three substrate temperatures of 580 ° C., 610 ° C., and 640 ° C.
Here semiconductor I2 is AlAs layer 103, the semiconductor II3 is Al _0.4 Ga _0.6 As layer 104, the semiconductor III 4 is AlAs layer 105, the semiconductor IV5 corresponds to Al _0.4 Ga _0.6 As layer 106.

  FIG. 14 is an AFM image 95 obtained by measuring the surface roughness of the crystal manufactured in Example 1 using an atomic force microscope (AFM). The GaAs substrate uses a plane orientation (100). Looking at the lower edge of the microscope image quadrilateral, it can be seen that it is wavy and has surface roughness.

As the growth n-GaAs substrate 100, an Al _0.4 Ga _0.6 As / AlAs staggered heterointerface having the structure shown in FIG. 13 is used by using a substrate whose plane orientation is selected to be 23.8 ° off from (100). A semiconductor crystal was prepared by a molecular beam epitaxy (MBE) method. This example is the same as Example 1 except that the surface orientation of the substrate 100 is different.

  FIG. 15 is an AFM image 96 of a crystal manufactured using a GaAs substrate having a plane orientation (23.8 ° off) in Example 2 and has the same scale as FIG. There is very little undulation, and an ultra flat growth surface with an RMS surface roughness of 0.14 nm is obtained.

  Combining this ultra-flat surface fabrication technology with the roughness of the staggered heterointerface excitons of the present invention makes it possible to provide a two-dimensional exciton system that does not have potential roughness. A semiconductor quantum device 1 having BE condensation can be realized.

In addition to the semiconductor crystal having the two types of Al _0.4 Ga _0.6 As / AlAs staggered hetero interface, the GaAs substrate 100 has a plane orientation of (411) A, (311) A, and a plane orientation. The crystal shown in FIG. 13 was grown using a substrate that was selected to be 20.9 ° off from (100).
However, when the RMS surface roughness was measured by AFM, the result was rougher than Example 2 selected to be off by 23.8 °, and it was found that the semiconductor quantum device 1 of the present invention was not suitable.

As the GaAs substrate 100 for crystal growth, five types of substrates are used: plane orientation (100), plane orientation (23.8 ° off), plane orientation (411) A, plane orientation (311) A, and plane orientation (20.9 ° off). Thus, a semiconductor crystal having an Al _0.6 Ga _0.4 As / AlAs staggered hetero interface was fabricated.
When the RMS surface roughness was measured by AFM, the roughness of the surface was large, and it was found that this was not suitable as the semiconductor quantum device 1 of the present invention.

As the GaAs substrate 100 for crystal growth, five kinds of substrates of plane orientation (100), plane orientation (23.8 ° off), plane orientation (411) A, plane orientation (311) A, and plane orientation (20.9 ° off) are used. Thus, a semiconductor crystal having an Al _0.8 Ga _0.2 As / AlAs staggered hetero interface was fabricated.
When the RMS surface roughness was measured by AFM, the roughness of the surface was large, and it was found that this was not suitable as the semiconductor quantum device 1 of the present invention.

FIG. 16 shows an element structure fabricated for applying an electric field to the Al _0.4 Ga _0.6 As / AlAs staggered heterointerface excitons as the semiconductor quantum element 1 according to the present invention. Here, the semiconductor I2 corresponds to the GaAs buffer layer 101, the semiconductor II3 corresponds to the Al _0.4 Ga _0.6 As layer 102, the semiconductor III4 corresponds to the AlAs layer 103, and the semiconductor IV5 corresponds to the Al _0.4 Ga _0.6 As layer 104.

In the sixth embodiment, the semiconductor I2 is changed from AlAs to GaAs. However, since the portions necessary for the staggered heterointerface excitons are the semiconductor II3 and the semiconductor III4, there is no problem in operation.
A crystal manufactured by the same method as in Example 1 was used to form the electrode 110 and the electrode 111, and then a DC voltage 113 was applied between the electrode 110 and the electrode 111. The surface-side electrode 111 had a hole in the center, and was excited by a semiconductor laser beam 112 having a wavelength of 405 nm from there to generate electrons 114 and holes 115 at the interface between the layer 102 and the layer 103.

In the following, the photoluminescence evaluation for each example will be compared and explained in a cross-sectional manner.
FIG. 17 is an example of a photoluminescence spectrum at 13 K of the substrate having a heterostructure obtained in Example 1 and Example 2. The horizontal axis is photon energy, and the vertical axis is emission intensity in arbitrary units. In FIG. 17, the photoluminescence spectrum 71 of the crystal of Example 1 grown at 580 ° C. using GaAs of (100) plane orientation shows broad emission and Al _0.4 Ga _0.6 As / AlAs staggered heterointerface excitation. The emission peak is not observed where it corresponds to the Γ-X transition 70 of the child.

On the other hand, the photoluminescence spectrum 72 of the crystal of Example 2 grown at 580 ° C. using a GaAs substrate with a plane orientation (23.8 ° off) shows the Al _0.4 Ga _0.6 As / AlAs staggered heterointerface exciton. There is a clear peak corresponding to the Γ-X transition 70, and no other light emission is observed.

FIG. 18 is a photoluminescence spectrum at 13 K of the staggered heterointerface crystal in the heterostructure grown in Example 1, in which the spectral change due to the growth temperature is observed. Only the photoluminescence spectrum 80 with a growth temperature of 580 ° C shows a broad emission at 1920 meV, which seems to be the Γ-X transition of Al _0.4 Ga _0.6 As / AlAs. In the spectrum 81 at a temperature of 640 ° C., other transitions are dominant. The broad emission of 1920 meV is significantly different from 1821 meV, which is the Γ-X transition of excitons in FIG.

  FIG. 19 is a photoluminescence spectrum at 13K of a crystal grown on a GaAs substrate having a plane orientation (23.8 ° off) in Example 2, and comparison is made for three growth temperatures: 580 ° C., growth temperature 610 ° C., and growth temperature 640 ° C. It is carried out. In Example 2, single emission peaks 84, 85, and 86 are observed in the vicinity of 1821 meV that becomes the Γ-X transition 83 of the exciton of FIG. 1 at any growth temperature.

Although not shown, the photoluminescence spectrum when the x composition of Al _x Ga _1-x As / AlAs is changed using a (100) GaAs substrate is 60% for Al and 80% for the sample. Compared with the case where the emission intensity is 40%, the intensity decreased by an order of magnitude or more.
Similarly, when the x composition of Al _x Ga _1-x As / AlAs is changed using a GaAs substrate with a plane orientation (23.8 ° off), the sample of Al is 60% and 80%. Then, the intensity decreased by an order of magnitude or more compared to the case where the emission intensity was 40%. Further, the position of the emission peak does not exist in the vicinity of 1821 meV that becomes the Γ-X transition 83 of the exciton in FIG. 1, and 1940 meV that is the Γ-X transition or Γ-Γ transition of Al _x Ga _1-x As itself. It was also found that it exists only in 2060 meV and is not suitable for the gist of the present invention.

FIG. 18 shows an example in which an electric field of 40 kV / cm is applied to the interface between the Al _0.4 Ga _0.6 As layer 102 and the AlAs layer 103 using the semiconductor quantum device 1 shown in Example 6 and cooled to 4 K in an optical cryostat. It is the photoluminescence spectrum measured by measuring. When there is no electric field, only a broad emission 91 is observed, but a sharp emission peak 92 is observed at 1800.8 meV close to 1821 meV when an electric field of 40 kV / cm is applied. This corresponds to the Γ-X transition 70 of the Al _0.4 Ga _0.6 As / AlAs staggered heterointerface exciton.

In the measurement in which only the applied electric field strength is changed, when the electric field is weakened, this peak does not appear and only the broad light emission 91 is present. Therefore, this sharp light emission peak 92 is present in the semiconductor quantum device 1 of the present invention. It is thought to be exciton emission by electrons and holes in the triangular potential to be used. This sharp emission peak 92 has an extremely narrow half-value width of 0.57 meV. As a result of BE condensation on the Al _0.4 Ga _0.6 As / AlAs staggered heterointerface exciton, which is the subject of the present invention, such sharp emission is obtained. Can be interpreted.

So far, the Al _x Ga _1-x As / AlAs staggered hetero interface has been described as the semiconductor quantum device 1 of the present invention. In this example, the Si / Si _0.7 Ge _0.3 system as shown in FIG. A staggered hetero interface was fabricated.
FIG. 21 is a sectional view of a crystal when a SiGe / Si based semiconductor crystal is used for the semiconductor quantum device according to the present invention.
The p--Si / Si _0.7 Ge _0.3 superlattice layer 201 (Si thickness 5 nm / Si _0.7 Ge _0.3 thickness is formed on the p ⁺ -Si substrate 200 with a sufficiently slow growth rate so as to obtain a flat interface. 10 pairs of 5 nm), i-Si _0.7 Ge _0.3 buffer layer 202 (thickness 40 nm), p-Si layer 203 (thickness 20 nm), i-Si layer 204 (thickness 8 nm), i-Si _0.7 Ge _0.3 layer 205 (thickness 8 nm), n-Si _0.86 Ge _0.14 layer 206 (thickness 20 nm), i-Si _0.7 Ge _0.3 layer 207 (thickness 5 nm), n-Si _0.86 Ge _0.14 layer 208 (thickness 10 nm), n The -Si layer 209 (thickness 5 nm) was epitaxially grown using the MOCVD method generally used in Si / Si _x7 Ge _1-x growth.

In the semiconductor configuration of the semiconductor quantum device 1 of this embodiment, the semiconductor I2 is the p-Si layer 203, the semiconductor II3 is the i-Si layer 204, the semiconductor III4 is the i-Si _0.7 Ge _0.3 layer 205, and the semiconductor IV5 is n-Si _0.86. Ge _0.14 layer 206. When an electrode is formed and an electric field is applied, electrons 210 and holes 211 are relatively trapped in the triangular potential at the interface between the i-Si layer 204 and the i-Si _0.7 Ge _0.3 layer 205 and trapped in a staggered pattern.・ It becomes a heterointerface exciton. In this system, the recombination emission probability is low because of indirect transition, and the BE condensation state is maintained for a longer time.

FIG. 22 is a cross-sectional view of the semiconductor quantum device 1 produced in Example 8. In the semiconductor configuration of the semiconductor quantum device 1 of this example, as in Example 7, the semiconductor I2 is the p-Si layer 203, the semiconductor II3 is the i-Si layer 204, the semiconductor III4 is the i-Si _0.7 Ge _0.3 layer 205, the semiconductor IV5 is an n-Si _0.86 Ge _0.14 layer 206. The other layers 207 and 208 are electric field adjustment layers. FIG. 22 illustrates a method of confining the Si / Si _0.7 Ge _0.3- based staggered heterointerface excitons described in Example 7 in the lateral direction of the surface.
In FIG. 22, on a p ⁺ -Si substrate 200, a p-Si / Si _0.7 Ge _0.3 superlattice layer 201 (10 pairs of Si thickness 5 nm / Si _0.7 Ge _0.3 thickness 5 nm), i-Si _0.7 Ge _0.3 buffer Layer 202 (thickness 40 nm), p-Si layer 203 (thickness 20 nm), i-Si layer 204 (thickness 8 nm), i-Si _0.7 Ge _0.3 layer 205 (thickness 8 nm), i-Si _0.86 Ge _0.14 A layer 212 (thickness 20 nm), an i-Si _0.7 Ge _0.3 layer 213 (thickness 5 nm), an i-Si _0.86 Ge _0.14 layer 214 (thickness 5 nm), and an i-Si layer 215 (thickness 100 nm) are grown.

  When the electric field distribution applied to the crystal surface is changed two-dimensionally by using an undoped semiconductor from the surface-side layer from the electron / hole pair, the distribution of electrons / electrons generated in the layer 204 and the layer 205 It is reflected in the hole pair. As in Example 7, when a strongly doped layer is inserted, even if the electric field distribution is changed two-dimensionally on the layer, the distribution is two-dimensionally uniform below the layer. Because.

  After the above-described epitaxy growth using the MOCVD method, after patterning with a photoresist, phosphorus ions are implanted, and an n-type region 216 into which ions are implanted deeply and an n-type region 217 into which shallow ions are implanted are formed. Make it. Further, an n-side electrode 218 and a p-side electrode 219 are formed, and an electric field is applied to the heterointerface of the element using the power source 220.

At this time, the ratio of the electric field in the lower portion of the deep ion implantation portion 216 and the shallow portion 217 is the total thickness of the undoped layers 204, 205, 212, 213, and 214, and the ion implantation in the layer 215. The ratio of the reciprocal of the total thickness of the portions remaining undoped is obtained.
Therefore, by selecting the difference in ion implantation depth to about 100 nm, the potential barrier felt by the excitons can be set to about 10 meV, and the exciton can be sufficiently confined in the lateral direction.

  In Example 8, the two-dimensional distribution of the electric field was adjusted by changing the depth of the ion-implanted portion. However, in addition to this, the thickness of the undoped layer by etching or the method of changing the depth of thermal diffusion for each location. It is obvious that the object of the present invention can be achieved by using various semiconductor processes such as controlling the two-dimensional distribution of the electric field intensity by changing the above.

Further, by providing a region where the electrode on the surface side of the semiconductor quantum device 1 is removed so as to have an arbitrary shape, the electric field is strong under the part where the electrode is present, and weak under the part where the electrode is absent. It is possible.
Therefore, in the element shown in FIG. 16, excitons gather under a portion where there is no electrode. By adjusting the size of the portion without the electrode and the distance to the exciton, the electric field generated from the edge portion of the electrode can be adjusted to spread appropriately to the portion without the electrode. This is a matter that can be easily designed by a finite element method, including conditions such as electrode shape, semiconductor layer thickness, and dielectric constant. The semiconductor quantum element 1 that performs quantum operation is obtained by making the plurality of BE condensed states thus obtained “entangled”.

  The semiconductor quantum device 1 in the present invention is not limited to the above-described embodiment, and various modifications are possible within the scope of the invention described in the claims, and these are also included in the scope of the present invention. Needless to say.

1: Semiconductor quantum device 2: Semiconductor I
3: Semiconductor II
4: Semiconductor III
5: Semiconductor IV
6: Electron ground level in triangular potential 7: Hole ground level in triangular potential 8: Conduction band of semiconductor quantum device heterostructure 9: Valence band of semiconductor quantum device heterostructure 10: Electron wave in electric field Function 11: Wave function of hole in electric field 12: Ground level of hole in quantum well in electric field 13: Ground level of electron in quantum well in electric field 21: Conduction band 22 of semiconductor III: Semiconductor II conduction band 23: conduction band step 24: electron wave function 25: semiconductor III valence band 26: semiconductor II valence band 27: valence band step 28: hole wave function 29: electron quasi Energy difference between level and hole level 30: AlAs layer 31: Al _0.4 Ga _0.6 As layer 32: Γ-Γ transition of AlAs 33: Γ-Γ transition of Al _0.4 Ga _0.6 As 34: Electron of X band of AlAs 35: Al _0.4 Ga _0.6 As Γ band hole 36: Γ-X exciton transition 37: Heterojunction interface position 38: Junction heterointerface position 39 at another location: Electron level 40 corresponding to heterojunction interface 37: Electron level 41 corresponding to heterojunction interface 38: Positive corresponding to heterojunction interface 37 Hole level 42: Hole level 43 corresponding to the heterojunction interface 38: Energy of transition between electron level 39 and hole level 41 44: Transition between electron level 40 and hole level 22 Energy 51: Electron wave function when electric field is 1 kV / cm 52: Electron wave function when electric field is 1 kV / cm 53: Electron wave function when electric field is 20 kV / cm 54: Electron wave function when electric field is 20 kV / cm Wave function 55: electron wave function when electric field is 40 kV / cm 56: hole wave function when electric field is 40 kV / cm 57: electric field strength dependence of exciton binding energy 58: electric field strength dependence of exciton Bohr radius 59 : Exciton emission Electric field strength dependence of optical recombination probability 60: Electric field strength dependence of exciton energy shift 70: Γ-X transition 71 of Al _0.4 Ga _0.6 As / AlAs staggered heterointerface exciton 71: Crystal of Example 1 Photoluminescence (PL) spectrum 72: PL spectrum of crystal of Example 2 80: PL spectrum of heterostructure with growth temperature of 580 ° C of Example 1 81: PL spectrum of heterostructure with growth temperature of 610 ° C of Example 1 82: PL spectrum 83 of heterostructure with growth temperature of 640 ° C. in Example 1: Γ-X transition 84 of Al _0.4 Ga _0.6 As / AlAs staggered heterointerface excitons 84: PL of heterostructure with growth temperature of 580 ° C. in Example 2 Spectrum 85: PL spectrum of heterostructure having a growth temperature of 610 ° C. in Example 2 86: PL spectrum of heterostructure having a growth temperature of 640 ° C. in Example 2 91: An electric field of 40 kV / cm was applied to the device of Example 6. PL spectrum background 92 measured after cooling to 4K: Γ of staggered heterointerface excitons in the PL spectrum measured by applying an electric field of 40 kV / cm to the device of Example 6 and cooling to 4K -X transition 95: AFM image 96 of the crystal produced in Example 1 100: AFM image of the crystal produced in Example 2 100: n-GaAs substrate 101: n-GaAs buffer layer 102: Al _0.4 Ga _0.6 As layer 103: AlAs layer 104: Al _0.4 Ga _0.6 As layer 105: AlAs layer 106: Al _0.4 Ga _0.6 As layer 107: AlAs layer 108: n-AlGaAs layer 109: n-GaAs layer 110: electrode 111: surface-side electrode 112: laser light 113: DC voltage 114: electron 115: hole 200: p ⁺ -Si substrate 201: p-Si / Si _0.7 Ge _0.3 superlattice layer 202: i-Si _0.7 Ge _0.3 buffer layer 203: p-Si layer 204: i -Si layer 205: i-Si _0.7 Ge _0.3 layer 206: n-Si _0.86 Ge _0.14 layer 207: i-Si _0.7 Ge _0.3 layer 208: n-Si _0.86 Ge _0.14 layer 209: n-Si layer 210: electron 211: hole 212: i-Si _0.86 Ge _0.14 layer 213: i-Si _0.7 Ge _0.3 layer 214 : I-Si _0.86 Ge _0.14 layer 215: i-Si layer 216: n-type region 217 in which phosphorus ions are implanted deeply 217: n-type region in which phosphorus ions are implanted shallowly 218: n-side electrode 219: p-side electrode 220: Power supply 221: Electron 222: Hole 301: Conduction band of double quantum well in electric field 302: Valence band of double quantum well in electric field 303: Wave function of electrons in conduction band of double quantum well in electric field 304: Wave function of holes in the valence band of a double quantum well in an electric field 305: Temperature dependence of exciton photoluminescence spectrum and half width in a double quantum well (no electric field)
306: Temperature dependence of exciton photoluminescence, spectrum and half-width in double quantum well (when electric field is 40 kV / cm)
307: Exciton energy two-dimensional in-plane roughness calculation example 308: Exciton spatial distribution in a double quantum well (7K)
309: Spatial distribution of excitons in a double quantum well (4K)
310: Spatial distribution of excitons in a double quantum well with BE condensation (50mK)
400: conduction band representing Γ band of AlGaAs / GaAs / AlAs / AlGaAs heterostructure 401: conduction band representing X band of AlGaAs / GaAs / AlAs / AlGaAs heterostructure 402: Γ band of AlGaAs / GaAs / AlAs / AlGaAs heterostructure 403: GaAs quantum well 404: AlAs quantum well 405: Indirect transition between electron and hole levels 406: Electron level in GaAs quantum well 407: Electron level in AlAs quantum well 410: AlGaAs Layer 411: GaAs layer 412: AlAs layer 413: AlGaAs layer

Claims (11)

With a semiconductor heterointerface composed of semiconductor I, semiconductor II, semiconductor III, and semiconductor IV in this order,
The conduction band of semiconductor II has a higher energy for electrons than the conduction band of semiconductor III, so that the conduction band of the heterointerface forms a step,
At the same time, the semiconductor II and the semiconductor III were selected so that the valence band of the heterointerface formed a step because the valence band of the semiconductor II was energetically lower for holes than the valence band of the semiconductor III. Made of semiconductor crystals,
An electric field is applied perpendicular to the heterointerface,
Electrons and holes are generated at the heterointerface between semiconductor II and semiconductor III by photoexcitation, or electrons and holes are supplied to the heterointerface electrically, or both photoexcitation and electrical excitation are performed. Done,
In the heterostructure formed by the three semiconductors II, III, and IV, the ground state of the electrons is at the energy level determined by the quantum well potential due to the heterostructure formed by the semiconductor II, semiconductor III, and semiconductor IV. Without increasing the thickness of the semiconductor III so that the energy level of the triangular potential formed by the conduction band step and the conduction band of the semiconductor III having a gradient due to the electric field, and
In the heterostructure formed by the three types of semiconductors I, II, and III, the ground state of the holes is the energy level determined by the quantum well type potential of the heterostructure formed by the semiconductors I, II, and III. The semiconductor quantum device is characterized in that the semiconductor II is made thick so that it becomes the energy level of the triangular potential formed by the valence band step and the valence band of the semiconductor II having a gradient by an electric field. .   2. The semiconductor quantum device according to claim 1, wherein the electron of the electron-hole pair is an X band electron of the semiconductor III, and the hole is a Γ band hole of the semiconductor II. Semiconductor quantum device. In the semiconductor quantum device, the semiconductor II is Al _0.4 Ga _0.6 As having a thickness of 20 nm or more, the semiconductor III is AlAs having a thickness of 20 nm or more, and an electric field applied to the heterointerface between the semiconductor II and the semiconductor III is The semiconductor quantum device according to claim 1, wherein the electric field is higher than 10 kV / cm.   4. The semiconductor quantum according to claim 1, wherein in the semiconductor quantum device, the crystal growth substrate is a GaAs substrate whose plane orientation is 23.8 ° off from the (100) direction. 5. element.   5. The semiconductor quantum device according to claim 1, wherein the substrate temperature during molecular beam epitaxy crystal growth is 580 ° C. to 640 ° C. in the semiconductor quantum device. 3. The semiconductor quantum device according to claim 1, wherein the semiconductor II is Si and the semiconductor III is Si _0.7 Ge _0.3 .   In the semiconductor quantum device, the strength of the in-plane distribution of the electric field strength on the surface where the electrons and holes are opposed to each other gives the strength to the two-dimensional in-plane distribution of the gradient of the triangular potential with respect to the electrons and holes. The semiconductor according to any one of claims 1 to 6, wherein an electron / hole pair is trapped in a region having a gentle gradient by forming a region having a gentle gradient surrounded by a steep region. Quantum element.   In the semiconductor quantum device, the in-plane distribution of the electric field strength is a two-dimensional electrode shape, or a three-dimensional conductive region formed by ion implantation, thermal diffusion, or etching of a semiconductor crystal in a semiconductor undoped layer. The electron-hole pair is trapped by the in-plane distribution of the electric field strength in the in-plane distribution obtained by applying different voltages to the shape or the divided electrodes. Semiconductor quantum device.   9. A semiconductor quantum arithmetic device comprising the semiconductor quantum element according to claim 1 and comprising a cooling means.   The semiconductor quantum computing device according to claim 9, wherein a cooling temperature by the cooling unit is 13 K or less.   The semiconductor quantum operation device according to claim 9, wherein a cooling temperature by the cooling unit is 4K or less.