- 著者
- Natori Kenji Kimura Yoji Shimizu Tomo
- 出版者
- American Institute of Physics
- 雑誌
- Journal of applied physics (ISSN:00218979)
- 巻号頁・発行日
- vol.97, no.3, pp.034306, 2005-02
- 被引用文献数
- 94
A general expression of the current-voltage characteristics of a ballistic nanowire field-effect transistor (FET) is derived. At T=0, the conductance, which is equal to the quantum conductance multiplied by the number of channels at zero bias, decreases stepwise toward current saturation as the drain bias is increased. The current-voltage characteristics of a single-wall carbon nanotube FET in ballistic conduction are discussed based on the band structure of the nanotube. When both the gate overdrive and the drain bias are equal to 1 V, the device made of a (19,0) nanotube and a 2-nm high-k gate insulator (epsilon=40epsilon(0)) flows a current of 183 muA, which amounts to a current density 48 times as large as the counterpart of a silicon device. The high performance originates from a high carrier density due to the enhanced gate capacitance, and a large carrier velocity caused by the large group velocity of the original graphene band. Quantum capacitance also plays an important role in the device's characteristics.
- 著者
- Tanaka Masanori Sawai Shinya Sengoku Masaya Kato Manabu Masumoto Yasuaki 舛本 泰章
- 出版者
- American Institute of Physics
- 雑誌
- Journal of applied physics (ISSN:00218979)
- 巻号頁・発行日
- vol.87, no.12, pp.8535-8540, 2000-06
- 被引用文献数
- 30
Nanocrystalline particles of ZnS:(Ag, Al) semiconductor phosphor, whose sizes are mostly 3–5 nm in diameter, are prepared by the gas-evaporation method with cw CO2 laser heating. The Raman scattering spectrum as well as the transmission electron microscope observation demonstrates that the crystallization of the nanoparticles was caused successfully through the gas-phase condensation. Under irradiation of ultraviolet light, the nanoparticles exhibit blue luminescence, as in the case of the starting material of ZnS:(Ag, Al) bulk powder. The peak of the luminescence spectrum of the nanoparticles shifts to lower energy with increasing delay time and also with decreasing excitation intensity, showing that the luminescence originates from the donor–acceptor pair recombination. However, it is concluded that the luminescence of the nanoparticles is not ascribed to the blue Ag luminescence mechanism responsible for the luminescence of the bulk powder, by taking into account the spatial confinement of an electron trapped at the donor and a hole at the acceptor. It is argued that the luminescence mechanism of the nanoparticles is the so called self-activated luminescence, which involves zinc vacancies.
2 0 0 0 OA Investigation of the recombination mechanism of excess carriers in undoped BaSi2 films on silicon
- 著者
- Hara K. O. Usami N. Toh K. Baba M. Toko K. Suemasu T.
- 出版者
- American Institute of Physics
- 雑誌
- Journal of applied physics (ISSN:00218979)
- 巻号頁・発行日
- vol.112, no.08, pp.083108, 2012-10
- 被引用文献数
- 83
Excess-carrier recombination mechanisms in undoped BaSi2 epitaxial films grown by molecular beam epitaxy on n-type silicon substrates have been studied by the microwave-detected photoconductivity decay measurement. The measured excess-carrier decay is multiexponential, and we divided it into three parts in terms of the decay rate. Measurement with various excitation laser intensities indicates that initial rapid decay is due to Auger recombination, while the second decay mode with approximately constant decay to Shockley-Read-Hall recombination. Slow decay of the third decay mode is attributed to the carrier trapping effect. To analyze Shockley-Read-Hall recombination, the formulae are developed to calculate the effective lifetime (time constant of decay) from average carrier concentration. The measurement on the films with the thickness of 50–600 nm shows that the decay due to Shockley-Read-Hall recombination is the slower in the thicker films, which is consistent with the formulae. By fitting the calculated effective lifetime to experimental ones, the recombination probability is extracted. The recombination probability is found to be positively correlated with the full width at half-maximum of the X-ray rocking curves, suggesting that dislocations are acting as recombination centers.
- 著者
- Ishizuka Shogo Yamada Akimasa Islam Muhammad Monirul Shibata Hajime Fons Paul Sakurai Takeaki Akimoto Katsuhiro Niki Shigeru
- 出版者
- American Institute of Physics
- 雑誌
- Journal of applied physics (ISSN:00218979)
- 巻号頁・発行日
- vol.106, no.3, pp.034908, 2009-08
- 被引用文献数
- 144 57
The systematic variations in the structural, optical, and electrical properties of polycrystalline Cu(In,Ga)Se2 (CIGS) thin films with Na doping level were investigated. Precise control of the Na concentration in CIGS films was demonstrated using alkali-silicate glass thin layers of various thicknesses deposited on substrates prior to CIGS growth. The CIGS grain size was observed to decrease with increasing Na concentration, although the surface morphology became smoother and exhibited a stronger (112) texture, which has been demonstrated consequence of larger grain size. The Ga composition gradient in the CIGS films was found to become large due to the presence of Na during growth, which in turn led to a decrease in the nominal band gap energy. Variations in the photoluminescence spectra and electrical properties suggested that the formation of an acceptor energy state, which may originate from OSe point defects, was enhanced in the presence of Na. This result suggests that not only Na, but also the presence of O in combination with Na contributes to the compensation of point defects and enhances p-type conductivity in CIGS films.
2 0 0 0 OA Coherent optical control of the ultrafast dephasing and mobility in a polar semiconductor
- 著者
- Lee J. D. Gomi H. Hase Muneaki
- 出版者
- American Institute of Physics
- 雑誌
- Journal of applied physics (ISSN:00218979)
- 巻号頁・発行日
- vol.106, no.8, pp.083501, 2009-10-16
- 被引用文献数
- 1 3
Using the nonperturbative many-body time-dependent approach, we investigate the nonequilibrium dynamics of the coherent longitudinal optical phonon-plasmon coupled (LOPC) modes in a polar semiconductor and explore their coherent optical control and eventually the carrier mobility of the semiconductor. The basic idea for a control of the carrier mobility is to manipulate the ultrafast dephasing of the coherent carrier-relevant LOPC mode. We theoretically propose two possible options to realize the idea and reach the final goal. One is to optimize a semiconductor by finely balancing two kinds of carrier densities by chemical doping and optical doping (or photodoping), where the relaxation of the coherent carrier-relevant LOPC mode would respond in a (weak) singular way. It is found that, in this way, the carrier mobility could be enhanced by a few tens of percent. The other is to optimize the optical pumping laser. In this option, the pulse train creating pure virtual carriers through the below-band-gap excitation would be incorporated for an optical pumping, which can make possible the dephasing-free dynamics of the coherent carrier-relevant LOPC mode. The carrier mobility can then be efficiently controlled and dramatically enhanced by synchronizing the pulse train with its coherent oscillation. This might imply one of ultimate ways to control the carrier mobility of the semiconductor
- 著者
- Natori Kenji
- 出版者
- American Institute of Physics
- 雑誌
- Journal of applied physics (ISSN:00218979)
- 巻号頁・発行日
- vol.76, no.8, pp.4879-4890, 1994-10
- 被引用文献数
- 28 516
Experiments on ultra-small metal-oxide-semiconductor field effect transistors (MOSFETs) less than 100 nm have been widely reported recently. The frequency of carrier scattering events in these ultra-small devices is diminished, so that further suppression of carrier scattering may bring these devices close to the regime of ballistic transport. Carrier scattering is suppressed by constructing their channel regions with intrinsic Si and also by low temperature operation. This article proposes the ballistic transport of carriers in MOSFETs, and presents the current-voltage characteristics of the ballistic n-channel MOSFET. The current is expressed with the elementary parameters without depending on the carrier mobility. It is independent of the channel length and is proportional to the channel width. The current value saturates as the drain voltage is increased and the triode and the pentode operation are specified as in the conventional MOSFET. Similar current-voltage characteristics in the ballistic transport regime are also investigated for the p-channel MOSFET, the dual gate ultra-thin silicon on insulator MOSFET, and the high electron mobility transistor device. The obtained current gives the maximum current limitation of each field effect transistor geometry. The current control mechanism of ballistic MOSFETs is discussed. The current value is governed by the product of the carrier density near the source edge in the channel, and the velocity with which carriers are injected from the source into the channel.Influence of optical phonon emission to the transport is discussed. It is suggested that if the device is operated with relatively low carrier density at low temperatures, and if the scattering processes other than the optical phonon emission are suppressed so as to attain the ballistic transport, the optical phonon emission is also suppressed and ballistic transport is sustained. A convenient figure of merit to show the ballisticity of carrier transport in an experimental MOSFET is proposed. Its value is estimated for some examples of the recent ultra-small MOSFET experiment. The proposed current voltage characteristics are evaluated for a dual gate silicon on insulator MOSFET geometry. The result is compared with the recently reported elaborate Monte Carlo simulation with satisfactory agreement.
1 0 0 0 OA Favorable electronic structure for organic solar cells induced by strong interaction at interface
- 著者
- Wang Shenghao Sakurai Takeaki Hao Xia Fu Wei Masuda Shigeru Akimoto Katsuhiro
- 出版者
- American Institute of Physics
- 雑誌
- Journal of applied physics (ISSN:00218979)
- 巻号頁・発行日
- vol.114, no.18, pp.183707, 2013-11
- 被引用文献数
- 8 2
To clarify the role of buffer layer in organic solar cells (OSCs), the electronic properties of bathocuproine (BCP)/Mg interface were systematically investigated by using ultraviolet photoemissions spectroscopy, high-resolution X-ray photoemission spectroscopy, angle-resolved X-ray photoemission spectroscopy and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The results show there are gap states at the interface, which are caused by the interaction between BCP and Mg. The formation of Mg-N bond was found at the interface. The NEXAFS measurements show that BCP molecules for 1-2 monolayers are lying-down on the substrate, whereas orient randomly for thick BCP layer. It was supposed that the gap states and the highly-ordered orientation of thin BCP layer are the reasons for improving the performance of OSC with BCP buffer layer and low work function metal cathode.
- 著者
- Sasaki Shuichi Yagi Ichimasa Murakami Masato
- 出版者
- American Institute of Physics
- 雑誌
- Journal of Applied Physics (ISSN:00218979)
- 巻号頁・発行日
- vol.95, no.4, pp.2090-2093, 2004-01-01 (Released:2016-05-17)
- 被引用文献数
- 9
An iron ball floats in midair in a plastic box when several iron balls were attracted by a permanentmagnet. A complex interaction between magnetized sphere materials and a lifting magnet enabledthe suspension of an iron ball. The balls in the first row are simply attracted by the lifting magnet.The ball in the second row is also attracted by the lifting magnet, however, due to the repulsiveforces exerted from the balls sitting above, it can float in midair. We also found that there are twostable positions for the ball to float. The floating ball could be transported from one equilibriumposition to another by simply rotating the lifting magnet. This will make it possible to construct anoncontact load transport device.
1 0 0 0 OA Hard x-ray photoelectron spectroscopy study on valence band structure of semiconducting BaSi2
- 著者
- Baba Masakazu Ito Keita Du Weijie Sanai Tatsunori Okamoto Kazuaki Toko Kaoru Ueda Shigenori Imai Yoji Kimura Akio Suemasu Takashi
- 出版者
- American Institute of Physics
- 雑誌
- Journal of applied physics (ISSN:00218979)
- 巻号頁・発行日
- vol.114, no.12, pp.123702, 2013-09
- 被引用文献数
- 15
The valence band structures of a 35-nm-thick BaSi2 epitaxial film on Si(111) have been explored at room temperature by hard x-ray photoelectron spectroscopy (HAXPES). The experimentally obtained photoelectron spectrum is well reproduced by first-principles calculations based on the pseudopotential method. The top of the valence band consists mainly of Si 3s and 3p states in BaSi2, suggesting that the effective mass of holes is small in BaSi2. This is favorable from the viewpoint of solar cell applications. The observed spectrum shifted slightly to the lower energy side due to n-type conductivity of BaSi2. The valence band top was observed at about 0.8 eV below the Fermi level in the HAXPES spectrum.
- 著者
- Harada Shunta Tanaka Katsushi Inui Haruyuki
- 出版者
- AMER INST PHYSICS
- 雑誌
- JOURNAL OF APPLIED PHYSICS (ISSN:00218979)
- 巻号頁・発行日
- vol.108, no.8, 2010-10
- 被引用文献数
- 152
The thermoelectric properties of Magnèli phase titanium oxides TinO2n−1 n=2, 3, ... have been investigated, paying special attention to how the thermoelectric performance can be altered by changing the microstructure. Dense polycrystalline specimens with nominal composition of TiO2−x x=0.05, 0.10, 0.15, and 0.20 prepared by conventional hot-pressing are all identified to be one of the Magnèli phases, in which crystallographic shear planes are regularly introduced according to the oxygen deficiency. Electrical conduction is n-type for all specimens and the carrier concentration increases with the increase in the oxygen deficiency. The values of lattice thermal conductivity, on the other hand, decrease with the increase in the oxygen deficiency, which can be attributed to phonon scattering at the crystallographic shear plane. The largest value of thermoelectric figure of merit Z, 1.6 10−4 K−1 was obtained at 773 K for the hot-pressed specimen of TiO1.90
- 著者
- Benseman T. M. Koshelev A. E. Kwok W.-K. Welp U. Vlasko-Vlasov V. K. Kadowaki K. Minami H. Watanabe C.
- 出版者
- American Institute of Physics
- 雑誌
- Journal of applied physics (ISSN:00218979)
- 巻号頁・発行日
- vol.113, no.13, pp.133902, 2013-04
- 被引用文献数
- 55
Stacks of intrinsic Josephson junctions (IJJs) made from high-temperature superconductors such as Bi2Sr2CaCu2O8+δ (Bi-2212) (BSCCO) are a promising source of coherent continuous-wave terahertz radiation. It is thought that at electrical bias conditions under which THz-emission occurs, hot spots may form due to resistive self-heating, and that these spots may be highly beneficial for the generation of high levels of THz power. Here, we perform an imaging study of the temperature distribution at the surface of BSCCO stacks utilizing the temperature-dependent 612 nm fluorescence line of Eu3+ in a europium chelate. The images directly reveal a highly non-uniform temperature distribution in which the temperature in the middle of the stack can exceed the superconducting transition temperature by tens of Kelvin under biasing conditions typical for THz-emission.
- 著者
- Nakamura K. Baba M. Ajmal Khan M. Du W. Sasase M. Hara K. O. Usami N. Toko K. Suemasu T.
- 出版者
- American Institute of Physics
- 雑誌
- Journal of applied physics (ISSN:00218979)
- 巻号頁・発行日
- vol.113, no.5, pp.053511, 2013-02
- 被引用文献数
- 21 11
A 180-nm-thick boron (B) layer was deposited on a 300-nm-thick a-axis-oriented BaSi2 epitaxial film grown by molecular beam epitaxy on Si(111) and was annealed at different temperatures in ultrahigh vacuum. The depth profiles of B were investigated using secondary ion mass spectrometry (SIMS) with O2+, and the diffusion coefficients of B were evaluated. The B profiles were reproduced well by taking both the lattice and the grain boundary (GB) diffusions into consideration. The cross-sectional transmission electron microscopy (TEM) image revealed that the GBs of the BaSi2 film were very sharp and normal to the sample surface. The plan-view TEM image exhibited that the grain size of the BaSi2 film was approximately 0.6 μm. The temperature dependence of lattice and GB diffusion coefficients was derived from the SIMS profiles, and their activation energies were found to be 4.6 eV and 4.4 eV, respectively.
- 著者
- Hurley D. H. Wright O. B. Matsuda O. Shinde S. L.
- 出版者
- American Institute of Physics
- 雑誌
- Journal of Applied Physics (ISSN:00218979)
- 巻号頁・発行日
- vol.107, no.2, pp.023521, 2010-01-15
- 被引用文献数
- 23
We use ultrashort optical pulses to microscopically image carrier and thermal diffusion in two spatial dimensions in pristine and mechanically polished surfaces of crystalline silicon. By decomposing changes in reflectivity in the latter sample into a transient component that varies with delay time and a steady-state component that varies with pump chopping frequency, the influence of thermal diffusion is isolated from that of carrier diffusion and recombination. Additionally, studies using carrier injection density as a parameter are used to clearly identify the carrier recombination pathway.
1 0 0 0 OA Cu-dependent phase transition in polycrystalline CuGaSe2 thin films grown by three-stage process
- 著者
- Islam M. M. Yamada A. Sakurai T. Kubota M. Ishizuka S. Matsubara K. Niki S. Akimoto K.
- 出版者
- American Institute of Physics
- 雑誌
- Journal of applied physics (ISSN:00218979)
- 巻号頁・発行日
- vol.110, no.1, pp.014903, 2011
- 被引用文献数
- 8 6
The Cu-dependent phase transition in polycrystalline CuGaSe2 thin films has been studied by an electron probe micro-analyzer (EPMA) and the synchrotron x-ray diffraction method. A Cu-deficiency parameter, Z, defined as (1 − Cu/Ga) was used to study the phase transition. Upon increasing the Z-value, the composition of the films on the Cu2Se-Ga2Se3 pseudo binary tie line was found to shift from the stoichiometric CuGaSe2 (1:1:2) (Z = 0) to the Ga-rich composition through the formation of several ordered defect compounds.The structural modification in the Cu-poor CuGaSe2 film has been investigated by the synchrotron x-ray diffraction method. The existence of the Cu-poor surface phase over the near-stoichiometric bulk CuGaSe2 film was confirmed by the fitting of the accelerated voltage dependent EPMA data.
- 著者
- Yanagihara H. Uwabo K. Minagawa M. Kita Eiji Hirota Noriyuki
- 出版者
- American Institute of Physics
- 雑誌
- Journal of applied physics (ISSN:00218979)
- 巻号頁・発行日
- vol.109, no.7, pp.07C122, 2011-04
- 被引用文献数
- 57 16
We report on the magnetic properties of epitaxial cobalt-ferrite films with orientations parallel to [001] and [111] grown by a reactive molecular beam epitaxy method using pure ozone gas as an oxidation agent. Both Mössbauer spectroscopy and magnetization measurement of the CoFe2O4(001) film grown on MgO(001) indicate that the film has perpendicular magnetic anisotropy (PMA) with high coercivity, whereas the film of CoFe2O4(111) grown on α-Al2O3(0001) appears to be paramagnetic. The maximum uniaxial anisotropy energy for CoFe2O4(001) estimated from the magnetization and coercivity at room temperature is ≈ 3×106 erg/cm3.
- 著者
- Takakura K. Ohyama H. Takarabe K. Suemasu T. Hasegawa F.
- 出版者
- American Institute of Physics
- 雑誌
- Journal of applied physics (ISSN:00218979)
- 巻号頁・発行日
- vol.97, no.09, pp.093716, 2005-04
- 被引用文献数
- 24 13
The hole mobility of intentionally undoped p-type beta-FeSi2 thin films grown by a multilayer method was investigated. With increasing annealing temperature and time, the hole mobility increased to approximately 450 cm2/V s at room temperature (RT). The observed hole mobility was analyzed by considering various carrier scatterings such as acoustic-phonon and polar-optical-phonon scatterings, intervalley scattering, ionized impurity scattering, and grain-boundary scattering. The nice fit of the mobility to the experimental results reveals that the polar-optical-phonon scattering determines the hole mobility at RT.
- 著者
- Egorov A. Yu. Kalevich V. K. Afanasiev M. M. Shiryaev A. Yu. Ustinov V. M. Ikezawa M. Masumoto Y.
- 出版者
- American Institute of Physics
- 雑誌
- Journal of applied physics (ISSN:00218979)
- 巻号頁・発行日
- vol.98, no.1, pp.013539, 2005-07
- 被引用文献数
- 24
The paper studies the circularly polarized photoluminescence (PL) from dilute GaAsN alloys with nitrogen content of 1%–3.4%, grown on GaAs substrates. The room-temperature PL is found to consist of two bands whose splitting grows with increasing nitrogen content. The analysis of the PL circular polarization has shown that the PL bands originate from the splitting of light- and heavy-hole subbands, induced by an elastic strain in GaAsN layer. The dependence of the energy gap of unstrained GaAsN on the nitrogen content has been calculated using the measured light- and heavy-hole splittings.
- 著者
- Li Cheng Lai Hongkai Chen Songyan Suemasu T. Hasegawa F.
- 出版者
- American Institute of Physics
- 雑誌
- Journal of applied physics (ISSN:00218979)
- 巻号頁・発行日
- vol.100, no.2, pp.023506, 2006-07
- 被引用文献数
- 5 4
The temperature dependence of electroluminescence from silicon p-i-n light-emitting diodes with a layer of beta-FeSi2 particles inserted in intrinsic silicon was investigated. Anomalous blueshift of the peak energy and enhanced electroluminescence intensity of the silicon band-edge emission were observed at temperatures from 50 to 200 K. The electroluminescence intensity was enhanced due to longer diffusion paths of the injected electrons at elevated temperature, as well as thermal escape of the electrons from the beta-FeSi2 particles. The low peak energy compared to that from bulk silicon at low temperature is due to the bound electron-hole pairs induced by the strain potential at the interface between silicon and beta-FeSi2 particles. The blueshift of the peak is ascribed to the transition of bound electron-hole pairs into free excitons at elevated temperature. Room temperature electroluminescence from such a silicon light-emitting diode can be obtained at a low current density of 0.3 A/cm2.
- 著者
- Fukata N. Oshima T. Okada N. Murakami K. Kizuka T. Tsurui T. Ito S.
- 出版者
- American Institute of Physics
- 雑誌
- Journal of applied physics (ISSN:00218979)
- 巻号頁・発行日
- vol.100, no.2, pp.024311, 2006-07
- 被引用文献数
- 44 33
The phonon confinement and self-limiting oxidation effects of silicon nanowires (SiNWs) synthesized by laser ablation were investigated. The size of SiNWs was controlled by the synthesis parameters during laser ablation and the subsequent thermal oxidation. Thermal oxidation increases the thickness of the SiNWs' surface oxide layer, resulting in a decrease in their crystalline Si core diameter. This effect causes a downshift and asymmetric broadening of the Si optical phonon peak due to phonon confinement, while excess oxidation causes an upshift due to compressive stress. The compressive stress retarded the oxidation of the SiNWs by self-limiting oxidation effect. This result shows that the Si core diameter can be controlled by compressive stress.
- 著者
- Koyano T. Nomiyama T. Kanoh N. Numata H. Ohba T. Kita E. Ohtsuka H.
- 出版者
- American Institute of Physics
- 雑誌
- Journal of applied physics (ISSN:00218979)
- 巻号頁・発行日
- vol.100, no.3, pp.033906, 2006-08
- 被引用文献数
- 7
The gamma iron nitride (nitrogen austenite) was subjected to high magnetic field process in order to drive the fcc-->bct martensitic transformation. Molar fraction of martensite monotonically increased with increasing the magnetic field and reached 94% at 35 T. With a combination of magnetization and 57Fe Mössbauer spectroscopy data, magnetization of bulk processed alpha[prime] phase with 9.6 at. % N is determined to be 229 emu/g, the same as that for dc sputtered thin films.