論文 - 小堀 裕己
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Spatial fluctuation enhancement and nonradiative-recombination-center generation due to high Si-doping into GaAs/AlAs short-period-superlattices(共著)
H. Kobori, A. Shigetani, I. Umezu and A. Sugimura
Physica B 376-377 861 - 863 2006年
共著
担当区分:筆頭著者
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Intensified spin-dependent-transport and localized-spin freezing in magnetite sinter made from low size-dispersion hematite nanoparticles with low temperature calcination(共著) 査読あり
H. Kobori, K. Ohnishi, A. Sugimura and T. Taniguchi
Physica Status Solidi (c) 12 4200 - 4203 2006年
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担当区分:筆頭著者
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Intensified spin-dependent-transport and localized-spin freezing in magnetite sinter made from low size-dispersion hematite nanoparticles with low temperature calcination 査読あり
H. Kobori, K. Ohnishi, A. Sugimura, T. Taniguchi
Physica Status Solidi (C) Current Topics in Solid State Physics 3 ( 12 ) 4200 - 4203 2006年
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The spin-dependent-transport (SDT) has been studied for magnetite (Fe 3O4) nano-particle sinter (MNPS) made from low size-dispersion hematite (α-Fe2O3) nanoparticles (LSDHN's) with low temperature calcination. Two kinds of LSDHN's are grown by the hydrothermal synthesis. The average sizes of them are 30 nm and 60 nm. The MNPS is produced by calcining the LSDHN's at 500 °C for 5 hours in the atmos phere of Ar(90%)/H2(10%) mixed gases. As compared with a bulk single crystal, the considerable intensification of negative-differential- magnetoresistance (ND-MR) has been observed for the MNPS. We have: not observed abrupt change of the electrical resistivity in the vicinity of the temperature of the Verwey transition (which is the metal-insulator transition) appeared for a bulk single crystal. The ND-MR for 30 nm shows larger values than that of 60 nm on the temperature dependence. From the X-ray diffraction experiment, the MNPS is found to include crystalline magnetite regions. We consider that the MNPS is composed of large amorphous-like grain-boundaries and small crystalline grains. The electrical current is inferred to flow in grain-boundary regions. In grain-boundary regions, since the localized spins are relatively random distributed, the spin-polarized conduction electrons show the SDT. Below the Verwey temperature, we have observed the magnetization difference between zero-field cooling (ZFC) and field cooling (FC). This phenomenon indicates that the localized spins in the amorphous-like grain-boundaries; are frozen in some degree. Above the Verwey temperature, the magnetoresistance is well fitted by the square of the Langevin function. We consider that the localized spins in the amorphous-like grainboundaries do not form perfectly random configuration and are somewhat ordered in a short range region. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.
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Reversal magnetoresistance and unusual localized-spin freezing in magnetite sinter made from low size-dispersion hematite nano-particles with high temperature calcination 査読あり
H. Kobori, K. Ohnishi, A. Sugimura, T. Taniguchi
Physica Status Solidi (C) Current Topics in Solid State Physics 3 ( 12 ) 4204 - 4207 2006年
共著
The magneto-resistance and magnetization have been studied for magnetite (Fe3O4) sinter made from low size-dispersion hematite (α-Fe2O3) nanoparticles (LSDHN's) with high temperature calcination. Two kinds of LSDHN's were grown by the hydrothermal synthesis. The average particle sizes of them are 30 nm and 60 nm. The magnetite sinter was produced by calcining the LSDHN's at 800 °C for 5 hours in the atmosphere of Ar(90%)/H2(10%) mixed gases. We have observed an abrupt change of the electrical resistivity by one order of magnitude in the vicinity of the Verwey temperature (123 K) of a bulk single crystal. From the X-ray diffraction experiment, we have found that the magnetite sinter includes crystalline region. The magnetite sinter is considered to be composed of relatively narrow grain-boundary regions of amorphous-like magnetite and large grain regions of crystalline magnetite. It is regarded that the grainboundary-conduction is dominant below the Verwey temperature and the inter-grain-conduction is dominant above the Verwey temperature. We have observed the positive differential magnetoresistance (PD-MR) in low temperature regions and the negative differential magnetoresistance (ND-MR) in high temperature regions. The ND-MR is an ordinary phenomenon for magnetite, but the PD-MR is a peculiar one In addition, an unusual localized-spin-freezing phenomenon has been also observed. Below the Verwey temperature, the magnetization difference between zero-field-cooling and field-cooling has been observed. The magnetization difference shows a sudden change in the vicinity of the Verwey temperature. © 2006 WILEY-VCH Verlag GmbH & Co. KGaA.
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Considerable enhancement of PL intensity for free exciton in ZnO ultra-fine-particles and oscillatory green band emergence in PL spectrum for Cu-doped ZnO ultra-fine-particles with heat treatment 査読あり
H. Kobori, T. Nanao, S. Kawaguchi, I. Umezu, A. Sugimura
AIP Conference Proceedings 772 867 - 868 2005年6月
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For the ultra-fine-particles of ZnO with the heat treatment and Cu-doping, we have observed the considerable enhancement of the PL intensity for free excitons and the oscillatory structure of the green band. These experimental results are explained by the localization model of excitons and the donor to Cu-acceptor recombination, respectively. © 2005 American Institute of Physics.
DOI: 10.1063/1.1994381
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Unusual behavior of far-infrared magneto-photoconduction in electric field for n-GaAs near metal-insulator-transition 査読あり
H. Kobori, M. Inoue, K. Fujii, T. Ohyama
AIP Conference Proceedings 772 127 - 128 2005年6月
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To study the influence of the electric field on the magnetic-field induced metal-insulator-transition, we have carried out far-infrared magneto-photoconductivity measurements in various electric fields for n-GaAs near the metal-insulator transition by use of the far-infrared laser with 119μm between 2.0K and 4.2K. © 2005 American Institute of Physics.
DOI: 10.1063/1.1994026
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Unusual Behavior on Line-Broadening of Photoluminescence Spectrum for Type-II Excitons in Highly Si-Doped GaAs/AlAs Short-Period-Superlattices(共著) 査読あり
H. Kobori, A. Shigetani, I. Umezu and A. Sugimura
Proceedings of 24th International Conference on Low Temperature Physics PD-Tu-228 (Orland, USA 2005) 1522 - 1523 2005年
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担当区分:筆頭著者
Proceedings of 24th International Conference on Low Temperature Physics
PD-Tu-229 (Orland, USA 2005) -
Localization and Transport of Type-II Excitons in Spatially Enhanced Random Potential for Highly Si-Doped GaAs/AlAs Short-Period-Superlattices(共著) 査読あり
H. Kobori, A. Shigetani, I. Umezu and A. Sugimura
Proceedings of 24th International Conference on Low Temperature Physics PD-Tu-228 (Orland, USA 2005) 1524 - 1525 2005年
共著
担当区分:筆頭著者
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Estimation of conduction as well as donor electron density through far-infrared resonant faraday effect 査読あり
Masato Suzuki, Ken Ichi Fujii, Tyuzi Ohyama, Hiromi Kobori
International Journal of Infrared and Millimeter Waves 24 ( 12 ) 2043 - 2050 2003年12月
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We have investigated resonant Faraday effect (RFE), so-called nonlinear Faraday effect, caused by conduction and donor electrons in n-InSb and n-GaAs. Experiments were carried out with using the magneto-optical spectroscopic system combined with two linear polarizers put in before and behind a sample. The rotation angle and the ellipticity for the far-infrared light with elliptical polarization transmitted through the sample were analyzed on the basis of spectra obtained under different experimental configuration for angles between the axes of the polarizer and the analyzer. We have observed some characteristic features associated with RFE in spectra of two samples. Tapping into these features, we could successfully determine the relaxation times and the densities of conduction and donor electrons in the semiconductors.
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Far-infrared resonant Faraday effect in semiconductors 査読あり
Masato Suzuki, Ken Ichi Fujii, Tyuzi Ohyama, Hiromi Kobori, Nobuo Kotera
Journal of the Physical Society of Japan 72 ( 12 ) 3276 - 3285 2003年12月
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We have studied resonant Faraday effect (RFE) related to the intraband transitions in various semiconductors at low temperature through direct measurements for the Faraday rotation angle and ellipticity of the probe far-infrared (FIR) light. Through cyclotron resonance due to electrons in a thin n-InSb sample and two-dimensional electrons in the interface of GaAs/AlGaAs as well as the impurity absorption by donors in the n-InSb, we have made clear that RFE is dominated by the off-diagonal components of dielectric tensor. Experimental results for bulk n-InSb samples with various thicknesses have revealed a lot of properties of RFE as saturation effect on absorption. The oscillatory spectra induced by several twirls of the polarization plane have been observed in the extremely thick InSb sample. Spectra of the thick n-InSb also show high sensitivity of ellipticity for interference of circularly polarized lights. Besides, making use of the characteristic behavior on RFE, we can classify absorption lines due to impurities in Ge, i.e., the electron-type absorption or the hole-type one. By referring the experimental results to the theory based on Lorentz-oscillator model, we have made clear some characteristic features on RFE. © 2003 The Physical Society of Japan.
DOI: 10.1143/JPSJ.72.3276
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Far-infrared transient-resonant Faraday rotation induced by non-equilibrium electrons in compensated p-InSb under pulsed-photoexcitation 査読あり
Masato Suzuki, Hiromi Kobori, Nobuo Kotera, Ken Ichi Fujii, Tyuzi Ohyama
Physica B: Condensed Matter 329-333 ( II ) 1096 - 1098 2003年5月
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We have made our first attempt to investigate the resonant-transient Faraday effect induced by conduction and bound electrons in compensated p-InSb under pulsed-photoexcitation at 4.2 K with use of a far-infrared laser. The Faraday rotation angle is extremely sensitive to the refractive index for the left-hand and right-hand circularly polarized waves. Meanwhile ionized donors in compensated semiconductors are neutralized by photoexcitation and the resonant phenomena by these neutralized impurities bring a big change of refractive index in semiconductors. As donor electrons excited by the photo-pulse relax with a finite lifetime, the refractive index dominated by these donor electrons has time-dependent nature, and thus we are able to observe the transient-Faraday effect through the time-resolved experiments. © 2003 Elsevier Science B.V. All rights reserved.
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Studies of excited states for shallow donors in magnetic field on bulk n-InP 査読あり
Masato Suzuki, Hiromi Kobori, Tyuzi Ohyama
Journal of the Physical Society of Japan 72 ( 5 ) 1127 - 1130 2003年5月
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Through far-infrared (FIR) magneto-optical absorption measurements we have investigated excited states of shallow donors in bulk n-InP at 4.2 K. By utilizing advantage of thick bulk samples we have observed transitions from Is ground state of donors to various excited states as 2p+1 3p +1 and 3d+1 and a series of oscillatory absorptions caused by transitions to magnetically-induced states. By the optical saturation effect it is found that comparatively weak absorptions as the oscillatory ones become prominent due to suppression of strong absorptions. In order to make clear the excited states of donors under a magnetic field signals due to the 1s-3p +1 and 1s-3d+1 transitions are extremely helpful, since the resonance positions and the peak heights include various informations for excited states. Based on variation of the oscillation peaks with increases in donor concentration, we conclude that the oscillatory absorptions originate in transitions from the Is ground state to impurity bands. © 2003 The Physical Society of Japan.
DOI: 10.1143/JPSJ.72.1127
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Far-infrared resonant Faraday effect in Semiconductors(共著) 査読あり
M. Suzuki, K. Fujii, T. Ohyama, H. Kobori and N.Kotera
Journal of the Physical Society of Japan 72 3276 - 3285 2003年
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Sizable Enhancement of Anti-Weak Localization Effect in In2O3-X Thin Film caused by H2 Gas Mixing in N2 Gas Atmosphere on Heat Treatment(共著) 査読あり
H. Kobori, M. Kawaguchi, N. Hatta and T. Ohyama
Physica E 18 296 - 297 2003年
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担当区分:筆頭著者
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Far-infrared transient-resonant Faraday rotation induced by non-equilibrium electrons in compensated p-InSb under pulsed-photoexcitation(共著) 査読あり
M. Suzuki, H. Kobori, N.Kotera, K. Fujii and T. Ohyama
Physica B 239-333 1096 - 1098 2003年
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Crossover from positive to negative magnetoresistance by the rise of electron temperature for Si:Sb in the variable-range hopping regime 査読あり
A. Fujimoto, H. Kobori, T. Ohyama, S. Ishida, K. Satoh, T. Kusaka, Y. Kakehi
Physica B: Condensed Matter 324 ( 1-4 ) 1 - 8 2002年11月
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Magnetoresistance (MR) measurements in Si:Sb with the Sb concentration just below the critical concentration for metal-insulator transition have been carried out by stepping into the non-ohmic region of the electric current density. We have found that the MR sensitively depends on the electric current density. For the insulating sample positive MR is observed in the low current density region. A crossover from positive to negative MR is found as the current density increases. It is considered that these phenomena originate from the rise of the electron temperature and are related to the transport in the upper-Hubbard band. © 2002 Elsevier Science B.V. All rights reserved.
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Weak Localization and Weak Anti-localization in Polycrystalline In2O3-X Thin Films grown by Sputtering Method:(共著) 査読あり
H. Kobori, M. Kawaguchi, N. Hatta, T. Ohyama and S. Ishida
physica status solidi (b) 230 277 - 280 2002年
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担当区分:筆頭著者
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Weak anti-localization in δ-doped Sb layer of Si 査読あり
A. Fujimoto, H. Kobori, T. Ohyama, S. Ishida
Physica Status Solidi (B) Basic Research 230 ( 1 ) 273 - 276 2002年
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The spin-orbit (SO) interaction in a δ-doped Si: Sb with 0.11 monolayer of Sb atoms is studied, based on the first observation of the positive magnetoresistance in weak perpendicular magnetic fields due to the two-dimensional weak anti-localization in this system. From the fits of the magnetoconductance data in fields perpendicular to the layer, the SO scattering time τSO as well as the inelastic scattering time τin have been extracted as τSO ≈ 3 × 10-11 s and τin ∝ T-1, respectively. The ratio is τSO/4τin ≈ 0.60 at T = 3 K, which is larger than any other value reported, indicating that the strength of the SO interaction in Si:Sb with 0.1 monolayer of Sb is very small compared with the ones found in the thin metal films.
DOI: 10.1002/1521-3951(200203)230:1<273::AID-PSSB273>3.0.CO;2-S
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Quantum magneto-optical oscillation on far-infrared Zeeman spectrum of n-InP 査読あり
M. Suzuki, H. Kobori, T. Ohyama
Physica B: Condensed Matter 298 ( 1-4 ) 203 - 206 2001年4月
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An oscillatory absorption spectrum which could not be detected in thin samples was observed for FIR magneto-optical absorption measurements in bulk n-InP at 4.2 K. It was found that the peak positions of the oscillation did not correspond to a series of direct transitions from the 1s ground state of donors into the Landau levels, and these peak positions considerably changed with the donor concentration. We have concluded that those oscillations are associated with a series of transitions from the 1s ground state into donor bands formed by the excited states and their accompanying the Landau levels. © 2001 Elsevier Science B.V.
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Two-to-three dimensional transition by magnetic field on weak localization phenomena for tilted magneto-conductance in In2O3-x films 査読あり
N. Hatta, H. Kobori, T. Ohyama
Physica B: Condensed Matter 298 ( 1-4 ) 482 - 485 2001年4月
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To study the two-to-three dimensional transition on the weak localization phenomena in thin metallic In2O3-x films, we have carried out the magneto-conductance measurements for those films with various thickness up to the magnetic field of 9 T. We have measured the magneto-conductance as functions of the film thickness and the angle between the directions of the electric current and the magnetic field. From the magnitude correlation between the film thickness and the cyclotron diameter, we found that the anisotropic behavior of the magneto-conductance observed in the low magnetic field has been disappeared as the magnetic field increases. As a result we have clearly observed the two-to-three dimensional transition of the electronic system and the crossover effect on the positive magneto-conductance in the weak localization regime. © 2001 Published by Elsevier Science B.V.