記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We report the experimental demonstration of the single-photon interference of bidirectionally extracted photons from epitaxially grown semiconductor quantum dots. The quantum dots were directly connected to single-mode optical fibers. Single-photon nature between transmission and reflection directions was confirmed through detection of antibunching in second-order photon correlation measurements. A Mach-Zehnder interferometer that was naturally formed by introducing the two outputs into a 2 x 2-fiber coupler was used to perform first-order photon correlation measurements. (C) 2015 The Japan Society of Applied Physics

DOI： 10.7567/APEX.8.112002

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC  

Cooper pairs form spin singlet states and are regarded as entangled electron pairs. Extracting entangled electrons has been actively studied by the use of superconductor-normal metal junctions. We have proposed to convert Cooper pairs to entangled photon pairs via interband radiative recombination of Cooper pairs penetrated into a semiconductor by the proximity effect. We fabricated a superconducting (SC) light emitting diode, where a superconductor is used for the n-type electrode. We observed light output enhancement and recombination lifetime shortening below the SC critical temperature. Our observations were very well explained with an analysis based on a time-dependent perturbation theory of the radiative recombination. Superconductivity was included via the Bogoliubov transformation. We present our measurements on the Cooper-pair-enhanced luminescence from InAs quantum dots. We demonstrate the observation of sharp edge in the luminescence spectra that reflects the SC density of states.

DOI： 10.1109/JSTQE.2014.2346617

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

Metallic cavities have been extensively studied to realize small-volume nanocavities and nanolasers. However cavity-resonance quality (Q) factors of nanolasers observed up to now remain low (up to similar to 500) due to metal optical absorption. In this paper, we report the observation of highest Q factors of 9000 at low temperature and similar to 6000 near room temperature in a metallic cavity with a probe of sub-bandgap emission of Si-doped GaAs. We analyze the temperature dependence of cavity-mode resonance wavelengths and show that the refractive-index term dominates the measured temperature dependence. We also show that this refractive-index term is cavity-mode dependent and the fitting procedure offers a new method to identify cavity modes. We simulate the metallic cavity with finite-element method and attribute the high-Q cavity mode to a whispering gallery optical mode. This mode is shown to have isotropic polarization dependence of the output emission, which is preferable for quantum information applications.

DOI： 10.1088/0957-4484/26/8/085201

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Institute of Physics (AIP)  

We studied InAs quantum dots (QDs) where electron Cooper pairs penetrate from an adjacent niobium (Nb) superconductor with the proximity effect. With time-resolved luminescence measurements at the wavelength around 1550 nm, we observed luminescence enhancement and reduction of luminescence decay time constants at temperature below the superconducting critical temperature (T C) of Nb. On the basis of these measurements, we propose a method to determine the contribution of Cooper-pair recombination in InAs QDs. We show that the luminescence enhancement measured below T C is well explained with our theory including Cooper-pair recombination.

DOI： 10.1063/1.4928621

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記述言語：英語   出版者・発行元：American Physical Society  

We demonstrate the generation of a Werner-like state from a single semiconductor quantum dot. The tomographic analysis with temporal gating brings us to a systematic understanding of the relation between the time evolution of quantum correlation and a set of parameters characterizing the exciton states, including fine-structure splitting and cross-dephasing time. The Werner state relates the Bell's parameter in the Clauser, Horne, Shimony, and Holt inequality with a fidelity, which facilitates the evaluation of nonlocality.

DOI： 10.1103/PhysRevB.91.205437

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevB.92.035308

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その他リンク： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.92.035308/fulltext

記述言語：英語   掲載種別：研究論文（学術雑誌）  

The emission cascade of a single quantum dot is a promising source of entangled photons. A prerequisite for this source is the use of a symmetric dot analogous to an atom in a vacuum, but the simultaneous achievement of structural symmetry and emission in a telecom band poses a challenge. Here we report the growth and characterization of highly symmetric InAs/InAlAs quantum dots self-assembled on C3v symmetric InP(111)A. The broad emission spectra cover the O (λ∼1.3 μm), C (λ∼1.55 μm), and L (λ∼1.6 μm) telecom bands. The distribution of the fine-structure splittings is considerably smaller than those reported in previous works on dots at similar wavelengths. The presence of dots with degenerate exciton lines is further confirmed by the optical orientation technique. Thus, our dot systems are expected to serve as efficient entangled photon emitters for long-distance fiber-based quantum key distribution. © 2014 American Physical Society.

DOI： 10.1103/PhysRevB.90.081301

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER PHYSICAL SOC  

The emission cascade of a single quantum dot is a promising source of entangled photons. A prerequisite for this source is the use of a symmetric dot analogous to an atom in a vacuum, but the simultaneous achievement of structural symmetry and emission in a telecom band poses a challenge. Here we report the growth and characterization of highly symmetric InAs/InAlAs quantum dots self-assembled on C-3 upsilon symmetric InP(111)A. The broad emission spectra cover the O (lambda similar to 1.3 mu m), C (lambda similar to 1.55 mu m), and L (lambda similar to 1.6 mu m) telecom bands. The distribution of the fine-structure splittings is considerably smaller than those reported in previous works on dots at similar wavelengths. The presence of dots with degenerate exciton lines is further confirmed by the optical orientation technique. Thus, our dot systems are expected to serve as efficient entangled photon emitters for long-distance fiber-based quantum key distribution.

DOI： 10.1103/PhysRevB.90.081301

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

We have recently reported the successful fabrication of bright single-photon sources based on Ag-embedded nanocone structures that incorporate InAs quantum dots. The source had a photon collection efficiency as high as 24.6%. Here, we show the results of various types of photonic characterizations of the Ag-embedded nanocone structures that confirm their versatility as regards a broad range of quantum optical applications. We measure the first-order autocorrelation function to evaluate the coherence time of emitted photons, and the second-order correlation function, which reveals the strong suppression of multiple photon generation. The high indistinguishability of emitted photons is shown by the Hong-Ou-Mandel-type two-photon interference. With quasi-resonant excitation, coherent population flopping is demonstrated through Rabi oscillations. Extremely high single-photon purity with a g((2))(0) value of 0.008 is achieved with pi-pulse quasi-resonant excitation. (C) 2014 AIP Publishing LLC.

DOI： 10.1063/1.4891224

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本物理学会  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We have realized metal-coated semiconductor nanostructures for a stable and efficient single-photon source (SPS) and demonstrated improved single-photon extraction efficiency by the selection of metals and nanostructures. We demonstrate with finite-difference time-domain (FDTD) simulations that inclination of a pillar sidewall, which changes the structure to a nanocone, is effective in improving the photon extraction efficiency. We demonstrate how such nanocone structures with inclined sidewalls are fabricated with reactive ion etching. With the optimized design, a photon extraction efficiency to outer airside as high as similar to 97% generated from a quantum dot in a nanocone structure is simulated, which is the important step in realizing SPS on-demand operations. We have also examined the direct contact of such a metal-embedded nanocone structure with a single-mode fiber facet as a simple and practical method for preparing fiber-coupled SPS and demonstrated practical coupling efficiencies of similar to 16% with FDTD simulation.

DOI： 10.1088/0957-4484/24/45/455205

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

Metallic nanocavities have been actively studied for realizing nanolasers with low threshold. Presence of resonance modes with high cavity Q values is the indication of low internal loss that leads to low threshold lasing. However, cavity Q values observed in metallic nanocavities below lasing threshold remain low at present on the order of 100 to 500. We study the possibility to realize higher resonance Q values with a metallic nanocavity. For probing purpose of cavity modes we propose to employ broad mid-gap-state optical emission of n-type GaAs. With this method we report the observation of a resonance mode with the high Q value of 3800 at room temperature with the metallic nanocavity. The cavity mode is identified as a whispering-gallery mode with finite-element- method simulation. (c) 2013 AIP Publishing LLC.

DOI： 10.1063/1.4828351

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

We report on the experimental demonstration of a single-photon source based on an InAs quantum dot (QD) on InP grown by molecular-beam epitaxy emitting in the telecommunication band. We develop a method to reduce the QD density to prevent inter-dot coupling via tunneling through coupled excited states. A single InAs QD embedded in an as-etched pillar structure exhibits intense and narrow emission lines. Photon antibunching is clearly observed using superconducting single-photon detectors with high sensitivity, and further improvement of the generated single-photon purity is demonstrated with below-barrier-bandgap excitation. © 2013 AIP Publishing LLC.

DOI： 10.1063/1.4817940

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

We report on the experimental demonstration of a single-photon source based on an InAs quantum dot (QD) on InP grown by molecular-beam epitaxy emitting in the telecommunication band. We develop a method to reduce the QD density to prevent inter-dot coupling via tunneling through coupled excited states. A single InAs QD embedded in an as-etched pillar structure exhibits intense and narrow emission lines. Photon antibunching is clearly observed using superconducting single-photon detectors with high sensitivity, and further improvement of the generated single-photon purity is demonstrated with below-barrier-bandgap excitation. © 2013 AIP Publishing LLC.

DOI： 10.1063/1.4817940

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER PHYSICAL SOC  

An ideal emitter of entangled photon pairs combines the perfect symmetry of an atom with the convenient electrical trigger of light sources based on semiconductor quantum dots. Our source consists of strain-free GaAs dots self-assembled on a triangular symmetric (111)A surface. The emitted photons reveal a fidelity to the Bell state as high as 86(+/- 2)% without postselection. We show a violation of Bell's inequality by more than five times the standard deviation, a prerequisite to test a quantum cryptography channel for eavesdropping. Due to the strict nonlocal nature the source can be used for real quantum processing without any postprocessing. The remaining decoherence channel of the photon source is ascribed to random charge and nuclear spin fluctuations in and near the dot.

DOI： 10.1103/PhysRevB.88.041306

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER PHYSICAL SOC  

We report a comprehensive investigation of carrier-transfer dynamics in a single InAs quantum dot (QD) based on second-order photon correlation measurements. The experimentally obtained auto and crosscorrelation functions as well as photoluminescence intensities are successfully explained on the basis of a series of rate equations with common excitation and also single-carrier-capture/escape rates to/from a QD. This approach enables us to understand the carrier-transfer dynamics responsible for the stability of a quantum two-level system formed in a single QD under various excitation conditions. We clarify that the transition between neutral and charged excitonic states is suppressed by one order of magnitude under quasiresonant excitation.

DOI： 10.1103/PhysRevB.88.045324

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER PHYSICAL SOC  

We report a comprehensive investigation of carrier-transfer dynamics in a single InAs quantum dot (QD) based on second-order photon correlation measurements. The experimentally obtained auto and crosscorrelation functions as well as photoluminescence intensities are successfully explained on the basis of a series of rate equations with common excitation and also single-carrier-capture/escape rates to/from a QD. This approach enables us to understand the carrier-transfer dynamics responsible for the stability of a quantum two-level system formed in a single QD under various excitation conditions. We clarify that the transition between neutral and charged excitonic states is suppressed by one order of magnitude under quasiresonant excitation.

DOI： 10.1103/PhysRevB.88.045324

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1103/PhysRevB.88.041306

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER PHYSICAL SOC  

An ideal emitter of entangled photon pairs combines the perfect symmetry of an atom with the convenient electrical trigger of light sources based on semiconductor quantum dots. Our source consists of strain-free GaAs dots self-assembled on a triangular symmetric (111)A surface. The emitted photons reveal a fidelity to the Bell state as high as 86(+/- 2)% without postselection. We show a violation of Bell's inequality by more than five times the standard deviation, a prerequisite to test a quantum cryptography channel for eavesdropping. Due to the strict nonlocal nature the source can be used for real quantum processing without any postprocessing. The remaining decoherence channel of the photon source is ascribed to random charge and nuclear spin fluctuations in and near the dot.

DOI： 10.1103/PhysRevB.88.041306

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

Fiber-based bidirectional photon detection from nanoscale emitters and photon antibunching behavior between two outputs of two single-mode fibers (SMFs) are experimentally demonstrated. Flakes containing the epitaxially grown quantum dots (QDs) are mechanically fixed by both sides with the edge faces of the SMF patch cables. The emitting photons from a single QD are directly taken out of both sides through the SMFs. Single-photon emission between two SMF outputs is confirmed by detecting nonclassical antibunching in second-order photon correlation measurements. This simple optomechanical alignment-free single-photon emitter is advantageous because of its robust stability of more than three months and low-cost fabrication. (C) 2013 The Japan Society of Applied Physics

DOI： 10.7567/APEX.6.065203

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We have fabricated silver microcolumnar photon reflectors to enhance the photon extraction efficiency from a quantum dot. The mechanically robust planar structure is favorable to couple to optical fibers for stable and efficient single-photon sources. A high photon extraction efficiency of up to 18% is achieved. Furthermore, strong suppression of multiphoton generation is confirmed. The proposed structure is quite promising toward the implementation of practical quantum key distribution systems with dot-fiber-coupled photon sources. (C) 2013 The Japan Society of Applied Physics

DOI： 10.7567/APEX.6.062801

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

We have fabricated silver microcolumnar photon reflectors to enhance the photon extraction efficiency from a quantum dot. The mechanically robust planar structure is favorable to couple to optical fibers for stable and efficient single-photon sources. A high photon extraction efficiency of up to 18% is achieved. Furthermore, strong suppression of multiphoton generation is confirmed. The proposed structure is quite promising toward the implementation of practical quantum key distribution systems with dot-fiber-coupled photon sources. (C) 2013 The Japan Society of Applied Physics

DOI： 10.7567/APEX.6.062801

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：JAPAN SOC APPLIED PHYSICS  

Fiber-based bidirectional photon detection from nanoscale emitters and photon antibunching behavior between two outputs of two single-mode fibers (SMFs) are experimentally demonstrated. Flakes containing the epitaxially grown quantum dots (QDs) are mechanically fixed by both sides with the edge faces of the SMF patch cables. The emitting photons from a single QD are directly taken out of both sides through the SMFs. Single-photon emission between two SMF outputs is confirmed by detecting nonclassical antibunching in second-order photon correlation measurements. This simple optomechanical alignment-free single-photon emitter is advantageous because of its robust stability of more than three months and low-cost fabrication. (C) 2013 The Japan Society of Applied Physics

DOI： 10.7567/APEX.6.065203

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：JAPAN SOC APPLIED PHYSICS  

Fiber-based bidirectional photon detection from nanoscale emitters and photon antibunching behavior between two outputs of two single-mode fibers (SMFs) are experimentally demonstrated. Flakes containing the epitaxially grown quantum dots (QDs) are mechanically fixed by both sides with the edge faces of the SMF patch cables. The emitting photons from a single QD are directly taken out of both sides through the SMFs. Single-photon emission between two SMF outputs is confirmed by detecting nonclassical antibunching in second-order photon correlation measurements. This simple optomechanical alignment-free single-photon emitter is advantageous because of its robust stability of more than three months and low-cost fabrication. (C) 2013 The Japan Society of Applied Physics

DOI： 10.7567/APEX.6.065203

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人電子情報通信学会  

半導体量子ドットのカスケード遷移を用いて、もつれた光子対を発生することができる.提案は10年以上前に遡るが、量子ドットに内在する、わずかな形状異方性のために、実現は困難だった.これまで様々の超絶技巧で光学等方性を回復し、もつれあい光子対を検証する実験はあったが、いずれも拡張性に乏しい.我々は、液滴エピタキシー成長法を用いて、対称性の高いGaAs/AlGaAs量子ドットの自己形成に成功した.鍵は、成長基板面としてGaAs(111)A面を用いたことである.その結果、高いもつれあい度の光子対発生を観測できたので報告する.

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

High photon-extraction efficiency is strongly required for a practical single-photon source. We succeed in fabricating metal (sliver)-embedded nanocone structure incorporating an InAs quantum dot. Efficient photon emission of similar to 200 000 photons per second is detected and single-photon emission is demonstrated using autocorrelation measurements. The photon-extraction efficiency as high as 24.6% is obtained from the structure. (C) 2013 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4801334]

DOI： 10.1063/1.4801334

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

High photon-extraction efficiency is strongly required for a practical single-photon source. We succeed in fabricating metal (sliver)-embedded nanocone structure incorporating an InAs quantum dot. Efficient photon emission of similar to 200 000 photons per second is detected and single-photon emission is demonstrated using autocorrelation measurements. The photon-extraction efficiency as high as 24.6% is obtained from the structure. (C) 2013 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4801334]

DOI： 10.1063/1.4801334

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

GaSb based quantum wells (QWs) show promising optical properties in near-infrared spectral range. In this paper, we present photoluminescence (PL) spectroscopies of InxGa1-xSb/AlyGa 1-ySb QWs and discuss the possible thermal quenching and non-radiative carrier recombination mechanisms of the QW structures. The In and Al concentrations as well as the QW thicknesses were precisely determined with the X-ray diffraction measurements. Temperature dependent time-integrated and time-resolved PL spectroscopies resulted in the thermal activation energies of ∼45 meV, and the overall self-consistent calculation of the band parameters based on the measured physical values confirmed that the activation energies are due to the hole escape from the QW to the barriers. The relation of the present single carrier escape mechanism with the other escape mechanisms reported with other material systems was discussed based on the estimated band offset. The relation of the present thermal hole escape to the Auger recombination was also discussed. © 2013 American Institute of Physics.

DOI： 10.1063/1.4789374

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

GaSb based quantum wells (QWs) show promising optical properties in near-infrared spectral range. In this paper, we present photoluminescence (PL) spectroscopies of InxGa1-xSb/AlyGa 1-ySb QWs and discuss the possible thermal quenching and non-radiative carrier recombination mechanisms of the QW structures. The In and Al concentrations as well as the QW thicknesses were precisely determined with the X-ray diffraction measurements. Temperature dependent time-integrated and time-resolved PL spectroscopies resulted in the thermal activation energies of ∼45 meV, and the overall self-consistent calculation of the band parameters based on the measured physical values confirmed that the activation energies are due to the hole escape from the QW to the barriers. The relation of the present single carrier escape mechanism with the other escape mechanisms reported with other material systems was discussed based on the estimated band offset. The relation of the present thermal hole escape to the Auger recombination was also discussed. © 2013 American Institute of Physics.

DOI： 10.1063/1.4789374

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記述言語：英語   出版者・発行元：The Japan Society of Applied Physics  

Growth of 90° interfacial-misfit-dislocation (IMF) array at heterointerfaces offers low dislocation densities in highly mismatched heterostructures such as GaSb/GaAs. We investigated time-integrated and time-resolved photoluminescence (PL) properties of a GaSb/AlGaSb quantum well (QW) structure grown on (001) GaAs substrate with and without IMF array at the GaSb-buffer/GaAs interface. Our observation reveals that the low-temperature PL from the QW with IMF is twice more intense than that of the QW without IMF, indicating higher quantum efficiency with IMF. The QW with IMF also exhibited the band filling effect at higher excitation power revealed from the spectrally resolved PL decay measurements. These results are the indication of subdued dislocation density with the IMF growth mode. Our PL measurement results along with supportive band-structure calculation of the GaSb/AlGaSb QW show that the luminescence efficiency of the present QW structure is limited by the hole leakage at elevated temperature. Therefore the IMF effect will be more clearly demonstrated by replacing the heterostructure with the one with higher band-offsets.

DOI： 10.7567/JJAP.52.022101

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その他リンク： http://hdl.handle.net/2115/52473

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：JAPAN SOC APPLIED PHYSICS  

Growth of 90 degrees interfacial-misfit-dislocation (IMF) array at heterointerfaces offers low dislocation densities in highly mismatched heterostructures such as GaSb/GaAs. We investigated time-integrated and time-resolved photoluminescence (PL) properties of a GaSb/AlGaSb quantum well (QW) structure grown on (001) GaAs substrate with and without IMF array at the GaSb-buffer/GaAs interface. Our observation reveals that the low-temperature PL from the QW with IMF is twice more intense than that of the QW without IMF, indicating higher quantum efficiency with IMF. The QW with IMF also exhibited the band filling effect at higher excitation power revealed from the spectrally resolved PL decay measurements. These results are the indication of subdued dislocation density with the IMF growth mode. Our PL measurement results along with supportive band-structure calculation of the GaSb/AlGaSb QW show that the luminescence efficiency of the present QW structure is limited by the hole leakage at elevated temperature. Therefore the IMF effect will be more clearly demonstrated by replacing the heterostructure with the one with higher band-offsets. (C) 2013 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.52.022101

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：JAPAN SOC APPLIED PHYSICS  

Growth of 90 degrees interfacial-misfit-dislocation (IMF) array at heterointerfaces offers low dislocation densities in highly mismatched heterostructures such as GaSb/GaAs. We investigated time-integrated and time-resolved photoluminescence (PL) properties of a GaSb/AlGaSb quantum well (QW) structure grown on (001) GaAs substrate with and without IMF array at the GaSb-buffer/GaAs interface. Our observation reveals that the low-temperature PL from the QW with IMF is twice more intense than that of the QW without IMF, indicating higher quantum efficiency with IMF. The QW with IMF also exhibited the band filling effect at higher excitation power revealed from the spectrally resolved PL decay measurements. These results are the indication of subdued dislocation density with the IMF growth mode. Our PL measurement results along with supportive band-structure calculation of the GaSb/AlGaSb QW show that the luminescence efficiency of the present QW structure is limited by the hole leakage at elevated temperature. Therefore the IMF effect will be more clearly demonstrated by replacing the heterostructure with the one with higher band-offsets. (C) 2013 The Japan Society of Applied Physics

DOI： 10.7567/JJAP.52.022101

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

InAs quantum dots (QDs) grown on InP substrates can be used as light emitters in the telecommunication bands. In this paper, we present optical characterization of high-density circular quantum dots (QDots) grown on InP(311)B substrates and elongated dots (QDashes) grown on InP(001) substrates. We study the charge carrier transfer and luminescence thermal quenching mechanisms of the QDots and QDashes by investigating the temperature dependence of their time-integrated and time-resolved photoluminescence properties. This results in two different contributions of the thermal activation energies. The larger activation energies are attributed to the carrier escape to the barrier layer and the wetting layer (WL) from QDots and QDashes, respectively. The smaller activation energies are found to be originated from inter-dot/dash carrier transfer via coupled excited states. The variation of the average oscillator strength associated with the carrier re-distribution is discussed. The relation of the two activation energies is also quantitatively studied with the measurements of excited-state and ground-state energy separations. Finally, we show an approach to isolate individual quantum dots or dashes in a suitable nanostructure. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4775768]

DOI： 10.1063/1.4775768

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

InAs quantum dots (QDs) grown on InP substrates can be used as light emitters in the telecommunication bands. In this paper, we present optical characterization of high-density circular quantum dots (QDots) grown on InP(311)B substrates and elongated dots (QDashes) grown on InP(001) substrates. We study the charge carrier transfer and luminescence thermal quenching mechanisms of the QDots and QDashes by investigating the temperature dependence of their time-integrated and time-resolved photoluminescence properties. This results in two different contributions of the thermal activation energies. The larger activation energies are attributed to the carrier escape to the barrier layer and the wetting layer (WL) from QDots and QDashes, respectively. The smaller activation energies are found to be originated from inter-dot/dash carrier transfer via coupled excited states. The variation of the average oscillator strength associated with the carrier re-distribution is discussed. The relation of the two activation energies is also quantitatively studied with the measurements of excited-state and ground-state energy separations. Finally, we show an approach to isolate individual quantum dots or dashes in a suitable nanostructure. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4775768]

DOI： 10.1063/1.4775768

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

We report on the experimental demonstration of single-photon source based on a single InAs quantum dot emitting in the telecommunication band. The low-density quantum dots grown by epitaxial method are embedded in an as-etched pillar structure. Photoluminescence spectrum of a single InAs quantum dot exhibits intense and narrow emission lines. Photon antibunching behavior is clearly observed using superconducting single-photon detectors with high sensitivity, which indicates the single-photon emission.

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：量子情報技術時限研究専門委員会  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

We report the observation of an anomalous antibunching dip in intensity autocorrelation function with photon correlation measurements on a single-photon emitter (SPE). We show that the anomalous dip observed is a manifestation of quantum nature of SPEs. Taking population dynamics in a quantum two-level system into account correctly, we redefine intensity autocorrelation function. This is of primary importance for precisely evaluating the lowest-level probability of multiphoton generation in SPEs toward realizing versatile pure SPEs for quantum information and communication. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4760222]

DOI： 10.1063/1.4760222

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記述言語：英語   出版者・発行元：AMER INST PHYSICS  

We report the observation of an anomalous antibunching dip in intensity
autocorrelation function with photon correlation measurements on a
single-photon emitter (SPE). We show that the anomalous dip observed is a
manifestation of quantum nature of SPEs. Taking population dynamics in a
quantum two-level system into account correctly, we redefine intensity
autocorrelation function. This is of primary importance for precisely
evaluating the lowest-level probability of multiphoton generation in SPEs
toward realizing versatile pure SPEs for quantum information and communication.

DOI： 10.1063/1.4760222

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その他リンク： http://arxiv.org/pdf/1207.6472v1

記述言語：英語   掲載種別：研究論文（学術雑誌）  

We have investigated the optical properties of a single InAsP quantum dot embedded in a standing InP nanowire. Elongation of the transverse exciton-spin relaxation time of the exciton state with decreasing excitation power was observed by first-order photon correlation measurements. This behavior is well explained by the motional narrowing mechanism induced by Gaussian fluctuations of environmental charges in the nanowire. The longitudinal exciton-spin relaxation time is evaluated by the degree of the random polarization of emission originating from exciton states confined in a single-nanowire quantum dot by using Mueller calculus based on Stokes parameters representation. The reduction in the random polarization component with decreasing excitation power is caused by suppression of the exchange interaction of electron and hole due to an optically induced internal electric field by the dipoles at the wurtzite and zinc-blende heterointerfaces in the InP nanowire. © 2012 American Physical Society.

DOI： 10.1103/PhysRevB.85.075324

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER PHYSICAL SOC  

We have investigated the optical properties of a single InAsP quantum dot embedded in a standing InP nanowire. Elongation of the transverse exciton-spin relaxation time of the exciton state with decreasing excitation power was observed by first-order photon correlation measurements. This behavior is well explained by the motional narrowing mechanism induced by Gaussian fluctuations of environmental charges in the nanowire. The longitudinal exciton-spin relaxation time is evaluated by the degree of the random polarization of emission originating from exciton states confined in a single-nanowire quantum dot by using Mueller calculus based on Stokes parameters representation. The reduction in the random polarization component with decreasing excitation power is caused by suppression of the exchange interaction of electron and hole due to an optically induced internal electric field by the dipoles at the wurtzite and zinc-blende heterointerfaces in the InP nanowire.

DOI： 10.1103/PhysRevB.85.075324

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IOP PUBLISHING LTD  

The injection of Cooper pairs into a normal medium such as a semiconductor is known as the proximity effect at the superconductor/normal interface. We confirm this injection as well as the contribution of Cooper pairs to a drastic enhancement of inter-band optical transitions in semiconductor heterostructures. In this paper we investigate and clarify the relation of internal quantum efficiencies and radiative lifetimes in Cooper-pair light emitting diodes (CP-LEDs). A quantitative description of the dynamic photon generation processes is given, and the contribution of the Cooper-pair recombination relative to normal-electron recombination in CP-LEDs is discussed in detail. (C) 2012 The Japan Society of Applied Physics

DOI： 10.1143/JJAP.51.010114

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG  

Superconductivity and optoelectronics have developed almost independently and had very rare interactions with each other in science and technologies. However recent interdisciplinary research opens up the potential for developing new optoelectronic devices. This review paper presents our recent theoretical and experimental demonstrations that superconductivity significantly modifies and accelerates photon generation processes. We have prepared superconducting light emitting diodes (LEDs) emitting at similar to 1.6-mu m optical-fiber communication band for the experimental demonstrations. This new-type LED operation is based on a unique physics related to Cooper-pair interband transition in a semiconductor, and further research leads to the solid-state simultaneously generated photon-pair sources for the potential application in quantum information and communication.

DOI： 10.1587/elex.9.1184

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記述言語：日本語   出版者・発行元：応用物理学会  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：1  

Blueshifts of luminescence observed in type-II heterostructures are quantitatively examined in terms of a self-consistent approach including excitonic effects. This analysis shows that the main contribution to the blueshift originates from the well region rather than the variation of triangular potentials formed in the barrier region. The power law for the blueshift, ΔEPL ∝ Plaserm, from m = 1/2 for lower excitation Plaser to m = 1/4 for higher excitation, is obtained from the calculated results combined with a rate equation analysis, which also covers the previously believed m = 1/3 power law within a limited excitation range. The present power law is consistent with the blueshift observed in a GaAsSb/GaAs quantum well. © 2012 Jo et al.

DOI： 10.1186/1556-276X-7-654

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PubMed

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1143/JJAP.51.010114

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER PHYSICAL SOC  

We experimentally demonstrate Cooper pairs' drastic enhancement of the band-to-band radiative recombination rate in a semiconductor. Electron Cooper pairs injected from a superconducting electrode into an active layer by the proximity effect recombine with holes injected from a p-type electrode. The recombination of a Cooper pair with p-type carriers dramatically increases the photon generation probability of a light-emitting diode in the optical-fiber communication band. The measured radiative decay time rapidly decreases with decreasing temperature below the superconducting transition temperature of the niobium electrodes. Our results indicate the possibility to open up new interdisciplinary fields between superconductivity and optoelectronics.

DOI： 10.1103/PhysRevLett.107.157403

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER PHYSICAL SOC  

We experimentally demonstrate Cooper pairs' drastic enhancement of the band-to-band radiative recombination rate in a semiconductor. Electron Cooper pairs injected from a superconducting electrode into an active layer by the proximity effect recombine with holes injected from a p-type electrode. The recombination of a Cooper pair with p-type carriers dramatically increases the photon generation probability of a light-emitting diode in the optical-fiber communication band. The measured radiative decay time rapidly decreases with decreasing temperature below the superconducting transition temperature of the niobium electrodes. Our results indicate the possibility to open up new interdisciplinary fields between superconductivity and optoelectronics.

DOI： 10.1103/PhysRevLett.107.157403

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：応用物理学会分科会日本光学会  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OPTICAL SOC AMER  

We experimentally prepare bi-photon mixed states in polarization employing an entangled-classical hybrid photon emitter which can properly model solid-state entangled photon sources with uncorrelated background photons. Polarization-uncorrelated photon pairs in totally mixed (TM) states are embodied with classical thermal radiation, while the polarization-entangled ones in a Bell state are generated by conventional parametric down conversion. The bi-photon states generated from the hybrid photon emitter are characterized in terms of a linear entropy-tangle plane, which reveals the formation of two-qubit Werner states. We also propose a direct way for evaluating the Werner states by means of minimal coincidence counts measurements. This simple method can be widely applicable in examining the bi-photon states from solid-state entangled photon sources, in which the polarization-entangled photon pairs have temporal correlation while the background photons in the TM states do not. (C)2011 Optical Society of America

DOI： 10.1364/OE.19.014249

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

Interband optical transition probability (usually given as the B coefficient) is normally fixed for a given semiconductor structure. Here we will show the B coefficient can be drastically enhanced effectively with electron injection in paired states. © 2011 IEEE.

DOI： 10.1109/IQEC-CLEO.2011.6193687

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記述言語：日本語   出版者・発行元：一般社団法人 日本物理学会  

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：WILEY-V C H VERLAG GMBH  

We introduce a novel metal-embedded semiconductor pillar structure including quantum dots as highly efficient single-photon sources for quantum information applications. We have developed related processes for fabricating the proposed structure and have demonstrated strongly suppressed multi-photon generation and improved photon extraction efficiency. As a result, under non-resonant excitation, which is highly preferable for practical use, single-photon purity with g(2)(0) as low as 0.015 has been measured. The extremely small semiconductor volume of the metal embedded structure is a crucial factor for this observation. Moreover, single-photon generation from a single quantum dot at a rate of up to 6.4 million per second has been achieved. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssc.201000519

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：WILEY-V C H VERLAG GMBH  

We introduce a novel metal-embedded semiconductor pillar structure including quantum dots as highly efficient single-photon sources for quantum information applications. We have developed related processes for fabricating the proposed structure and have demonstrated strongly suppressed multi-photon generation and improved photon extraction efficiency. As a result, under non-resonant excitation, which is highly preferable for practical use, single-photon purity with g(2)(0) as low as 0.015 has been measured. The extremely small semiconductor volume of the metal embedded structure is a crucial factor for this observation. Moreover, single-photon generation from a single quantum dot at a rate of up to 6.4 million per second has been achieved. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssc.201000519

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人電子情報通信学会  

超伝導電極を付加した通信波長帯の光子を放出する発光ダイオード構造を作製し,電子クーパー対の発光再結合過程への寄与を調べた.本構造を低電流で駆動させ,発光再結合寿命の温度依存性を測定したところ,超伝導転移温度以下で顕著な短縮効果を確認した.これは超伝導体から半導体へ近接効果により侵入した電子クーパー対が振動子強度を増強したことによるものである.

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

We report the experimental demonstration of single-photon and cascaded photon pair emission in the infrared, originating from a single InAsP quantum dot embedded in a standing InP nanowire. A regular array of nanowires is fabricated by epitaxial growth on an electron-beam patterned substrate. Photoluminescence spectra taken on single quantum dots show narrow emission lines. Superconducting single photon detectors, which have a higher sensitivity than avalanche photodiodes in the infrared, enable us to measure auto and cross correlations. Clear antibunching is observed [g((2))(0) = 0.12] and we show a biexciton-exciton cascade, which can be used to create entangled photon pairs. (C) 2010 American Institute of Physics. [doi:10.1063/1.3506499]

DOI： 10.1063/1.3506499

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Photon interference indicating wave-like nature of a single photon emitted from a single quantum dot is demonstrated. Photon state as a superposition of two orthogonal linear polarization modes is prepared inside a solid-state single photon source, which causes the first-order interference analogous to the Young's double slit experiment. The lack of which-mode information is essential for observing the single photon interference. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physe.2009.11.029

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Photon interference indicating wave-like nature of a single photon emitted from a single quantum dot is demonstrated. Photon state as a superposition of two orthogonal linear polarization modes is prepared inside a solid-state single photon source, which causes the first-order interference analogous to the Young's double slit experiment. The lack of which-mode information is essential for observing the single photon interference. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physe.2009.11.029

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人電子情報通信学会  

量子情報分野への応用に向けた量子ドットの研究において、量子ドットを含む半導体ピラー構造を金属層中に埋め込む金属埋め込み構造を新規に提案し、その作製を行い、単一光子発生に関して単一光子純度(多光子発生の抑制)・光子取り出し効率の2つの観点から評価を行った。金属埋め込み構造による非共鳴励起下での高純度な単一光子発生、光子取出し効率の向上について報告する。

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人電子情報通信学会  

量子情報分野への応用に向けた量子ドットの研究において、量子ドットを含む半導体ピラー構造を金属層中に埋め込む金属埋め込み構造を新規に提案し、その作製を行い、単一光子発生に関して単一光子純度(多光子発生の抑制)・光子取り出し効率の2つの観点から評価を行った。金属埋め込み構造による非共鳴励起下での高純度な単一光子発生、光子取出し効率の向上について報告する。

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：JAPAN SOC APPLIED PHYSICS  

A light-emitting diode (LED) in the optical-fiber communication band showed special features after replacing the n-type electrode with niobium (Nb) superconducting metal. Nb electrodes prepared on an InGaAs-based semiconductor surface formed a superconductor/semiconductor/superconductor junction, and the current-voltage characteristics exhibited both DC and AC Josephson junction properties. This was a result of the injection of electron Cooper-pairs into the n-InGaAs active layer of an LED. The drastic enhancement of the electroluminescence output observed below the Nb superconducting critical temperature, T(c), demonstrates the active role of electron Cooper-pairs in radiative recombination. Lifetime measurements of this LED and accurate evaluation of the luminescence output made it possible to estimate the radiative recombination lifetimes. A theoretical formula derived for the Cooper-pair radiative recombination accurately describes both the measured steep reduction of the radiative recombination lifetime and the observed enhancement of the internal quantum efficiency below Tc. This work will assist the development of interdisciplinary physics and new applications in superconductivity and optoelectronics. (C) 2010 The Japan Society of Applied Physics

DOI： 10.1143/APEX.3.054001

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記述言語：英語   出版者・発行元：HINDAWI PUBLISHING CORPORATION  

Single-photon as well as polarization-correlated photon pair emission from a single semiconductor quantum dots is demonstrated. Single photon generation and single photon-pair generation with little uncorrelated multiphoton emission and the feasibility of media conversion of the quantum states between photon polarization and electron spin are fundamental functions for quantum information applications. Mutual media conversion for the angular momentum between photon polarization and electron spin is also achieved with high fidelity via positively charged exciton state without external magnetic field. This is a clear indication that the coupling of photon polarizations and electron spins keeps secured during whole processes before photon emission. Possibility of a metal-embedded structure is demonstrated with the observation of drastic enhancement of excitation and/or collection efficiency of luminescence as well as clear antibunching of photons generated from a quantum dot.

DOI： 10.1155/2010/391607

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：HINDAWI PUBLISHING CORPORATION  

Single-photon as well as polarization-correlated photon pair emission from a single semiconductor quantum dots is demonstrated. Single photon generation and single photon-pair generation with little uncorrelated multiphoton emission and the feasibility of media conversion of the quantum states between photon polarization and electron spin are fundamental functions for quantum information applications. Mutual media conversion for the angular momentum between photon polarization and electron spin is also achieved with high fidelity via positively charged exciton state without external magnetic field. This is a clear indication that the coupling of photon polarizations and electron spins keeps secured during whole processes before photon emission. Possibility of a metal-embedded structure is demonstrated with the observation of drastic enhancement of excitation and/or collection efficiency of luminescence as well as clear antibunching of photons generated from a quantum dot.

DOI： 10.1155/2010/391607

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-V C H VERLAG GMBH  

High degree of preservation of spin states mediated by optical phonons is demonstrated with a positive trion state in a single quantum dot. At the optical phonon resonance suppression of spin relaxation is clearly identified as a dip structures in photoluminescence excitation spectra under cross-circularly polarize detection with respect to a pumping. As a result, distinguishably high degree of circular polarization up to similar to 0.85 is achieved in the absence of external magnetic field, which is no the case for neutral excitons with finite fine structure splitting. The absence of continuum states plays a crucial role for this observation. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssb.200880619

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-V C H VERLAG GMBH  

High degree of preservation of spin states mediated by optical phonons is demonstrated with a positive trion state in a single quantum dot. At the optical phonon resonance suppression of spin relaxation is clearly identified as a dip structures in photoluminescence excitation spectra under cross-circularly polarize detection with respect to a pumping. As a result, distinguishably high degree of circular polarization up to similar to 0.85 is achieved in the absence of external magnetic field, which is no the case for neutral excitons with finite fine structure splitting. The absence of continuum states plays a crucial role for this observation. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssb.200880619

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

We studied the novel structure for improving the emission properties of semiconductor light sources both theoretically and experimentally. The proposed structure is a semiconductor pillar buried in a metal except for one end surface of the pillar. Photons are extracted only from the air-exposed surface. The structure consists of the GaAs nanopillar structures embedded in metal and is analyzed by the finite-difference-time-domain method. InAs quantum dots buried in a GaAs pillar are assumed to be the photon emitters. Simulations are performed on GaAs pillars with different diameters buried in Niobium. Consequently, the simulation showed 75% light extraction efficiency from the pillar to air with the optimization of the structure. In addition, we experimentally measured photoluminescence intensities of up to 40 times enhancement in embedded structures compared to normal pillar structure. These are promising for future applications to overcome single photon sources. © 2009 SPIE.

DOI： 10.1117/12.828183

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IOP PUBLISHING LTD  

We report optical properties of InP/InAsP/InP nanowire quantum dots and single-photon Fourier spectroscopy of an exciton in a single InAsP quantum dot embedded in an InP nanowire. The coherent length of the time-averaged emission originating from the single InAsP QD was measured by a Mach-Zehnder interferometer inserted in the photoluminescence path. Effects of fluctuations in surrounding excess charges trapped in the InP nanowire were investigated by excitation power and energy dependencies.

DOI： 10.1088/1742-6596/193/1/012132

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：WILEY-V C H VERLAG GMBH  

Observation of drastically enhanced luminescence emitted from InAs quantum dots (QDs) which were in direct contact to superconducting Niobium (Nb) is reported. Although the PL intensity was essentially temperature independent without Nb stripe, drastic temperature dependence was observed with the presence of the Nb stripe. PL intensity was substantially increased below the Nb superconducting critical temperature (T-c). About 3-times enhancement was observed below T-c. This phenomenon is attributed to the Cooper pairs penetrated from the superconducting Nb stripe to adjacent InAs QDs by the proximity effect. This is the first experimental demonstration that the Cooper pairs enhance radiative recombination through QDs. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssc.200880669

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

Photoluminescence (PL) in the blue wavelength region originating from a no-phonon (NP) transition at 2.734 eV and longitudinal optical (LO) phonon sidebands of Te isoelectronic centers (ICs) were clearly resolved after thermal annealing by delta-doping of Te in ZnSe layers. Broad luminescence (conventionally called the S1 band) had been previously observed in this region (i.e., around 2.65 eV). The PL intensities of the NP line and the phonon replicas followed a Poisson distribution with a mean phonon number (Huang-Rhys factor) of S similar to 1.1. This indicates that the broadening of the 2.65 eV emission band is due to the superposition of the NP lines and their LO phonon replicas originating from the Te ICs with slight variations in their transition energies. The origin of the luminescence is discussed in relation to linearly polarized PL measurements. (C) 2008 American Institute of Physics.

DOI： 10.1063/1.2966697

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER PHYSICAL SOC  

High degree of excitonic spin-state preservation during energy relaxation is demonstrated in a single quantum dot. Optical-phonon resonances and corresponding suppression of spin relaxation are clearly identified as dip structures in photoluminescence excitation spectra probed by the positive trion emission. Consequently, under the longitudinal optical-phonon resonant excitation, a distinguishably high degree of circular polarization up to similar to 0.85 is achieved. Extended spin-relaxation time in the positive trion ground state compared to that in neutral exciton ground state is also revealed.

DOI： 10.1103/PhysRevB.78.081306

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER PHYSICAL SOC  

High degree of excitonic spin-state preservation during energy relaxation is demonstrated in a single quantum dot. Optical-phonon resonances and corresponding suppression of spin relaxation are clearly identified as dip structures in photoluminescence excitation spectra probed by the positive trion emission. Consequently, under the longitudinal optical-phonon resonant excitation, a distinguishably high degree of circular polarization up to similar to 0.85 is achieved. Extended spin-relaxation time in the positive trion ground state compared to that in neutral exciton ground state is also revealed.

DOI： 10.1103/PhysRevB.78.081306

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Single photon emission with high degree of circular polarization (DCP) from a positively charged exciton (trion) state in a single quantum dot (QD) is demonstrated under zero magnetic field. Obtained high DCP as large as 0.6 is a clear manifestation of highly effective mutual polarization conversion between single photon and single electron spin. This finding also reveals that the spin relaxation is strongly suppressed during capture and thermalization processes and also in trion ground states in a QD. Moreover, exciton charging state control is shown to be possible by modifying the electron capture probability through the excitation energy tuning, which leads to an exclusive formation of the positive trion in a QD. (c) 2007 Published by Elsevier B.V.

DOI： 10.1016/j.physe.2007.10.041

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Single photon emission with high degree of circular polarization (DCP) from a positively charged exciton (trion) state in a single quantum dot (QD) is demonstrated under zero magnetic field. Obtained high DCP as large as 0.6 is a clear manifestation of highly effective mutual polarization conversion between single photon and single electron spin. This finding also reveals that the spin relaxation is strongly suppressed during capture and thermalization processes and also in trion ground states in a QD. Moreover, exciton charging state control is shown to be possible by modifying the electron capture probability through the excitation energy tuning, which leads to an exclusive formation of the positive trion in a QD. (c) 2007 Published by Elsevier B.V.

DOI： 10.1016/j.physe.2007.10.041

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCI LTD  

Origin of sharp photoluminescence lines observed from an InAlAs quantum dot was identified with the measurements of excitation-power dependences and polarization correlations, together with photon correlation measurements. Single photon emission with high degree of circular polarization (DCP) up to 60% was observed from a positively charged exciton (trion) state in the single quantum dot under non-resonant excitation at zero magnetic field. (C) 2007 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.mejo.2007.07.098

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCI LTD  

Generation of entangled photon pairs from semiconductor quantum dots (QDs) is highly desirable for realizing practical solid-state photon sources for quantum information processing and quantum cryptography. However, the energy splitting of exciton states in QDs almost prevent the generation of entangled photon pairs. This paper discusses the new possibility with the injection of electron as well as hole Cooper pairs into QDs. (C) 2007 Published by Elsevier Ltd.

DOI： 10.1016/j.mejo.2007.07.009

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCI LTD  

Generation of entangled photon pairs from semiconductor quantum dots (QDs) is highly desirable for realizing practical solid-state photon sources for quantum information processing and quantum cryptography. However, the energy splitting of exciton states in QDs almost prevent the generation of entangled photon pairs. This paper discusses the new possibility with the injection of electron as well as hole Cooper pairs into QDs. (C) 2007 Published by Elsevier Ltd.

DOI： 10.1016/j.mejo.2007.07.009

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCI LTD  

Origin of sharp photoluminescence lines observed from an InAlAs quantum dot was identified with the measurements of excitation-power dependences and polarization correlations, together with photon correlation measurements. Single photon emission with high degree of circular polarization (DCP) up to 60% was observed from a positively charged exciton (trion) state in the single quantum dot under non-resonant excitation at zero magnetic field. (C) 2007 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.mejo.2007.07.098

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：JAPAN SOC APPLIED PHYSICS  

A light emitting diode with superconducting Nb electrodes was fabricated to investigate the contribution of cooper pairs to radiative recombination in a semiconductor. Electroluminescence observed from the active layer in which electron cooper pairs and normal holes are injected was drastically enhanced at the temperature lower than the superconducting transition temperature of the Nb electrodes. This is the first experimental evidence that cooper pairs enhance radiative recombinations by the superradiance effect. (c) 2008 The Japan Society of Applied Physics.

DOI： 10.1143/APEX.1.011701

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：JAPAN SOC APPLIED PHYSICS  

A light emitting diode with superconducting Nb electrodes was fabricated to investigate the contribution of cooper pairs to radiative recombination in a semiconductor. Electroluminescence observed from the active layer in which electron cooper pairs and normal holes are injected was drastically enhanced at the temperature lower than the superconducting transition temperature of the Nb electrodes. This is the first experimental evidence that cooper pairs enhance radiative recombinations by the superradiance effect. (c) 2008 The Japan Society of Applied Physics.

DOI： 10.1143/APEX.1.011701

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.1109/LEOS.2008.4688744

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：SPIE-INT SOC OPTICAL ENGINEERING  

Quantum information processing and quantum cryptography are expected to realize highly secure future information networks. How to control photon qubits will be one of the major issues for this direction, but the technologies related to generations and detections of individual photons are still being developed. Semiconductor quantum dots (QDs) have been expected to play major role for on-demand generations of single photons as well as entangled photon pairs. In this talk, photon generation processes from a single QD will be studied for the control of the quantum states of generated photons. Generation of entangled photon pairs from QDs based on biexciton-exciton cascade recombination processes is presently in a difficult situation due to exciton states energy splitting related to growth-related issues. An approach to open new paradigm will be discussed with preliminary results.

DOI： 10.1117/12.764104

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：IEEE  

To demonstrate the contribution of Cooper pairs to radiative recombination in a semiconductor, a n-InGaAs/p-InP light emitting diode with superconducting Nb electrodes was fabricated. Electroluminescence as well as photoluminescence from the n-InGaAs into which electron Cooper pairs were expected to penetrate from the superconducting Nb electrodes by the proximity effect was drastically enhanced at the temperature lower than the superconducting transition temperature. This is the experimental evidence that Cooper pairs enhance radiative recombinations by the superradiance effect.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：WILEY-V C H VERLAG GMBH  

We report the photon-correlation Fourier spectroscopy of exciton and exciton complexes in single self-assembled In0.75Al0.25As/Al0.3Ga0.7As quantum dots. A Michelson interferometer inserted in the photoluminescence path was used to measure the coherent length of the time-averaged emission of neutral exciton, biexciton, and positive trion. As comparing with their coherence time and their excitation energy dependence, the effects of the exchange interaction and the fluctuation of the surrounding excess charge are discussed.

DOI： 10.1002/pssc.200776553

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：WILEY-V C H VERLAG GMBH  

To investigate the contribution of Cooper pairs to radiative recombination in a semiconductor, a junction field-effect transistor (FET) with a Nb/n-InGaAs/Nb junction was fabricated. Electroluminescence was observed from a 11.0nm-wide gap between the source and drain Nb electrodes in addition to the confirmation of the FET operation. Micro-photoluminescence observed from the gap in the Nb electrodes was drastically enhanced at the temperature lower than the superconducting critical value of similar to 8K. This new finding is discussed based on the proximity effect at the super-normal junction. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssc.200779278

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.1109/DRC.2008.4800850

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SPRINGER  

We investigated optical pumping of nuclear spin polarizations in a single self-assembled In0.75Al0.25As/Al0.3Ga0.7As quantum dot. The nuclear spin polarization exhibits the abrupt jump and hysteresis in the excitation power dependence at a particular excitation polarization. Measurement of circular polarization rate of the photoluminescence reveals that the abrupt change of the nuclear spin polarization is created mainly by the spin flip-flop process between nuclei and an electron of a positive charged exciton in this single quantum dot. Model calculation explains well the experimentally observed bistable behavior in InAlAs quantum dot. By using this abrupt change, the sign and magnitude of electron and hole g-factors in z-direction are verified.

DOI： 10.1007/s10948-007-0240-9

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SPRINGER  

We investigated optical pumping of nuclear spin polarizations in a single self-assembled In0.75Al0.25As/Al0.3Ga0.7As quantum dot. The nuclear spin polarization exhibits the abrupt jump and hysteresis in the excitation power dependence at a particular excitation polarization. Measurement of circular polarization rate of the photoluminescence reveals that the abrupt change of the nuclear spin polarization is created mainly by the spin flip-flop process between nuclei and an electron of a positive charged exciton in this single quantum dot. Model calculation explains well the experimentally observed bistable behavior in InAlAs quantum dot. By using this abrupt change, the sign and magnitude of electron and hole g-factors in z-direction are verified.

DOI： 10.1007/s10948-007-0240-9

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Isoelectronically substitutional material systems are proposed as offering a unique possibility to study the physics of different regimes from single isoelectronic centers (ICs) to self-assembled quantum dots (QDs) within the same material combinations. Luminescence evolution of ZnSe:Te system were investigated as such isoelectronically substitutional system. A successive change in the spectral dominance of luminescence with increasing ZnTe layer thickness indicates the evolution from ICs to QDs in ZnSe:Te system. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2006.11.292

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Isoelectronically substitutional material systems are proposed as offering a unique possibility to study the physics of different regimes from single isoelectronic centers (ICs) to self-assembled quantum dots (QDs) within the same material combinations. Luminescence evolution of ZnSe:Te system were investigated as such isoelectronically substitutional system. A successive change in the spectral dominance of luminescence with increasing ZnTe layer thickness indicates the evolution from ICs to QDs in ZnSe:Te system. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2006.11.292

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

High-quality ZnO thin films were grown by plasma-enhanced molecular-beam epitaxy on sapphire substrates. In the edge emission geometry, lasing action has been demonstrated in ZnO thin films. The physical origin responsible for lasing action is discussed. The well-defined longitudinal modes could be observed, the mode spacing of 0.9 nm corresponds to a cavity of around 17.5 mu m, and result from accidentally or naturally formed cavities. The lasing threshold was measured as a function of temperature, and the threshold was found to show weak temperature dependence. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jlumin.2006.01.300

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

High-quality ZnO thin films were grown by plasma-enhanced molecular-beam epitaxy on sapphire substrates. In the edge emission geometry, lasing action has been demonstrated in ZnO thin films. The physical origin responsible for lasing action is discussed. The well-defined longitudinal modes could be observed, the mode spacing of 0.9 nm corresponds to a cavity of around 17.5 mu m, and result from accidentally or naturally formed cavities. The lasing threshold was measured as a function of temperature, and the threshold was found to show weak temperature dependence. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jlumin.2006.01.300

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記述言語：英語   掲載種別：論文集(書籍)内論文   出版者・発行元：Springer Berlin Heidelberg  

DOI： 10.1007/978-3-540-47235-3_5

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記述言語：英語   出版者・発行元：Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physics  

DOI： 10.1143/jjap.45.9264

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その他リンク： http://hdl.handle.net/2115/33907

記述言語：英語   出版者・発行元：Japan Society of Applied Physics  

DOI： 10.1143/JJAP.45.L529

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その他リンク： http://hdl.handle.net/2115/33910

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：JAPAN SOC APPLIED PHYSICS  

The role of nitrogen (N) in emission wavelengths from InAs quantum dots (QDs) was studied with intentional supplies of a N precursor (monomethylhydrazine) to InAs dot surfaces just before burying them with GaAs capping layers by metalorganic molecular-beam epitaxy. Luminescence from the InAs QDs showed a red shift with the N-precursor supplies on the dot surfaces, and more clear separations of the luminescence sub peaks originating from QD excited-state transitions were observed. The increase in the N precursor supplies on the dot surfaces however changed the relative variation in the emission wavelengths from the red shift to the blue shift. Additional observations of the dot sizes, as well as the model calculations of the emission peaks and of the energy separations of the lowest and QD excited-state transitions showed that the red shift is due to the reduced Ga inclusion in the InAs QDs and that the blue shift is due to the reduced dot sizes.

DOI： 10.1143/JJAP.45.L529

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：JAPAN SOC APPLIED PHYSICS  

The role of nitrogen (N) in emission wavelengths from InAs quantum dots (QDs) was studied with intentional supplies of a N precursor (monomethylhydrazine) to InAs dot surfaces just before burying them with GaAs capping layers by metalorganic molecular-beam epitaxy. Luminescence from the InAs QDs showed a red shift with the N-precursor supplies on the dot surfaces, and more clear separations of the luminescence sub peaks originating from QD excited-state transitions were observed. The increase in the N precursor supplies on the dot surfaces however changed the relative variation in the emission wavelengths from the red shift to the blue shift. Additional observations of the dot sizes, as well as the model calculations of the emission peaks and of the energy separations of the lowest and QD excited-state transitions showed that the red shift is due to the reduced Ga inclusion in the InAs QDs and that the blue shift is due to the reduced dot sizes.

DOI： 10.1143/JJAP.45.L529

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Triggered single-photon generation from InAlAs quantum dot (QD) was demonstrated for the first time. Emitted photon energy coincides with high detection efficiency range of Si single-photon detectors, which is highly suitable for free-space communication. Single-QD spectroscopy and crossed photon correlation measurements unambiguously revealed that several emitting lines observed in a single mesa structure originated from the identical QD, and two temporary competing decay processes associated with neutral states and charged states were identified. Presence of the competing process is also inferred from an analysis of steady-state photoluminescence intensities. Formation process of charged exciton in QD is also discussed. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physe.2005.12.027

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Triggered single-photon generation from InAlAs quantum dot (QD) was demonstrated for the first time. Emitted photon energy coincides with high detection efficiency range of Si single-photon detectors, which is highly suitable for free-space communication. Single-QD spectroscopy and crossed photon correlation measurements unambiguously revealed that several emitting lines observed in a single mesa structure originated from the identical QD, and two temporary competing decay processes associated with neutral states and charged states were identified. Presence of the competing process is also inferred from an analysis of steady-state photoluminescence intensities. Formation process of charged exciton in QD is also discussed. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physe.2005.12.027

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER SCIENTIFIC PUBLISHERS  

Photon emission with nonclassical photon statistics is discussed with a single InAlAs quantum dot. The deterministic single-photon generation in which the emitted photon wavelength matches well to the highly sensitive wavelength region of highly efficient, low-noise Si-single-photon detectors and also to an atmospheric transmission window is demonstrated. Competing transition processes between neutral and charged exciton species originating from an exclusive formation in the same single quantum dot are clarified. It was found that suppressing the charged exciton formation is possible by a quasi-resonant excitation for a deterministic monochromatic single-photon generation. Polarization-dependent photoluminescence spectroscopy clearly indicates the preservation of photon polarizations between photons emitted by biexciton/exciton recombinations. Furthermore, the deterministic polarization-correlated photon pair generation with biexciton-exciton cascaded transition occurring in a single quantum dot is directly confirmed by the polarized second-order photon correlation measurements. This indicates a longer polarization flip time than the exciton lifetime, which is an essential requirement for the deterministic Einstein-Podolsky-Rosen photon pair generation under the present biexciton-exciton cascaded transition scheme.

DOI： 10.1166/jno.2006.003

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記述言語：英語   出版者・発行元：AMER SCIENTIFIC PUBLISHERS  

Photon emission with nonclassical photon statistics is discussed with a single InAlAs quantum dot. The deterministic single-photon generation in which the emitted photon wavelength matches well to the highly sensitive wavelength region of highly efficient, low-noise Si-single-photon detectors and also to an atmospheric transmission window is demonstrated. Competing transition processes between neutral and charged exciton species originating from an exclusive formation in the same single quantum dot are clarified. It was found that suppressing the charged exciton formation is possible by a quasi-resonant excitation for a deterministic monochromatic single-photon generation. Polarization-dependent photoluminescence spectroscopy clearly indicates the preservation of photon polarizations between photons emitted by biexciton/exciton recombinations. Furthermore, the deterministic polarization-correlated photon pair generation with biexciton-exciton cascaded transition occurring in a single quantum dot is directly confirmed by the polarized second-order photon correlation measurements. This indicates a longer polarization flip time than the exciton lifetime, which is an essential requirement for the deterministic Einstein-Podolsky-Rosen photon pair generation under the present biexciton-exciton cascaded transition scheme.

DOI： 10.1166/jno.2006.003

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

High-quality ZnO thin films have been grown by plasma-enhanced molecular-beam epitaxy on sapphire substrates. Free-exciton absorption and exciton-LO phonon absorption peaks are observed in the films at room temperature, indicating that the exciton states are stable even at room temperature. Three excitonic transitions associated with valence bands A, B, and C are clearly revealed in the reflectance spectrum measured at low temperatures. This result indicates that the ZnO thin films have a perfect wurtzite crystal structure. Biexciton emission is observed in the photoluminescence spectra at low temperatures, from which the biexciton binding energy is estimated to be 14.5 meV, in good agreement with previous results. Exciton-LO (Ex-LO) and exciton-2LO (Ex-2LO) photon emission peaks are observed at low temperature. The energy difference between the Ex-LO and Ex-2LO bands is about 72.5 meV, which coincides with previously reported values of the LO phonon energy for ZnO thin films. (c) 2006 American Institute of Physics.

DOI： 10.1063/1.2183354

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

High-quality ZnO thin films have been grown by plasma-enhanced molecular-beam epitaxy on sapphire substrates. Free-exciton absorption and exciton-LO phonon absorption peaks are observed in the films at room temperature, indicating that the exciton states are stable even at room temperature. Three excitonic transitions associated with valence bands A, B, and C are clearly revealed in the reflectance spectrum measured at low temperatures. This result indicates that the ZnO thin films have a perfect wurtzite crystal structure. Biexciton emission is observed in the photoluminescence spectra at low temperatures, from which the biexciton binding energy is estimated to be 14.5 meV, in good agreement with previous results. Exciton-LO (Ex-LO) and exciton-2LO (Ex-2LO) photon emission peaks are observed at low temperature. The energy difference between the Ex-LO and Ex-2LO bands is about 72.5 meV, which coincides with previously reported values of the LO phonon energy for ZnO thin films. (c) 2006 American Institute of Physics.

DOI： 10.1063/1.2183354

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：WILEY-V C H VERLAG GMBH  

It is well-recognized that exciton-state energy splitting makes it difficult to generate entangled photon pairs (EPP) from a single quantum dot (QD). It will be shown that the splitting of the exciton states originates from not only QD anisotropy but also ionization of residual impurities. This result shows that the growth of highly pure barrier layers will be necessary for the generation of EPP. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssc.200671611

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

We report optical pumping of nuclear spin polarization in a single self-assembled In0.75 Al0.25 As/Al0.3Ga 0.7As quantum dot where the exciton has a fine structure. Through the change of state mixing that is induced by the anisotropic exchange interaction and the applied magnetic field, the relationship between the magnitude of the Overhauser shift and the optically injected electron spin polarization is discussed. © 2006 WILEY-VCH Verlag GmbH &amp
Co. KGaA.

DOI： 10.1002/pssc.200672810

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：WILEY-V C H VERLAG GMBH  

We report optical pumping of nuclear spin polarization in a single self-assembled In0.75Al0.25As/Al0.3Ga0.7As quantum dot where the exciton has a fine structure. Through the change of state mixing that is induced by the anisotropic exchange interaction and the applied magnetic field, the relationship between the magnitude of the Overhauser shift and the optically injected electron spin polarization is discussed. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssc.200672810

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：WILEY-VCH, INC  

Atomically flat terraced ZnO surfaces were prepared with thermal annealing in air. CdO dots were successfully formed on the ZnO substrate surfaces with in-situ post-growth thermal annealing of CdO layers grown by metalorganic molecular-beam epitaxy. Well-organized alignment of the CdO dots along surface atomic-step edges on the terraced surfaces is demonstrated.

DOI： 10.1002/pssc.200564746

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人電子情報通信学会  

単一光子の不可分性に基づく極めて高い秘匿性を持つ高効率量子鍵配送の実現に向け、シリコン単一光子検出器の検出感度が高い波長での光子生成が可能な半導体量子ドットを形成し、単一の励起子遷移による高純度の単一の光子数状態にある光子発生を確認した。応用上、複数光子の同時発生を抑制する必要があるが、多励起子状態の関与が単一光子発生動作に大きな影響を与えることを、光子同時計数確率の励起光強度依存性の検討により明らかにした。さらに、励起子分子-励起子の時系列的遷移過程による光子対発生の検証についても実施した。

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人電子情報通信学会  

単一光子の不可分性に基づく極めて高い秘匿性を持つ高効率量子鍵配送の実現に向け、シリコン単一光子検出器の検出感度が高い波長での光子生成が可能な半導体量子ドットを形成し、単一の励起子遷移による高純度の単一の光子数状態にある光子発生を確認した。応用上、複数光子の同時発生を抑制する必要があるが、多励起子状態の関与が単一光子発生動作に大きな影響を与えることを、光子同時計数確率の励起光強度依存性の検討により明らかにした。さらに、励起子分子-励起子の時系列的遷移過程による光子対発生の検証についても実施した。

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人電子情報通信学会  

単一光子の不可分性に基づく極めて高い秘匿性を持つ高効率量子鍵配送の実現に向け、シリコン単一光子検出器の検出感度が高い波長での光子生成が可能な半導体量子ドットを形成し、単一の励起子遷移による高純度の単一の光子数状態にある光子発生を確認した。応用上、複数光子の同時発生を抑制する必要があるが、多励起子状態の関与が単一光子発生動作に大きな影響を与えることを、光子同時計数確率の励起光強度依存性の検討により明らかにした。さらに、励起子分子-励起子の時系列的遷移過程による光子対発生の検証についても実施した。

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人電子情報通信学会  

単一光子の不可分性に基づく極めて高い秘匿性を持つ高効率量子鍵配送の実現に向け、シリコン単一光子検出器の検出感度が高い波長での光子生成が可能な半導体量子ドットを形成し、単一の励起子遷移による高純度の単一の光子数状態にある光子発生を確認した。応用上、複数光子の同時発生を抑制する必要があるが、多励起子状態の関与が単一光子発生動作に大きな影響を与えることを、光子同時計数確率の励起光強度依存性の検討により明らかにした。さらに、励起子分子-励起子の時系列的遷移過程による光子対発生の検証についても実施した。

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：LIPPINCOTT WILLIAMS & WILKINS  

The present study was performed to assess cerebral glucose metabolism in patients with panic disorder using positron emission tomography. F-18-fluorodeoxyglucose positron emission tomography with voxel-based analysis was used to compare regional brain glucose utilization in 12 nonmedicated panic disorder patients, without their experiencing panic attacks during positron emission tomography acquisition, with that in 22 healthy controls. Panic disorder patients showed appreciably high state anxiety before scanning, and exhibited significantly higher levels of glucose uptake in the bilateral amygdala, hippocampus, and thalamus, and in the midbrain, caudal pons, medulla, and cerebellum than controls. These results provided the first functional neuroimaging support in human patients for the neuroanatomical hypothesis of panic disorder focusing on the amygdala-based fear network. NeuroReport 16:927-931 (c) 2005 Lippincott Williams & Wilkins.

DOI： 10.1097/00001756-200506210-00010

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：INST PURE APPLIED PHYSICS  

Single-photon emitters and detectors are key devices to realize secure communications with single-photon-based quantum cryptography and single-photon-based quantum computing. InAlAs quantum dots (QDs) cover the wavelength range with high quantum efficiencies of Si-based single-photon detectors. Clear photon antibunching was observed from an InAlAs single QD under weak excitations. To realize single-photon emitters on demand, complete population of the QD energy states before the photon emission events is necessary, but the measured antibunching properties were dependent substantially on the photo-excitation powers. The physical origin of this problem is discussed. The criterion to distinguish the real deviation from the photon antibunching condition and the artifact of the measurements is clarified. The capability of single-photon emissions on demand will be demonstrated with photon antibunching under pulsed operations.

DOI： 10.1143/jjap.44.L793

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：WILEY-VCH Verlag GmbH & Co  

Regulated single-photon generation from an InAlAs quantum dot was demonstrated at a wavelength in which Si-avalanche photodiode single-photon detector has high quantum efficiency. Measured excitation power dependence of photon coincidence counts revealed that highly pure single-photon emission was realized at low excitation powers. Beyond a critical excitation, population of multi-exciton states in the quantum dot degraded the purity of single-photon emission.

DOI： 10.1002/pssc.200562027

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

DOI： 10.1002/pssc.200562032

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：INST PURE APPLIED PHYSICS  

The role of nitrogen (N) in InAs quantum dots (QDs) surfaces was studied by supplying a nitrogen (N) precursor to InAs QDs surfaces just before burying them under GaAs capping layers. Monomethylhydrazine was used as the N precursor. InAs QDs treated by such N exposure of their upper surfaces showed the following distinct improvements in their uniformity and efficiency: the peaks of histograms showing QD size distributions observed by atomic-force microscopy became narrower. Photoluminescence (PL) subpeaks originating from QD energy states showed clearer structures. The full widths at half maximum of the PL linewidths were reduced to 20 meV at room temperature, which is among the lowest reported. In addition to these observations of higher QD uniformities, the thermal activation energy for the temperature dependence of integrated PL intensity increased from 150 to 310 meV and also the PL efficiency increased similar to 6-folds with the N-exposure of the InAs QD surfaces. The role of N in these marked improvements in characteristics was discussed on the basis of valence-force field model calculations.

DOI： 10.1143/JJAP.44.L1512

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

High-quality ZnO thin films were grown by plasma-enhanced molecular-beam epitaxy on sapphire substrates. Three excitonic transitions associated with the valence bands A, B, and C were clearly revealed in the reflectance spectrum measured at 33 K. This result indicates that the ZnO thin films have the wurtzite crystalline structure. The emission spectra were measured with backscattering geometry at room temperature. When the excitation exceeded a certain value, linewidth narrowing, nonlinear rise of emission intensity, and the shortening of the carrier lifetime were clearly observed and these demonstrate the onset of stimulated emission. Together with the ZnO thickness dependence, we conclude that the observation of a stimulated emission in a direction perpendicular to the film surface is predominantly due to scattering of the in-plane stimulated emission by slightly remaining surface undulations in the ZnO films. (C) 2004 American Institute of Physics.

DOI： 10.1063/1.1778216

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記述言語：英語   掲載種別：学位論文（博士）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-V C H VERLAG GMBH  

Dynamical properties of exciton localization into spatially isolated localized states with atom-like density of states caused by alloy potential fluctuations were examined. Submicron-sized mesa-shaped structures were prepared to resolve the contribution of single localized states to the optical spectra, which makes it possible to observe atom-like emission lines and to discuss the dynamical properties of exciton energy relaxations by employing micro-time-resolved PL measurements. It will be shown that in the samples with high exciton energy transfer efficiency, photogenerated excitons can relax into the spatially isolated localized centers with strong zero-dimensional nature, which leads to the limited number of atom-like emission lines. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssb.200304270

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-V C H VERLAG GMBH  

Formation of ohmic contacts to p-type zinc oxide (ZnO) was studied. The p-type ZnO samples were grown by metalorgarric molecular-beam epitaxy with diethylzinc, deionized water vapor and monomethythidrazine and were annealed under oxygen gas ambient at 650 degreesC or 700 degreesC for 20 min to activate doped nitrogen acceptors. Although the current-voltage characteristics measured through gold p-contacts were not perfectly ohmic, they showed perfectly ohmic properties after rapid thermal annealing (RTA) in the temperature range of 300 to 520 degreesC for 2 min. The ohmic contact resistivity was measured with the transmission-line measurement method and it was decreased to approximately 1/64 with increasing the RTA temperature. The minimum contact resistivity of 3.15 x 10(-3) Ohm cm(2) was observed with RTA at 520 degreesC for 2 min. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssb.200304286

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-V C H VERLAG GMBH  

Control of ZnO and CdO crystalline structures and p-type doping in ZnO were studied. Formation of zincblende ZnO layers as well as zincblende CdO/ZnO short-period superlattices (SPSL) are demonstrated and bright luminescence was observed even at room temperature from the CdO/ZnO SPSL. p-Type conductivity observed in N-doped ZnO is studied and the relation to the photoluminescence peaks is discussed. (C) 2004 WILEY-VCH Vertag GmbH & Co. KGaA, Weinheim.

DOI： 10.1002/pssb.200304290

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人電子情報通信学会  

最近の量子情報科学の著しい進展に伴い、量子暗号通信用光振として用いられる単一光子光源や、量子演算の中核を担う単一量子ゲート等々,種々の新規な単一量子デバイスの展開が急となっている。絶対的に安全な秘匿情報通信を可能とする単一光子光源の実現のためには、現在の減衰コヒーレント光に代わり光子数揺らぎのない非古典光の発生が必須である。我々はピラミッド型半導体三次元微小光共振器と、半導体中に形成される原子様の単一量子状態の結合により非古典的単一光子光源を実現することを提案し、その作製技術及び光学物性の検討を行っている。本講演では,大きな振動子強度のためより効率的な光子発生が期待されるII-VI族広禁制帯半導体を用いて形成したピラミッド型三次元微小光共振器の作製及び共振特性と、混晶半導体中に形成される局在準位を利用した原子様単一量子準位の形成に関して報告する。

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人電子情報通信学会  

最近の量子情報科学の著しい進展に伴い、量子暗号通信用光振として用いられる単一光子光源や、量子演算の中核を担う単一量子ゲート等々,種々の新規な単一量子デバイスの展開が急となっている。絶対的に安全な秘匿情報通信を可能とする単一光子光源の実現のためには、現在の減衰コヒーレント光に代わり光子数揺らぎのない非古典光の発生が必須である。我々はピラミッド型半導体三次元微小光共振器と、半導体中に形成される原子様の単一量子状態の結合により非古典的単一光子光源を実現することを提案し、その作製技術及び光学物性の検討を行っている。本講演では,大きな振動子強度のためより効率的な光子発生が期待されるII-VI族広禁制帯半導体を用いて形成したピラミッド型三次元微小光共振器の作製及び共振特性と、混晶半導体中に形成される局在準位を利用した原子様単一量子準位の形成に関して報告する。

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

Two kinds of self-assembled InAs quantum dots (QDs) grown on GaAs (001) substrates were studied. One is capped with GaAs layers and the other with GaNAs strain-compensating layers. Photoluminescence (PL) measurements on the two kinds of InAs QDs showed distinct dependence on the selection of the capping layers. The homogeneity and luminescence efficiency of the InAs QDs were much improved when the net strain was reduced with GaNAs layers. These results demonstrate the importance of net strain compensation for the improved optical quality of InAs QDs. (C) 2003 American Institute of Physics.

DOI： 10.1063/1.1629803

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記述言語：英語   出版者・発行元：Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physics  

GaNAs strain-compensating layers (SCLs) are applied to bury InAs quantum dots (QDs) grown on GaAs substrates. The main idea is the compensation of the compressive strain induced by InAs QDs with the tensile strain in the GaNAs SCLs to keep the total strain of the system minimum. The application of the GaNAs SCLs resulted in a systematic shift of photoluminescence (PL) peaks of the InAs QDs toward the longer wavelengths with the increase of the nitrogen (N) composition in GaNAs, and luminescence at a wavelength of 1.55 μm has been achieved from the InAs QDs for the N composition of 2.7% in the GaNAs SCL. This result is promising for the application of GaNAs SCL for InAs-QDs-based long-wavelength light sources for optical-fiber communication systems.

DOI： 10.1143/jjap.42.5598

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

Sharp and discrete emission lines from single localized states in ZnCdS ternary alloys were clearly observed from selectively grown mesa structures. This is a demonstration that compound semiconductor alloy systems, which usually show broad emission spectra due to alloy fluctuations, are able to exhibit emissions from discrete energy levels with quasi-zero-dimensional density of states in limited mesa areas where limited number of deeper localized states will contribute. Introduction of ZnCdS/MgS short-period superlattices is found to play a significant role for the exciton migration enhancement from shallower to deeper localized states, which makes the observation of the emission lines from the single localized states possible in the ZnCdS alloy layers. (C) 2003 American Institute of Physics.

DOI： 10.1063/1.1583859

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Transmission electron microscopy (TEM) and transmission electron diffraction (TED) examination has been made to investigate the microstructural behaviour of rock-salt CdO layers grown on (0 0 1) GaAs substrates with two different buffer layers of ZnS and ZnO/ZnS. It is shown that the CdO layer grown on the ZnS buffer layer has epitaxial relationship to the GaAs substrate, even though a low density of CdO nano-crystallites (18-25 nm across) are formed at the CdO/ZnS interface region. TEM and TED results show that the CdO layer grown on the ZnO/ZnS buffer layer is polycrystalline. TED results also show that the ZnO buffer layer is polycrystalline with a mixture of wurtzite and zinc-blende phases, which results in the formation of polycrystalline CdO layers. (C) 2003 Published by Elsevier Science B.V.

DOI： 10.1016/S0022-0248(02)02521-6

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

II-VI quantum dots (QDs) have been Linder debate on their ripening properties for some time, and a unified understanding of this phenomenon will be given in this paper. Improvement of QD size uniformity is the main concern for practical applications. Scaling of the dot size distributions on some II-VI QDs will be discussed for the better understanding of the size distributions and for the improvement of the dot size uniformity. QD size distributions also tend to smear out the special features of QDs which are expected to modulate electron-photon interactions in optical microcavities coupled with QDs. Study of energy relaxation processes in QDs reveals the possibility of selectively exciting QDs which are in resonance with longitudinal optical (LO)-phonon emission processes. This scheme will be applied to the study of the strong coupling regime of optical microcavities coupled with QDs. CdS/ZnS QDs embedded in pyramidal three-dimensional microcavities are also examined to study the capability to observe enhanced spontaneous emissions by the coupling with cavity modes in pyramidal microcavities. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0022-0248(02)01862-6

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

Self-assembled InAs quantum dots (QDs) embedded in GaN0.007As0.993 strain compensating layers have been grown by metalorganic-molecular-beam epitaxy on a GaAs (001) substrate with a high density of 1x10(11) cm(-2). The photoluminescence properties have been studied for two periods of InAs quantum dots layers embedded in GaN0.007As0.993 strain compensating layers. Four well-resolved excited-state peaks in the photoluminescence spectra have been observed from these highly packed InAs QDs embedded in the GaN0.007As0.993 strain compensating layers. This indicates that the InAs QDs are uniformly formed and that the excited states in QDs due to the quantum confinement effect are well defined. This is explained by tensile strain in GaNAs layers instead of the usual GaAs layers to relieve the compressive strain formed in InAs QDs to keep the total strain of the system at a minimum. (C) 2002 American Institute of Physics.

DOI： 10.1063/1.1516873

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：INST PURE APPLIED PHYSICS  

Nitrogen (N) doping in ZnO is studied to realize reproducible p-type conductivity. Undoped ZnO layers prepared on a-face of sapphire substrates with H2O vapor-assisted growth showed n-type conductivity. However, N-doped ZnO (ZnO:N) layers grown in the similar manner showed the type conversion to p-type conductivity. As-grown p-type ZnO:N layers showed low net acceptor concentrations (N-A-N-D) of similar to10(14) cm(-3), but thermal annealing of the N-doped ZnO samples as well as the optimization of growth parameters increased the N-A-N-D up to similar to5 x 10(16) cm(-3). Photoluminescence measurements showed consistent spectra with the electrical properties by a clear conversion from neutral donor-bound exciton emission in n-ZnO to neutral acceptor-bound exciton emission in the p-ZnO layers.

DOI： 10.1143/JJAP.41.L1281

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

The energy relaxation processes of CdS self-assembled quantum dots (QDs) embedded in ZnSe were investigated. Longitudinal-optical (LO)-phonon resonant structures were discerned in the photoluminescence spectra under the CdS selective excitation, especially under nearly resonant excitation conditions. Strong energy selectivity among the Gaussian distributed energy levels of the QDs are observed in energy relaxation processes, in which excitons are dominantly injected into the QDs whose ground state energies with respect to the excitation energy are equal to the multi-LO-phonon energy of ZnSe. Detection-energy dependent photoluminescence excitation (PLE) measurements also suggest that the coupling strength between the excitons and LO phonons is strongly size-dependent, i.e., coupling is strongly enhanced in smaller QDs. In addition, type-II band alignment of the CdS/ZnSe heterostructure is experimentally confirmed directly by PLE measurements. (C) 2002 American Institute of Physics.

DOI： 10.1063/1.1504161

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

H2O vapor-activated ZnO layers have been grown on the a-face of sapphire substrates. The grown ZnO layers revealed a crystalline orientation of c-face ZnO ∥ a-face sapphire. For the II/VI flux ratio of 14, the ZnO layers showed a bandedge luminescence with the emission energy of 3.376 and 3.304 eV at 17 K and room temperature, respectively. The amount of the blue-shifted energy in the Zn-rich ZnO is estimated to be ∼30 meV in comparison to the donor-bound exciton emission reported previously. The energy shifting towards the higher level could be attributed to the drastic reduction of carrier concentration in the order of ∼1017 cm-3 for the II/VI flux ratio of 14. With this growth condition, electron mobility is recorded typically to be ∼90 cm2/Vs which is considerably higher for the same carrier concentrations reported previously with plasma as oxygen source.

DOI： 10.1002/1521-396X(200207)192:1<224::AID-PSSA224>3.0.CO;2-#

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：INST PURE APPLIED PHYSICS  

ZnO layers have been grown on a-face sapphire substrates using H2O vapor and O-2 plasma as oxygen sources. The growth rate of HO-vapor-assisted growth of ZnO (v-ZnO) is similar to3 times higher than that of plasma-assisted growth of ZnO (p-ZnO) for the same DEZn flux. This report addresses the higher growth activation of ZnO layers with H2O vapor than with O-2 plasma at the same substrate temperature. A sharp and intense photoluminescence (PL) spectrum is observed in v-ZnO at the neutral donor-bound exciton energy of 3.368eV at 16K. The PL excitation spectrum measurement revealed A and B free exciton energies of 3.382 and 3.388eV, respectively. On the other hand, the p-ZnO showed the band-edge emission energy of 3.373eV but with a very weak PL intensity and broader half width, The PL intensity from v-ZnO was similar to10(4) times brighter than that of p-ZnO and the integrated PL intensity measured at room temperature was kept to similar to1/8 of that measured at 16 K.

DOI： 10.1143/JJAP.41.2851

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

DOI： 10.1016/S0022-0248(01)01956-X

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Er doping in GaP was studied with metalorganic molecular-beam epitaxy employing a Knudsen cell for Er doping. Coherent growth of the Er-doped Gap layer was observed with relatively smooth surfaces up to Er concentration as high as similar to0.5%. Sharp 1.54-mum luminescence from Er3+ 4f-4f intra-shell transitions showed a weak temperature dependence and was observed up to room temperature. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0022-0248(01)02232-1

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Modified spontaneous emission properties in the presence of confined photon modes inside the three-dimensional (3-D) optical microcavities are demonstrated, Self-formed pyramidal-shaped semiconductor structures fabricated by selective-area growth technique are utilized as an optical microcavity in which discrete photon modes are generated. Noticeable modification of spontaneous emission from active layers embedded in microcavity structures is clearly observed in mu-PL spectra at room temperature, Almost perfect coincidence between enhanced photoluminescence peak wavelengths and the resonance modes inside microcavity is observed. Furthermore. Purcell factors calculated from the obtained Q values reach similar to9, which is inaccessible in the planar microcavitics with only one-dimensional photon confinement normal to the layers. These results indicate that the effective coupling between electronic system and 3-D confined optical fields is realized by the achievement of present low-loss 3-D microcavities with small cavity volume V-c whose dimension is comparable with lambda(3). (C) 2002 Elsevier Science B.V. All rights reserved.

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

Microcavities in the visible wavelength region were fabricated based on ZnSe-based distributed Bragg reflectors and US quantum dots were inserted in the cavities. Strong coupling of photonic fields with the US quantum dots in the II-VI semiconductor microcavities was studied, and the Rabi vacuum-field splitting of similar to3 meV was observed. The rationality of observing the strong coupling with the quantum dots is discussed. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S1386-9477(02)00152-2

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記述言語：英語   出版者・発行元：社団法人応用物理学会  

Erbium (Er) doping in GaNP during growth by metalorganic molecular-beam epitaxy was studied. Nitrogen (N) doping in GaP was possible up to ${\sim}\,2$% and exhibited large band-gap bowing consistent with previous reports. Er was doped in GaNP to study the codoping effect of Er and N. Er concentration was estimated to be about 0.2–0.8 at.% depending on the Er Knudsen cell temperature. Er doping in GaNP resulted in photoluminescence (PL) spectra similar to that of GaP in the visible-wavelength region, but the PL subpeaks at energies near the longitudinal-optical-phonon replica observed in GaP exhibited variations with Er doping. Although no sharp Er emissions originating from the 4f-4f inner-shell transitions were observed with the codoping, intense wide-band infrared (IR) luminescence covering the wavelength range from 1.1 to 1.6 $\mu$m was observed with the codoping of Er and N. The IR luminescence was linearly increased for the higher excitations, while the corresponding IR-PL intensity in undoped GaNP was weak and easily saturated.

DOI： 10.1143/JJAP.41.1030

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その他リンク： https://jlc.jst.go.jp/DN/JALC/00156583013?from=CiNii

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-V C H VERLAG GMBH  

CdS quantum dots (QDs) embedded in ZnSe-based microcavities were studied. The distributed Bragg reflectors (DBRs) consisted of quarter-wavelength-thick ZnSe, and ZnSe-MgS superlattices were grown, which exhibited a high reflectivity of 92% with just five periods. Microcavities with ZnSe lambda cavities were sandwiched with the DBRs and clear cavity resonance modes were observed. The US QDs were embedded at the antinode position of the ZnSe lambda cavity and were selectively excited by longitudinal-optical (LO) phonon-assisted energy relaxation to the QDs coupled to the cavity modes. This scheme made it possible to observe vacuum-field Rabi splitting with a coupling with QDs for the first time.

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY-V C H VERLAG GMBH  

Optical cavity properties of selectively grown ZnS pyramidal structures were studied. The resonance wavelengths were shifted with the pyramidal size, and pyramidal size dependence of the resonance wavelength was reasonably interpreted by an approximate calculation. Luminescence properties of the ZnS pyramidal photonic dot structures with embedded CdS active layers were studied and a clear modulation of the spontaneous emission was observed at room temperature. Modulated luminescence peaks showed very little temperature dependence of their peaks and their half-line width, which was 2.1 x 10(-4) nm/K and about 4.4 x 10(-3) meV/K, respectively. These properties will demonstrate the possibility of the future application to the temperature-stabilized light emitters with pyramidal photonic dot structures.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

We demonstrated the 1.55 μm light emission at room temperature from self-assembled InAs quantum dots embedded inside the GaNAs strain-compensating layer. InAs quantum dots have been capped with tensile strained GaNAs instead of InGaAs and GaAs to compensate the compressive strain formed due to InAs QDs to keep the total strain of the system minimum as a result the PL peak of InAs QDs shifts towards longer wavelength depending on the N% in GaNAs. The wavelength of 1.55 μm is the longest wavelength so far achieved in self-assembled quantum dots grown on Gads substrates, which would be promising for application to light source in long-wavelength optical-fiber communication system.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：World Scientific Publishing Co. Pte Ltd  

The effect of exciton localization is investigated in ZnCdS ternary alloys. Zn1-xCdxS films with Cd composition x(x=0.21-0.79) were prepared and transient optical properties of photoexcited excitons during the energy relaxation as well as steady-state photoluminescence (PL) properties are examined as a function of crystalline quality of the grown films. The sample with x=0.56 that is closely lattice matched to the GaAs substrate was found to show the maximum integrated band-edge PL (BEPL) intensity. The samples with larger lattice mismatch showed stronger quenching of the BEPL intensity, which is well correlated to the crystalline quality evaluated by X-ray rocking curve measurement. In order to study the contribution of exciton localization, time-resolved PL measurements were carried out. It is clearly revealed that the excitons fully relaxed to the localized states exhibit high luminescence efficiency, while the relaxation process of excitons toward the localization states is shown to be influenced by the crystalline quality of the films.

DOI： 10.1142/s0217979201008500

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

In this letter, we report the growth of single-crystalline rocksalt CdO layers on (001) GaAs substrates using ZnS buffer layers. The growth processes of CdO layers were studied by reflection high-energy electron diffraction (RHEED), and the grown CdO layers were evaluated with atomic force microscopy (AFM), and x-ray diffraction (XRD) measurements. After an initial growth delay, the formation of polycrystalline CdO was observed in RHEED measurements during the initial growth of very thin CdO layers. With the increase of the CdO layer thicknesses, streaky RHEED patterns were observed, which indicate the formation of single-crystalline cubic-phase CdO layers. Surface morphology of the CdO layers observed by AFM was atomically flat with root-mean-square roughness of similar to1 nm. The crystalline structures were elucidated from XRD measurements by the determination of the lattice constant to be 4.686 +/-0.001 Angstrom, indicating the single-phase rocksalt CdO structure. (C) 2001 American Institute of Physics.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：SPRINGER-VERLAG BERLIN  

Steady-state optical properties of CdS/ZnSe self-assembled quantum dots structures (QD's) were investigated, Transition energies obtained by both photoluminescence (PL) and photoluminescence excitation (PLE) measurements showed clear blue shift as the average height of CdS dots was reduced and the shift of PLE peaks was well coincided with the calculated transition energy using type-II band alignment Sharp PL spike peaks reflecting the inherent density of state of zero-dimensional systems showed up when the probe area was reduced. LO phonon resonant structures were also discerned in the PL spectra under the CdS selective excitation, especially in the nearly resonant excitation conditions. It is revealed that the observed LO phonon assisted relaxation of CdS QD's can be attributed to the energy relaxation of photoexcited holes in the ZnSe barrier layers.

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：SPRINGER-VERLAG BERLIN  

Optical properties of self-organized CdS quantum dots (QDs) embedded in monolithic ZnSe/MgS-superlattice microcavity were examined. In the photoluminescence (PL) of CdS QDs, the energy relaxation process was dominated by the photoexcited holes in the ZnSe barrier layers which is in resonance with the ZnSe LO phonon energies. Moreover this energy relaxation process formed the dispersion branches independent of the cavity mode. In the PL measurements of the on/off-resonant excitation, it was observed that the enhancement of the spontaneous emission occurs by the selected excitation of the CdS QDs which is in the resonance with the cavity mode and the LO phonon-assisted relaxations.

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

ZnS buffer layers were used to grow ZnO films on GaAs(001) substrates. The role of ZnS buffer layers in the growth of zincblende ZnO films on GaAs(001) substrates was investigated by atomic force microscopy. X-ray diffraction, and photoluminescence (PL) measurements. The optimization of the ZnS buffer layer thickness resulted in improvements of the surface morphology and crystalline quality of ZnO films by homogeneous nucleation. With the optimized ZnS buffer layer thickness of similar to 72 nm the surface root-mean-square roughness of the grown ZnO film was minimized to similar to 14 nm and the deep-level PL intensity was reduced to 1/76 of the near-band edge PL intensity at room temperature. (C) 2000 Elsevier Science B.V. All rights reserved.

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：MINERALS METALS MATERIALS SOC  

Main factors which determine the size, the standard deviations which show the degree of the size fluctuations for the average dot height and diameter, and density in ZnSe self-organized quantum dots (QDs) grown on ZnS layers were studied. By lowering the growth temperature the QDs average size and its standard deviation decreased and the density increased due to the slower surface migration. With the application of the scaling theory, it was revealed that the normalized size distributions were uniquely determined by the nucleation process although the apparent standard deviations of the QD sizes were dependent on the growth temperature. The influence of surface roughness of the underneath layer on the formation of the relations of the dot height and diameter was also examined. It was shown that the fluctuation of the surface potential contributes significantly to the apparent standard deviations of ZnSe self-organized QDs sizes.

DOI： 10.1007/s11664-000-0037-0

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記述言語：英語   出版者・発行元：社団法人応用物理学会  

Microspectroscopy of luminescence and optical reflection properties was performed on MgS/ZnSe superlattices with the spatial resolutions of ~µm and ~10 µm, respectively, to examine the origin of excitonic transitions. C1-HH1 well-defined excitonic peaks which originate from multi-monolayer (ML) variation of 4–5 ML height, formed predominantly at the ZnSe surfaces of MgS/ZnSe heterointerfaces, were found to make a significant contribution to the optical spectra. The detailed identification of these inhomogeneous C1-HH1 excitonic peaks and intrinsic C1-LH1 excitonic peaks, which are close in energy levels, is discussed on the basis of results of the present microspectroscopy studies and with respect to the temperature dependence of the luminescence spectra.

DOI： 10.1143/JJAP.39.501

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その他リンク： http://hdl.handle.net/2115/59642

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

A stable wurtzite phase of ZnO is commonly observed. In this letter, we report the growth and characterization of zinc-blende ZnO on GaAs(001) substrates. The ZnO films grown on GaAs(001) substrates using microwave-plasma-assisted metalorganic molecular-beam epitaxy were characterized by reflection high-energy electron diffraction, x-ray diffraction, transmission electron microscope, and atomic force microscope measurements. The use of a ZnS buffer layer was found to lead to the growth of the zinc-blende ZnO films. Although the zinc-blende ZnO films were polycrystalline with columnar structures, they showed bright band-edge luminescence at room temperature. (C) 2000 American Institute of Physics. [S0003-6951(00)01005-6].

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記述言語：英語   出版者・発行元：American Institute of Physics  

We have investigated the effects of In doping on the optical properties of GaN films grown bygas-source molecular-beam epitaxy. Time-resolved photoluminescence was carried out to study thetransient optical properties of the epitaxial films. In comparison to the undoped GaN film, thespontaneous emission lifetime was prolonged from below 20 to 70 ps by doping with In. Underhigh-excitation density, stimulated emission was observed from both samples. The thresholdexcitation density was found to be reduced in the In-doped sample. These significant improvementsof the optical properties are attributed to the effective suppression of the formation of thenonradiative recombination centers caused by a change of the growth kinetics induced by a smallamount of In supplied during growth of the GaN films.

DOI： 10.1063/1.125178

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

Self-organized ZnSe quantum dots (QDs) were grown on (100) ZnS/GaAs surfaces to study the relation of the size dispersion and luminescence. The exact dot sizes were obtained by measurements of atomic force microscope with its tip calibration and transmission electron microscope. The average dot size was 2.0 nm high and 11 nm in its diameter and the density was 1 x 10(10) cm(-2). Transition energies of ZnSe QDs were calculated using these measured dot sizes. These calculated peaks were in reasonable agreement with measured photoluminescence (PL) peaks. It was also revealed that the broadening of the PL spectra from ZnSe QDs were consistently explained by the dot size distribution. (C) 1999 American Institute of Physics. [S0003-6951(99)03928-5].

DOI： 10.1063/1.124333

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AMER INST PHYSICS  

Here we describe a strategy toward constructing semiconductor photonic dots in the ultraviolet to blue region. An array of ZnS dots was grown on a GaAs substrate with a selective growth method. The ZnS dots have a pyramidal structure with the base plane of 800 nm square and the height of 300 nm. The {034} crystallographic planes form the sidewalls of the pyramids. Therefore, the size of the pyramidal dots is uniquely determined by the mask patterning. The optical reflection spectra showed clear resonance peaks which are reasonably assigned by the calculation of the resonance modes. Each resonance showed the Q values on the order of 160-300, a reasonable value to observe the modification of the total spontaneous emission rate in this kind of photonic dots. (C) 1999 American Institute of Physics. [S0003-6951(99)03614-1].

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Institute of Physics Inc.  

Optical properties of a ZnSe/MgS superlattice (SL) were studied by reflection and photoluminescence (PL) spectroscopies. Excitonic structures were clearly observed in the reflection spectra up to room temperature, and the exciton absorption peak energy and linewidth were well coincident with the PL peak energy and linewidth. The origin of the lowest luminescence peak was indicated to be C1-HH1 exciton up to room temperature. The lineshape broadening due to longitudinal-optical-phonon scattering of excitons is much decreased in this SL compared to bulk ZnSe. © 1997 American Institute of Physics.

DOI： 10.1063/1.118867

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Excitonic properties of newly developed zinc-blende ZnSe/MgS superlattices (SLșs) were measured by reflection spectroscopy. The modification of the excitonic peaks by the multiple reflection in the SL films was treated theoretically and a fitting method to estimate the exciton absorption peak positions and exciton linewidths was developed. Although zinc-blende MgS did not exist before, excellent optical properties were observed in the ZnSe/MgS SL"s. Excitonic structures were clearly observed from 13 K up to the measured room temperature. In spite of strong ionicity of MgS barrier layers in the ZnSe/MgS SLșs, the reduction of exciton-LO-phonon coupling was clearly observed in narrower wells. This indicates that the quantum confinement effect on excitons is large due to the large band offsets and it overcomes the enhancement of exciton-LO-phonon scattering due to high ionicity in barrier layers. © 1997 The American Physical Society.

DOI： 10.1103/PhysRevB.55.4449

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

We report the growth of zinc-blende ZnSe/MgS superlattices (SLs) on GaAs (001) substrates. The SLs were grown with metalorganic vapor phase epitaxy by selecting appropriate precursors for Mg and S. MgS naturally forms rocksalt structures, but zinc-blende MgS layers were grown. The lattice constant of MgS was estimated to be 5.59 Å. X-ray diffraction measurements show that the ZnSe/MgS SLs are grown coherently to the GaAs substrates up to the total thicknesses of ∼3000 Å. © 1996 American Institute of Physics.

DOI： 10.1063/1.116552

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記述言語：英語   出版者・発行元：公益社団法人 応用物理学会  

The effect of organic As flow during the thermal cleaning of GaAs substrates in metalorganic vapor phase epitaxy (MOVPE) and the initial growth of ZnSe on the cleaned GaAs surfaces are investigated using atomic force microscopy, X-ray diffraction and photoluminescence measurements. The thermal cleaning with organic As flow in MOVPE is effective to form atomically flat GaAs surfaces and to grow high-quality ZnSe films. The initial growth processes of ZnSe films are critically dependent on the GaAs surface and on the VI/II flow ratio for the ZnSe growth. The initial growth process of ZnSe films on GaAs surfaces is dominated by the two-dimensional growth mode for Zn-rich growth conditions, while three-dimensional island growth becomes dominant as the Se flow rate increases.

DOI： 10.1143/jjap.35.L1006

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記述言語：英語   出版者・発行元：一般社団法人電子情報通信学会  

Single-photon sources of high photon-extraction efficiency are strongly needed for the practical use in quantum field. We succeed in fabricating metal (sliver)-embedded GaAs nanocone structure incorporating single InAs quantum dots. Efficient single-photon emission is demonstrated using autocorrelation measurements and the photon-extraction efficiency as high as 24.6% is obtained from the structure.

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掲載種別：機関テクニカルレポート，技術報告書，プレプリント等  

We investigate the long wavelength (1.2 to 1.55 micro-m) photoluminescence of
high-density InAs quantum dots and dashes, which were grown on InP substrates.
We analyze the temperature dependence of the recombination and carrier
distribution on the alloy composition of the barrier materials, InGaAlAs, and
on the existence of a wetting layer. Carrier escape and transfer are discussed
based on temperature dependent photoluminescence measurements and theoretical
considerations about the heterostructures' confinement energies and band
structure. We propose two different contributions to the thermal quenching,
which can explain the observations for both the quantum dot and dash samples.
Among these one is a unique phenomenon for high density quantum dot/dash
ensembles which is related to significant inter-dot/dash coupling. With the
goal ahead to use these dots and dashes for quantum optical applications on the
single-dot/dash level in the telecommunication C band as well as at elevated
temperatures we present first steps towards the realization of such devices.

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その他リンク： http://arxiv.org/pdf/1202.1360v1

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DOI： 10.1063/1.3666428

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記述言語：日本語   出版者・発行元：一般社団法人電子情報通信学会  

従来,独立して取り扱われていた半導体量子ドットおよび不純物準位を用いた単一光子発生を単一固体内で制御する構造として,同族元素による等電子中心を利用する方法を提案し,ZnSe:Te系を用いた単一光子源の検討を行った.400℃成長試料において,埋め込みZnTe量の増加に伴いTe_2等電子中心,Te_<n>2>等電子中心,ZnTe量子ドットへの発光中心の遷移を確認し,発光過程制御の足がかりを得た.

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記述言語：英語   出版者・発行元：IEEE  

Luminescence efficiency of InAs quantum dots (QDs) was shown to improve with strain compensation of the compressive strain in InAs QDs with tensile-strained GaNAs burying layers. The improved luminescence efficiency is discussed with the viewpoint of the average strain compensation in the strained semiconductor system. The red shift of the luminescence peak up to 1.55 mu m is also discussed from the same viewpoint of the strain compensation. The valence-force field model calculation of the strain field in the InAs QDs buried with the GaNAs strain compensating layer shows that the strain induced by nitrogen (N) atoms is significant and localized to respective N atoms and the more detailed information how the N atoms are incorporated during the burying process of the QDs with the GaNAs layers is necessary for the full description.

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記述言語：日本語   掲載種別：記事・総説・解説・論説等（学術雑誌）   出版者・発行元：日本学術振興会光電相互変換第125委員会  

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記述言語：日本語   出版者・発行元：北海道大学  

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