Directory of Researchers
| HARADA Yukihiro |  |
| Graduate School of Engineering / Department of Electrical and Electronic Engineering | |
| Assistant Professor | |
| Electro-Communication Engineering |
Researcher Profile and Settings
Affiliation
＜Faculty / Graduate School / Others＞
Graduate School of Engineering / Department of Electrical and Electronic Engineering＜Related Faculty / Graduate School / Others＞
Faculty of Engineering / Department of Electrical and Electronic Engineering
Teaching
- Faculty of Engineering / Department of Electrical and Electronic Engineering, 2022, Electrical and Electronics Engineering Laboratory ⅡA
- Faculty of Engineering / Department of Electrical and Electronic Engineering, 2022, Electrical and Electronics Engineering Laboratory ⅡA
- Faculty of Engineering / Department of Electrical and Electronic Engineering, 2022, Electrical and Electronics Engineering Laboratory ⅡB
- Faculty of Engineering / Department of Electrical and Electronic Engineering, 2022, Electrical and Electronics Engineering Laboratory ⅡB
Research Activities
Research Areas
- Manufacturing technology (mechanical, electrical/electronic, chemical engineering) / Electric/electronic material engineering
Published Papers
- May 2023, Journal of Physics and Chemistry of Solids
Scientific journal
- 01 Feb. 2022, AIP Advances
[Refereed]
Scientific journal
- SPIE, 01 Apr. 2021, Photonic Heat Engines: Science and Applications III
[Refereed]
International conference proceedings
- Society of Materials Science, Japan, 15 Oct. 2020, Journal of the Society of Materials Science, Japan, 69 (10), 727 - 732
[Refereed]
Scientific journal
- AIP Publishing, 10 Aug. 2020, Applied Physics Letters, 117 (6), 061106 - 061106
[Refereed]
Scientific journal
- 28 Jul. 2020, Applied Physics Letters, 117 (4), 041104-1 - 041104-5, English
[Refereed]
Scientific journal
- SPIE, 24 Feb. 2020, Photonic Heat Engines: Science and Applications II
[Refereed]
International conference proceedings
- IOP Publishing, 01 Dec. 2019, Applied Physics Express, 12 (12), 125008 - 125008
[Refereed]
Scientific journal
- The Optical Society, 25 Nov. 2019, Optics Express, 27 (24), 34961 - 34961
[Refereed]
Scientific journal
- Society of Materials Science, Japan, 15 Oct. 2019, Journal of the Society of Materials Science, Japan, 68 (10), 762 - 766
[Refereed]
Scientific journal
- Aug. 2019, Semiconductor Science and Technology, 34, 094003 - 1-5, English
[Refereed]
- Springer Singapore, 2019, Green Energy and Technology
[Refereed]
Development of high-efficiency solar cells is one of the attractive challenges in renewable energy technologies. Photon up-conversion can reduce the transmission loss and is one of the promising concepts which improve conversion efficiency. Here we present an analysis of the conversion efficiency, which can be increased by up-conversion in a single-junction solar cell with a hetero-interface that boosts the output voltage. We confirm that an increase in the quasi-Fermi gap and substantial photocurrent generation result in a high conversion efficiency.
Nature Publishing Group, 01 Dec. 2018, Scientific Reports, 8 (1), pp. 872 - 1-8, English[Refereed]
Scientific journal
- Nov. 2018, Proceedings of the 35th European Photovoltaic Solar Energy Conference and Exhibition, 126 - 128, English
International conference proceedings
- Jul. 2018, Applied Physics Express, Vol. 11 (No. 1), pp.082303 - 1-4, EnglishHot-Carrier Generation in a Solar Cell Containing InAs/GaAs Quantum-Dot Superlattices as a Light Absorber
[Refereed]
Scientific journal
- Apr. 2018, Scientific Reports, 8, 6457 - 1-10, English
[Refereed]
Scientific journal
Small numbers of nitrogen dopants dramatically modify the electronic properties of GaAs, generating spatially localized resonant states within the conduction band, pair and cluster states in the band gap, and very large shifts in the conduction-band energies with nonlinear concentration dependence. Cross-sectional scanning tunneling microscopy provides the local electronic structure of single nitrogen dopants at the (110) GaAs surface, yielding highly anisotropic spatial shapes when the empty states are imaged. Measurements of the resonant states relative to the GaAs surface states and their spatial extent allow an unambiguous assignment of specific features to nitrogen atoms at different depths below the cleaved (110) surface. Multiband tight-binding calculations around the resonance energy of nitrogen in the conduction band match the imaged features, verifying that the Green's function method can accurately describe the isolated isovalent nitrogen impurity. The spatial anisotropy is attributed to the tetrahedral symmetry of the bulk lattice and will lead to a directional dependence for the interaction of nitrogen atoms. Additionally, the voltage dependence of the electronic contrast for two features in the filled state imaging suggests these features could be related to a locally modified surface state.
AMER PHYSICAL SOC, Oct. 2017, PHYSICAL REVIEW B, 96 (15), pp. 155210 - 1-8, English[Refereed]
Scientific journal
- Sep. 2017, 材料 別冊, 66 (9), pp. 629 - 633, JapaneseInAs/GaAs量子ドット超格子を用いたホットキャリア型太陽電池の基礎特性
[Refereed]
Scientific journal
We studied the effects of the internal electric field on two-step photocarrier generation in InAs/GaAs quantum dot superlattice (QDSL) intermediate-band solar cells (IBSCs). The external quantum efficiency of QDSL-IBSCs was measured as a function of the internal electric field intensity, and compared with theoretical calculations accounting for interband and intersubband photoexcitations. The extra photocurrent caused by the two-step photoexcitation was maximal for a reversely biased electric field, while the current generated by the interband photoexcitation increased monotonically with increasing electric field intensity. The internal electric field in solar cells separated photogenerated electrons and holes in the superlattice (SL) miniband that played the role of an intermediate band, and the electron lifetime was extended to the microsecond scale, which improved the intersubband transition strength, therefore increasing the two-step photocurrent. There was a trade-off relation between the carrier separation enhancing the two-step photoexcitation and the electric-field-induced carrier escape from QDSLs. These results validate that long-lifetime electrons are key to maximising the two-step photocarrier generation in QDSL-IBSCs.
NATURE PUBLISHING GROUP, Jul. 2017, SCIENTIFIC REPORTS, 7, pp. 5865 - 1-10, English[Refereed]
Scientific journal
We studied the effects of miniband formation on the photocurrent generated by two-step intersubband absorption in an intermediate-band solar cell incorporating an InAs/GaAs quantum dot superlattice (QDSL). The two-step photocarrier generation increases with the electronic state coupling of InAs QDSLs in the intrinsic layer. Because carriers that are excited into the superlattice minibands spatially separate in an internal electric field, the electron-hole recombination rate for the photoexcited carriers decreases, and therefore, the electron lifetime increases. The long-lived electrons in the intermediate states of the QDSL miniband increase the intersubband absorption strength. We confirmed a systematic sensitive change in the two-step photocurrent generation depending on the miniband formation controlled by the temperature. Published by AIP Publishing.
AMER INST PHYSICS, May 2017, APPLIED PHYSICS LETTERS, 110 (19), pp. 193104 - 1-5, English[Refereed]
Scientific journal
We studied time-resolved photocarrier transport through InAs/GaAs quantum dot superlattice (QDSL) solar cells (SCs) using time-of-flight spectroscopy with an optical probe QD structure beneath the QDSL. Carriers optically pumped in the top p-GaAs layer were transported through the intrinsic layer, including the QDSLs, before arriving at the probe QDs. The photoexcited carrier density significantly influenced the time-resolved photoluminescence (PL) of the QDSLs and probe QDs. The time-resolved PL profile of the probe QDs indicated that excitation densities in excess of 25nJ/cm(2) drastically decreased the rise time, suggesting rapid carrier transport through the QDSLs. This was also confirmed by QDSL carrier transport dynamics, for which the PL intensity of the excited states decayed rapidly above this excitation power density, 25nJ/cm(2), while the ground state remained constant. These results demonstrate that filling the ground states of QDSLs and starting to populate the excited state miniband accelerates carrier transport in QDSL SCs. Furthermore, according to two-step photon absorption measurements taken with a 1.3-mu m infrared laser light source, electrons play a key role in the generation of extra photocurrent by sub-band-gap photon irradiation.
AMER PHYSICAL SOC, Nov. 2016, PHYSICAL REVIEW B, 94 (19), pp. 195313 - 1 -9, English[Refereed]
Scientific journal
We studied the polarization anisotropy of electroluminescence (EL) and net modal gain characteristics of laser device structures containing 40 stacked InAs/GaAs quantum dot (QD) layers. The electronic coupling between the closely stacked QDs enhanced the transverse-magnetic (TM) polarization component owing to the heavy-and light-hole mixing. Thereby, the [110]-waveguide devices exhibited a laser oscillation of not only the transverse-electric (TE) but also the TM component. Laser oscillation occurred at 1137nm from the first excited state for the 300-mu m-long cavity, while it occurred at 1167 nm from the ground state for the 1000-mu m-long cavity. The polarization anisotropy of the EL intensity strongly depended on the injection current density. The polarized EL intensity was almost isotropic at low injection current density. As the injection current density was increased, the TE component was gradually enhanced, which resulted in a markedly TE-dominant anisotropy above the threshold current density for laser oscillation. The net modal gains evaluated using the Hakki-Paoli method also exhibited a TE-enhanced characteristic with increasing injection current density. As the EL spectra of the TE component have an inhomogeneous broadening narrower than that of the TM component, the TE-mode intensity is likely to be enhanced by the concentration of the injected carriers. Published by AIP Publishing.
AMER INST PHYSICS, Oct. 2016, JOURNAL OF APPLIED PHYSICS, 120 (13), pp. 134313 - 1-6, English[Refereed]
Scientific journal
- Sep. 2016, 日本材料学会会誌「材料」, 65 (9), pp. 647 - 651, Japanese量子ドット超格子太陽電池における2段階光励起電流生成ダイナミクスの電界依存特性
[Refereed]
Scientific journal
We report the time-resolved photoluminescence spectroscopy of nanoseconds-scale hot-carrier (HC) cooling dynamics in InAs/GaAs quantum dot superlattices (QDSLs). We demonstrate supra 1000-K time-averaged carrier temperature in the InAs/GaAs QDSLs from one-dimensional density of states restricting the phase space and energy-momentum conservation in the carrier scattering processes. The InAs/GaAs QDSLs HC energy dissipation rate was much smaller than that for InAs/GaAs multiple quantum wells and nearly excitation-photon-density independent, implying reduced efficiency of carrier-carrier scattering.
AMER PHYSICAL SOC, Mar. 2016, PHYSICAL REVIEW B, 93 (11), pp. 115303 - 1-5, English[Refereed]
Scientific journal
We have conducted rapid thermal annealing (RTA) for improving the two-dimensional (2D) arrangement of electronic states in the epitaxial nitrogen (N) delta-doped layer in GaAs. RTA rearranged the N-pair configurations in the GaAs (001) plane and reduced the number of non-radiative recombination centers. Furthermore, a Landau shift, representing the 2D delocalized electronic states in the (001) plane, was observed at around zero magnetic field intensity in the Faraday configuration. (C) 2016 AIP Publishing LLC.
AMER INST PHYSICS, Mar. 2016, APPLIED PHYSICS LETTERS, 108 (11), pp. 111905 - 1-4, English[Refereed]
Scientific journal
- IEEE, 2016, 2016 COMPOUND SEMICONDUCTOR WEEK (CSW) INCLUDES 28TH INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE & RELATED MATERIALS (IPRM) & 43RD INTERNATIONAL SYMPOSIUM ON COMPOUND SEMICONDUCTORS (ISCS), EnglishPolarization anisotropy of electroluminescence and net-modal gain in highly stacked InAs/GaAs quantum-dot laser devices
[Refereed]
International conference proceedings
- Transverse-magnetic laser oscillation from highly stacked InAs/GaAs quantum dots
We studied electroluminescence and net-modal gain in 40-stacked InAs/GaAs quantum dot (QD) laser devices. Since the electronic coupling between the QDs enhanced the transverse-magnetic (TM) component, the [110] waveguide devices exhibited a laser oscillation in the TM component as well as the transverse-electric (TE) component.
IEEE, 2016, 2016 INTERNATIONAL SEMICONDUCTOR LASER CONFERENCE (ISLC), English[Refereed]
International conference proceedings
- IEEE, 2016, 2016 COMPOUND SEMICONDUCTOR WEEK (CSW) INCLUDES 28TH INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE & RELATED MATERIALS (IPRM) & 43RD INTERNATIONAL SYMPOSIUM ON COMPOUND SEMICONDUCTORS (ISCS), EnglishTwo-Dimensional Energy Dispersion in Thermally Annealed Epitaxial Nitrogen Atomic Sheet in GaAs
[Refereed]
International conference proceedings
- Sep. 2015, Journal of the Society of Materials Science, 64 (9), pp. 685 - 689, Japanese近接積層InAs/GaAs量子ドット半導体光アンプの光導波モード解析
[Refereed]
Scientific journal
We studied the two-step photon absorption (TSPA) process in InAs/GaAs quantum-dot superlattice (QDSL) solar cells. TSPA of subband-gap photons efficiently occurs when electrons are pumped from the valence band to the states above the inhomogeneously distributed fundamental states of QDSLs. The photoluminescence (PL)-excitation spectrum demonstrates an absorption edge attributed to the higher excited states of the QDSLs in between the InAs wetting layer states and the fundamental states of QDSLs. When the absorption edge of the excited state was resonantly excited, the superlinear excitation power dependence of the PL intensity demonstrated that the electron and hole created by the interband transition separately relax into QDSLs. Furthermore, time-resolved PL measurements demonstrated that the electron lifetime is extended by thereby inhibiting recombination with holes, enhancing the second subband-gap absorption.
AMER PHYSICAL SOC, May 2015, PHYSICAL REVIEW B, 91 (20), pp. 201303 - 1-6, English[Refereed]
Scientific journal
We studied energy transfer from AlN to doped Gd3+ ions as a function of the post-thermal annealing temperature. Gd-doped AlN thin films were deposited on fused-silica substrates using a reactive radio-frequency magnetron sputtering technique. The film is a c-axis oriented polycrystal. The intra-orbital electron transition in Gd3+ showed an atomically sharp luminescence at 3.9 eV (318nm). The photoluminescence (PL) excitation spectrum exhibited a resonant peak, indicating efficient energy transfer from the host AlN crystal to Gd3+ ions. The PL intensity increases approximately ten times by thermal annealing. The PL decay lifetime becomes long with annealing, and mid-gap luminescence relating to the crystal defects in AlN was also found to be reduced by annealing. These results suggest that energy dissipation of excited carriers in AlN was suppressed by annealing, and the efficiency of energy transfer into Gd3+ was improved. (C) 2015 AIP Publishing LLC.
AMER INST PHYSICS, Apr. 2015, JOURNAL OF APPLIED PHYSICS, 117 (16), pp. 193105 - 1-5, English[Refereed]
Scientific journal
We studied the two-step photon absorption (TSPA) process in InAs/GaAs quantum-dot superlattice (QDSL) solar cells. The photoluminescence (PL) and its excitation spectrum (PLE) showed the contribution of the higher excited states (ESs) forming the miniband of the QDSLs above the in homogeneously distributed ground states (GSs). TSPA of subbandgap photons efficiently occurs when electrons are pumped from the valence band (VB) to the higher ESs. When the higher ESs were resonantly excited, the superlinear excitation power dependence of the PL intensity appeared. Moreover, time-resolved PL showed that the electron lifetime is extended. These results demonstrate that the excited electron and hole separately relax into QDSLs, and thereby, enhancing the second sub-bandgap absorption.
IEEE, 2015, 2015 IEEE 42ND PHOTOVOLTAIC SPECIALIST CONFERENCE (PVSC), English[Refereed]
International conference proceedings
We propose a high-conversion-efficiency solar cell (SC) utilizing the hot carrier (HC) population in an intermediate-band (IB) of a quantum dot superlattice (QDSL) structure. The bandgap of the host semiconductor in this device plays an important role as an energy-selective barrier for HCs in the QDSLs. According to theoretical calculation using the detailed balance model with an air mass 1.5 spectrum, the optimum IB energy is determined by a trade-off relation between the number of HCs with energy exceeding the conduction-band edge and the number of photons absorbed by the valence band-IB transition. Utilizing experimental data of HC temperature in InAs/GaAs QDSLs, the maximum conversion efficiency under maximum concentration (45 900 suns) has been demonstrated to increase by 12.6% as compared with that for a single-junction GaAs SC. (C) 2014 AIP Publishing LLC.
AMER INST PHYSICS, Oct. 2014, APPLIED PHYSICS LETTERS, 105 (17), pp. 1 - 5, English[Refereed]
Scientific journal
The polarized optical gain characteristics of highly stacked InAs/GaAs quantum dots (QDs) with a thin spacer layer fabricated on an n(+)-GaAs (001) substrate were studied in the sub-threshold gain region. Using a 4.0-nm-thick spacer layer, we realized an electronically coupled QD superlattice structure along the stacking direction, which enabled the enhancement of the optical gain of the [001] transverse-magnetic (TM) polarization component. We systematically studied the polarized electroluminescence properties of laser devices containing 30 and 40 stacked InAs/GaAs QDs. The net modal gain was analyzed using the Hakki-Paoli method. Owing to the in-plane shape anisotropy of QDs, the polarization sensitivity of the gain depends on the waveguide direction. The gain showing polarization isotropy between the TM and transverse-electric polarization components is high for the [110] waveguide structure, which occurs for higher amounts of stacked QDs. Conversely, the isotropy of the [similar to 110] waveguide is easily achieved even if the stacking is relatively low, although the gain is small. (C) 2014 AIP Publishing LLC.
AMER INST PHYSICS, Jun. 2014, JOURNAL OF APPLIED PHYSICS, 115 (23), 233512 - 1-5, English[Refereed]
Scientific journal
We studied the efficient indirect excitation of Gd3+ ions in AlN thin films. C-axis oriented polycrystalline thin films of Al0.997Gd0.003N/AlN were grown on fused silica substrates using a reactive radio-frequency magnetron sputtering technique. The intra-orbital electron transition in Gd3+ showed a narrow luminescence line at 3.9 eV. The photoluminescence (PL) excitation (PLE) spectrum exhibited a peak originating from efficient indirect energy transfer from the band edge of AlN to Gd3+ ions. The PLE peak shifted and the PL intensity showed a dramatic change when the AlN band gap was varied by changing the temperature. Energy scanning performed by changing the band-gap energy of AlN with temperature revealed several resonant channels of energy transfer into the higher excited states of Gd3+. (C) 2014 AIP Publishing LLC.
AMER INST PHYSICS, May 2014, JOURNAL OF APPLIED PHYSICS, 115 (17), 173508 - 1-6, English[Refereed]
Scientific journal
We studied time-resolved carrier recombination in InAs/GaAs quantum dot (QD) solar cells. The electric field in a p-i-n diode structure spatially separates photoexcited carriers in QDs, strongly affecting the conversion efficiency of intermediate-band solar cells. The radiative decay lifetime is dramatically reduced in a strong electric field (193 kV/cm) by efficient recombination due to strong carrier localization in each QD and significant tunneling-assisted electron escape. Conversely, an electric field of the order of 10 kV/cm maintains electronic coupling in the stacked QDs and diminishes tunneling-assisted electron escape. (C) 2014 AIP Publishing LLC.
AMER INST PHYSICS, Feb. 2014, JOURNAL OF APPLIED PHYSICS, 115 (8), 083510 - 1-5, English[Refereed]
Scientific journal
We have grown an epitaxial two-dimensional nitrogen (N) atomic sheet in GaAs by using the site-controlled N delta-doping technique. We observed a change of the electronic states in N delta-doped GaAs from the isolated impurity centers to the delocalized impurity band at 1.49 eV with increasing N-doping density. According to the excitation-power-and temperature-dependent photoluminescence (PL) spectra, the emission related to localized levels below the impurity band edge was dominant at low excitation power and temperature, whereas the effects of the localized levels can be neglected by increasing the excitation power and temperature. Furthermore, a clear Landau shift of the PL-peak energy was observed at several Tesla in the Faraday configuration, in contrast to the case in the impurity limit. (C) 2014 AIP Publishing LLC.
AMER INST PHYSICS, Jan. 2014, APPLIED PHYSICS LETTERS, 104 (4), 041907 - 1~4, English[Refereed]
Scientific journal
We have developed a technique to control the stacking direction of InAs/GaAs quantum dots (QDs) grown on GaAs(001) by varying the direction of the In flux. Transmission-electron microscope images of the stacked QDs reveal that the stacking direction tilts along the [110] direction according to the projection of the In flux direction on the (-110) and does not tilt in the [-110] direction. This anisotropic tilting behavior of the stacked QDs is considered to be caused by an anisotropic migration of In atoms on the (001) growth front. The linear polarization feature of the edge-emitted photoluminescence (PL) demonstrates a strong anisotropy of the strain distribution attributable to the tilted direction of the stacked QDs. According to multidirectional observations of the polarized PL, anisotropic valence band mixing was caused by strain symmetry lowering owing to the tilted stacking direction. (C) 2013 AIP Publishing LLC.
AMER INST PHYSICS, Jul. 2013, JOURNAL OF APPLIED PHYSICS, 114 (3), 033517 - 1-5, English[Refereed]
Scientific journal
We studied state-filling-dependent intraband carrier dynamics in InAs/GaAs self-assembled quantum dots using two-color photoexcitation spectroscopy. The photoluminescence (PL) intensity was observed to be dramatically reduced by selectively pumping carriers from the intermediate state to the continuum state located above the conduction band edge, and the PL-intensity reduction decreased with an increase in the continuous-wave excitation power. We analyzed the observed state-filling-dependent intraband carrier dynamics by detailed modeling of carrier excitation and relaxation processes in which the two-photon absorption for the interband transition, Pauli blocking, and saturable absorption for the intraband transition is considered. © 2013 AIP Publishing LLC.
14 Jun. 2013, Journal of Applied Physics, 113 (22), 223511 - 1-5, English[Refereed]
Scientific journal
We have studied the electronic states of closely stacked InAs/GaAs quantum dots (QDs) with a 4.0-nm spacer layer using linearly polarized photoluminescence (PL) and time-resolved PL measurements. An increase in the stacking-layer number (SLN) leads to an increase in the linear polarization anisotropy in the (001) plane; the [-110]-polarization component becomes dominant. These SLN-dependent polarization characteristics result from the valence-band mixing induced by the vertically coupled electronic states. The PL spectrum of the stacked QDs shows clear blueshifts with an increase in the excitation power because of the band filling. In addition, the radiative recombination lifetime has been found to obey the T-1/2 dependence, which directly confirms the one-dimensional translational motion of excitons in the closely stacked QDs.
AMER PHYSICAL SOC, Jun. 2013, PHYSICAL REVIEW B, 87 (23), 2353323 - 1-6, English[Refereed]
Scientific journal
- Carrier Dynamics in Intermediate States of InAs/GaAs Quantum Dots Embedded in Photonic Cavity Structure
We have studied time-resolved intra band transition from the intermediate state to the continuum state of the conduction band in InAs/GaAs self-assembled quantum dots (QDs) embedded in a one-dimensional photonic cavity structure using a two-color photoexcitation spectroscopy. The photonic gap was tuned to enhance the excitation from the intermediate state to the conduction band, whose energy is selected to be less than the interband transition energy between the intermediate state and the quantized hole state. The photoluminescence intensity was observed to be dramatically reduced by selectively pumping carriers in the intermediate state. This effect has been analyzed by modeling detailed carrier relaxation process.
IEEE, 2013, 2012 IEEE 38TH PHOTOVOLTAIC SPECIALISTS CONFERENCE (PVSC), VOL 2, English[Refereed]
International conference proceedings
We have studied time-resolved intraband transition from the intermediate state to the continuum state of the conduction band in InAs/GaAs self-assembled quantum dots embedded in a one-dimensional photonic cavity structure using a two-color photoexcitation spectroscopy. The photonic gap was tuned to enhance the excitation from the intermediate state to the conduction band, whose energy is selected to be less than the interband transition energy between the intermediate state and the quantized hole state. The photoluminescence intensity was observed to be dramatically reduced by selectively pumping carriers in the intermediate state. This effect has been analyzed by modeling detailed carrier relaxation process. © 2013 Copyright SPIE.
2013, Proceedings of SPIE - The International Society for Optical Engineering, 8620, 862008 - 1-7, English[Refereed]
International conference proceedings
We have controlled the electronic states of closely-stacked InAs/GaAs quantum dots with a 4.0 nm spacer layer and investigated the optical gain characteristics. With an increase in the stacking-layer number (SLN), the [001] transverse-magnetic (TM) polarization component increases as well as the linear polarization anisotropy in the (001) plane becomes remarkable. These SLN-dependent polarization characteristics result from the valence-band mixing induced by the vertically-coupled electronic states in stacked QDs. We have systematically studied polarized electroluminescence properties of a semiconductor-optical amplifier devise containing 30-stacked InAs/GaAs QDs. The net modal gain was analyzed by using the Hakki-Paoli method. The injection current dependence of the gain spectra shows a state filling effect and a change in the contribution of the TM polarization component. The polarization insensitive gain feature within +/-1 dB has been achieved in the low injection current condition. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
WILEY-V C H VERLAG GMBH, 2013, PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 10, NO 11, 10 (11), 1492 - 1495, English[Refereed]
International conference proceedings
We have studied the time-resolved intraband transition from the intermediate state to the continuum state of the conduction band in InAs/GaAs self-assembled quantum dots ( QDs) embedded in a one-dimensional photonic cavity structure using two-color photoexcitation spectroscopy. The resonant energy of the photonic cavity was tuned to enhance the intraband transition with an energy smaller than the interband transition energy between the intermediate state and the quantized hole states. The interband photoluminescence intensity was observed to be drastically reduced due to the pumping out of carriers in the intermediate state using near-infrared laser light. We proposed a model describing the carrier relaxation process in the InAs/GaAs QD system, where the two-photon absorption and the Pauli blocking in QDs are considered.
AMER PHYSICAL SOC, Jul. 2012, PHYSICAL REVIEW B, 86 (3), 035301 - 1-7, English[Refereed]
Scientific journal
We have studied the broadened emission lines of CdTe/Cd0.75Mn0.25Te tilted superlattices (TSLs) in contrast to the sharp emission lines of the nonmagnetic CdTe/Cd0.74Mg0.26Te TSLs by using near-field scanning optical microscopy. The broadening of the photoluminescence (PL) spectra reflect the statistical fluctuation in the magnetization of Mn spins in the exciton magnetic polaron (EMP). The EMP PL strongly depends on the temperature; the line width of the EMP PL spectrum becomes narrow and the spatial distribution of the EMP PL intensity has been found to be reduced with rising the temperature from 5 to 11 K, because of annihilation of the EMP. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
WILEY-V C H VERLAG GMBH, 2012, PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 9, NO 2, 9 (2), English[Refereed]
International conference proceedings
Recently, there has been an increasing interest in broad-band light sources to develop a biomolecular imaging technique called optical coherence tomography (OCT). We fabricated superluminescent diodes (SLDs) using three kinds of quantum dot (QD) layers with different emission wavelength in the active region. The emission wavelength was controlled by reducing the strain in QDs by using In0.1Ga0.9As strain-reducing layer. The SLD device showed a broad electroluminescence spectrum with the center wavelength of 1104 nm and the spectral line-width of 122 nm at the injection of 40 mA, which corresponds to the theoretical axial resolution of 4.4 mu m. To estimate the actual resolution of the OCT system using fabricated SLD, we measured the interference signal in the Michelson interferometer. An axial resolution of 5.4 mu m, which is close to the theoretical limit, was obtained. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
WILEY-V C H VERLAG GMBH, 2012, PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 9, NO 12, 9 (12), 2473 - 2476, English[Refereed]
International conference proceedings
- Nov. 2011, Progress in Photovoltaics:Research and Applications, Vol. 19, Issue8, pp. 1~9, EnglishIntermediate Band Photovoltaics Based on Interband-intraband Transitions Using In0.53Ga0.47As/InP Superlattice
[Refereed]
Scientific journal
We studied the spatial localization of excitons bound to nitrogen (N) pairs in N delta-doped GaAs to make clear origin of bound exciton lines. An extremely high uniformity of the emission wavelength was achieved for the exciton bound to the N pairs because of the uniform strain field in the N delta-doped layer fabricated in the (001) plane in the atomically controlled way. The magneto-photoluminescence spectra in the Faraday configuration showed a mixing of the bright-and dark-exciton components in the exciton fine structure and diamagnetic shift. The spatial distribution of the excitons localized at different N pairs was estimated using the diamagnetic shift coefficient and confirmed by the radiative lifetime of the bright-exciton component. According to the estimated spatial distribution of bound-exciton wave function, it was found that the exciton for the 1.444-eV line is localized stronger than that for the 1.493-eV line. The strong electron confinement for the 1.444-eV line results in the reduction of exciton-phonon interaction. (C) 2011 American Institute of Physics. [doi:10.1063/1.3654015]
AMER INST PHYSICS, Oct. 2011, JOURNAL OF APPLIED PHYSICS, 110 (8), English[Refereed]
Scientific journal
Recent experimental measurements, without any theoretical guidance, showed that isotropic polarization response can be achieved by increasing the number of quantum-dot (QD) layers in a QD stack. Here we analyze the polarization response of multilayer QD stacks containing up to nine QD layers by linearly polarized photoluminescence (PL) measurements and by carrying out a systematic set of multimillion atom simulations. The atomistic modeling and simulations allow us to include correct symmetry properties in the calculations of the optical spectra, a factor critical to explain the experimental evidence. The values of the degree of polarization (DOP) calculated from our model follows the trends of the experimental data. We also present detailed physical insight by examining strain profiles, band edges diagrams, and wave function plots. Multidirectional PL measurements and calculations of the DOP reveal a unique property of InAs QD stacks that the TE response is anisotropic in the plane of the stacks. Therefore, a single value of the DOP is not sufficient to fully characterize the polarization response. We explain this anisotropy of the TE modes by orientation of hole-wave functions along the [(1) over bar 10] direction. Our results provide a new insight that isotropic polarization response measured in the experimental PL spectra is due to two factors: (i) TM001-mode contributions increase due to enhanced intermixing of HH and LH bands, and (ii) TE110-mode contributions reduce significantly due to hole-wave function alignment along the [(1) over bar 10] direction. We also present optical spectra for various geometry configurations of QD stacks to provide a guide to experimentalists for the design of multilayer QD stacks for optical devices. Our results predict that the QD stacks with identical layers will exhibit lower values of the DOP than the stacks with nonidentical layers.
AMER PHYSICAL SOC, Sep. 2011, PHYSICAL REVIEW B, 84 (11), English[Refereed]
Scientific journal
We studied polarization anisotropy observed in photoluminescence from closely stacked InAs/GaAs quantum dots (QDs). As the number of stacked layers was increased, the anisotropy in the (001) plane became drastically larger and the [001]-polarization component became larger than the [110] component when observed from the [(1) over bar 10] direction. However, the polarization intensity of the [(1) over bar 10] component remained stronger than that of the [001] component in the stacked QDs. Such varied polarization anisotropies depending on the observation direction have been found to result from the valence-band mixing in the vertically coupled electronic states. (C) 2011 The Japan Society of Applied Physics
JAPAN SOC APPLIED PHYSICS, Jun. 2011, APPLIED PHYSICS EXPRESS, 4 (6), English[Refereed]
Scientific journal
We have studied the detailed fine structure splitting of the photoluminescence lines exhibiting the superlinear excitation power dependence in nitrogen delta-doped GaAs. The symmetric splitting energy observed between the 1.493 and 1.509 eV lines suggests that these two lines originate from the same impurity center because the mixing of the bright- and dark-exciton components depends on the electron-hole exchange energy and the local-strain field. The excitation power dependence of these two lines indicates that the 1.509 eV line is attributed to the biexciton luminescence corresponding to the 1.493 eV line. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
WILEY-V C H VERLAG GMBH, Feb. 2011, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 248 (2), 464 - 467, English[Refereed]
Scientific journal
Two-photon transition modelling is developed to study quantum mechanism and simulate device operation in intermediate band solar cell (IBSC). The interband-intranband transition, the detailed balance and carrier transport are coupled with each other. IB formation mechanism is studied within one-band envelope-function framework (Kronig-Penney type). Well-designed GaInAs/InP superlattice structures have been proved to separate IB from valence band (VB) and conduction band (CB), which is the precondition of IBSC operations. Further, we calculate two-photon absorption spectra and firstly combine quantum transitions into recent drift-diffusion and detail balanced model. With this model, we have studied a novel IBSC consist of In0.53Ga0.47As/InP superlattices (SLs). Our results show the interband-intraband transition determines the conversion efficiency. With well-designed quantum structure, the efficiency in 1.2 μm thick SLs is 46.13% under the maximum concentration. However, as the well or barrier thickness increases to 10 nm, the absorption peak of the intraband transition gradually redshifts and narrows, so the efficiency correspondingly decreases to below 40%. © 2011 IEEE.
2011, Conference Record of the IEEE Photovoltaic Specialists Conference, 002625 - 002628, English[Refereed]
International conference proceedings
We have studied sharp emission lines created by interacting between the GaAs host-matrix conduction-band edge and nitrogen-related localized levels in nitrogen delta-doped GaAs by using magneto-photoluminescence spectroscopy. According to the decreased diamagnetic coefficient of 75 mu eV/T-2 at the 1.515-eV line, the interaction between the conduction-band edge and localized levels has been confirmed. Furthermore, we have observed a linear polarization anisotropy for these emission lines. This polarization splitting demonstrates that the electronic states of the nitrogen pair couple with the GaAs conduction-band edge. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
WILEY-V C H VERLAG GMBH, 2011, PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 8, NO 2, 8 (2), English[Refereed]
International conference proceedings
We have studied the magnetic-field evolution of the fine structure splitting of the exciton bound to nitrogen (N) pairs in GaAs in the Faraday configuration. With applying the magnetic field, the photoluminescence (PL) spectrum splits into several signals and changes their intensities. The observed magneto-PL spectra indicate the mixing between the split exciton states having the orthogonal linear polarization components in the zero-magnetic field, which demonstrates the characteristic Zeeman effects of the anisotropic exciton structure bound to the N pairs.
AMER INST PHYSICS, 2011, PHYSICS OF SEMICONDUCTORS: 30TH INTERNATIONAL CONFERENCE ON THE PHYSICS OF SEMICONDUCTORS, 1399, English[Refereed]
International conference proceedings
We have theoretically studied the emission-line width in Mn-composition modulated Cd1-xMnxTe quantum wires by using the multiband effective mass theory and fluctuation-dissipation theorem. The calculated emission-line width exhibits a broadening because of a statistical fluctuation in the magnetization of Mn spins in the exciton magnetic polaron. The line width is sensitive to both the temperature and the magnetic field in the Voigt configuration, which exhibits remarkable anisotropy depending on the external magnetic field direction. The anisotropic behavior is a typical feature of the one-dimensional system resulting from heavy-hole and light-hole mixing.
AMER INST PHYSICS, Feb. 2010, JOURNAL OF APPLIED PHYSICS, 107 (4), English[Refereed]
Scientific journal
We theoretically studied anisotropic linear optical polarization properties in CdTe/Cd(0.75)Mn(0.25)Te quantum wires (QWRs) by using the multi-band effective mass method. In this QWR system. the spatial distribution of the Mn composition influences both the lateral quantum confinement and the sp-d exchange coupling. The calculated expectation value of the hole spin demonstrates that the hole spin is reoriented along the external magnetic field when applying the magnetic field parallel to the QWR. The hole-spin reorientation causes anisotropic behavior in the Zeeman shift and the linearly polarized optical transitions, which sensitively depends on the Mn spatial distribution. Such characteristic features appeared in the QWR have been demonstrated experimentally and compared with the theoretical calculations. (C) 2009 Elsevier B.V. All rights reserved.
ELSEVIER SCIENCE BV, Dec. 2009, JOURNAL OF LUMINESCENCE, 129 (12), 1448 - 1453, English[Refereed]
Scientific journal
Anisotropic magneto-optical effects in CdTe/CdMnTe quantum wire structures have been studied theoretically by using the multiband effective-mass method. The Mn spatial distribution influences not only the lateral quantum confinement of the carrier wave function but also the exchange coupling of spins between the carrier and Mn ions. The anisotropic configuration between the spin of holes confined in the wire and the Mn spin oriented by the magnetic field causes anisotropy in the magnetic-field dependence of the valence-band structure, and this results in the anisotropic Zeeman shift and linear polarization properties of the optical transition depending on the spin configuration.
AMER PHYSICAL SOC, Aug. 2008, PHYSICAL REVIEW B, 78 (7), English[Refereed]
Scientific journal
We have studied the fine structure polarization splitting of exciton emission lines related to isoelectronic centers in an nitrogen-doped GaAs. The nitrogen doping has been performed in atomically controlled way using the (3 X 3) nitrogen stable surface of GaAs(001), which forms a series of distinct, strong, narrow bandwidth luminescence lines. The localized bound excitons have been found to consist of four signals, which can be selected by linear polarization. Magnetic-field-induced change in the splitting shows a quadratic dependence of the bright exciton splitting owing to the in-plane Zeeman interaction. Our calculations of the optical selection characteristics considering both the J-J coupling and local-field effects demonstrate the polarization splitting depending on the symmetry of the isoelectronic center.
AMER PHYSICAL SOC, May 2008, PHYSICAL REVIEW B, 77 (19), English[Refereed]
Scientific journal
- EXCITON FINE STRUCTURE OF NITROGEN ISOELECTRONIC CENTERS IN GaAs
We have studied the exciton fine structures of nitrogen isoelectronic centers in GaAs. Atomically controlled nitrogen doping into GaAs realizes a series of distinct, strong, narrow bandwidth bound-exciton luminescences. The exciton fine structure has been found to consist of four signals, which can be selected by the linear polarization. Our calculations have succeeded in reproducing the optical selection characteristics when considering both the J-J coupling and local-field effects in the C(2 nu) symmetry.
IEEE, 2008, 2008 IEEE 20TH INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE AND RELATED MATERIALS (IPRM), 231 - 233, English[Refereed]
International conference proceedings
- Anisotropic magnetic-field evolution of valence-band states in one-dimensional diluted magnetic semiconductors
We have theoretically studied the anisotropic magnetic-field evolution of the valence-band states in CdMnTe quantum wires by using a multiband effective-mass method. The Zeeman diagram depends on the direction of the magnetic field against the wire direction. The optical transition probability has been found to show a dramatic change in the polarization because of the valence-band mixing. The calculated magneto-optical properties are carefully compared with experimental results observed in CdTe/CdMnTe tilted superlattices.
AMER INST PHYSICS, 2007, PHYSICS OF SEMICONDUCTORS, PTS A AND B, 893, 1245 - +, English[Refereed]
International conference proceedings
Anisotropic magneto-optical effects have been studied theoretically by using multi-band effective mass method. We focus on a model of an ideal CdMnTe quantum wire surrounded by infinite potential barriers. The mixing of heavy- and light-hole bands is caused by both the one-dimensional quantum confinement and the sp-d exchange interaction. As a result of the valence-band mixing characteristic to the one-dimensional diluted magnetic semiconductor, the Zeeman splitting in the magnetic field parallel to the wire direction becomes smaller than that in the perpendicular magnetic field. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.
2006, Physica Status Solidi C: Conferences, 3 (3), 667 - 670, English[Refereed]
International conference proceedings
Highly sensitive control of anisotropic optical polarization in CdMnTe quantum wires has been studied theoretically using multi-band effective mass method. A magnetic field dramatically changes the transition probability via the sp-d exchange interaction. © 2006 Optical Society of America.
2006, Conference on Lasers and Electro-Optics and 2006 Quantum Electronics and Laser Science Conference, CLEO/QELS 2006, English[Refereed]
International conference proceedings
- Valence-band mixing induced by sp-d exchange interaction in CdMnTe quantum wires
Anisotropic magneto-optical effects have been studied theoretically by using multi-band effective mass method. We focus on a model of an ideal CdMnTe quantum wire surrounded by infinite potential barriers. The mixing of heavy- and light-hole bands is caused by both the one-dimensional quantum confinement and the sp-d exchange interaction. As a result of the valence-band mixing characteristic to the one-dimensional diluted magnetic semiconductor, the Zeeman splitting in the magnetic field parallel to the wire direction becomes smaller than that in the perpendicular magnetic field. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
WILEY-VCH, INC, 2006, PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 3 NO 3, 3 (3), 667 - +, English[Refereed]
International conference proceedings
Anisotropic magnetic-field evolution of the valence-band states in ideal Cd1-x Mnx Te quantum wire structures have been studied theoretically by using multiband effective-mass method. The heavy- and light-hole bands show significant mixing owing to both the one-dimensional quantum confinement and the p-d exchange interaction. Because of the anisotropy of the initial quantization condition determined by the one-dimensional confinement, the Zeeman diagram of the valence bands exhibits anisotropic characteristics depending on the direction of the external magnetic field. According to the magnetic-field evolution of the valence-band states, the optical transition probability shows a dramatic change in the polarization. © 2006 The American Physical Society.
2006, Physical Review B - Condensed Matter and Materials Physics, 74 (24), English[Refereed]
Scientific journal
We have studied anisotropic exchange interactions in (CdTe)(0.5)(Cd0.75Mn0.25Te)(0.5) tilted superlattices fabricated by fractional monolayer growth onto a 1 degrees off vicinal surface. Compositionally modulated wire structures in the (0 0 1) plane have been confirmed by polarized PL measurements, which shows the lateral quantization perpendicular to the wire direction. The Zeeman shift in the Voigt configuration depends on the direction of the external magnetic field in the (0 0 1) plane. Linear-polarization measurements of the magneto-PL reveal reorientation of the hole spin in the CdTe-rich wire into the external field direction. Moreover, in the magnetic field parallel to the wire direction, valence-band mixing occurs, which results in the anisotropic Zeeman shift. (C) 2004 Elsevier B. V. All rights reserved.
ELSEVIER SCIENCE BV, Feb. 2005, JOURNAL OF CRYSTAL GROWTH, 275 (1-2), E2221 - E2224, English[Refereed]
Scientific journal
We have studied hole-spin reorientation in CdTe/CdMnTe nano-wire structures grown on CdMgTe (001) vicinal surface. Experimental results have been compared with calculations based on ideal CdMnTe QWR model, using multiband effective mass method.
2005, IQEC, International Quantum Electronics Conference Proceedings, 2005, 265 - 266, English[Refereed]
International conference proceedings
- Hole-spin reorientation in (CdTe)(0.5)(Cd0.75Mn0.25Te)(0.5) tilted superlattices grown on Cd0.74Mg0.26Te(001) vicinal surface
We have studied anisotropic exchange interaction in (CdTe)(0.5)(Cd0.75Mn0.25Te)(0.5) tilted superlattices fabricated by fractional monolayer growth onto a 1 degrees off vicinal surface. The Zeeman shift in the Voigt configuration depends on the direction of the external magnetic field in the (001) plane. When applying the external magnetic field parallel to the wire direction, linear polarization of the magneto-PL reveals reorientation of hole spins into the external field direction. Moreover, in the parallel magnetic field the valence-band mixing occurs for fields larger than similar to 3.5 T, which results in anisotropic Zeeman shifts.
AMER INST PHYSICS, 2005, Physics of Semiconductors, Pts A and B, 772, 1353 - 1354, English[Refereed]
International conference proceedings
MISC
- Jul. 2017, 電気評論, 642, 67 - 71, Japanese半導体量子ドット超格子におけるホットキャリアダイナミクス
[Invited]
Introduction commerce magazine
- May 2014, 応用物理, 83, 348 - 355, Japanese中間バンド型高効率太陽電池―量子ナノ構造中における光キャリアダイナミックス―
[Refereed]
Introduction scientific journal
Presentations
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Oral presentation
- 41st Electronic Materials Symposium, 21 Oct. 2022, JapaneseIntraband Transition in Two-Step Photon Up-Conversion Solar Cells
Poster presentation
- The 35th International Conference on the Physics of Semiconductors, 29 Jun. 2022, EnglishIntraband Absorptivity in Two-Step Photon Up-Conversion Solar Cells
Oral presentation
- The 6th International Conference on New Energy and Future Energy Systems, Nov. 2021Route to High Conversion Efficiency Solar cell
- 第40回電子材料シンポジウム, Oct. 2021Anti-Stokes photoluminescence of GaAs:Er,O for laser cooling in photonic crystal nano-cavity
- 第82回応用物理学会秋季学術講演会, Sep. 2021エピタキシャル成長を利用した固体レーザー冷却用高品質Yb:Y-Al-O厚膜の作製
- Compound Semiconductor Week (CSW) 2021, May 2021Lateral Photoconductivity of Multiple-Stacked InAs/GaAs Quantum Dot Structure for Photoconductive Antenna Device
- SPIE Photonics West 2021, Mar. 2021Yb-doped Yttrium Aluminum Perovskite for Radiation Balanced Laser Application
- 第68回応用物理学会春季学術講演会, Mar. 2021光伝導アンテナ応用へ向けた多重積層InAs/GaAs量子ドットの光学特性評価
- 第68回応用物理学会春季学術講演会, Mar. 2021光伝導アンテナ応用へ向けた多重積層InAs/GaAs量子ドットの電気特性評価
- 第68回応用物理学会春季学術講演会, Mar. 2021相分離したYb添加Y-Al-O透明薄膜における結晶相間エネルギー移動
- 第39回電子材料シンポジウム, Oct. 2020Anti-Stokes Photoluminescence Caused by Energy Transfer in Ytterbium-Doped Yttrium Aluminum Perovskite
- 応用物理学会KOSENスチューデントチャプター第1回VR学術講演会, Jul. 2020量子ドット超格子を利用した高効率太陽電池
[Invited]
Public discourse
- 第67回応用物理学会春季学術講演会, Mar. 2020, Japanese2段階フォトンアップコンバージョン太陽電池におけるバンド内遷移特性
Oral presentation
- 第67回応用物理学会春季学術講演会, Mar. 2020, Japanese多重積層InAs/GaAs量子ドットを用いた光伝導アンテナの作製
Oral presentation
- 第67回応用物理学会春季学術講演会, Mar. 2020Yb添加YAG-YAM共晶透明薄膜におけるAnti-Stokes PL過程と理想レーザー冷却効率
Oral presentation
- SPIE Photonics West 2020, Feb. 2020, EnglishEnhancement of laser cooling efficiency in rare-earth-doped oxide at elevated high temperature
[Invited]
Invited oral presentation
- 第十三回紀州吉宗セミナー, Jan. 2020, Japanese量子構造太陽電池における光励起キャリアダイナミクス
[Invited]
Public discourse
- 第30回光物性研究会, Dec. 2019, JapaneseYb:YAG薄膜からの強いAnti-Stokes発光とレーザー冷却特性
Poster presentation
- 第30回光物性研究会, Dec. 2019, Japanese(Yb:Y)AGセラミックスにおけるAnti-Stokes PL過程
Poster presentation
- 第3回ISYSE研究会, Nov. 2019, Japanese光物性の基礎
[Invited]
Public discourse
- 第38回電子材料シンポジウム, Oct. 2019, EnglishHot-Carrier Extraction from InAs/GaAs Quantum Dot Superlattices Embedded in GaAs Solar Cells
Poster presentation
- 第38回電子材料シンポジウム, Oct. 2019, EnglishEfficient Laser Cooling in Rare-Earth Doped Oxides at High Temperature
Poster presentation
- 7th International Workshop on Epitaxial Growth and Fundamental Properties of Semiconductor Nanostructures, Sep. 2019, EnglishExcitation Energy Dependence of Hot-Carrier Extraction Process in InAs/GaAs Quantum Dot Superlattice Solar Cells
Oral presentation
- 7th International Workshop on Epitaxial Growth and Fundamental Properties of Semiconductor Nanostructures, Sep. 2019, EnglishLaser Cooling Utilizing Anti-Stokes Photoluminescence in Yb-Doped Yttrium Aluminum Garnet
Poster presentation
- 第80回応用物理学会秋季学術講演会, Sep. 2019, JapaneseInAs/GaAs量子ドット超格子におけるホットキャリア生成過程
Oral presentation
- 第80回応用物理学会秋季学術講演会, Sep. 2019, Japanese(Y:Yb)AGにおける高温でのAnti-Stokes発光増強メカニズム
Oral presentation
- 46th IEEE Photovoltaic Specialists Conference, Jul. 2019, English, Chicago, International conferenceHot-Carrier Extraction in InAs/GaAs Quantum Dot Superlattice Solar Cells
Oral presentation
- Optics&Photonics International Congress 2019, Apr. 2019, English, Yokohama, International conferenceEfficient Hot-Carrier Generation in InAs/GaAs Quantum Dot Superlattices
Oral presentation
- 第66回応用物理学会春季学術講演会, Mar. 2019, Japanese, Domestic conferenceInAs/GaAs量子ドット超格子を用いたホットキャリア型太陽電池における開放電圧の向上
Oral presentation
- 第66回応用物理学会春季学術講演会, Mar. 2019, Japanese, Domestic conference(Y:Yb)AGにおける高温でのanti-Stokes発光増強
Oral presentation
- 第37回電子材料シンポジウム, Oct. 2018, Japanese, Domestic conferenceVoltage boost effect in two-step photon up-conversion solar cell with partial absorptivity
Poster presentation
- 第37回電子材料シンポジウム, Oct. 2018, Japanese, Domestic conferenceLaser Cooling in Yb-Doped Yttrium Aluminum Compounds
Poster presentation
- 35th European PV Solar Energy Conference and Exhibition, Sep. 2018, English, Belgium, International conferenceOptimal Band Gap Energies for Two-Step Photon Up-Conversion Solar Cells with Partial Absorptivity
Oral presentation
- 第79回応用物理学会秋季学術講演会, Sep. 2018, Japanese, Domestic conferenceInAs/GaAs量子ドット超格子太陽電池におけるホットキャリア電流取り出し特性
Oral presentation
- 第79回応用物理学会秋季学術講演会, Sep. 2018, Japanese, Domestic conference2段階フォトンアップコンバージョン太陽電池における理論変換効率の入射光スペクトル形状依存性
Oral presentation
- 平成30年度半導体エレクトロニクス部門委員会第1回研究会, Jul. 2018, Japanese, 奈良先端科学技術大学院大学, Domestic conferenceYb添加Fttrium-Aluminum化合物によるもの固体レーザー冷却
Oral presentation
- The 12th International Conference on Excitonic and Photonic Processes in Condensed Matter and Nano Materials, Jul. 2018, English, Nara, International conferenceOptimization of Excitation Wavelengh in YAG:Yb for Laser cooling
Oral presentation
- 9th International Workshop on Bismuth-Containing Semiconductors, Jul. 2018, English, Kyoto, International conferenceExciton Hopping Dynamics in GaAsBi
Oral presentation
- 応用物理学会関西支部平成30年度第1回講演会, May 2018, Japanese, 神戸大学, Domestic conference入射光スペクトル形状を考慮した2段階フォトンアップコンバージョン太陽電池の理論変換効率
Poster presentation
- International Conference on Nanophotonics and Nano-optoelectronics 2018, Apr. 2018, English, Yokohama, International conferencePolarization Dependent Photocurrent in InAs/GaAs Quantum Dot Superlattice Solar Cells
Oral presentation
- 第65回応用物理学会春季学術講演会, Mar. 2018, Japanese, Domestic conference吸収率を考慮した2段階フォトンアップコンバージョン太陽電池の理論変換効率
Oral presentation
- 第65回応用物理学会春季学術講演会, Mar. 2018, Japanese, Domestic conferenceYAG:Ybにおけるanti-Stokes発光の励起波長依存性
Oral presentation
- 第65回応用物理学会春季学術講演会, Mar. 2018, Japanese, Domestic conferenceInAs/GaAs量子ドット超格子を用いたホットキャリア型太陽電池動作実証
Oral presentation
- 応用物理学会関西支部平成29年度第3回講演会, Feb. 2018, Japanese, Domestic conferenceInAs/GaAs量子ドット超格子を用いたホットキャリア型太陽電池の動作評価
Poster presentation
- 第28回光物性研究会, Dec. 2017, Japanese, Domestic conferenceYAG:YbにおけるAnti-Stokes発光
Poster presentation
- The 27th Photovoltaic Science and Engineering Conference, Nov. 2017, English, Otsu, International conferenceTwo-Step Photn Up-Conversion Solar Cells Incorporating a Voltage Booster Hetero-Interface
Oral presentation
- The 27th Photovoltaic Science and Engineering Conference, Nov. 2017, English, Otsu, International conferenceEfficient Two-Step Photocurrent in Intermediate Band Solar Cells Using Highly Homogeneous InAs/GaAs Quantum-Dot Superlattice
Oral presentation
- 第36回電子材料シンポジウム, Nov. 2017, Japanese, Domestic conferenceAnti-Stokes photoluminescence in Yb-doped yttrium aluminum garnet
Poster presentation
- 第78回応用物理学会秋季学術講演会, Sep. 2017, Japanese, Domestic conference低温キャップInAs/GaAs量子ドット超格子中間バンド型太陽電池における熱脱出の抑制
Oral presentation
- 日本材料学会半導体エレクトロニクス部門委員会平成29年度第1回研究会, Sep. 2017, Japanese, Domestic conference低温キャップInAs/GaAs量子ドット超格子中間バンド型太陽電池における2段階光吸収の増強
Oral presentation
- 第78回応用物理学会秋季学術講演会, Sep. 2017, Japanese, Domestic conferenceInAs/GaAs量子ドット超格子太陽電池におけるバンド内遷移の偏光特性
Oral presentation
- 29th International Conference on Defects in Semiconductors, Jul. 2017, English, International conferenceTwo-energy-scales of localized states on photoluminescence thermal quenching in GaAsBi
Oral presentation
- 29th International Conference on Defects in Semiconductors, Jul. 2017, English, Matsue, International conferenceStokes and Anti-Stokes Photoluminescence in Nitrogen ð-Doped Layer in GaAs
Oral presentation
- 8th International Workshop on Bismuth-Containing Semiconductors, Jul. 2017, English, International conferenceSelective excitation of bulk GaAs1-xBix to assess the effects of short and long-range disorder on minority carrier transport properties
Oral presentation
- International Workshop on Advanced Smart Materials and Engineering for Nano- and Bio-Technologies, Jul. 2017, English, International conferencePhotoluminescence spectroscopy of isoelectronic impurity doped GaAs
[Invited]
Invited oral presentation
- 8th International Workshop on Bismuth-Containing Semiconductors, Jul. 2017, English, International conferenceDensity-of-states of localized states in GaAsBi
Oral presentation
- 応用物理学会関西支部平成29年度第1回講演会, May 2017, Japanese, Domestic conferenceレーザー冷却に向けたYbドープ酸化物の作製
Poster presentation
- 第64回応用物理学会春季学術講演会, Mar. 2017, Japanese, Domestic conferenceGaAs中のエピタキシャル窒素膜における反ストークス発光
Oral presentation
- 第27回光物性研究会, Dec. 2016, Japanese, Domestic conferenceGaAs中のデルタドーピング窒化層を利用した光によるフォノン制御
Poster presentation
- Energy, Materials, and Nanotechnology Meeting on Epitaxy, Sep. 2016, English, International conferenceTwo-dimensional delocalized electronic states of epitaxial N d-doped layer in GaAs
[Invited]
Invited oral presentation
- HEMP 2016: Hot Electrons and Solar Energy, Sep. 2016, English, International conferenceNanosecond-scale hot-carrier cooling dynamics in one-dimensional InAs/GaAs quantum dot superlattices
[Invited]
Invited oral presentation
- 第77回応用物理学会秋季学術講演会, Sep. 2016, Japanese, Domestic conferenceInAs/GaAs量子ドット中間バンド型太陽電池における電子の熱脱出過程の解明
Oral presentation
- 33rd International Conference on the Physics of Semiconductors, Aug. 2016, English, Beijing, International conferenceSpatial Electronic Structure of an Isovalent Nitrogen Center in GaAs
Oral presentation
- 第35回電子材料シンポジウム, Jul. 2016, Japanese, Domestic conferenceThermal carrier-escape process from the intermediate band in InAs/GaAs quantum dot solar cells
Poster presentation
- UK Semiconductors 2016, Jul. 2016, English, Sheffield, International conferencePolarization-Insensitive Intraband Transition in InAs/GaAs Quantum Dot Superlattices
Oral presentation
- 2016 Compound Semiconductor Week, Jun. 2016, English, Toyama, International conferenceTwo-Dimensional Energy Dispersion in Thermally Annealed Epitaxial Nitrogen Atomic Sheet in GaAs
Oral presentation
- 2016 Compound Semiconductor Week, Jun. 2016, English, Toyama, International conferencePolarization Anisotropy of Electroluminescence and Net-Modal Gain in Highly Stacked InAs/GaAs Quantum-Dot Laser Devices
Oral presentation
- 32nd European Photovoltaic Solar Energy Conference and Exhibition, Jun. 2016, English, Munich, International conferenceEnhancement of Two-Step Photon Absorption Due to Miniband Formation in InAs/GaAs Quantum Dot Superlattice Solar Cell
Oral presentation
- 第63回応用物理学会春季学術講演会, Mar. 2016, Japanese, Domestic conference急速熱アニールしたGaAs中のエピタキシャル窒素膜の輻射再結合寿命
Oral presentation
- 17th International Conference on Physics of Light-Matter Coupling in Nanostructures, Mar. 2016, English, Nara, International conferenceTime-Resolved Photoluminescence of Thermally-Annealed Nitrogen Atomic Sheet in GaAs
Oral presentation
- 第63回応用物理学会春季学術講演会, Mar. 2016, Japanese, Domestic conferenceInAs/GaAs量子ドット超格子太陽電池におけるミニバンド形成が2段階光吸収に与える影響
Oral presentation
- 日本材料学会半導体エレクトロニクス部門委員会平成27年度第1回研究会, Nov. 2015, Japanese, Domestic conferenceポリマー薄膜中のコロイドPbS量子ドットにおけるパリティ選択則の緩和
Oral presentation
- 日本物理学会2015年秋季大会, Sep. 2015, Japanese, Domestic conferenceポリマー膜中のPbSコロイド量子ドットにおける磁気光学応答のヒステリシス特性
Poster presentation
- 第76回応用物理学会秋季学術講演会, Sep. 2015, Japanese, Domestic conferenceInAs/GaAs量子ドット超格子を利用したホットキャリア型太陽電池
Oral presentation
- 第76回応用物理学会秋季学術講演会, Sep. 2015, Japanese, Domestic conferenceInAs/GaAs量子ドット超格子におけるホットキャリア冷却過程
Oral presentation
- 5th International Workshop on Epitaxial Growth and Fundamental Properties of Semiconductor Nanostructures, Sep. 2015, English, Taiwan, International conferenceEpitaxial Nitrogen Atomic Sheet in GaAs Grown by Nitorogen δ-Doping Technique
[Invited]
Invited oral presentation
- 日本材料学会半導体エレクトロニクス部門委員会平成27年度第1回研究会, Jul. 2015, Japanese, Domestic conference急速熱アニールによるGaAs中のエピタキシャル窒素シートにおける2次元物性の制御
Oral presentation
- 21st International Conference on Electronic Properties of Two-Dimensional Systems/17th International Conference on Modulated Semiconductor Structures, Jul. 2015, English, Sendai, International conferenceRelaxation of Parity Selection Rules in Colloidal PbS Quantum Dots Embedded in Polymer Films
Oral presentation
- 34th Electronic Materials Symposium, Jul. 2015, Japanese, Domestic conferenceHot-Carrier Distribution in InAs/GaAs Quantum Dot Superlattices and Its Application to Solar Cells
Poster presentation
- 21st International Conference on Electronic Properties of Two-Dimensional Systems/17th International Conference on Modulated Semiconductor Structures, Jul. 2015, English, Sendai, International conferenceEnhancement of Two Dimensionality in Epitaxial Nitrogen Atomic Sheet in GaAs by Rapid Thermal Annealing
Oral presentation
- 34th Electronic Materials Symposium, Jul. 2015, Japanese, Domestic conferenceAnnealing effects on the delocalized electronic states of epitaxial two-dimensional nitrogen atomic sheet in GaAs
Poster presentation
- 42nd IEEE Photovoltaic Specialists Conference, Jun. 2015, English, New Orleans, International conferenceTwo-Step Photocarrier Generation in InAs/GaAs Quantum Dot Superlattice Intermediate Band Solar Cell
Oral presentation
- 11th International Conference on Excitonic and Photonic Processes in Condensed Matter and Nano Materials, Montreal, May 2015, English, Montreal, International conferenceHot-Carrier Cooling Dynamics in InAs/GaAs Quantum Dot Superlattices
Oral presentation
- 第62回応用物理学会春季学術講演会, Mar. 2015, Japanese, Domestic conferenceポリマー薄膜中のコロイドPbS量子ドットにおける励起緩和過程の偏光異方性
Oral presentation
- 日本物理学会第70回年次大会（2015年）, Mar. 2015, Japanese, Domestic conferenceInAs/GaAs量子ドット超格子におけるホットキャリアダイナミクス
Oral presentation
- 第62回応用物理学会春季学術講演会, Mar. 2015, Japanese, Domestic conferenceGaAs中のエピタキシャル二次元窒素膜におけるアニール効果
Oral presentation
- 第24回光物性研究会, Dec. 2014, Japanese, Domestic conferenceポリマー薄膜中のコロイドPbS量子ドットにおける励起緩和過程の偏光異方性
Poster presentation
- 第24回光物性研究会, Dec. 2014, Japanese, Domestic conferenceInAs/GaAs量子ドット太陽電池におけるキャリア脱出の影響
Poster presentation
- 第24回光物性研究会, Dec. 2014, Japanese, Domestic conferenceGaAs中のエピタキシャル2次元窒素シート非局在電子状態の発光ダイナミクス
Poster presentation
- 日本材料学会半導体エレクトロニクス部門委員会平成26年度第2回研究会, Nov. 2014, Japanese, Domestic conference低次元量子構造を利用したホットキャリア型太陽電池の提案
Oral presentation
- 日本材料学会半導体エレクトロニクス部門委員会平成26年度第2回研究会, Nov. 2014, Japanese, Domestic conferenceポリマー中に埋め込まれたPbSコロイド量子ドットにおける磁気発光強度のヒステリシス特性
Oral presentation
- International Symposium on Recent Progress of Photonic Devices and Materials, Nov. 2014, English, International conferenceTwo-dimensional electronic states of epitaxial nitrogen atomic sheet in GaAs
[Invited]
Invited oral presentation
- International Symposium on Recent Progress of Photonic Devices and Materials, Nov. 2014, English, Kobe University, International conferencePhotoluminescence Decay Dynamics in Epitaxial Two-Dimensional Nitrogen Atomic Sheet in GaAs
Oral presentation
- WCPEC-6, Nov. 2014, English, Kyoto International Conference Center, International conferenceHot Carrier Intermediate Band Solar Cell Using Low-Dimensioned Quantum Structures
Oral presentation
- International Symposium on Recent Progress of Photonic Devices and Materials, Nov. 2014, English, Kobe University, International conferenceControl of Electronic States Colloidal PbS Quantum Dots Embedded in Polymer Films
Oral presentation
- 第75回応用物理学会学術講演会, Sep. 2014, Japanese, Domestic conference低次元量子構造を利用したホットキャリア中間バンド型太陽電池
Oral presentation
- 第75回応用物理学会学術講演会, Sep. 2014, Japanese, Domestic conferenceGaAs中のエピタキシャル二次元窒素膜の電子状態 (II)
Oral presentation
- 第75回応用物理学会学術講演会, Sep. 2014, Japanese, Domestic conferenceGaAs中のエピタキシャル二次元窒素膜における発光ダイナミクス
Oral presentation
- 32nd International Conference on Physics of Semiconductors, Aug. 2014, English, International conferenceTwo-dimensional electronic states of epitaxial nitrogen atomic sheet in GaAs grown by nitrogen delta-doping technique
Oral presentation
- 33rd Electronic Materials Symposium, Jul. 2014, Japanese, Domestic conferenceEnhancement of interaction among nitrogen pair centers in epitaxial two-dimensional nitrogen atomic sheet in GaAs
Poster presentation
- 第61回応用物理学会春季学術講演会, Mar. 2014, Japanese, 青山学院大学, Domestic conferenceGaAs中のエピタキシャル二次元窒素膜の電子状態
Oral presentation
- EMN Fall Meeting, Dec. 2013, English, Orland, Florida, USA, International conferenceIntraband Carrier Dynamics in Self-Assembled Quantum Dots for Infrared Optical Devices
[Invited]
Invited oral presentation
- 第23回光物性研究会, Dec. 2013, Japanese, 大阪市立大学, Domestic conferenceInAs/GaAs量子ドットにおけるbound-to-continuum型サブバンド間遷移の吸収係数
Poster presentation
- 第23回光物性研究会, Dec. 2013, Japanese, 大阪市立大学, Domestic conferenceGaAs中におけるエピタキシャル2次元窒素膜の磁気発光特性
Poster presentation
- 日本物理学会2013年秋季大会, Sep. 2013, Japanese, 徳島大学, Domestic conference積層方向を制御した InAs/GaAs量子ドットの発光偏光特性
Poster presentation
- 2013 JSAP-MRS Joint Symposia, Sep. 2013, English, Doshisya University, International conferenceElectron Localization in GaAs:N Grown by Using δ-Doping Technique
Oral presentation
- The 40th International Symposium on Compound Semiconductors, May 2013, English, Kobe, International conferencePolarization Controlled Emisson from Closely Stacked InAs/GaAs Quantum Dots
Oral presentation
- ISCS2013, May 2013, English, Kobe, International conferenceEnergy Relaxation of Photoexcited Electrons in Direct Si-Doped InAs/GaAs Quantum Dots
Oral presentation
- ISCS2013, May 2013, English, Kobe, International conferenceEffect of State Filling on Intraband Carrier Dynamics in InAs/GaAs quantum Dots
Oral presentation
- 第60回応用物理学会春季学術講演会, Mar. 2013, Japanese, 神奈川工科大学, Domestic conference窒素を高濃度デルタドープしたGaAsの磁気光学特性
Oral presentation
- 第60回応用物理学会春季学術講演会, Mar. 2013, Japanese, 神奈川工科大学, Domestic conference斜め積層InAs/GaAs量子ドットの端面発光特性
Oral presentation
- 第60回応用物理学会春季学術講演会, Mar. 2013, Japanese, 神奈川工科大学, Domestic conferenceSi直接ドーピングInAs/GaAs量子ドットのキャリア緩和過程
Oral presentation
- SPIE Photonics West 2013, Feb. 2013, English, California, United States, International conferenceIntraband Carrier Dynamics in InAs/GaAs Quantum Dots Studied by Two-Color Excitation Spectroscopy
Oral presentation
- 第23回光物性研究会, Dec. 2012, Japanese, 大阪市立大学, Domestic conference窒素デルタドーピングによるGaAs電子状態の制御
Poster presentation
- 4th International Workshop on Quantum Nanostructure Solar Cells/8th Seminar on Quantum Nanostructure Materials, Dec. 2012, English, Kobe Ubiversity, International conferenceIntermediate-Band Solar Cells using InGaAs/InP Superlattices
[Invited]
Invited oral presentation
- 第23回光物性研究会, Dec. 2012, Japanese, 大阪市立大学, Domestic conferenceIn0.53Ga0.47As/InP超格子における2段階光吸収を利用した中間バンド型太陽電池
Poster presentation
- 日本物理学会2012年秋季大会, Sep. 2012, Japanese, 横浜国立大学, Domestic conference光共振器構造中のInAs/GaAs量子ドットにおけるサブバンド間遷移ダイナミクス
Oral presentation
- 第73回応用物理学会学術講演会, Sep. 2012, Japanese, 愛媛大学・松山大学, Domestic conference光共振器構造中のInAs/GaAs量子ドットにおける2段階光吸収の増強
Oral presentation
- 第73回応用物理学会学術講演会, Sep. 2012, Japanese, 愛媛大学・松山大学, Domestic conferenceSiダイレクトドーピングによるInAs量子ドットのフェルミ準位の変化
Oral presentation
- The17th International Conference on Molecular Beam Epitaxy, Sep. 2012, English, MBE, Nara, International conferenceMiniband Formation in Closely-Stacked InAs GaAs Quantum Dots
Oral presentation
- 第73回応用物理学会学術講演会, Sep. 2012, Japanese, 愛媛大学・松山大学, Domestic conferenceInフラックスによるInAs/GaAs量子ドットの積層方向の制御
Oral presentation
- 第73回応用物理学会学術講演会, Sep. 2012, Japanese, 愛媛大学・松山大学, Domestic conferenceInAs供給量を制御した近接積層InAs/GaAs量子ドットの発光特性
Oral presentation
- The17th International Conference on Molecular Beam Epitaxy, Sep. 2012, English, MBE, Nara, International conferenceEffects of Excess Electrons on Recombination Lifetime in Directly Si-doped InAs GaAs Quantum Dots
Oral presentation
- The17th International Conference on Molecular Beam Epitaxy, Sep. 2012, English, MBE, Nara, International conferenceControl of Stacking Direction of InAs GaAs Quantum Dots
Oral presentation
- The17th International Conference on Molecular Beam Epitaxy, Sep. 2012, English, MBE, Nara, International conferenceControl of Electronic Structure of GaAs Using Nitrogen δ-doping Technique
Oral presentation
- 第2回光科学異分野横断萌芽研究会, Aug. 2012, Japanese, 岡崎コンファレンスセンター, Domestic conferenceGaAs中の配列制御された窒素ペアに束縛された励起子の光物性
Oral presentation
- The 10th International Conference on Excitonic Processes in Condensed Mattsr, Nanostructured and Molecular Materials, Jul. 2012, English, EXCON, Groningen, Netherlands, International conferenceStrong Electron-Hole Correlation in Bound Exciton in Nitrogen δ-Doped GaAs
Oral presentation
- The 10th International Conference on Excitonic Processes in Condensed Mattsr, Nanostructured and Molecular Materials, Jul. 2012, English, Groningen, Netherlands, International conferenceIntraband Optical Response in InAsGaAs Quantum Dots
Oral presentation
- 31st Electronic Materials Symposium, Jul. 2012, Japanese, ラフォーレ修善寺, Domestic conferenceDelocalization of electronic states formed by nitrogen pairs in GaAs
Poster presentation
- International Conference on Optical, Optoelectronic and Photonic Materials and Applications, Jun. 2012, English, ICOOPMA, Nara, International conferenceExtremely Uniform Excitonic States in Nitrogen δ-Doped GaAs
[Invited]
Invited oral presentation
- 38th IEEE Photovoltaic Specialist Conference, Jun. 2012, English, IEEE, Austin, United States of America, International conferenceCarrier Dynamics in Intermediate States of InAs/GaAs Quantum Dots Embedded in Photonic Cavity Structure
[Invited]
Invited oral presentation
- 第59回応用物理学関係連合講演会, Mar. 2012, Japanese, 日本応用物理学会, 東京都, Domestic conference窒素をデルタドープしたGaAsにおける束縛励起子発光線幅の温度依存性
Oral presentation
- 第59回応用物理学関係連合講演会, Mar. 2012, Japanese, 応用物理学会, 新宿区, Domestic conference近接積層InAs/GaAs量子ドットの光物性
Oral presentation
- 第59回応用物理学関係連合講演会, Mar. 2012, Japanese, 応用物理学会, 新宿区, Domestic conferenceGaAsエピタキシャル界面への窒素のデルタドーピングと高均一発光特性
Invited oral presentation
- 21st International Photovoltaic Science ａｎｄ Engineering Conference PVSECPVSEC-21, Dec. 2011, English, Fukuoka, International conferenceSuppression of Nonradiative Recombination Process in Directly Si-Doped InAs Quantum Dots
Poster presentation
- 第22回光物性研究会, Dec. 2011, Japanese, 光物性研究会組織委員, 熊本市, Domestic conferenceGaAs中の窒素ペアに束縛された励起子における励起子-格子相互作用
Poster presentation
- 8th International Conference on Flow Dynamics, Nov. 2011, English, ICFD organizing committee, 仙台市, International conferenceOptical Properties of Quantum Dot Superlattices
Poster presentation
- 平成23年度第1回半導体エレクトロニクス部門委員会研究会, Oct. 2011, Japanese, 材料学会半導体エレクトロニクス部門委員会, 神戸市, Domestic conference光共振器を有する中間バンド型太陽電池の光吸収増強効果
Oral presentation
- 平成23年度第1回半導体エレクトロニクス部門委員会研究会, Oct. 2011, Japanese, 材料学会半導体エレクトロニクス部門委員会, 神戸市, Domestic conference近接積層量子ドット成長を利用した偏波無依存光応答の実現
Oral presentation
- 第72回応用物理学会学術講演会, Sep. 2011, Japanese, 日本応用物理学会, 山形市, Domestic conference窒素をデルタドープしたGaAsにおける束縛励起子発光線の起源
Oral presentation
- 第72回応用物理学会学術講演会, Sep. 2011, Japanese, 応用物理学会, 山形市, Domestic conference近接積層に伴う量子ドットのフォトルミネッセンス偏光特性
Oral presentation
- Epitaxial Growth and Fundamental Properties of Semiconductor Nanostructures, Sep. 2011, English, Austria, International conferencePhotoluminescence Polarization Anisotropy in Closely Stacked InAs/GaAs Quantum Dots
Oral presentation
- 日本物理学会2011年秋季大会, Sep. 2011, Japanese, 日本物理学会, 富山市, Domestic conferenceGaAs中の窒素ペアに束縛された励起子分子の磁気光学特性
Poster presentation
- 第72回応用物理学会学術講演会, Sep. 2011, Japanese, 日本応用物理学会, 山形市, Domestic conferenceGaAs中の窒素ペアに束縛された励起子のフォノンサイドバンド発光
Oral presentation
- 2011 International Conference on Solid State Devices and Materials, Sep. 2011, English, SSDN組織委員会, Aichi, International conferenceEffect of Capping Layer Growth on Bound Exciton Luminescence in Nitrogen δ-Doped GaAs
Poster presentation
- 37th IEEE Photovoltaic Specialist Conference, Jul. 2011, English, Seattle, International conferenceTwo-Photons Transition in Intermediate Band Solar Cells
Oral presentation
- 第30回電子材料シンポジウム, Jul. 2011, Japanese, EMS組織委員, 大津市, Domestic conferenceElectronic states in multiply stacked InAs/GaAs quantum dots studied by polarized photoluminescence spectroscopy
Poster presentation
- 第30回電子材料シンポジウム, Jul. 2011, Japanese, EMS組織委員, 大津市, Domestic conferenceCapping layer dependence of bound exciton luminescence in nitrogen delta-doped GaAs
Poster presentation
- 38th International Symposium on Compound Semiconductors, May 2011, English, ISCS組織委員会, Germany, International conferenceNear-Field Photoluminescence Spectroscopy of CdTe/Cd0.75Mn0.25Te Tilted Superlattices
Poster presentation
- 38th International Symposium on Compound Semiconductors, May 2011, English, ISCS組織委員会, Berling, Germany, International conferenceDiamagnetic shift of exciton bound to the nitrogen pairs in GaAs
Oral presentation
- 第60回応用物理学関係連合講演会, Mar. 2011, Japanese, 応用物理学会, 厚木市, Domestic conference窒素をデルタドープしたGaAsにおける束縛励起子発光線のキャップ層成長条件依存性
Oral presentation
- 第58回応用物理学関係連合講演会, Mar. 2011, Japanese, 日本応用物理学会, 厚木市, Domestic conference窒素をデルタドープしたGaAsにおける束縛励起子発光線のキャップ層成長条件依存性
Oral presentation
- 第58回応用物理学関係連合講演会, Mar. 2011, Japanese, 応用物理学会, 厚木市, Domestic conference近接多層積層量子ドットのフォトルミネッセンス偏光特性
Oral presentation
- 「ナノ構造・物性」第3回研究会, Mar. 2011, Japanese, 神戸大学自然科学系融合研究環ナノエンジニアリング研究チーム, ナノ学会ナノ構造・物性部会, 神戸市, Domestic conferenceGaAs中の窒素ペアに束縛された励起子の輻射再結合寿命
Oral presentation
- 第59回応用物理学関係連合講演会, Mar. 2011, Japanese, 応用物理学会, 厚木市, Domestic conferenceGaAs 中の窒素ペアに束縛された励起子の磁気光学特性
Oral presentation
- 第58回応用物理学関係連合講演会, Mar. 2011, Japanese, 日本応用物理学会, 厚木市, Domestic conferenceGaAs中の窒素ペアに束縛された励起子の磁気光学特性
Oral presentation
- 第21回光物性研究会, Dec. 2010, Japanese, 光物性研究会組織委員, 大阪市, Domestic conference窒素をデルタドープしたGaAsにおける励起子微細構造の反磁性シフト
Poster presentation
- 第22回光物性研究会, Dec. 2010, Japanese, 光物性研究会組織委員会, 大阪市, Domestic conferenceGaAs中の窒素等電子トラップ束縛励起子の発光ダイナミクス
Poster presentation
- 日本材料学会平成22年度第2回半導体エレクトロニクス部門研究会, Nov. 2010, Japanese, 日本材料学会, 堺市, Domestic conference量子ドットの多層積層化に伴う偏光異方性の発現と制御
Oral presentation
- The 6th International Workshop on Nano-scale Spectroscopy and Nanotechnology, Oct. 2010, English, NSS organizing committee, 神戸市, International conferenceIn-Plane Polarization Anisotropy in Vertically Stacked InAs Quantum Dots
Oral presentation
- 2010年秋季第71回応用物理学会学術講演会, Sep. 2010, Japanese, 応用物理学会, 長崎市, Domestic conferenceIII-V半導体中不純物制御と励起子物性
Invited oral presentation
- The 30th International Conference on the Physics of Semiconductors, Jul. 2010, English, ICPS organizing committee, Seoul, Korea, International conferenceMagneto-Photoluminescence Spectroscopy of Exciton Fine Structure in Nitrogen d-Doped GaAs
Poster presentation
- The 9th International Conference on Excitonic and Photonic Processes in Condensed and Nano Materials, Jul. 2010, English, EXCON organizing committee, Brisbane, Australia, International conferenceBound Biexciton Luminescence in Nitrogen d-Doped GaAs
Poster presentation
- The 37th International Symposium on Compound Semiconductors, Jun. 2010, English, 応用物理学会, 高松市, International conferenceInteraction between Conduction-Band Edge and Nitrogen-Related Localized Levels in Nitrogen d-Doped GaAs
Oral presentation
- 37th International Symposium on Compound Semiconductors, Jun. 2010, English, ISCS組織委員会, 高松市, International conferenceInteraction between conduction-band edge and Nitrogen-related localized levels in Nitrogen d-doped GaAs
Oral presentation
- The International Conference on Nanophotonics 2010, May 2010, English, ICNP organizing committee, つくば市, International conferenceEmission properties of excitons strongly localized to nitrogen pairs in GaAs
[Invited]
Invited oral presentation
- 日本物理学会第65回年次大会, Mar. 2010, Japanese, 日本物理学会, 岡山市, Domestic conference窒素をデルタドープしたGaAsにおける発光スペクトルの反磁性シフト
Poster presentation
- 第57回応用物理学関係連合講演会, Mar. 2010, Japanese, 日本応用物理学会, 平塚市, Domestic conference窒素をデルタドープしたGaAs における電子状態の磁場依存性
Poster presentation
- 第20回光物性研究会, Dec. 2009, Japanese, 光物性研究会組織委員会, 大阪市, Domestic conferenceGaAs中の窒素等電子束縛励起子における励起子ダイナミクス
Poster presentation
- 第70回応用物理学会学術講演会, Sep. 2009, Japanese, 応用物理学会, 富山市, Domestic conference窒素をデルタドープしたGaAsにおける束縛励起子分子発光
Oral presentation
- 日本物理学会2009年秋季大会, Sep. 2009, Japanese, 日本物理学会, 熊本市, Domestic conferenceGaAs中の窒素等電子束縛励起子微細構造におけるポピュレーション
Poster presentation
- 第28回電子材料シンポジウム, Jul. 2009, Japanese, 電子材料シンポジウム運営委員会, 大津市, Domestic conferenceMagnetic-field control of the exciton fine polarization splitting of nitrogen pair centers in GaAs
Poster presentation
- 14th International Conference on Modulated Semiconductor structures, Jul. 2009, English, MSS組織委員会, 神戸市, International conferenceMagnetic-field control of exciton fine structure splitting in nitrogen -doped GaAs
Oral presentation
- Abstr. 14th International Conference on Modulated Semiconductor Structures, Jul. 2009, English, Kobe, International conferenceMagnetic-Field Control of Exciton Fine Structure Splitting in Nitrogen Delta-Doped GaAs
Oral presentation
- Abstr. 15th International Symposium on Intercalation Compounds, Mar. 2009, English, Beijing, International conferenceControl of Exciton Fine Structure of Nitrogen Nanospace in GaAs
Oral presentation
- Abstr. The 15th International Conference on Luminescence and Optical Spectroscopy of Condenced Matter, Jul. 2008, English, Lyon, International conferenceFine structure of bound excitons in nitrogen-doped GaAs
Oral presentation
- Abstr. The 15th International Conference on Luminescence and Optical Spectroscopy of Condenced Matter, Jul. 2008, English, Lyon, International conferenceAnisotropic Linear Polarization Luminescence in CdTe/CdMnTe Quantum Wires
Oral presentation
- Abstr. 8th International Conference on Excitonic Process in Condensed Matter, Jun. 2008, English, Kyoto,, International conferenceNear-Field Photoluminescence of Exciton Magnetic Polarons in CdTe/Cd0.75Mn0.25Te Quantum Wires
Oral presentation
- Proc. 20th International Conference on Indium Phosphide and Related Materials, May 2008, English, Paris, International conferenceExciton Fine Structure of Nitrogen Isoelectronic Center
Oral presentation
Research Projects
- 日本学術振興会, 科学研究費助成事業 基盤研究(C), 基盤研究(C), 神戸大学, 01 Apr. 2022 - 31 Mar. 2025量子ドット超格子における電場増強効果を利用したホットキャリア型太陽電池
- Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C), Grant-in-Aid for Scientific Research (C), Kobe University, 01 Apr. 2022 - 31 Mar. 2025Realization of integrated high sensitivity electric field sensor using quantum dot superlattice
- Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C), Grant-in-Aid for Scientific Research (C), Kobe University, Apr. 2019 - Mar. 2022Photoconductive devices based on quantum dot superlattice for THz generation and detection
本年度は、量子ドット(QD)超格子を用いた光伝導アンテナ(PCA)デバイスに向けた結晶作製方法の開発、超高速分光法によるこの結晶の超高速キャリア緩和特性の確認、さらに基本的なPCAデバイスの作製を実行した。また、PCAにおける電場増強効果の可能性に関する理論検討を開始した。 結晶成長・デバイス作製関連では、まず分子線エピタキシによる低温成長（LT-）GaAs層の成長条件を確立した後、半絶縁性GaAs(001)基板上にInAs QDs(2.0分子層)とGaAs中間層(50 nm)を20層積層し、さらにLT-GaAs層(30 nm)を成長することによりデバイス結晶を得た。デバイス作製では、Ti/Au電極間ギャップ約5 μmのダイポール型PCA電極形成、およびメサエッチ加工を行った。メサ構造の採用により、暗電流の値を2桁抑制できることが判明し、デバイス特性評価に十分適用できるものと判断した。 結晶の光学特性評価に関しては、量子ドット超格子試料に対して反射型ポンププローブ法を適用し、キャリア緩和ダイナミクスを測定した。現在広く使用されている市販のLT-GaAsを用いたPCAとの性能の比較を行うために、超短パルスレーザーの波長を810 nmとして、室温において測定を行った。パルス幅が約100フェムト秒程度の超短パルスを照射して測定した結果、0.6ピコ秒程度のキャリア寿命を得、十分にPCAデバイスとして使用できる高速性を確認できた。 電場増強による最適化デバイス構造の検討に関しては、光励起キャリアによる、InAs量子ドットにおける電場増強効果を境界要素法によって解析した。GaAsホスト結晶に埋め込まれた半球状のInAs量子ドットにおいて、局在表面プラズモンに起因する電場増強効果を10E18/cm3程度の自由電子密度において10μm帯で確認した。
- 日本学術振興会, 科学研究費助成事業 基盤研究(C), 基盤研究(C), 神戸大学, Apr. 2019 - Mar. 2022量子ドット超格子太陽電池におけるホットキャリア型太陽電池動作の実証
本研究では、InAs/GaAs量子ドット超格子を内包する太陽電池において、幅広い励起波長域における高効率なホットキャリア電流取り出しを実現し、単接合型太陽電池の変換効率限界を突破するホットキャリア型太陽電池の学理の構築と高効率化技術の開発を目的とする。2019年度は、InAs/GaAs量子ドット超格子太陽電池における、ホットキャリア電流と開放電圧の励起波長依存性を解明した。具体的な研究成果は以下の通りである。 〇InAs/GaAs量子ドット超格子太陽電池において、ホスト結晶であるGaAsのバンドギャップエネルギー以下の入射光を用いて電流―電圧特性の励起波長依存性を低温（15 K）で測定し、ホットキャリア電流の取り出し過程を明らかにした。短絡電流密度と開放電圧の関係が励起波長に依存しなかった結果は、InAs/GaAs量子ドット超格子太陽電池固有のホットキャリア電流の取り出し過程を電流―電圧特性から議論できることを示唆している。 〇9層近接積層InAs/GaAs量子ドットによって構成される量子ドット超格子の層数を増加させることによって、短絡電流密度と開放電圧が増加することを実証した。短絡電流密度は励起光強度にほぼ比例して増加したのに対して、開放電圧は励起光強度の増加に伴って飽和傾向を示した。開放電圧が励起波長に依存せずほぼ一定の電圧で飽和傾向を示した結果は、ホットキャリアとして量子ドット超格子から取り出された電子が隣接する量子ドット超格子に捕獲されていることを示唆している。以上の結果より、単接合型太陽電池の変換効率限界を突破するホットキャリア型太陽電池の実現に向けて、内部電場の最適化が必要な事が明らかになった。
- 学術研究助成基金助成金／国際共同研究加速基金(国際共同研究強化(B)), Oct. 2018 - Mar. 2021
Competitive research funding
- 学術研究助成基金助成金／挑戦的研究（萌芽）, Jun. 2018 - Mar. 2020
Competitive research funding
- 学術研究助成基金助成金／若手研究(B), Apr. 2017 - Mar. 2019, Principal investigator
Competitive research funding
- 科学研究費補助金／基盤研究(B), Apr. 2016 - Mar. 2019
Competitive research funding
- 学術研究助成基金助成金／挑戦的萌芽研究, Apr. 2015 - Mar. 2017
Competitive research funding
- 学術研究助成基金助成金／挑戦的萌芽研究, Apr. 2013 - Mar. 2015
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- 科学研究費補助金／基盤研究(B), Apr. 2012 - Mar. 2015
Competitive research funding
- 学術研究助成基金助成金／挑戦的萌芽研究, 2011
Competitive research funding
- 科学研究費補助金／若手研究(B), 2010, Principal investigator
Competitive research funding
- 科学研究費補助金／若手研究(スタートアップ), 2009, Principal investigator
Competitive research funding