Prethreshold Lasing with Time-Delayed Pulse Emission from a Single Crystal of Thiophene/Phenylene Co-Oligomer

2011-06-08T09:00:00+09:00

Authors: Hisao Yanagi, Yusuke Marutani, Fumio Sasaki, Yoshitaka Makino, Takeshi Yamao, and Shu Hotta
Unusual time-delayed pulse emissions with spectrally narrowed band splitting were observed from a single-crystal thiophene/phenylene co-oligomer at room temperature. Under pulsed optical excitation, the Fabry–Pérot lasing oscillation caused by a pair of the crystal facets emerges with peculiar spectral splitting in the prethreshold fluence range. Time-resolved measurements of those “prethreshold lasing” peaks reveal a pulse-shaped profile with a time delay up to 300 ps. This observation is not explained in terms of usual cooperative interaction reported as superfluorescence for inorganic emitters at low temperature, but might be more relevant to unknown phase correlation overwhelming thermal perturbation among perfectly aligned molecules.©2011 The Japan Society of Applied Physics

Above 600 mS/mm Transconductance with 2.3 A/mm Drain Current Density AlN/GaN High-Electron-Mobility Transistors Grown on Silicon

2011-06-08T09:00:00+09:00

Authors: Farid Medjdoub, Malek Zegaoui, Nicolas Waldhoff, Bertrand Grimbert, Nathalie Rolland, and Paul-Alain Rolland
AlN/GaN high-electron-mobility transistors (HEMTs) capped with an in-situ grown SiN have been successfully developed on 100 mm Si substrates. A unique combination of maximum output current density exceeding 2 A/mm and a record extrinsic transconductance above 600 mS/mm has been reached, which is well beyond the highest reported values of any GaN-on-Si HEMTs. The current gain extrinsic cutoff frequency f_{T} and the maximum oscillation frequency f_{max} were 85 and 103 GHz with 0.16-µm gate length, respectively, resulting in a high f_{T}·L_{g} product that promises low-cost, high performance millimeter wave electronics.©2011 The Japan Society of Applied Physics

Development of Textured Magnesium Oxide Templates on Amorphous Polymer Surfaces Using Ion-Beam-Assisted Deposition

Alan J. Elliot, Ronald N. Vallejo, Rongtao Lu, and Judy Z. Wu — 2011-06-08T09:00:00+09:00

Authors: Alan J. Elliot, Ronald N. Vallejo, Rongtao Lu, and Judy Z. Wu
Biaxially textured MgO templates have been successfully fabricated on several amorphous polymer films including Kapton tapes, polyimide, poly(methyl methacrylate) (PMMA), and photoresist films using ion-beam-assisted deposition (IBAD). With a Y_{2}O_{3} buffer layer on polymer surfaces, roughening of the polymer surfaces due to preferential ion beam sputtering can be effectively reduced to meet the surface compatibility requirement for IBAD-MgO texturing. In-plane full-width-at-half-maximum (FWHM) of ∼10.7° and out-of-plane FWHM ∼3.5° have been obtained on homoepitaxial MgO films grown on top of the IBAD-MgO template. This method provides a practical route for fabricating epitaxial devices on polymers needed for flexible optoelectronics.©2011 The Japan Society of Applied Physics

InGaN Laser Diode Mini-Arrays

2011-06-07T09:00:00+09:00

Authors: Piotr Perlin, Lucja Marona, Katarzyna Holc, Przemek Wisniewski, Tadek Suski, Mike Leszczynski, Robert Czernecki, Stephen Najda, Marcin Zajac, and Robert Kucharski
We demonstrate the operation of high-power InGaN laser diode “mini-arrays” consisting of three or five stripes in a common p-contact configuration and compare the results with a single stripe emitter. We observed the following sequence of maximum output powers: 1.1 W for a single emitter, 2.5 W for a three emitter array, and 0.55 W for a five emitter array. The devices emitted light at 408–412 nm wavelength range. The most promising high-power laser diode design turned out to be a three stripe solution. The five stripe “mini-array” suffers from overheating, which causes the device to thermally roll-over at relatively low optical power. In addition to the high power operation, the three stripe device has good spectral characteristics accompanied by very reasonable differential efficiency making it a good candidate for ultra-high optical power systems like laser projectors.©2011 The Japan Society of Applied Physics

Broad Repetition-Rate Tunable Quantum-Dot External-Cavity Passively Mode-Locked Laser with Extremely Narrow Radio Frequency Linewidth

2011-06-07T09:00:00+09:00

Authors: Ying Ding, Maria Ana Cataluna, Daniil Nikitichev, Igor Krestnikov, Daniil Livshits, and Edik Rafailov
We report on a systematic investigation of a repetition-rate-tunable quantum-dot external-cavity passively mode-locked laser with a quasi-continuous frequency tuning range from 1 GHz to a record-low value of 191 MHz. A nearly constant pulse peak power at the different pulse repetition rates is revealed in the continuous frequency tuning range. The trend and optimization of the stable fundamental mode-locking are presented and interpreted. An RF linewidth of a record value of ∼30 Hz is demonstrated, which indicates the low noise operation and high stability of the quantum-dot external-cavity passively mode-locked laser.©2011 The Japan Society of Applied Physics

Graphene Growth from a Spin-Coated Polymer without a Reactive Gas

Satoru Suzuki, Yusuke Takei, Kazuaki Furukawa, and Hiroki Hibino — 2011-06-07T09:00:00+09:00

Authors: Satoru Suzuki, Yusuke Takei, Kazuaki Furukawa, and Hiroki Hibino
Few-layer graphene films were grown from spin-coated polystyrene films deposited on polycrystalline Ni substrates simply by heating in an Ar atmosphere. In this method, it is not necessary to use any reactive gas. Instead, the graphene film thickness is simply controlled by the initial thickness of the polystyrene film. This method of growing few-layer graphene film is safer and uses a much simpler apparatus than thermal chemical vapor deposition.©2011 The Japan Society of Applied Physics

Investigation of GaN-Based Light-Emitting Diodes Grown on Patterned Sapphire Substrates by Contact-Transferred and Mask-Embedded Lithography

2011-06-02T09:00:00+09:00

Authors: Chien-Chih Kao, Yan-Kuin Su, Yi-Ta Hsieh, Yung-Chun Lee, Chiao-Yang Cheng, and Chuing-Liang Lin
The influences of pattern size and etching depth of patterned sapphire substrates (PSSs) on crystal quality and light output power of light-emitting diodes (LEDs) were investigated by contact-transferred and mask-embedded lithography. The present results indicate that a smaller pattern size facilitates superior light extraction efficiency. However, a suitable pattern size and etching depth should be chosen to obtain the highest quality of GaN film. In comparison with the conventional sapphire substrate, the largest light output enhancement (∼28.9%) was observed when the pattern diameter and the etching depth of PSS were 400 and 400 nm, respectively.©2011 The Japan Society of Applied Physics

High-Resolution Measurement of Fiber Length Change with Optical Low-Coherence Reflectometer Based on a Fiber-Ring Structure

Shuguang Li, Xinwan Li, Weiwen Zou, Jianguo Shen, Zehua Hong, and Jianping Chen — 2011-06-02T09:00:00+09:00

Authors: Shuguang Li, Xinwan Li, Weiwen Zou, Jianguo Shen, Zehua Hong, and Jianping Chen
A simple approach is proposed and experimentally demonstrated to improve measurement precision of short fiber length or fiber length change with an optical low-coherence reflectometer (OLCR). A fiber-ring structure composed of a coupler and a circulator is introduced in the test arm of OLCR to virtually multiply the length of the fiber under test. By measuring the multiplied fiber length under test, the measurement precision is enhanced. A precision enhancement of 10 times is successfully achieved.©2011 The Japan Society of Applied Physics

RF Performance of AlGaN/GaN High-Electron-Mobility Transistors Grown on Silicon (110)

2011-06-02T09:00:00+09:00

Authors: Diego Marti, C. R. Bolognesi, Yvon Cordier, Magdalena Chmielowska, and Mohammed Ramdani
We report the first microwave performance for AlGaN/GaN HEMT structures grown by molecular beam epitaxy on Si(110) high-resistivity substrates. Transistors were fabricated with gate lengths of 50, 75, and 100 nm, achieving short-circuit current cutoff frequencies as high as f_{T} = 70 GHz and maximum oscillation frequencies of f_{MAX(U)} = 93 GHz. Because complementary metal–oxide–semiconductor (CMOS) technology is compatible with (110) substrates, this demonstration establishes a foundation for the future integration of GaN devices into mainstream CMOS on a common Si(110) platform.©2011 The Japan Society of Applied Physics

High-Electron-Mobility Ge n-Channel Metal–Oxide–Semiconductor Field-Effect Transistors with High-Pressure Oxidized Y_{2}O_{3}

2011-06-02T09:00:00+09:00

Authors: Tomonori Nishimura, Choong Hyun Lee, Toshiyuki Tabata, Sheng Kai Wang, Kosuke Nagashio, Koji Kita, and Akira Toriumi
This letter presents a significant improvement of electron mobility in a germanium (Ge) n-channel metal–oxide–semiconductor field-effect transistor with a yttrium oxide (Y_{2}O_{3}) gate dielectric film annealed in high-pressure O_{2}. Interface state density in the upper half of the band gap is reduced to 10^{11} cm^{-2} eV^{-1} and the peak effective mobility is increased up to 1,500 cm^{2} V^{-1} s^{-1}. This mobility enhancement is attributed to the suppression of GeO desorption or to passivation of the imperfect interface GeO_{2} layer by diffused Y_{2}O_{3}. There is no temperature dependence of the observed mobility, which suggests that intrinsic phonon scattering is still not dominant.©2011 The Japan Society of Applied Physics

Top-Emission Ultraviolet-Light-Emitting Diodes Containing Solution-Processed ZnO Nanocrystals

Toshihiko Toyama, Hayato Kawasaki, Kazuki Itatani, and Hiroaki Okamoto — 2011-06-02T09:00:00+09:00

Authors: Toshihiko Toyama, Hayato Kawasaki, Kazuki Itatani, and Hiroaki Okamoto
Top-emission light-emitting diodes containing nanoparticles (NanoLEDs) were prepared for flexible electronics applications. Transmission electron microscopy images revealed that solution-processed ZnO nanocrystals (NCs) embedded in a printed emission layer were nearly monodisperse with a crystal size of about 10 nm. To improve the UV electroluminescent emission of ZnO excitons and suppress visible emission from surface defects of the NCs, the low-power deposition of indium tin oxide (ITO) top electrodes was examined together with the deposition of a MoO_{3} layer before ITO. Finally, conversion from UV to green light via a phosphor is demonstrated, revealing the color tunability of the NanoLEDs.©2011 The Japan Society of Applied Physics

Temporal Donor Generation in Undoped Hydrogenated Amorphous Silicon Induced by Swift Proton Bombardment

2011-06-01T09:00:00+09:00

Authors: Shin-ichiro Sato, Hitoshi Sai, Takeshi Ohshima, Mitsuru Imaizumi, Kazunori Shimazaki, and Michio Kondo
Seebeck coefficient variations of undoped hydrogenated amorphous silicon (a-Si:H) semiconductors due to swift proton irradiation were investigated using an in-situ thermoelectric power measurement system. Undoped a-Si:H irradiated with 3.0 MeV protons at a fluence regime of 3.1×10^{11}–5.0×10^{12}/cm^{2} showed a negative Seebeck coefficient although the Seebeck effect was not observed at fluences above 5.3×10^{13}/cm^{2}. These results suggest that donor like centers are generated by low fluence proton irradiation, whereas the donor centers are compensated by radiation-induced defects or themselves disappear after high fluence proton irradiation. These effects decay with time, giving the donor centers a temporal nature.©2011 The Japan Society of Applied Physics

Magnetic Vortex Excitation Frequencies and Eigenmodes in a Pair of Coupled Circular Dots

Oksana V. Sukhostavets, Julian M. Gonzalez, and Konstantin Y. Guslienko — 2011-06-01T09:00:00+09:00

Authors: Oksana V. Sukhostavets, Julian M. Gonzalez, and Konstantin Y. Guslienko
The low frequency dynamics of two coupled magnetic vortices oscillating in a pair of laterally patterned circular dots are calculated. The linearized Thiele equations of motion of the vortex core positions are applied to describe the dynamics. The main emphasis is put on the symmetry of the excited spin eigenmodes and the possibility to excite them by applying the variable driving magnetic fields in different directions. The importance of the high-order multipole terms in the interdot coupling integrals decomposition is underlined. Some recent experiments on the coupled magnetic vortex dynamics in patterned films are interpreted.©2011 The Japan Society of Applied Physics

Determination of Mechanical Properties of Single-Crystal CdS Nanowires from Dynamic Flexural Measurements of Nanowire Mechanical Resonators

2011-06-01T09:00:00+09:00

Authors: Young Duck Kim, Kwang Heo, Myung Rae Cho, Sungwan Cho, Duhee Yoon, Hyeonsik Cheong, Jikang Jian, Seunghun Hong, and Yun Daniel Park
The mechanical properties of hexagonal single-crystal CdS nanowires (NWs) were determined by means of dynamic flexural measurements. CdS NWs were fashioned into freely suspended doubly clamped mechanical resonators with lengths varying from 3 to 20 µm. A high-frequency response (3–8 MHz) and a high quality factor (500–600) were observed at room temperature. Based on the resonant frequency dependence on the length of the resonator, Young's modulus (∼62 GPa) and the internal stress (7–30 MPa) were measured. Furthermore, the CdS NW resonators under the conditions of high strain and tension presented nonlinear mechanical responses.©2011 The Japan Society of Applied Physics

Design and Evaluation of a Planar Single-Channel Shim Coil for a Permanent Magnetic Resonance Imaging Magnet

Daiki Tamada, Yasuhiko Terada, and Katsumi Kose — 2011-06-01T09:00:00+09:00

Authors: Daiki Tamada, Yasuhiko Terada, and Katsumi Kose
We propose a straightforward method of designing a planar single-channel shim coil for magnetic resonance imaging (MRI) using a narrow-gap permanent magnet. The design method is based on the superposition of the current densities produced by planar second-order shim coil elements and optimization of the coefficients used for the superposition. The magnetic field homogeneity was improved from 13 to 3.3 ppm (root mean square) in the central spherical area (diameter = 18 mm), revealing that the planar single-channel shim coil is a useful device for narrow-gap permanent MRI magnets.©2011 The Japan Society of Applied Physics

Effective Ex-situ Fabrication of F-Doped SmFeAsO Wire for High Transport Critical Current Density

2011-05-31T09:00:00+09:00

Authors: Masaya Fujioka, Tomohiro Kota, Masanori Matoba, Toshinori Ozaki, Yoshihiko Takano, Hiroaki Kumakura, and Yoichi Kamihara
We demonstrate the fabrication of superconducting SmFeAsO_{1-x}F_{x} (Sm-1111) wires by using the ex-situ powder-in-tube technique. Sm-1111 powder and a binder composed of SmF_{3}, samarium arsenide, and iron arsenide were used to synthesize the superconducting core. Although the F content of Sm-1111 is reduced in the process of ex-situ fabrication, the binder compensates by sufficiently supplementing the F content, thereby preventing a decrease in the superconducting transition temperature and a shrinkage of the superconducting volume fraction. Thus, in the superconducting Sm-1111 wire with the binder, the transport critical current density reaches the highest value of ∼4 kA/cm^{2} at 4.2 K.©2011 The Japan Society of Applied Physics

Magnetic Domain Wall Ferromagnetic Resonance in Ferromagnetic Nanowires Due to the Spin Transfer Torque

Jungbum Yoon, Chun-Yeol You, Younghun Jo, Seung-Young Park, and Myung-Hwa Jung — 2011-05-30T09:00:00+09:00

Authors: Jungbum Yoon, Chun-Yeol You, Younghun Jo, Seung-Young Park, and Myung-Hwa Jung
The influence of the spin transfer torque on a domain wall is investigated by domain wall ferromagnetic resonance micromagnetic simulations. When current is applied to the pinned domain wall in a ferromagnetic nanowire, we find two resonance frequencies of the domain wall around 2 and 7 GHz. The lower peaks represent the vibration of the whole domain wall. The higher peaks are due to the resonance frequency of the spins inside the domain wall, which show remarkable (>1.6 GHz) shifts with the spin torque. Since no domain wall displacement is involved, we can exclude the effects of the unwanted extrinsic pinning sites.©2011 The Japan Society of Applied Physics

284–300 nm Quaternary InAlGaN-Based Deep-Ultraviolet Light-Emitting Diodes on Si(111) Substrates

Sachie Fujikawa and Hideki Hirayama — 2011-05-26T09:00:00+09:00

Authors: Sachie Fujikawa and Hideki Hirayama
We have demonstrated 280–300-nm-band quaternary InAlGaN based deep-ultraviolet (DUV) light-emitting diodes (LEDs) fabricated on Si(111) substrates, grown by low-pressure metal–organic chemical vapor deposition (LP-MOCVD). An ammonia pulsed-flow growth method was used in the initial stages of AlN growth on Si substrates in order to achieve low threading dislocation densities with thin AlN layer. We obtained single-peaked spectra from the DUV LEDs at wavelengths between 284 and 300 nm under room temperature continuous-wave (cw) operation. It is expected that low-cost and large-size DUV LEDs could become available in the near future by increasing light-extraction by removing the Si substrate.©2011 The Japan Society of Applied Physics

High Normalized Strain Obtained in Li-Modified (K,Na)NbO_{3} Lead-Free Piezoceramics

Ke Wang, Jing-Feng Li, and Jia-Jun Zhou — 2011-05-26T09:00:00+09:00

Authors: Ke Wang, Jing-Feng Li, and Jia-Jun Zhou
Lead-free Li-(K,Na)NbO_{3} (KNN) piezoceramics shows surprisingly high normalized strain d_{33}^{*} up to 538 pm/V at electric fields as low as 1 kV/mm, comparable to a commercial soft lead zirconate titanate (PZT) sample. The special treating process of aging and re-poling is essential for this achievement. The extrinsic piezoelectric contribution related to domain wall motion is proposed of primary responsibility for the strain, which endows the sample with a direct piezoelectric coefficient of 324 pC/N. Strain behavior with regard to both electric field level and frequency was investigated to prove the assumption. The present study proves the possibility of preparing PZT-comparable lead-free piezoceramics in simply Li-doped KNN by conventional sintering.©2011 The Japan Society of Applied Physics

Chemical–Mechanical Lift-Off Process for InGaN Epitaxial Layers

2011-05-26T09:00:00+09:00

Authors: Ming-Shiou Lin, Chia-Feng Lin, Wan-Chun Huang, Guei-Miao Wang, Bing-Cheng Shieh, Jing-Jie Dai, Shou-Yi Chang, D. S. Wuu, Po-Liang Liu, and Ray-Hua Horng
An InGaN-based light-emitting diode (LED) structure was separated from a GaN/sapphire structure by inserting sacrificial Si-doped InGaN/GaN superlattice layers through a chemical–mechanical lift-off (CMLO) process. The CMLO process consisted of a band-gap-selective photoelectrochemical lateral wet etching process and a mechanical lift-off process. A lower elastic modulus and hardness of the lateral-etched LED structure were measured compared with the conventional LED structure, which indicated a weak mechanical property of the treated LED structure. The photoluminescence blue-shift phenomenon and the Raman redshift phenomenon indicated that the compressive strain from the bottom GaN/sapphire structure was released through the CMLO process.©2011 The Japan Society of Applied Physics

Amplitude Noise in Spin-Torque Oscillators

Tazumi Nagasawa, Koichi Mizushima, Hirofumi Suto, Kiwamu Kudo, and Rie Sato — 2011-05-26T09:00:00+09:00

Authors: Tazumi Nagasawa, Koichi Mizushima, Hirofumi Suto, Kiwamu Kudo, and Rie Sato
Amplitude fluctuations in an output signal of a tunnel-type spin-torque oscillator are examined by a time-domain measurement using a real-time oscilloscope (40 GS/s). Unsteady intermittent oscillation just above the threshold changes gradually to steady oscillation with increasing current. The amplitude fluctuation in the steady oscillation state is well described by a recent nonlinear theory, which is essentially based on a macrospin model under the thermal fluctuation, indicating that the fluctuation is attributed to the thermal magnetization fluctuation rather than to (nonthermal) mode instabilities.©2011 The Japan Society of Applied Physics

Aluminum Nanotransmission Lines with No Grain Boundaries and No Surface Roughness

2011-05-26T09:00:00+09:00

Authors: Myunggil Kang, Jongwoon Lee, Donghoon Hwang, Byung-Sung Kim, Byunghak Hong, Dongmok Whang, and Sungwoo Hwang
Ideal metallic interconnects and transmission lines should be free of grain boundaries and surface roughness. In this study, we demonstrated microwave transmission through transmission lines fabricated from single-crystalline aluminum nanowires (AlNWs) with no surface roughness and no grain boundaries. These nanotransmission lines showed an intrinsic loss of 3 dB at the frequency of 140 GHz. The extracted parameters from the measured microwave data exhibited resistance values consistent with the ideal DC resistivity of pure aluminum.©2011 The Japan Society of Applied Physics

Modeling Microwave Resonance of Curling Probe for Density Measurements in Reactive Plasmas

Iji Liang, Keiji Nakamura, and Hideo Sugai — 2011-05-26T09:00:00+09:00

Authors: Iji Liang, Keiji Nakamura, and Hideo Sugai
A compact new type of microwave resonator probe called curling probe is proposed for electron density measurements in reactive plasmas, where a spiral slot is excited by a monopole antenna. The resonance characteristic of the curling probe is simulated by the finite-difference time-domain (FDTD) method. The frequency dependence of power reflection coefficient and the electromagnetic field structures revealed two types of resonance at the same density: the high-frequency volume wave resonance along a spiral slot and the low-frequency surface wave resonance in an aperture of the probe. The analytical formulae of resonance frequencies as a function of electron density are derived.©2011 The Japan Society of Applied Physics

Current-Induced Magnetic Domain Wall Motion in Co/Ni Nanowire at Low Temperature

2011-05-25T09:00:00+09:00

Authors: Kohei Ueda, Tomohiro Koyama, Daichi Chiba, Kazutoshi Shimamura, Hironobu Tanigawa, Shunsuke Fukami, Tetsuhiro Suzuki, Norikazu Ohshima, Nobuyuki Ishiwata, Yoshinobu Nakatani, and Teruo Ono
Magnetic domain wall (DW) motion induced by currents in a perpendicularly magnetized Co/Ni nanowire has been investigated both at room temperature and low temperature. The threshold current density was almost independent of temperature, although the external magnetic field to depin a DW was doubled at low temperature. The result is consistent with the theory based on the adiabatic spin transfer model.©2011 The Japan Society of Applied Physics

Magnetization Dependent Current Rectification in (Ga,Mn)As Magnetic Tunnel Junctions

Yoshiaki Hashimoto, Hiroaki Amano, Yasuhiro Iye, and Shingo Katsumoto — 2011-05-25T09:00:00+09:00

Authors: Yoshiaki Hashimoto, Hiroaki Amano, Yasuhiro Iye, and Shingo Katsumoto
We have found that the current rectification effect in triple-layer (double-barrier) (Ga,Mn)As magnetic tunnel junctions strongly depends on the magnetization alignment. The direction as well as the amplitude of the rectification changes with the alignment, which can be switched by bi-directional spin-injection with very small threshold currents. A possible origin of the rectification is the energy dependence of the density of states around the Fermi level. The tunneling density of states in (Ga,Mn)As shows a characteristic dip around zero bias indicating the formation of a correlation gap, the asymmetry of which would be a potential source of the energy-dependent density of states.©2011 The Japan Society of Applied Physics

Influence of High-Energy Electron Beam on Source Fluxes during Molecular Beam Epitaxy Growth on Photoluminescence Upconversion from the GaAs Band Gap

David M. Tex and Itaru Kamiya — 2011-05-25T09:00:00+09:00

Authors: David M. Tex and Itaru Kamiya
We investigated the influence of an unfocused electron beam (e-beam) passing in front of a sample during molecular beam epitaxy (MBE) growth of GaAs on the upconverted photoluminescence efficiency and found a strong influence on the intermediate states. A clear difference in the Stokes and anti-Stokes photoluminescence (PL) is observed. Time-resolved PL correlation spectroscopy results allow us to suggest that an unfocused e-beam increases the density of a specific GaAs bulk state also found in samples grown without an e-beam.©2011 The Japan Society of Applied Physics

High-Brightness GaN-Based Light-Emitting Diodes on Si Using Wafer Bonding Technology

2011-05-25T09:00:00+09:00

Authors: Seung-Jae Lee, Kang Ho Kim, Jin-Woo Ju, Tak Jeong, Cheul-Ro Lee, and Jong Hyeob Baek
GaN-based light-emitting diodes (LEDs) grown on Si(111) substrates were fabricated with a vertical electrode method by using wafer bonding technology. The fabricated vertical LEDs showed a lower operating voltage and larger light output power than conventional LEDs due to enhancement in current spreading and reduction in tensile strain. The light output power of the vertical structured LEDs was 2.6 times higher than that of conventional LEDs, with an operating voltage at 20 mA reduced from 3.5 to 3.2 V.©2011 The Japan Society of Applied Physics

X-ray Phase Imaging Using Lau Effect

Atsushi Momose, Hiroaki Kuwabara, and Wataru Yashiro — 2011-05-25T09:00:00+09:00

Authors: Atsushi Momose, Hiroaki Kuwabara, and Wataru Yashiro
X-ray phase imaging based on the Lau effect is demonstrated with an incoherent laboratory X-ray source. Its optical configuration resembles the inverse geometry of the X-ray Talbot–Lau interferometer, which employs a large-area amplitude grating. However, the proposed approach avoids the use and hence fabrication difficulty of such a grating, which is advantageous when constructing an X-ray phase imaging apparatus. With a Mo-target source, differential phase images of polymer spheres were successfully obtained and a design concept for downsizing the system is also described.©2011 The Japan Society of Applied Physics

Slow Positron Beam Apparatus for Surface and Subsurface Analysis of Samples in Air

2011-05-25T09:00:00+09:00

Authors: Nagayasu Oshima, Brian E. O’Rourke, Ryunosuke Kuroda, Ryoichi Suzuki, Hiromichi Watanabe, Shoji Kubota, Kazuki Tenjinbayashi, Akira Uedono, and Noriyosu Hayashizaki
A technique for investigating atomic-scale defects and/or nanometer (sub-nanometer)-order pores near the surface of samples mounted in air (without vacuum) by positron annihilation spectroscopy (PAS) has been developed. The method relies on the extraction of slow positron beams from the vacuum chamber to air through a thin SiN membrane vacuum window. Using a positron beam with an injection energy of 2.6 keV and a vacuum window with a thickness of 30 nm, samples mounted in air can be investigated by PAS to a depth of ∼100 nm.©2011 The Japan Society of Applied Physics

Computational Analysis of Thermal Energetic Disorder in a Pentacene Crystal: Temperature Dependence of Trap Levels and Possible Novel Thermoelectric Contribution

Toshihiro Shimada, Yu Ikuta, Yuya Tsuchida, Manabu Ohtomo, and Tetsuya Hasegawa — 2011-05-24T09:00:00+09:00

Authors: Toshihiro Shimada, Yu Ikuta, Yuya Tsuchida, Manabu Ohtomo, and Tetsuya Hasegawa
In organic semiconductors, the sudden appearance of deep traps (30–100 meV) below 100–200 K is frequently observed experimentally even in highly crystalline films and single crystals. We analyzed this phenomenon by molecular dynamics combined with semi-empirical quantum chemical calculation, and found that defect levels are concealed by thermal disorder at high temperatures but appear as hole traps at low temperatures. We propose that the thermal energetic disorder may lead to a considerably large thermoelectric effect in organic semiconductors.©2011 The Japan Society of Applied Physics

Self-Pulsation at Zero Absorber Bias in GaN-Based Multisection Laser Diodes

2011-05-24T09:00:00+09:00

Authors: Wolfgang G. Scheibenzuber, Christian Hornuss, Ulrich T. Schwarz, Luca Sulmoni, Julien Dorsaz, Jean-François Carlin, and Nicolas Grandjean
We study the influence of pump current and absorber bias voltage on the pulse width and frequency of sustained pulsation in GaN-based multisection laser diodes. The observed frequencies and pulse widths range from 1.5 to 4.5 GHz and 90 to 18 ps, respectively. Negative absorber bias is found to reduce the pulsation frequency and increase the pulse width. This behavior is explained by the tuneability of absorption and charge carrier lifetime in the absorber via the applied bias voltage.©2011 The Japan Society of Applied Physics

Nonpolar a-Plane AlGaN/GaN Heterostructure Field-Effect Transistors Grown on Freestanding GaN Substrate

2011-05-24T09:00:00+09:00

Authors: Yasuhiro Isobe, Hiromichi Ikki, Tatsuyuki Sakakibara, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Isamu Akasaki, Takayuki Sugiyama, Hiroshi Amano, Mamoru Imade, Yasuo Kitaoka, and Yusuke Mori
We fabricated and characterized nonpolar a-plane AlGaN/GaN heterostructure field-effect transistors (HFETs) grown on an a-plane freestanding GaN substrate. By optimizing the growth conditions, the unintentionally doped oxygen concentration was much reduced in the a-plane GaN buffer layer. As a result, the low leakage current in the buffer layer was realized without doping of deep acceptors, such as Fe and C, by which an impurity-contamination-free channel layer can be successfully grown. A maximum drain current of 220 mA/mm at a gate source voltage of +3.0 V, an on resistance of 10.4 mΩ·cm^{2}, and a threshold voltage of -1.6 V were realized.©2011 The Japan Society of Applied Physics

Enhanced Carrier Injection in Perovskite Field-Effect Transistors via Low-Barrier Contacts

Daisuke Sekiya, Hiroyuki Nakamura, and Tsuyoshi Kimura — 2011-05-24T09:00:00+09:00

Authors: Daisuke Sekiya, Hiroyuki Nakamura, and Tsuyoshi Kimura
The effects of the source–drain contact metal on carrier injection to undoped KTaO_{3} and SrTiO_{3}-channel field-effect transistors (FETs) were investigated. By using Al alloys (Al–Zn and Al–Sr) or Zn as contacts, the magnitude of channel current was significantly enhanced both at room temperature and at a low temperature (10 K). Moreover, the yield of KTaO_{3}-FETs showing carrier injection at 10 K improves dramatically with the use of Zn-containing metals combined with a current-induced forming step carried out at 300 K.©2011 The Japan Society of Applied Physics

Harvesting Infrared Solar Energy by Semiconducting Single-Walled Carbon Nanotubes

Yongfeng Li, Soichiro Kodama, Toshiro Kaneko, and Rikizo Hatakeyama — 2011-05-24T09:00:00+09:00

Authors: Yongfeng Li, Soichiro Kodama, Toshiro Kaneko, and Rikizo Hatakeyama
Semiconducting single-walled carbon nanotubes (S-SWNTs) are used to fabricate p–n heterojuctions with n-type Si in order to harvest near-infrared solar energy. Our results demonstrate that S-SWNTs can be used to convert near-infrared light into electrical energy. The performance of solar cells based on C_{60}-fullerene-encapsualted S-SWNTs is much better than that observed in solar cells fabricated by C_{60}-encapsulated SWNTs containing both metallic and semiconducting SWNTs. It is found that when the light photon energy exceeds two times the band-gap energy of S-SWNTs, the efficiency suddenly increases, suggesting the occurrence of multiple exciton generation.©2011 The Japan Society of Applied Physics

Soft X-ray Magnetic Circular Dichroism of a CoFe/MnIr Exchange Bias Film under Pulsed High Magnetic Field

2011-05-24T09:00:00+09:00

Authors: Tetsuya Nakamura, Yasuo Narumi, Toko Hirono, Misaki Hayashi, Kenji Kodama, Masakiyo Tsunoda, Shinji Isogami, Hirokazu Takahashi, Toyohiko Kinoshita, Koichi Kindo, and Hiroyuki Nojiri
Soft X-ray magnetic circular dichroism (XMCD) under pulsed high magnetic fields of up to 21 T has been measured using a nondestructive pulse magnet. XMCD effects at the Co and the Mn L_{2,3}-edges of a Co_{70}Fe_{30}/Mn_{75}Ir_{25} bilayer film have been investigated as an example of a high-magnetic-field XMCD measurement. A total electron yield method is adopted to detect absorption. Absorption is recorded by a 1-MHz time-resolved detection synchronized with a 50-ms high-magnetic-field pulse. Using this method, the XMCD effect is represented by µ_{m} (H), a function of magnetic field.©2011 The Japan Society of Applied Physics

High-Efficiency Oxide Solar Cells with ZnO/Cu_{2}O Heterojunction Fabricated on Thermally Oxidized Cu_{2}O Sheets

Tadatsugu Minami, Yuki Nishi, Toshihiro Miyata, and Jun-ichi Nomoto — 2011-05-23T09:00:00+09:00

Authors: Tadatsugu Minami, Yuki Nishi, Toshihiro Miyata, and Jun-ichi Nomoto
High conversion efficiencies were achieved in low cost n–p heterojunction oxide solar cells with an Al-doped ZnO (AZO)/non-doped ZnO (ZO)/Cu_{2}O structure. This achievement was made possible by the formation of an n-ZO thin-film layer, prepared with an appropriate thickness by low damage deposition, on high quality Cu_{2}O sheets produced by the thermal oxidization of copper sheets: n-ZO thin film optimal thickness ranges from 30 to 50 nm. Photovoltaic characteristics such as an open circuit voltage of 0.69 V, a fill factor of 0.55 and a conversion efficiency of 3.83% were attained under simulated AM1.5G solar illumination.©2011 The Japan Society of Applied Physics

Integrated High-Temperature Superconductor Radio-Frequency Superconducting Quantum Interference Device Covered with Superconducting Thin Films in Flip-Chip Configuration

Yoshimi Hatsukade, Makoto Takemoto, Ryuichi Kurosawa, and Saburo Tanaka — 2011-05-23T09:00:00+09:00

Authors: Yoshimi Hatsukade, Makoto Takemoto, Ryuichi Kurosawa, and Saburo Tanaka
We developed integrated high-temperature superconductor (HTS) rf superconducting quantum interference devices (SQUIDs) with various hole shapes on bicrystal SrTiO_{3} substrates. Single-layer YBa_{2}Cu_{3}O_{7-x} thin-film technology and bicrystal Josephson junctions were employed to take advantage of a simple fabrication process. The HTS rf SQUID with a hole of 800×50 µm^{2} had the lowest inductance and showed the best noise characteristics among the tested SQUIDs. The 1/f noise profile of the HTS rf SQUID, which was covered with HTS thin films on the grain boundary and/or the slit of the SQUID in a flip-chip configuration, was dramatically improved in a frequency range of less than 100 Hz.©2011 The Japan Society of Applied Physics

High Output Power (∼400 µW) Oscillators at around 550 GHz Using Resonant Tunneling Diodes with Graded Emitter and Thin Barriers

2011-05-20T09:00:00+09:00

Authors: Masato Shiraishi, Hirotaka Shibayama, Kaname Ishigaki, Safumi Suzuki, Masahiro Asada, Hiroki Sugiyama, and Haruki Yokoyama
We report resonant tunneling diode (RTD) oscillators with a high output power of around 400 µW at frequencies of 530–590 GHz. RTDs with a graded emitter and thin barriers were employed to obtain large negative differential conductance at high frequencies for high output power. An optimized structure of offset slot antennas was also used to maximize the radiation conductance. The highest output power obtained in this study was 420 µW at 548 GHz for an RTD with a peak current density of 24 mA/µm^{2}; the RTD was placed 58 µm apart from the center of a 130-µm-long slot antenna.©2011 The Japan Society of Applied Physics

Patterned Growth of TiO_{2} Nanowires on Titanium Substrates

2011-05-20T09:00:00+09:00

Authors: Jong-Yoon Ha, Brian D. Sosnowchik, Liwei Lin, Dong Heon Kang, and Albert V. Davydov
Single-crystalline rutile TiO_{2} nanowires (NWs) were synthesized by the vapor–liquid–solid (VLS) method on Ti foil substrates patterned with catalytic Sn nano-islands. NWs of 3 to 8 µm in length and 50 to 500 nm in diameter were grown along the [1-10] axis exhibiting a rectangular cross section with the (001) and (110) side facets. This facile approach to TiO_{2} NW fabrication with fast induction heating and short processing time utilizes the Ti foil both as a substrate and as a metal supply, thus eliminating the need for a separate titanium source.©2011 The Japan Society of Applied Physics

Neutron Analysis for Microvoids in an Adhesive Layer between High X-ray Attenuation Materials

Thanhhai Nguyen, Daniel Vavrik, Eberhard H. Lehmann, and Insu Jeon — 2011-05-20T09:00:00+09:00

Authors: Thanhhai Nguyen, Daniel Vavrik, Eberhard H. Lehmann, and Insu Jeon
We demonstrate the potential of neutron systems for detecting microscale defects in a thin epoxy adhesive layer between two metal plates. Neutron tomography has been used to ascertain the internal structure of the adhesive layer. The distribution of defects including microvoids is found in three-dimensionally reconstructed models that are obtained from neutron tomography images and is compared with that obtained from a magnified real image of the layer. From the results, we find that a neutron system can be the most suitable tool for detecting microscale defects in a thin adhesive layer that lies between two high X-ray attenuation plates.©2011 The Japan Society of Applied Physics

Three-Dimensional Structure Analysis of Metal–Oxide–Insulator Field Effect Transistors with Different Electrical Properties by Scanning Transmission Electron Microscopy

2011-05-20T09:00:00+09:00

Authors: Shiano Ono, Miyuki Yamane, Hirohisa Okushima, Masanari Koguchi, Hiroyuki Shinada, Hiroshi Kakibayashi, Fumiko Yano, Takaaki Tsunomura, Akio Nishida, and Tohru Mogami
To clarify the origin of on-state drain current (I_{ON}) variability in metal–oxide–semiconductor field-effect transistors (MOSFETs), we applied three-dimensional scanning transmission electron microscopy (3D STEM) observation to two transistors that had different I_{ON} values but the same threshold voltage (V_{T}). The results clearly showed a difference in the distance between the gate and source/drain silicide, suggesting that the I_{ON} difference between two transistors can be explained by the difference in the source/drain extension resistance. We showed that it is possible to discuss the 3D device structures in relation to their electrical characteristics.©2011 The Japan Society of Applied Physics

Exfoliation Route to Nanostructured Cobalt Oxide with Enhanced Thermoelectric Performance

Jong-Young Kim, Jin-Il Kim, and Won-Seon Seo — 2011-05-19T09:00:00+09:00

Authors: Jong-Young Kim, Jin-Il Kim, and Won-Seon Seo
We report on two dimensional (2D)-nanostructured Na_{x}CoO_{2} with enhanced thermoelectric properties prepared by the exfoliation/restacking method. We have shown that the exfoliation/restacking method is an effective route to constructing nanostructured cobalt oxide. Such a nanostructured sodium cobalt oxide results in an exceptionally low cross-plane conductivity, as low as 0.5 W m^{-1} K^{-1}. Due to the decrease of in-plane thermal conductivity, ZT values of the restacked samples increase in comparison to that of the pristine, which shows the beneficial effect of the nanostructure on the thermoelectric property.©2011 The Japan Society of Applied Physics

Generation of Runaway Electrons and X-rays in Repetitive Nanosecond Pulse Corona Discharge in Atmospheric Pressure Air

2011-05-19T09:00:00+09:00

Authors: Tao Shao, Victor F. Tarasenko, Cheng Zhang, Igor D. Kostyrya, Hui Jiang, Rong Xu, Dmitri V. Rybka, and Ping Yan
A pulsed corona discharge in an inhomogeneous electric field was studied in atmospheric air. A runaway electron beam from the corona discharge was detected with a collector at nanosecond-pulse duration. It is shown that with a nanosecond-pulse voltage of 300 kV, the full width at half maximum of the beam current during the pulsed corona discharge is about 100 ps. It is demonstrated that with a pulse voltage of 90 kV, a full width at half maximum of 40 ns, and pulse repetition frequencies of up to 1 kHz, the corona discharge is an X-ray source.©2011 The Japan Society of Applied Physics

Determination of Composition and Lattice Relaxation in Semipolar Ternary (In,Al,Ga)N Strained Layers from Symmetric X-ray Diffraction Measurements

Erin C. Young, Alexey E. Romanov, and James S. Speck — 2011-05-18T09:00:00+09:00

Authors: Erin C. Young, Alexey E. Romanov, and James S. Speck
We present a new method to simultaneously determine the composition and strain state for thin (In,Al,Ga)N layers grown in semipolar orientations using the data from one symmetric on-axis reciprocal space map or four symmetric on-axis rocking curve X-ray measurements. The method makes use of the one-dimensional nature of lattice mismatch relaxation in semipolar III–nitride heterostructures via operation of a unique slip system, i.e., (a/3) <11-20> (0001) in the basal plane. The correlation between lattice tilt and misfit dislocation density is applied to determine the degree of relaxation, whereas the composition is found from the Bragg's law accounting for the change in planar spacing in elastically strained anisotropic wurzite (In,AlGa)N layers.©2011 The Japan Society of Applied Physics

Spin-Torque Diode Measurements of MgO-Based Magnetic Tunnel Junctions with Asymmetric Electrodes

2011-05-17T09:00:00+09:00

Authors: Rie Matsumoto, André Chanthbouala, Julie Grollier, Vincent Cros, Albert Fert, Kazumasa Nishimura, Yoshinori Nagamine, Hiroki Maehara, Koji Tsunekawa, Akio Fukushima, and Shinji Yuasa
We present a detailed study of the spin-torque diode effect in CoFeB/MgO/CoFe/NiFe magnetic tunnel junctions. From the evolution of the resonance frequency with magnetic field at different angles, we clearly identify the free-layer mode and find an excellent agreement with simulations by taking into account several terms for magnetic anisotropy. Moreover, we demonstrate the large contribution of the out-of-plane torque in our junctions with asymmetric electrodes compared to the in-plane torque. Consequently, we provide a way to enhance the sensitivity of these devices for the detection of microwave frequency.©2011 The Japan Society of Applied Physics

Large Spin Accumulation with Long Spin Diffusion Length in Cu/MgO/Permalloy Lateral Spin Valves

Taro Wakamura, Kohei Ohnishi, Yasuhiro Niimi, and YoshiChika Otani — 2011-05-17T09:00:00+09:00

Authors: Taro Wakamura, Kohei Ohnishi, Yasuhiro Niimi, and YoshiChika Otani
We study the effect of interface resistance on the spin injection and detection efficiency in Cu/MgO/permalloy (Py) lateral spin valve devices. Insertion of the MgO layer enhances the spin accumulation by a factor of ten at 10 K: the maximum value is 10 mΩ at the interface resistance of 1.7×10^{-1} Ω (µm)^{2}. The spin diffusion length of Cu reaches 1.3 µm at 10 K, which is twice larger than that of Ag/MgO/Py spin valves. As the interface resistance increases furthermore, the spin accumulation exponentially decreases. This can be explained by the large reduction of the spin polarization in the insulating layer.©2011 The Japan Society of Applied Physics

Response Time-Shortened Zinc Oxide Scintillator for Accurate Single-Shot Synchronization of Extreme Ultraviolet Free-Electron Laser and Short-Pulse Laser

2011-05-16T09:00:00+09:00

Authors: Toshihiko Shimizu, Kohei Yamanoi, Kohei Sakai, Marilou Cadatal-Raduban, Tomoharu Nakazato, Nobuhiko Sarukura, Masataka Kano, Akira Wakamiya, Dirk Ehrentraut, Tsuguo Fukuda, Mitsuru Nagasono, Tadashi Togashi, Shinichi Matsubara, Kensuke Tono, Atsushi Higashiya, Makina Yabashi, Hiroaki Kimura, Haruhiko Ohashi, and Tetsuya Ishikawa
We report an over one-order-of magnitude improvement in the response time of conventional hydrothermal method-grown zinc oxide (ZnO) scintillator by introducing additional quenching channels via intentional indium ion doping. A 3-ps fluorescence decay time constant is achieved, therefore making it the fastest scintillator operating below 100 nm to date. Using this indium-doped ZnO, relative jitter between extreme ultraviolet free electron laser (EUV-FEL) probe and optical pump pulses is evaluated to be less than 3 ps. Moreover, pulses from these sources can be synchronized with 3-ps accuracy through in-situ observation of relative time difference in single-shot base.©2011 The Japan Society of Applied Physics

Plasma Decomposition of Clathrate Hydrates by 2.45 GHz Mircowave Irradiation at Atmospheric Pressure

2011-05-16T09:00:00+09:00

Authors: Shinfuku Nomura, Andi Erwin Eka Putra, Shinobu Mukasa, Hiroshi Yamashita, and Hiromichi Toyota
The purpose of this research is to develop a process to use the plasma decomposition of clathrate hydrates to produce fuel gas. An ordinary microwave (MW) oven is used as the source of 2.45 GHz MW radiation under atmospheric-pressure. The plasma decomposition of the hydrates could pave the way for a new utilization of atmospheric pressure plasma. Cyclopentane (CP) hydrate formed at atmospheric pressure was decomposed by plasma in a MW oven generating gas with a content of 65% hydrogen, 12% CO, and 8% CO_{2}. About 7% of the MW input power was consumed to decompose the hydrates.©2011 The Japan Society of Applied Physics

D-Limonene as a Chiral Dopant for Thermotropic Liquid Crystalline Systems

Rafael S. Zola, Shawn Hurley, and Deng-Ke Yang — 2011-05-12T09:00:00+09:00

Authors: Rafael S. Zola, Shawn Hurley, and Deng-Ke Yang
We used the chiral molecule D-limonene to induce thermotropic cholesteric phases. The methods used to characterize the chiral nematic phase and its features are given. We substituted D-limonene for conventional synthesized chiral dopants in the twisted nematic (TN) displays and showed an improvement in the response time. Despite the large number of synthesized chiral dopants, D-limonene can be used as a dopant for making cholesteric phases having the advantage of being a naturally occurring substance. It is surprising how many more synthesized chiral molecules have been used as the liquid crystal field moves forward in comparison to naturally occurring molecules.©2011 The Japan Society of Applied Physics

Temperature-Dependent Change in Shape of Platinum Nanoparticles Supported on CeO_{2} during Catalytic Reactions

2011-05-12T09:00:00+09:00

Authors: Hideto Yoshida, Koji Matsuura, Yasufumi Kuwauchi, Hideo Kohno, Satoshi Shimada, Masatake Haruta, and Seiji Takeda
The temperature dependence of the shape of Pt nanoparticles supported on CeO_{2} for CO oxidation was investigated using environmental transmission electron microscopy. Pt nanoparticles in CO/air become round at room temperature (when catalytic activity is low), while they become partially faceted at elevated temperature (when the catalytic activity is high). Based on a comparison between the shapes of the Pt nanoparticles in vacuum, N_{2}, O_{2}, CO, and CO/air at room temperature, 100, and 200 °C, we propose that the change in shape of the Pt nanoparticles is induced by the adsorption of CO molecules and O atoms.©2011 The Japan Society of Applied Physics

Two-Step Forming Process in Planar-Type Cu_{2}O-Based Resistive Switching Devices

Kazunori Suzuki, Norihide Igarashi, and Kentaro Kyuno — 2011-05-11T09:00:00+09:00

Authors: Kazunori Suzuki, Norihide Igarashi, and Kentaro Kyuno
The forming process in planar-type Cu_{2}O-based resistive switching devices is investigated. It is found that two forming processes occur in series, and the existence of a Cu filament is directly confirmed using transmission electron microscopy after each forming process. The time evolution of the surface is observed by an optical microscope during these processes. The first process accompanies the oxidation of the Cu_{2}O surface, and the filament is created ∼15 µm below the surface; the second process involves melting of the region between the electrodes with the creation of a new filament ∼1 µm below the surface.©2011 The Japan Society of Applied Physics

Nanostructured Multilayer Tailored-Refractive-Index Antireflection Coating for Glass with Broadband and Omnidirectional Characteristics

2011-05-11T09:00:00+09:00

Authors: Sameer Chhajed, David J. Poxson, Xing Yan, Jaehee Cho, E. Fred Schubert, Roger E. Welser, Ashok K. Sood, and Jong Kyu Kim
The design, fabrication, and characterization of a broadband, omnidirectional, graded-index anti-reflection (AR) coating on a glass substrate, fabricated by using nanostructured low-refractive-index (n = 1.05–1.40) silica, is reported. The AR coating is designed by using a genetic algorithm and fabricated by using oblique angle deposition. The AR coating is designed for the wavelength range of 400 to 2500 nm and 0 to 40° angle of incidence. The measured average optical transmittance between 1000 and 2000 nm is improved from 92.6 to 99.3% at normal incidence by using a two-layer AR coating deposited on both surfaces of the glass substrate.©2011 The Japan Society of Applied Physics

Formation of Silicon Nano Tips in Surfactant-Modified Wet Anisotropic Etching

Bin Tang and Kazuo Sato — 2011-05-11T09:00:00+09:00

Authors: Bin Tang and Kazuo Sato
In this letter, we present a simple, low cost, and complementary metal oxide semiconductor (CMOS)-compatible method for forming uniformly sharp silicon tips using the surfactant-modified wet anisotropic etching. By utilizing this process, the apex of each resultant tip typically having a radius of curvature of 3–4 nm after the treatment at 80 °C in surfactant-added wet etchants is obtained. The explanation for creating these tips has been analyzed as the change in the local etch rate brought about by the strong adsorption of surfactant molecules at the high curvature of a silicon tip.©2011 The Japan Society of Applied Physics

Epitaxial Growth of FeSe_{0.5}Te_{0.5} Thin Films on CaF_{2} Substrates with High Critical Current Density

2011-05-09T09:00:00+09:00

Authors: Ichiro Tsukada, Masafumi Hanawa, Takanori Akiike, Fuyuki Nabeshima, Yoshinori Imai, Ataru Ichinose, Seiki Komiya, Tatsuo Hikage, Takahiko Kawaguchi, Hiroshi Ikuta, and Atsutaka Maeda
In-situ epitaxial growth of FeSe_{0.5}Te_{0.5} thin films is demonstrated on a nonoxide substrate CaF_{2}. Structural analysis reveals that compressive stress is moderately added to 36-nm-thick FeSe_{0.5}Te_{0.5}, which pushes up the critical temperature to above 15 K, showing higher values than that of bulk crystals. The critical current density at T = 4.5 K reaches 5.9×10^{4} A cm^{-2} at µ_{0}H = 10 T, and 4.2×10^{4} A cm^{-2} at µ_{0}H = 14 T. These results indicate that fluoride substrates have high potential for the growth of iron-based superconductors in comparison with popular oxide substrates.©2011 The Japan Society of Applied Physics

Controlling Quantized Steps in Conductance of Gold Zigzag Nanowires

Yoshifumi Oshima, Yoshihiko Kurui, and Kunio Takayanagi — 2011-05-09T09:00:00+09:00

Authors: Yoshifumi Oshima, Yoshihiko Kurui, and Kunio Takayanagi
We demonstrate that a gold zigzag nanowire changes conductance stepwise between 1 and 2G_{0} (=2e^{2}/h, e is the elementary charge and h is Planck constant) upon slight stretching or compression at room temperature by a scanning tunneling microscope combined with a transmission electron microscope. The conductance change from 2 to 1G_{0} and vice versa occurred around the critical atomic distance of 0.32 nm, which is in agreement with theoretical calculations.©2011 The Japan Society of Applied Physics

Self-Organized Two-Dimensional Vidro-Nanodot Array on Laser-Irradiated Si Surface

Yutaka Yoshida, Norihito Sakaguchi, Seiichi Watanabe, and Takahiko Kato — 2011-05-09T09:00:00+09:00

Authors: Yutaka Yoshida, Norihito Sakaguchi, Seiichi Watanabe, and Takahiko Kato
We report a periodic two-dimensional (2D) array of uniquely shaped dotlike nanoprotrusions (NPs), which simultaneously self-organize on a Si surface under pulsed laser irradiation. The shape of the dotlike NPs can be controlled by adjusting the number of laser pulses. The flask-shaped dotlike NP array is named a vidro-nanodot (VND) array. We present a detailed analysis of the internal structure of VND using high-resolution electron microscopy.©2011 The Japan Society of Applied Physics

Assessment of GaN Surface Pretreatment for Atomic Layer Deposited High-k Dielectrics

2011-05-09T09:00:00+09:00

Authors: Neeraj Nepal, Nelson Y. Garces, David J. Meyer, Jennifer K. Hite, and Michael A. Mastro
We report the effects of GaN surface pretreatments on the material and electrical properties of Al_{2}O_{3} dielectric deposited by atomic layer deposition (ALD). A layer of Al_{2}O_{3} was deposited at different temperatures on metal organic chemical vapor deposition grown n-GaN that was treated with either H_{2}O_{2}:H_{2}SO_{4} (1:5, piranha), HCl:H_{2}O (1:1, HCl), or HF:H_{2}O (1:1, HF) prior to Al_{2}O_{3} deposition. The Al_{2}O_{3} layers on piranha- and HF-treated GaN were observed to be uniformly smooth. The piranha pretreatment resulted in the lowest hysteresis. Pretreatment of the GaN surface with piranha removes carbon and hydroxylates the surface, resulting in better quality ALD Al_{2}O_{3}.©2011 The Japan Society of Applied Physics

High-Power-Density High-Efficiency Bottom-Emitting Vertical-Cavity Surface-Emitting Laser Array

2011-05-06T09:00:00+09:00

Authors: Di Liu, Yongqiang Ning, Yugang Zeng, Li Qin, Yun Liu, Xing Zhang, Lisen Zhang, Jinsheng Zhang, Cunzhu Tong, and Lijun Wang
We report on the lasing characteristics of a two-dimensional (2D) vertical-cavity surface-emitting laser (VCSEL) array with three In_{0.2}GaAs/GaAs_{0.92}P QWs emitting at 977 nm. The contribution of a large-bandgap barrier material, GaAsP, to improve the output power was investigated. More than 123 W of pulsed peak power at 110 A was achieved, corresponding to 24.6 kW/cm^{2} of power density and 1.11 W/A of slope efficiency. The thermal effect dependence of the characteristics of the array was illustrated. Moreover, the device performance was estimated by a functional method using a p-parameter.©2011 The Japan Society of Applied Physics

InGaN-Based p–i–n Solar Cells with Graphene Electrodes

2011-05-06T09:00:00+09:00

Authors: Jae-Phil Shim, Minhyeok Choe, Seong-Ran Jeon, Dongju Seo, Takhee Lee, and Dong-Seon Lee
InGaN-based p–i–n solar cells with graphene electrodes were fabricated and compared with solar cells using indium tin oxide (ITO) electrodes. In particular, we analyzed the properties of graphene film by means of high-resolution transmission electron microscopic (HRTEM) and Raman spectroscopy, also comparing optical properties with those of ITO, conventionally used as transparent electrodes. The solar cells using graphene revealed a short circuit current density of 0.83 mA/cm^{2}, an open circuit voltage of 2.0 V, a fill factor of 75.2%, and conversion efficiency of 1.2%, comparable to the performance of solar cells using ITO.©2011 The Japan Society of Applied Physics

Optical Gain Spectroscopy of a Semipolar {20-21}-Oriented Green InGaN Laser Diode

2011-04-28T09:00:00+09:00

Authors: Yoon Seok Kim, Akio Kaneta, Mitsuru Funato, Yoichi Kawakami, Takashi Kyono, Masaki Ueno, and Takao Nakamura
Optical gain is assessed for a green laser diode (LD) grown on a semipolar {20-21} GaN substrate. The estimated internal loss is 20±5/cm, and the maximum gain becomes saturated with the injection current, suggesting the existence of gain suppression mechanisms. The quantum-confined Stark effect due to the pn junction, state filling, and screening of polarization-induced electric fields can explain shifts in the gain and the emission peaks with the injection current. The tail states in {20-21} LDs are much smaller than those in (0001) LDs, and are not the major cause of the gain suppression in {20-21} LDs, in contrast to (0001) LDs.©2011 The Japan Society of Applied Physics

Imaging Nanobubbles in Water with Scanning Transmission Electron Microscopy

2011-04-28T09:00:00+09:00

Authors: Edward R. White, Matthew Mecklenburg, Scott B. Singer, Shaul Aloni, and Brian Christopher Regan
We present a technique based on scanning transmission electron microscopy (STEM) that is capable of probing nanobubble dynamics with nanometer spatial resolution. A vacuum-tight vessel holds a sub-micrometer layer of water between two electron-transparent dielectric membranes. Electrical current pulses passing through a platinum wire on one of the membranes inject sufficient heat locally to initiate single bubble formation. In the absence of power input, all bubbles are observed to be unstable against collapse, but the STEM beam alone can cause a shrinking bubble to grow.©2011 The Japan Society of Applied Physics

Synthesis of Mica Thin Film by Pulsed Laser Deposition

2011-04-28T09:00:00+09:00

Authors: Yuta Nakasone, Hirokazu Nakai, Yumiko Miyake, Ryosuke Yamauchi, Nobuo Tsuchimine, Susumu Kobayashi, Yoshifumi Sano, Nobutaka Takezawa, Masahiko Mitsuhashi, Satoru Kaneko, Hiroshi Funakubo, and Mamoru Yoshimoto
Synthesis of crystalline biotite-mica thin films was examined by applying a two-step process: (1) low-temperature growth of the mica film precursor on an ultrasmooth sapphire (α-Al_{2}O_{3} single crystal) substrate by pulsed laser deposition using a sintered biotite ceramics target and (2) post-annealing in vacuum. X-ray diffraction and Raman scattering spectroscopy confirmed that a c-axis-oriented polycrystalline biotite-mica thin film was obtained by post-annealing the 500 °C-grown film precursor at temperatures above 700 °C in vacuum. An atomic-scale pattern corresponding to that of the cleaved natural mica surface was observed on the surface of thin film by atomic force spectroscopy.©2011 The Japan Society of Applied Physics

High-Performance Ge Metal–Oxide–Semiconductor Field-Effect Transistors with a Gate Stack Fabricated by Ultrathin SiO_{2}/GeO_{2} Bilayer Passivation

2011-04-27T09:00:00+09:00

Authors: Keisuke Yamamoto, Ryuji Ueno, Takeshi Yamanaka, Kana Hirayama, Haigui Yang, Dong Wang, and Hiroshi Nakashima
We fabricated Ge n- and p-channel metal–oxide–semiconductor field-effect transistors (MOSFETs) with (100) surface orientation by the gate-last process. The source/drain junctions for n- and p-MOSFETs were fabricated by thermal diffusion of P and ion implantation of B, respectively, which indicated high on/off ratios. An ultrathin SiO_{2}/GeO_{2} interlayer was used for fabricating the gate stack. The fabricated MOSFETs showed excellent electrical characteristics with a low interface state density. The peak electron and hole mobilities were 1097 and 376 cm^{2} V^{-1} s^{-1}, respectively, despite the very thin GeO_{2} thickness (2 nm). These are 1.5–1.6 times higher than those of Si MOSFETs.©2011 The Japan Society of Applied Physics

Dual-Function Beam Shapers Fabricated by Photoaligned Liquid Crystal Cells

2011-04-27T09:00:00+09:00

Authors: Chia-Yi Huang, Hong-Yi Tsai, Yi-Hong Wang, Chong-Ming Huang, Kuang-Yao Lo, and Chia-Rong Lee
A dual-function beam shaper is composed of a photoaligned liquid crystal (LC) cell and two polarizers. The photoaligned LC cell is formed by irradiating an intensity-gradient pump beam on each of the two surfaces of a dye-doped LC cell. The LC directors on the irradiated surfaces gradually transit from a homogeneous orientation to a mutually orthogonal homogeneous one. The LC cell under crossed (parallel) polarizers exhibits a lower (higher) transmittance in the center of the director-continuously-rotating region than at the edges of the region. The cell acts as a beam shaper with the function of a beam flattop (compression).©2011 The Japan Society of Applied Physics

Bistable Resistive Switching Characteristics of Poly(2-hydroxyethyl methacrylate) Thin Film Memory Devices

2011-04-27T09:00:00+09:00

Authors: Ying-Chih Chen, Yan-Kuin Su, Chun-Yuan Huang, Hsin-Chieh Yu, Chiao-Yang Cheng, and Tai-Hsiang Chang
The switching property of thin film memories with a sandwiched structure of Al/poly(2-hydroxyethyl methacrylate) (PHEMA)/ITO has been demonstrated. In terms of bistable current–voltage (I–V) characteristics, the conduction mechanisms at low and high resistance states were characterized by an ohmic behavior and the space charge limit current dominated, respectively. The resistive switching behavior was explained by the presence of the carbon filaments, which was confirmed by observing the carbon ions diffusing in the PHEMA film in time-of-flight secondary ion mass spectrometry. Our devices have high current on/off (>10^{3}), reliable switching endurance over 500 write–read–erase–read cycles, and long retention time (>10^{4} s).©2011 The Japan Society of Applied Physics

Erbium-Doped AlInGaN Alloys as High-Temperature Thermoelectric Materials

2011-04-26T09:00:00+09:00

Authors: Bed Nidhi Pantha, I-wen Feng, Krishna Aryal, Jing Li, Jing-Yu Lin, and Hong-Xing Jiang
The potential of Er-doped Al_{x}In_{0.1}Ga_{0.9-x}N quaternary alloys as high-temperature thermoelectric (TE) materials has been explored. It was found that the incorporation of Er significantly decreased the thermal conductivity (κ) of Al_{x}In_{0.1}Ga_{0.9-x}N alloys. The temperature-dependent TE properties were measured up to 1055 K for an Er and Si co-doped n-type Al_{0.1}In_{0.1}Ga_{0.8}N alloy. The figure of merit (ZT) showed a linear increase with temperature and a value of about 0.3 at 1055 K was estimated. The ability to survive such high temperature with reasonable TE properties suggests that low-In-content Er and Si-doped AlInGaN alloys are potential candidate of high-temperature TE materials.©2011 The Japan Society of Applied Physics

Simulation of Atmospheric Pressure Direct Current Glow Discharge along a Miniature Helium Flow in Nitrogen

Fumiyoshi Tochikubo, Naoki Shirai, and Satoshi Uchida — 2011-04-26T09:00:00+09:00

Authors: Fumiyoshi Tochikubo, Naoki Shirai, and Satoshi Uchida
In this work, we carried out two-dimensional numerical simulation of atmospheric pressure dc glow discharge with miniature helium flow in nitrogen. The glow discharge is generated along the helium flow, which is injected from the nozzle anode into the discharge region filled with nitrogen. The purpose of this study is to clarify the relationship between the glow discharge structure and the helium flow. We found that the glow discharge generation is limited in the region with a very high helium mole fraction. Therefore, the helium mole fraction is an important parameter to determine the discharge structure along the helium flow.©2011 The Japan Society of Applied Physics

Second Harmonic Vibrational Mode of Substitutional Carbon in Cast-Grown Multicrystalline Silicon

Haruhiko Ono and Hiroshi Yamada-Kaneta — 2011-04-25T09:00:00+09:00

Authors: Haruhiko Ono and Hiroshi Yamada-Kaneta
Light-element impurities in multicrystalline silicon (mc-Si) used for fabricating photovoltaic cells have been studied by Fourier transform infrared spectroscopy. Using this method, a new infrared absorption peak at 1206 cm^{-1} was found in B-doped mc-Si grown by the cast method with a Si_{3}N_{4}-coated crucible, and was attributed to B–N complexes. We have investigated this peak in detail and examined its origin, and we have concluded that it is not due to B–N complexes but arises from the second harmonic of the substitutional carbon (C_{s}), the fundamental peak of which is observed at 605 cm^{-1}.©2011 The Japan Society of Applied Physics

Ultrahigh-Resolution Optical Coherence Tomography in 1.7 µm Region with Fiber Laser Supercontinuum in Low-Water-Absorption Samples

Shutaro Ishida, Norihiko Nishizawa, Takefumi Ohta, and Kazuyoshi Itoh — 2011-04-25T09:00:00+09:00

Authors: Shutaro Ishida, Norihiko Nishizawa, Takefumi Ohta, and Kazuyoshi Itoh
Ultrahigh-resolution, high-penetration-depth optical coherence tomography (OCT) by use of an all-fiber supercontinuum source at 1.7 µm was demonstrated. A Gaussian-like supercontinuum with 358 nm bandwidth at a center wavelength of 1.7 µm was generated by an ultrashort-pulse Er-doped fiber laser system. A longitudinal resolution of 3.3 µm in tissue, with a sensitivity of 95 dB, was achieved. In vitro ultrahigh-resolution imaging of biological tissues was also demonstrated. To the best of our knowledge, this is the first demonstration of ultrahigh-resolution OCT in the 1.7 µm-wavelength region.©2011 The Japan Society of Applied Physics

Ab Initio Molecular Orbital Study on Acceleration Mechanism of Silane Plasma Chemical Vapor Deposition by Diborane

Kota Sato and Yasuyo Kubota — 2011-04-25T09:00:00+09:00

Authors: Kota Sato and Yasuyo Kubota
An acceleration mechanism of silane plasma chemical vapor deposition by diborane is proposed on the basis of an ab initio molecular orbital calculation. Hydrogen abstraction from the growing surface by BH_{2} is calculated to be much more favorable than that by SiH_{3} from both the kinetic and thermodynamic viewpoint. Thus, the abstraction by BH_{2} is predicted to occur frequently, although the concentration of BH_{2} is considerably lower than that of SiH_{3}. This process creates a dangling bond on the growing surface and then the deposition rate is increased.©2011 The Japan Society of Applied Physics

Polycrystalline Ceramic Er:YAG Laser In-Band Pumped by a High-Power Er,Yb Fiber Laser at 1532 nm

2011-04-22T09:00:00+09:00

Authors: Deyuan Shen, Hao Chen, Xiangpeng Qin, Jian Zhang, Dingyuan Tang, Xiaofang Yang, and Ting Zhao
We report on the high-power and efficient operation of a polycrystalline ceramic erbium-doped yttrium aluminum garnet (Er:Y_{3}Al_{5}O_{12}, Er:YAG) laser resonantly pumped by a cladding-pumped Er,Yb fiber laser. The pump fiber laser was wavelength-locked to the absorption peak of Er:YAG at ∼1532 nm using a volume Bragg grating. The ceramic laser yielded 13.8 W of continuous-wave output at 1645 nm for 27.3 W of incident pump power, corresponding to a slope efficiency of 54.5% with respect to the incident pump power. The laser output characteristics of different Er^{3+} doping levels are compared, and the prospects for improvement in lasing efficiency and output power are discussed.©2011 The Japan Society of Applied Physics

Visualization of Grain Boundary as Blocking Layer for Oxygen Tracer Diffusion and a Proposed Defect Model in Non Doped BaTiO_{3} Ceramics

Ken Watanabe, Isao Sakaguchi, Shunichi Hishita, Naoki Ohashi, and Hajime Haneda — 2011-04-22T09:00:00+09:00

Authors: Ken Watanabe, Isao Sakaguchi, Shunichi Hishita, Naoki Ohashi, and Hajime Haneda
We performed visualization of the oxygen diffusion path in oxidized and reduced BaTiO_{3} ceramics by utilizing an ion-imaging technique. The oxygen tracer diffused quickly from the surface up to the grain boundary, and then behaved as discontinuous steps at the grain boundary. The grain boundary acted as a blocking layer against oxygen diffusion. The reduction process enhanced the blocking effect. The blocking of oxygen diffusion at the grain boundary originated in the formation and distribution of complex defects between the charged oxygen vacancy and the reduced Ti near the grain boundary.©2011 The Japan Society of Applied Physics

Two-Facing Irradiation of Laser Pulses to Suppress Position Shift of Expanded Tin Microsphere for Extreme Ultraviolet Light Source

Yuji Matsuoka, Shinsuke Fujioka, and Hiroaki Nishimura — 2011-04-22T09:00:00+09:00

Authors: Yuji Matsuoka, Shinsuke Fujioka, and Hiroaki Nishimura
An essential requirement for extreme ultraviolet (EUV) lithography is to develop a debris-free, powerful EUV light source. Substantial mitigation of debris and high conversion efficiency have been achieved with a minimum mass and pure tin microsphere that is expanded by a laser pre-pulse irradiation. The pre-expanding sphere is pushed along the axis of the pre-pulse laser by ablation pressure. Counter irradiation of a laser pre-pulse was demonstrated to suppress the position shift of the tin microsphere. It was found that the density of the expanding tin microsphere reaches an optimal value for EUV light generation at 1000 ns after the pre-pulse irradiation.©2011 The Japan Society of Applied Physics

Ordered Array of Gold Nanoparticles Promoted by Functional Peptides

Nozomu Matsukawa and Ichiro Yamashita — 2011-04-21T09:00:00+09:00

Authors: Nozomu Matsukawa and Ichiro Yamashita
It was successfully demonstrated that 5-nm-diameter gold nanoparticles (GNPs) with 15% size distribution, the surface of which was modified by the synthesized peptides composed of the carbonaceous material affinity peptide (NHBP-1), linker of 11 amino acids and C-terminal cysteine, self-assembled into a two-dimensional (2D) ordered array on a silicon substrate in a spin drying process. NHBP-1 generated an attractive force large enough for the GNP to make 2D collections of GNPs in the course of the spin drying process, and the long linker of 11 amino acids cancelled out the ill effect of size distribution of GNP on the 2D ordered array formation.©2011 The Japan Society of Applied Physics

Self-Assembly of GaAs Quantum Wires Grown on (311)A Substrates by Droplet Epitaxy

2011-04-20T09:00:00+09:00

Authors: Masafumi Jo, Joris. G. Keizer, Takaaki Mano, Paul M. Koenraad, and Kazuaki Sakoda
We report the formation of GaAs quantum wires (QWRs) on (311)A substrates by droplet epitaxy. High-density quantum dots coalesce to form wires oriented along the [-233] direction as a result of atom diffusion triggered by thermal annealing. Luminescence from the QWRs is significantly polarized parallel to the wire direction, which would result in higher gain in lasers that use cleaved (01-1) surfaces as Fabry–Pérot mirrors. Lasing is obtained for a GaAs/AlGaAs QWR laser diode with fivefold-stacked QWR layers under pulsed operation at a low temperature.©2011 The Japan Society of Applied Physics

Ultrasonic Microspectroscopy Measurement of Fictive Temperature for Synthetic Silica Glass

Jun-ichi Kushibiki, Mototaka Arakawa, Yuji Ohashi, and Yuko Maruyama — 2011-04-20T09:00:00+09:00

Authors: Jun-ichi Kushibiki, Mototaka Arakawa, Yuji Ohashi, and Yuko Maruyama
Experimental procedures to evaluate the fictive temperature (T_{F}) of synthetic silica glass were developed using ultrasonic microspectroscopy (UMS) technology by measuring longitudinal-wave velocity (V_{l}). Two kinds of commercial synthetic silica glass (without and with water) were demonstrated, resulting in the establishment of calibration lines between V_{l} and T_{F} with a resolution within 1 °C and clear observation of their hydroxyl (OH) dependences. This ultrasonic method and system will be extremely useful and effective for improving mass-production conditions of glass ingots as well as for conducting basic studies on glass science.©2011 The Japan Society of Applied Physics

High-Power Bottom-Emitting Vertical-Cavity Surface-Emitting Lasers under Continuous-Wave, Quasi-Continuous-Wave, and Pulsed Operation

2011-04-19T09:00:00+09:00

Authors: Lisen Zhang, Yongqiang Ning, Yugang Zeng, Li Qin, Yun Liu, Xing Zhang, Di Liu, Huawei Xu, Jinsheng Zhang, and Lijun Wang
The characteristics of high-power bottom-emitting vertical-cavity surface-emitting lasers (VCSELs) with an aperture of 500 µm are reported. The output power and the spectra of the device are measured at different injection currents under CW, quasi-CW, and pulsed operation. The maximum peak output power of 92 W is achieved at room temperature, which is, to the best of our knowledge, the highest value reported for a single device. The thermal effect under pulsed operation is far lower than that at the other two operation modes.©2011 The Japan Society of Applied Physics

Internal Quantum Efficiency of Whole-Composition-Range AlGaN Multiquantum Wells

2011-04-18T09:00:00+09:00

Authors: Kazuhito Ban, Jun-ichi Yamamoto, Kenichiro Takeda, Kimiyasu Ide, Motoaki Iwaya, Tetsuya Takeuchi, Satoshi Kamiyama, Isamu Akasaki, and Hiroshi Amano
We analyze the internal quantum efficiency (IQE) of whole-composition-range AlGaN multiquantum wells (MQWs) on AlGaN with various dislocation densities (DDs) by excitation-density-dependent photoluminescence measurement. IQEs of deep ultraviolet/ultraviolet (DUV/UV) MQWs are strongly dependent on the DD. IQE with an excess carrier density of 1×10^{18} cm^{-3} changes from 4 to 64% when the DD changes from 6×10^{9} to 2×10^{8} cm^{-2}. This trend is almost the same for DUV/UV MQWs with emission wavelength ranging from 230 to 350 nm. Thus, the reduction of the DD is very important for the realization of a high-IQE DUV/UV active layer.©2011 The Japan Society of Applied Physics

Organic Complementary Inverters Based on Step-Edge Vertical Channel Organic Field-Effect Transistors

2011-04-18T09:00:00+09:00

Authors: Fanghua Pu, Hiroshi Yamauchi, Hiroyuki Iechi, Masakazu Nakamura, and Kazuhiro Kudo
An organic complementary inverter which consists of a p-channel pentacene step-edge vertical channel organic field-effect transistor (SVC-OFET) and an n-channel hexadecafluorophthalocyanine (F_{16}CuPc) SVC-OFET has been demonstrated. The two short-channel SVC-OFETs have been fabricated on the two steep side walls of a single gate line using a self-aligning technique. Such a structure significantly simplifies the layout and wiring of the inverter circuit. The inverter exhibited the same input and output swing ranges as the supply voltage, a logic threshold voltage very close to half of the supply voltage and a gain larger than 3.©2011 The Japan Society of Applied Physics

Large Transverse Piezoelectricity in Strained (Na,Bi)TiO_{3}–BaTiO_{3} Epitaxial Thin Films on MgO(110)

2011-04-15T09:00:00+09:00

Authors: Hideaki Adachi, Yoshiaki Tanaka, Takakiyo Harigai, Michihito Ueda, and Eiji Fujii
Large transverse piezoelectricity has been demonstrated in lead-free epitaxial (Na,Bi)TiO_{3}–BaTiO_{3} (NBT–BT) thin films grown on MgO(110) substrates. Through the internal strain caused by the difference in thermal expansion between NBT–BT and MgO, the crystal structure of the films was distorted to orthorhombic lattice, which does not form in bulk NBT–BT. The films showed a planar anisotropic nature where the effective transverse piezoelectricity along the orthorhombic b-axis was much larger than that along the orthorhombic a-axis. For the NBT–BT film with 9% BaTiO_{3}, transverse piezoelectric coefficient d_{31}^{*} along the orthorhombic b-axis reached as high as -221 pC/N.©2011 The Japan Society of Applied Physics

Direct Observation at Nanoscale of Resistance Switching in NiO Layers by Conductive-Atomic Force Microscopy

2011-04-14T09:00:00+09:00

Authors: Damien Deleruyelle, Carine Dumas, Marion Carmona, Christophe Muller, Sabina Spiga, and Marco Fanciulli
This paper reports a direct observation of resistive switching occurring on the nanoscale within NiO layers deposited on top of a tungsten pillar bottom electrode. Filamentary conduction was evidenced by atomic force microscopy using a conductive tip that enabled performing electroforming and reset operations at nanoscale. In the low resistive state, it is shown that the current is driven by multiple conductive nanometric regions in agreement with the filamentary conduction models. In the high resistive state, conduction originates from weak residual conductive regions remaining after reset operation. Finally, retention measurements performed at the nanoscale demonstrated the persistence of localized conductive regions after more than 30 days.©2011 The Japan Society of Applied Physics

Electrochemical Characterization of Pentacene Thin Films in Vacuum with an Ionic Liquid as Electrolyte

Shingo Maruyama, Yoko Takeyama, and Yuji Matsumoto — 2011-04-14T09:00:00+09:00

Authors: Shingo Maruyama, Yoko Takeyama, and Yuji Matsumoto
We propose a new method for the basic characterization of organic semiconductor properties: an electrochemical impedance analysis with an ionic liquid in vacuum. As a demonstration, we applied this method to the estimation of the acceptor density for c-axis-oriented pentacene films grown on an indium tin oxide substrate. The behavior in the growth of a depletion layer within pentacene could be well understood using the conventional simple capacitance model, and the acceptor density was successfully estimated from the Mott–Schottky plot, typically giving a value of 3.7×10^{15} cm^{-3}.©2011 The Japan Society of Applied Physics

In_{2}S_{3} Buffer Layers for Cu(InGa)Se_{2} Solar Cells Fabricated by a Nanoparticle-Coating Approach

Yiwen Zhang, Manabu Ito, Tomoaki Tamura, and Akira Yamada — 2011-04-14T09:00:00+09:00

Authors: Yiwen Zhang, Manabu Ito, Tomoaki Tamura, and Akira Yamada
A nanoparticle-coating approach is applied to prepare In_{2}S_{3} buffer layers in Cu(InGa)Se_{2} solar cells for the first time. In this research, the electric and optical characteristics of the In_{2}S_{3} films at different annealing temperatures are investigated. It is found that 275 °C is the optimum annealing temperature in our case and the highest efficiency of 10.0% solar cell is achieved at this temperature. The highest efficiency solar cell with the In_{2}S_{3} buffer layer exhibits a higher light absorption in the region of 350–500 nm than the reference cell with a CdS layer.©2011 The Japan Society of Applied Physics

Ultrathin Body InGaAs-on-Insulator Metal–Oxide–Semiconductor Field-Effect Transistors with InP Passivation Layers on Si Substrates Fabricated by Direct Wafer Bonding

2011-04-14T09:00:00+09:00

Authors: Masafumi Yokoyama, Hideki Takagi, Tetsuji Yasuda, Hisashi Yamada, Noboru Fukuhara, Masahiko Hata, Masakazu Sugiyama, Yoshiaki Nakano, Mitsuru Takenaka, and Shinichi Takagi
We demonstrated the formation of ultrathin-body (UTB) III–V-semiconductor-on-insulator (III–V-OI) n-channel metal–oxide–semiconductor field-effect transistors (nMOSFETs) on Si by low-damage direct wafer bonding, where channel thickness was been reduced to 7 nm. However, we found a significant reduction of the effective mobility of the InGaAs-OI nMOSFETs upon thinning InGaAs channels without surface passivation layers. Instead, we demonstrated the high electron mobility of 1004 cm^{2}·V^{-1}·s^{-1} in a 9-nm-thick InGaAs-OI nMOSFET with an InP surface passivation layer. This finding indicates that the proper surface passivation is important in realizing the high-performance UTB III–V-OI nMOSFETs.©2011 The Japan Society of Applied Physics

Optically Pumped Green (530–560 nm) Stimulated Emissions from InGaN/GaN Multiple-Quantum-Well Triangular-Lattice Nanocolumn Arrays

2011-04-14T09:00:00+09:00

Authors: Shusuke Ishizawa, Katsumi Kishino, Ryuichi Araki, Akihiko Kikuchi, and Shuichi Sugimoto
We report on optically pumped green stimulated emissions from regular nanocolumn arrays. Various InGaN-based triangular-lattice nanocolumn arrays with different lattice constants and nanocolumn diameters were prepared on a (0001) GaN/c-sapphire template using selective-area growth by rf-plasma-assisted molecular-beam epitaxy. The nanocolumn arrays were optically pumped at room temperature, and sharp peaks of stimulated emission were observed at green color wavelengths from 530 to 560 nm. The wavelengths varied with the photonic band edge, which was determined by the structural parameters of the nanocolumn arrays. The photonic crystal effect occurred, with the periodic arrangement of the nanocolumns contributing to the stimulated emission.©2011 The Japan Society of Applied Physics

High-Frequency Organic Complementary Ring Oscillator Operating up to 200 kHz

Masatoshi Kitamura, Yasutaka Kuzumoto, Shigeru Aomori, and Yasuhiko Arakawa — 2011-04-13T09:00:00+09:00

Authors: Masatoshi Kitamura, Yasutaka Kuzumoto, Shigeru Aomori, and Yasuhiko Arakawa
Organic complementary circuits consisting of bottom-contact p-channel pentacene and n-channel C_{60} thin-film transistors (TFTs) have been fabricated to evaluate their dynamic properties. Modified drain and source electrodes were used to balance the threshold voltages of the pentacene and C_{60} TFTs. The balanced threshold voltage allowed use of equal-size channel dimensions for both channel-type TFTs in the circuits. The signal delay per stage of a five-stage ring oscillator was consistent with the mobilities of the individual TFTs. The oscillation frequency increased with supply voltage up to 200 kHz, which is the highest frequency in organic five-stage complementary ring oscillators.©2011 The Japan Society of Applied Physics

InP/InGaAs Composite Metal–Oxide–Semiconductor Field-Effect Transistors with Regrown Source and Al_{2}O_{3} Gate Dielectric Exhibiting Maximum Drain Current Exceeding 1.3 mA/µm

2011-04-12T09:00:00+09:00

Authors: Ryousuke Terao, Toru Kanazawa, Shunsuke Ikeda, Yoshiharu Yonai, Atsushi Kato, and Yasuyuki Miyamoto
We have realized InP/InGaAs composite-channel metal–oxide–semiconductor field-effect transistors with both selectively regrown n^{+}-InGaAs source/drain regions and Al_{2}O_{3} as a gate dielectric. A 100-nm-long channel was fabricated by laterally buried regrowth in a channel undercut by metalorganic vapor phase epitaxy. The carrier density of the regrown layer was 2.9×10^{19} cm^{-3}. A drain current I_{d} of 1.34 mA/µm was achieved at a drain voltage V_{d} of 1 V and a gate voltage V_{g} of 3 V. A transconductance g_{m} of 817 µS/µm at V_{d} = 0.65 V was also observed at the same time. The improvement in the subthreshold slope can be explained by the decrease in dielectric/semiconductor interface trap density.©2011 The Japan Society of Applied Physics

Recent articles in Appl. Phys. Express

Prethreshold Lasing with Time-Delayed Pulse Emission from a Single Crystal of Thiophene/Phenylene Co-Oligomer

Above 600 mS/mm Transconductance with 2.3 A/mm Drain Current Density AlN/GaN High-Electron-Mobility Transistors Grown on Silicon

Development of Textured Magnesium Oxide Templates on Amorphous Polymer Surfaces Using Ion-Beam-Assisted Deposition

InGaN Laser Diode Mini-Arrays

Broad Repetition-Rate Tunable Quantum-Dot External-Cavity Passively Mode-Locked Laser with Extremely Narrow Radio Frequency Linewidth

Graphene Growth from a Spin-Coated Polymer without a Reactive Gas

Investigation of GaN-Based Light-Emitting Diodes Grown on Patterned Sapphire Substrates by Contact-Transferred and Mask-Embedded Lithography

High-Resolution Measurement of Fiber Length Change with Optical Low-Coherence Reflectometer Based on a Fiber-Ring Structure

RF Performance of AlGaN/GaN High-Electron-Mobility Transistors Grown on Silicon (110)

High-Electron-Mobility Ge n-Channel Metal–Oxide–Semiconductor Field-Effect Transistors with High-Pressure Oxidized Y_{2}O_{3}

Top-Emission Ultraviolet-Light-Emitting Diodes Containing Solution-Processed ZnO Nanocrystals

Temporal Donor Generation in Undoped Hydrogenated Amorphous Silicon Induced by Swift Proton Bombardment

Magnetic Vortex Excitation Frequencies and Eigenmodes in a Pair of Coupled Circular Dots

Determination of Mechanical Properties of Single-Crystal CdS Nanowires from Dynamic Flexural Measurements of Nanowire Mechanical Resonators

Design and Evaluation of a Planar Single-Channel Shim Coil for a Permanent Magnetic Resonance Imaging Magnet

Effective Ex-situ Fabrication of F-Doped SmFeAsO Wire for High Transport Critical Current Density

Magnetic Domain Wall Ferromagnetic Resonance in Ferromagnetic Nanowires Due to the Spin Transfer Torque

284–300 nm Quaternary InAlGaN-Based Deep-Ultraviolet Light-Emitting Diodes on Si(111) Substrates

High Normalized Strain Obtained in Li-Modified (K,Na)NbO_{3} Lead-Free Piezoceramics

Chemical–Mechanical Lift-Off Process for InGaN Epitaxial Layers

Amplitude Noise in Spin-Torque Oscillators

Aluminum Nanotransmission Lines with No Grain Boundaries and No Surface Roughness

Modeling Microwave Resonance of Curling Probe for Density Measurements in Reactive Plasmas

Current-Induced Magnetic Domain Wall Motion in Co/Ni Nanowire at Low Temperature

Magnetization Dependent Current Rectification in (Ga,Mn)As Magnetic Tunnel Junctions

Influence of High-Energy Electron Beam on Source Fluxes during Molecular Beam Epitaxy Growth on Photoluminescence Upconversion from the GaAs Band Gap

High-Brightness GaN-Based Light-Emitting Diodes on Si Using Wafer Bonding Technology

X-ray Phase Imaging Using Lau Effect

Slow Positron Beam Apparatus for Surface and Subsurface Analysis of Samples in Air

Computational Analysis of Thermal Energetic Disorder in a Pentacene Crystal: Temperature Dependence of Trap Levels and Possible Novel Thermoelectric Contribution

Self-Pulsation at Zero Absorber Bias in GaN-Based Multisection Laser Diodes

Nonpolar a-Plane AlGaN/GaN Heterostructure Field-Effect Transistors Grown on Freestanding GaN Substrate

Enhanced Carrier Injection in Perovskite Field-Effect Transistors via Low-Barrier Contacts

Harvesting Infrared Solar Energy by Semiconducting Single-Walled Carbon Nanotubes

Soft X-ray Magnetic Circular Dichroism of a CoFe/MnIr Exchange Bias Film under Pulsed High Magnetic Field

High-Efficiency Oxide Solar Cells with ZnO/Cu_{2}O Heterojunction Fabricated on Thermally Oxidized Cu_{2}O Sheets

Integrated High-Temperature Superconductor Radio-Frequency Superconducting Quantum Interference Device Covered with Superconducting Thin Films in Flip-Chip Configuration

High Output Power (∼400 µW) Oscillators at around 550 GHz Using Resonant Tunneling Diodes with Graded Emitter and Thin Barriers

Patterned Growth of TiO_{2} Nanowires on Titanium Substrates

Neutron Analysis for Microvoids in an Adhesive Layer between High X-ray Attenuation Materials

Three-Dimensional Structure Analysis of Metal–Oxide–Insulator Field Effect Transistors with Different Electrical Properties by Scanning Transmission Electron Microscopy

Exfoliation Route to Nanostructured Cobalt Oxide with Enhanced Thermoelectric Performance

Generation of Runaway Electrons and X-rays in Repetitive Nanosecond Pulse Corona Discharge in Atmospheric Pressure Air

Determination of Composition and Lattice Relaxation in Semipolar Ternary (In,Al,Ga)N Strained Layers from Symmetric X-ray Diffraction Measurements

Spin-Torque Diode Measurements of MgO-Based Magnetic Tunnel Junctions with Asymmetric Electrodes

Large Spin Accumulation with Long Spin Diffusion Length in Cu/MgO/Permalloy Lateral Spin Valves

Response Time-Shortened Zinc Oxide Scintillator for Accurate Single-Shot Synchronization of Extreme Ultraviolet Free-Electron Laser and Short-Pulse Laser

Plasma Decomposition of Clathrate Hydrates by 2.45 GHz Mircowave Irradiation at Atmospheric Pressure

D-Limonene as a Chiral Dopant for Thermotropic Liquid Crystalline Systems

Temperature-Dependent Change in Shape of Platinum Nanoparticles Supported on CeO_{2} during Catalytic Reactions

Two-Step Forming Process in Planar-Type Cu_{2}O-Based Resistive Switching Devices

Nanostructured Multilayer Tailored-Refractive-Index Antireflection Coating for Glass with Broadband and Omnidirectional Characteristics

Formation of Silicon Nano Tips in Surfactant-Modified Wet Anisotropic Etching

Epitaxial Growth of FeSe_{0.5}Te_{0.5} Thin Films on CaF_{2} Substrates with High Critical Current Density

Controlling Quantized Steps in Conductance of Gold Zigzag Nanowires

Self-Organized Two-Dimensional Vidro-Nanodot Array on Laser-Irradiated Si Surface

Assessment of GaN Surface Pretreatment for Atomic Layer Deposited High-k Dielectrics

High-Power-Density High-Efficiency Bottom-Emitting Vertical-Cavity Surface-Emitting Laser Array

InGaN-Based p–i–n Solar Cells with Graphene Electrodes

Optical Gain Spectroscopy of a Semipolar {20-21}-Oriented Green InGaN Laser Diode

Imaging Nanobubbles in Water with Scanning Transmission Electron Microscopy

Synthesis of Mica Thin Film by Pulsed Laser Deposition

High-Performance Ge Metal–Oxide–Semiconductor Field-Effect Transistors with a Gate Stack Fabricated by Ultrathin SiO_{2}/GeO_{2} Bilayer Passivation

Dual-Function Beam Shapers Fabricated by Photoaligned Liquid Crystal Cells

Bistable Resistive Switching Characteristics of Poly(2-hydroxyethyl methacrylate) Thin Film Memory Devices

Erbium-Doped AlInGaN Alloys as High-Temperature Thermoelectric Materials

Simulation of Atmospheric Pressure Direct Current Glow Discharge along a Miniature Helium Flow in Nitrogen

Second Harmonic Vibrational Mode of Substitutional Carbon in Cast-Grown Multicrystalline Silicon

Ultrahigh-Resolution Optical Coherence Tomography in 1.7 µm Region with Fiber Laser Supercontinuum in Low-Water-Absorption Samples

Ab Initio Molecular Orbital Study on Acceleration Mechanism of Silane Plasma Chemical Vapor Deposition by Diborane

Polycrystalline Ceramic Er:YAG Laser In-Band Pumped by a High-Power Er,Yb Fiber Laser at 1532 nm

Visualization of Grain Boundary as Blocking Layer for Oxygen Tracer Diffusion and a Proposed Defect Model in Non Doped BaTiO_{3} Ceramics

Two-Facing Irradiation of Laser Pulses to Suppress Position Shift of Expanded Tin Microsphere for Extreme Ultraviolet Light Source

Ordered Array of Gold Nanoparticles Promoted by Functional Peptides

Self-Assembly of GaAs Quantum Wires Grown on (311)A Substrates by Droplet Epitaxy

Ultrasonic Microspectroscopy Measurement of Fictive Temperature for Synthetic Silica Glass

High-Power Bottom-Emitting Vertical-Cavity Surface-Emitting Lasers under Continuous-Wave, Quasi-Continuous-Wave, and Pulsed Operation

Internal Quantum Efficiency of Whole-Composition-Range AlGaN Multiquantum Wells

Organic Complementary Inverters Based on Step-Edge Vertical Channel Organic Field-Effect Transistors