Appl. Phys. Express Vol.1, No.1 (2008) 011101

Appl. Phys. Express Vol.1, No.1 (2008) 011103

First Operation of AlGaN Channel HighElectron Mobility Transistors

Effects of Traps Formed by Threading
Dislocations on Off-State Breakdown
Characteristics in GaN Buffer Layer in AlGaN/
GaN Heterostructure Field-Effect Transistors

Takuma Nanjo*, Misaichi Takeuchi1,2, Muneyoshi Suita, Yuji Abe,
Toshiyuki Oishi, Yasunori Tokuda, and Yoshinobu Aoyagi1,2(Received November 1, 2007; accepted November 6, 2007; published online December 28, 2007)

A channel layer substitution of a wider bandgap AlGaN for conventional GaN in high electron mobility transistors (HEMTs) is one possible
method of enhancing the breakdown voltage for higher power operation. Wider bandgap AlGaN, however, should also increase the ohmic
contact resistance. We utilized a Si ion implantation doping techniqueto achieve sufficiently low resistive source/drain contacts, and realized
the first HEMT operation with an AlGaN channel layer. This result is very
promising for the further higher power operation of high-frequency
HEMTs. [DOI : 10.1143/APEX.1.011101]

Akihiro Hinoki, Junjiroh Kikawa1, Tomoyuki Yamada1, Tadayoshi
Tsuchiya1, Shinichi Kamiya1, Masahito Kurouchi1, Kenichi Kosaka,
Tsutomu Araki, Akira Suzuki1,2, and Yasushi Nanishi(Received November 6, 2007; accepted November 16, 2007; published online December 28, 2007)

Advanced Technology Research and Development Center, Mitsubishi Electric Corporation,
Amagasaki, Hyogo 661-8661, Japan
1 Nanoscience Development and Support Team, RIKEN, Wako, Saitama 351-0198, Japan
2 Department of Electronics and Applied Physics, Tokyo Institute of Technology, Yokohama
226-8502, Japan* E-mail address: Nanjo.Takuma@ap.MitsubishiElectric.co.jp

The off-state breakdown characteristics of GaN layers with different
thicknesses from 0.2 to 2 µm grown by metal organic chemical vapor
deposition on SiC substrates were discussed using the space-chargelimited current conduction mechanism. With decreasing thickness of the
GaN layer, the off-state breakdown voltage increased. The trap density
in the GaN layer was estimated from the traps-filled-limit voltage, which
determined the off-state breakdown voltage. We found that the thusestimated trap density increased with decreasing thickness of the GaN
layer. A higher density of threading dislocations in the thinner samples
was confirmed by transmission electron microscopy observations. These
results suggest that the traps formed by the threading dislocations influ-

Appl. Phys. Express Vol.1, No.1 (2008) 011102

ence the off-state breakdown voltage of the GaN layer.
[DOI : 10.1143/APEX.1.011103]

Continuous-Wave Operation of Blue Laser
Diodes Based on Nonpolar m-Plane Gallium
NitrideMasashi Kubota, Kuniyoshi Okamoto, Taketoshi Tanaka, and Hiroaki
Ohta*(Received November 1, 2007; accepted November 12, 2007; published online December 28, 2007)

The continuous-wave (cw) operation of m-plane InGaN-based blue
(460nm) laser diodes (LDs) has been achieved. The threshold current andthe corresponding threshold current density were 40mA and 5.0kA/cm2,
respectively, with a 459nm lasing wavelength under cw operation. The
electroluminescence peak wavelength shift in pulsed mode was only
10nm (58meV), from spontaneous emission (at 0.3mA) to stimulated
emission (at 32mA), which is extremely small when compared with thatof c-plane blue LDs. This is first clear experimental demonstration of theadvantage in fabricating nonpolar InGaN-based LDs beyond the blue
region. [DOI : 10.1143/APEX.1.011102]
Research and Development Headquarters, ROHM Co., Ltd., Kyoto 615-8585, Japan* E-mail address: Hiroaki.Ota@dsn.rohm.co.jp

Department of Photonics, Ritsumeikan University, 1-1-1 Noji-Higashi, Kusatsu, Shiga 525-8577,
Japan
1 R&D Association for Future Electron Devices, 1-1-1 Noji-Higashi, Kusatsu, Shiga 525-8577,
Japan
2 Research Organization of Science and Engineering, Ritsumeikan University, 1-1-1 NojiHigashi, Kusatsu, Shiga 525-8577, Japan

Appl. Phys. Express Vol.1, No.1 (2008) 011104

Blue Laser Diodes Fabricated on m-Plane GaN
Substrates
Yuhzoh Tsuda, Masataka Ohta, Pablo O. Vaccaro, Shigetoshi Ito,
Shuichi Hirukawa, Yoshinobu Kawaguchi, Yoshie Fujishiro, Yoshiyuki
Takahira, Yoshihiro Ueta, Teruyoshi Takakura, and Takayuki Yuasa(Received October 30, 2007; revised December 11, 2007; accepted December 15, 2007; published
online January 11, 2008)

Blue laser diodes (LDs) were fabricated on m-plane oriented GaN
substrates by atmospheric-pressure metalorganic chemical vapor deposition. Typical threshold current for stimulated emission at a wavelength λof 463nm was 69mA. Blueshift of the spontaneous emission peak withincreasing injection current was examined in LDs fabricated on m- andc-plane GaN substrates. Blueshifts for the m-plane LD (λ=463nm) andthe c-plane LD (λ=454nm) with an injection current density just below
threshold were about 10 and 26nm, respectively. These results confirm
that the blueshift in quantum-wells fabricated on m -plane oriented
substrates is smaller than on c -plane oriented substrates due to theabsence of polarization-induced electric fields.
[DOI : 10.1143/APEX.1.011104]
Advanced Technology Research Laboratories, Sharp Corporation, 2613-1 Ichinomoto-cho,
Tenri, Nara 632-8567, Japan

12        JSAP International   No.18 (July 2008)

Applied Physics Express

Appl. Phys. Express Vol.1, No.1 (2008) 011105

Appl. Phys. Express Vol.1, No.1 (2008) 011201

Vertical GaN-Based Trench Gate Metal Oxide
Semiconductor Field-Effect Transistors on GaN
Bulk Substrates

Germanium Nitride Interfacial Layer for
Chalcogenide Random Access Memory
Applications

Hirotaka Otake, Kentaro Chikamatsu, Atsushi Yamaguchi, Tatsuya
Fujishima, and Hiroaki Ohta*

Jie Shen1,2,*, Bo Liu1,**, Zhitang Song1, Cheng Xu1,2, Feng Rao1,2,
Shuang Liang1,2, Songlin Feng1, and Bomy Chen3(Received November 5, 2007; accepted November 12, 2007; published online January 11, 2008)(Received November 8, 2007; accepted November 15, 2007; published online December 28, 2007)

Completely vertical trench gate metal oxide semiconductor fieldeffect transistors (MOSFETs) have been produced using gallium nitride(GaN) for the first time. These MOSFETs exhibited enhancement-mode
operation with a threshold voltage of 3.7 V and an on-resistance of
9.3 mΩ·cm2. The channel mobility was estimated to be 131cm2/(V·s)
when all the resistances except for that of the channel are considered.
Such structures, which satisfy the key words “vertical”, “trench gate”,
and “MOSFET”, will enable us to fabricate practical GaN-based powerswitching devices. [DOI : 10.1143/APEX.1.011105]

This work reports on the performance improvement of a chalcogenide random access memory device by applying germanium nitride as
an interfacial layer. The device with an 8-nm-thick GeN film was fabricated using standard 0.18 µm complementary metal oxide semiconductor
technology. The as-deposited GeN is in the amorphous state and has
a smooth surface. An electrical test showed that this N-deficient layer
induces a lower threshold voltage during the operation. It is believed thatthe reduction mainly originated from the excellent interfacial properties,
high electrical resistivity, and low thermal conductivity of GeN, which iswould be a prospective interfacial material in CRAM devices.
[DOI : 10.1143/APEX.1.011201]

Research and Development Headquarters, ROHM Co., Ltd., Kyoto 615-8585, Japan* E-mail address: Hiroaki.Ota@dsn.rohm.co.jp

Appl. Phys. Express Vol.1, No.1 (2008) 011106

Monolithic Polychromatic Light-Emitting
Diodes Based on InGaN Microfacet Quantum
Wells toward Tailor-Made Solid-State Lighting
Mitsuru Funato*, Takeshi Kondou, Keita Hayashi, Shotaro Nishiura,
Masaya Ueda, Yoichi Kawakami, Yukio Narukawa1, and Takashi Mukai1(Received November 15, 2007; accepted December 9, 2007; published online January 17, 2008)

Monolithic polychromatic light-emitting diodes (LEDs) based on
micro-structured InGaN/GaN quantum wells are demonstrated. The
microstructure is created through regrowth on SiO2 mask stripes along––
the [1100] direction and consists of (0001) and {1122} facets. The LEDs
exhibit polychromatic emission, including white, due to the additive color
mixture of facet-dependent emission colors. Altering the growth conditions and mask geometry easily controls the apparent emission color.
Furthermore, simulations predict high light extraction efficiencies dueto their three-dimensional structures. Those observations suggest thatthe proposed phosphor-free LEDs may lead to highly efficient solid-state
lighting in which the color spectra of light sources are synthesized tosatisfy specific requirements for illuminations.
[DOI : 10.1143/APEX.1.011106]
Department of Electronic Science and Engineering, Kyoto University, Kyoto 615-8510, Japan
1 Nitride Semiconductor Research Laboratory, Nichia Corporation, Tokushima 774-8601,
Japan* E-mail address: funato@kuee.kyoto-u.ac.jp

1 Laboratory of Nanotechnology, Shanghai Institute of Microsystem and Information
Technology, Chinese Academy of Sciences, Shanghai 200050, P.R. China
2 Graduate University of Chinese Academy of Sciences, Beijing 100039, P.R. China
3 Silicon Storage Technology, Inc., 1171 Sonora Court, Sunnyvale, CA 94086, U.S.A.
* E-mail address: shenjie@mail.sim.ac.cn** E-mail address: liubo@mail.sim.ac.cn

Appl. Phys. Express Vol.1, No.1 (2008) 011202

Vertical Solar-Blind Deep-Ultraviolet Schottky
Photodetectors Based on β-Ga2O3 Substrates
Takayoshi Oshima*, Takeya Okuno, Naoki Arai1, Norihito Suzuki1,
Shigeo Ohira1, and Shizuo Fujita2(Received November 12, 2007; accepted November 25, 2007; published online January 11, 2008)

A vertical-type Schottky photodetector based on a (100)-oriented
β-Ga2O3 substrate has been fabricated with simple processes of thermal
annealing and vacuum evaporation. The photodetector exhibited a rectification ratio higher than 106 at ± 3 V, and showed deep-ultravioletlight detection at reverse bias. The spectral response showed solar-blindsensitivity with high photoresponsivities of 2.6–8.7A/W at wavelengthsof 200 – 260 nm. These values were 35 – 150 times higher than thosederived assuming the internal quantum efficiency to be unity. This fact
is attributed to the carrier multiplication occurring in the highly resistive
surface region that is subject to a high internal electric field of about
1.0MV/cm at the reverse bias of 10V. [DOI : 10.1143/APEX.1.011202]
Department of Electronic Science and Engineering, Kyoto University, Katsura, Nishikyo-ku,
Kyoto 615-8510, Japan
1 Nippon Light Metal Company, Ltd., Kambara, Shimizu-ku, Shizuoka 421-3291, Japan
2 Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8520,
Japan* E-mail address: t-oshima@iic.kyoto-u.ac.jp

JSAP International   No.18 (July 2008)        13Appl. Phys. Express Vol.1, No.1 (2008) 011301

Appl. Phys. Express Vol.1, No.1 (2008) 011501

Current-Driven Domain Wall Motion in
CoCrPt Wires with Perpendicular Magnetic
Anisotropy

Piezoelectric Properties of (K,Na)NbO3 Films
Deposited by RF Magnetron Sputtering

Hironobu Tanigawa, Kouta Kondou, Tomohiro Koyama, Kunihiro
Nakano, Shinya Kasai, Norikazu Ohshima1, Shunsuke Fukami1,
Nobuyuki Ishiwata1, and Teruo Ono(Received November 5, 2007; accepted November 12, 2007; published online January 11, 2008)

We report the direct observation of current-driven domain wall
(DW) motion in a CoCrPt wire with perpendicular magnetic anisotropy.
Magnetic force microscopy showed that a single DW introduced in thewire is displaced back and forth by positive and negative pulsed current.
This is the first demonstration of the current-driven DW motion in a
metallic magnetic wire with perpendicular magnetic anisotropy in theabsence of a magnetic field. [DOI : 10.1143/APEX.1.011301]
Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
1 Device Platforms Research Laboratories, NEC Corporation, 1120 Shimokuzawa, Sagamihara,
Kanagawa 229-1198, Japan

Appl. Phys. Express Vol.1, No.1 (2008) 011401

On Effects of Gate Bias on Hole Effective
Mass and Mobility in Strained-Ge Channel
Structures
Kentarou Sawano, Yugo Kunishi, Yuu Satoh, Kiyohiko Toyama1, Keisuke
Arimoto2, Toru Okamoto1, Noritaka Usami3, Kiyokazu Nakagawa2, andYasuhiro Shiraki(Received November 6, 2007; accepted November 25, 2007; published online January 11, 2008)

The effects of gate bias on hole effective mass (m*) and Hall mobility
were studied in strained-Ge channel modulation-doped structures. Shubnikov – de Haas oscillations were analyzed with and without the bias anda significant m* increase from 0.15 to 0.22 m0 was observed with theincrease in the carrier density due to the strong nonparabolicity of thevalence band. This is a clear demonstration that modification of carrier
density via gating considerably affects m*, which may have critical effects
on device properties. The gate bias dependence of Hall mobility was also
investigated and the dominant scattering mechanism was clarified invarious temperature and carrier density regions.
[DOI : 10.1143/APEX.1.011401]
Research Center for Silicon Nano-Science, Advanced Research Laboratories, Musashi Instituteof Technology, 8-15-1 Todoroki, Setagaya-ku, Tokyo 158-0082, Japan
1 Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033,
Japan
2 Center for Crystal Science and Technology, University of Yamanashi, 7 Miyamae-cho, Kofu
400-0021, Japan
3 Institute for Material Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai
980-8577, Japan

14        JSAP International   No.18 (July 2008)

Kenji Shibata, Fumihito Oka, Akio Ohishi, Tomoyoshi Mishima, andIsaku Kanno1(Received November 7, 2007; accepted December 3, 2007; published online January 11, 2008)

High-piezoelectricity lead-free films of (K,Na)NbO3 (KNN) weresuccessfully deposited on Pt / MgO and Pt / Ti / SiO2 / Si substrates by RFmagnetron sputtering. The KNN film was epitaxially grown on Pt / MgO
with a high <001> orientation in the pseudo-cubic perovskite structure. The KNN film on Pt / Ti / SiO2 / Si was polycrystalline with a preferential <001> orientation in the pseudo-cubic perovskite structure. The
piezoelectric properties of the KNN films were determined from the tip
displacement of KNN / Pt / MgO or KNN / Pt / Ti / SiO2 / Si unimorph cantilevers. The transverse piezoelectric coefficients e31* (d31 / s11E) of the KNN
films on Pt / MgO and Pt / Ti / SiO2 / Si were calculated to be -3.6 and -5.5C/
m2, respectively, which are amongst the highest values for KNN films
ever reported. [DOI : 10.1143/APEX.1.011501]
Advanced Electronic Materials Research Department, Research and Development Laboratory,
Hitachi Cable, Ltd., 3550 Kidamari, Tsuchiura, Ibaraki 300-0026, Japan
1 Department of Micro Engineering, Kyoto University, Yoshida-honmachi, Sakyo-ku, Kyoto
606-8501, Japan

Appl. Phys. Express Vol.1, No.1 (2008) 011502

Valence State of Mn-Doped BiFeO3 – BaTiO3
Ceramics Probed by Soft X-ray Absorption
Spectroscopy
Tohru Higuchi1,2, Wataru Sakamoto3, Naoyuki Itoh3, Tetsuo Shimura3,
Takeshi Hattori2, and Toshinobu Yogo3(Received November 16, 2007; accepted December 3, 2007; published online January 11, 2008)

The valence state of Mn-doped BiFeO 3 – BaTiO 3 ceramics has
been probed by soft X-ray absorption spectroscopy (XAS). Mn-doped
BiFeO3 – BaTiO3 has valence states of Fe3+ and Ti4+, although BiFeO3
and Mn-doped BiFeO3 have mixed valence states of Fe2+ and Fe3+.
The Mn 2p-XAS peak of Mn-doped BiFeO3 – BaTiO3 locates at a lower
energy side than that of Mn-doped BiFeO3 that corresponds to the Mn3+
valence state. These findings may indicate that the Fe3+ valence state of
Mn-doped BiFeO3 – BaTiO3 is stabilized by charge transfer from the Mn
3d state to the Fe 3d state through the Ti 3d state in BaTiO3.
[DOI : 10.1143/APEX.1.011502]
1 Advanced Light Source, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, MS
7R0222, Berkeley, CA 94720, U.S.A.
2 Department of Applied Physics, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku,
Tokyo 162-8601, Japan
3 EcoTopia Science Institute, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603,
Japan

Applied Physics Express

Appl. Phys. Express Vol.1, No.1 (2008) 011701

Appl. Phys. Express Vol.1, No.1 (2008) 012002

Superconductor-based Light Emitting Diode:
Demonstration of Role of Cooper Pairs inRadiative Recombination Processes

Two-Dimensional Photonic Crystal Composedof Ordered Polymer Nanopillar Arrays withHigh Aspect Ratios Using Anodic Porous
Alumina Templates

Yujiro Hayashi1,*, Kazunori Tanaka2,3, Tatsushi Akazaki3,4, Masafumi Jo1,
Hidekazu Kumano1,3, and Ikuo Suemune1,3

Takashi Yanagishita1,*, Kazuyuki Nishio1,2, and Hideki Masuda1,2(Received November 8, 2007; accepted December 9, 2007; published online January 17, 2008)(Received November 1, 2007; accepted November 25, 2007; published online January 11, 2008)

A light emitting diode with superconducting Nb electrodes was
fabricated to investigate the contribution of cooper pairs to radiative
recombination in a semiconductor. Electroluminescence observed fromthe active layer in which electron cooper pairs and normal holes are
injected was drastically enhanced at the temperature lower than the
superconducting transition temperature of the Nb electrodes. This is thefirst experimental evidence that cooper pairs enhance radiative recombinations by the superradiance effect. [DOI : 10.1143/APEX.1.011701]

Two-dimensional (2D) photonic crystals composed of orderedpolymer nanopillar arrays were fabricated using anodic porous alumina
templates. For the preparation of 2D photonic crystals with high aspectratios, polymer pillar arrays, in which both ends of nanopillars were
supported by supporting layers, were introduced. The diameter, interval
and length of nanopillar arrays could be controlled by changing the
preparation conditions of anodic porous alumina templates. The reflection properties of the ordered polymer nanopillar array obtained exhibited a stop band in the spectrum, which corresponds to the band gap in
the 2D photonic crystals. [DOI : 10.1143/APEX.1.012002]

1 Research Institute for Electronic Science, Hokkaido University, Sapporo 001-0021, Japan
2 Central Laboratory, Hamamatsu Photonics, Hiraguchi, Hamamatsu 434-8601, Japan
3 CREST, Japan Science and Technology Agency, Kawaguchi, Saitama 332-0012, Japan
4 NTT Basic Research Laboratory, Morinosato-Wakamiya, Atsugi, Kanagawa 243-0198, Japan* E-mail address: yhayashi@es.hokudai.ac.jp

Appl. Phys. Express Vol.1, No.1 (2008) 011801

Dual Self-Aligned Vertical Multichannel
Organic Transistors
Hidenori Naruse, Shigeki Naka, and Hiroyuki Okada*(Received November 1, 2007; accepted November 16, 2007; published online December 28, 2007)

A dual self-aligned vertical multichannel organic transistor (DSAVMCOT) is proposed and demonstrated. The layouts of the shadow gate
and transparent source/drain are sequentially determined using dual
back-surface exposure. Vertical 100-nm channel and multichannel structures are obtained using interdigital gate electrodes. This device concept
is promising for use as a backplane with high current driving capability.
[DOI : 10.1143/APEX.1.011801]
Graduate School of Science and Engineering, University of Toyama, 3190 Gofuku, Toyama
930-8555, Japan* E-mail address: okada@eng.u-toyama.ac.jp

Appl. Phys. Express Vol.1, No.1 (2008) 012001

Planar Avalanche Photodiode for Long-Haul
Single-Photon Optic Fiber Communications
Eiji Yagyu*, Kohei Sugihara, Tsuyoshi Nishioka1, Mitsuru Matsui1, Kiichi
Yoshiara, and Yasunori Tokuda(Received November 2, 2007; accepted November 20, 2007; published online December 28, 2007)

1 Kanagawa Academy of Science and Technology, 5-4-30 Nishihashimoto, Sagamihara,
Kanagawa 229-1131, Japan
2 Department of Applied Chemistry, Tokyo Metropolitan University, 1-1 Minamiosawa,
Hachioji, Tokyo 192-0397, Japan* E-mail address: tyanagishita@r7.dion.ne.jp

Appl. Phys. Express Vol.1, No.1 (2008) 012003

Tunable Liquid Crystal Laser Using Distributed
Feedback Cavity Fabricated by Nanoimprint
Lithography
Ryotaro Ozaki, Toshikazu Shinpo, Katsumi Yoshino1, Masanori Ozaki2,
and Hiroshi Moritake(Received November 1, 2007; accepted November 25, 2007; published online January 11, 2008)

Electrical tuning of laser wavelength is demonstrated using a liquidcrystal / polymer grating fabricated by nanoimprint lithography. Laseremission occurs at a wavelength near 700nm, which corresponds to thefirst order of a 200nm period grating. With increasing applied voltage,
the lasing spectrum begins to shift to shorter wavelengths at 10V, andthen a 10nm shift is achieved with an applied voltage of 30V. This is dueto the refractive index change of the liquid crystal in the trench of thepolymer grating by field-induced molecular reorientation.
[DOI : 10.1143/APEX.1.012003]
Department of Electrical and Electronic Engineering, National Defense Academy, 1-10-20
Hashirimizu, Yokosuka, Kanagawa 239-8686, Japan
1 Shimane Institute for Industrial Technology, 1 Hokuryo-cho, Matsue 690-0816, Japan
2 Division of Electrical, Electronic and Information Engineering, Graduate School ofEngineering, Osaka University, 2-1 Yamada-Oka, Suita, Osaka 565-0871, Japan

We present a high-performance planar GaInAs/InP avalanche photodiode (APD) for long-haul single-photon optic fiber communications, thatis, quantum cryptography. The APDs for single-photon communications
require a high single-photon detection efficiency (η det) relating to bitrate
and a low ratio of dark count probability (Pdc) to η det limiting communication distance. We fabricated the APD with the combination of a longmultiplication region length and a low carrier sheet density on the basisof numerical analysis. The Pdc / η det monotonically decreased with operation temperature lowered, and the ratio reached 5.9 × 10-6 with the ηdetof 13 % at 77K. The Pdc was 7.7 × 10-7, which corresponds to a darkcount rate of 0.38kHz. The useful APD and the effective layer design arereported. [DOI : 10.1143/APEX.1.012001]
Advanced Technology R&D Center, Mitsubishi Electric Corporation, Amagasaki, Hyogo
661-8661, Japan
1 Information Technology R&D Center, Mitsubishi Electric Corporation, Kamakura, Kanagawa
247-8501, Japan* E-mail address: Yagyu.Eiji@cb.MitsubishiElectric.co.jp

JSAP International   No.18 (July 2008)        15Appl. Phys. Express Vol.1, No.1 (2008) 012004

Appl. Phys. Express Vol.1, No.1 (2008) 012006

Generation of Intense and Monochromatic
Terahertz Radiation from Coherent
Longitudinal Optical Phonons in
GaAs/AlAs Multiple Quantum Wells at Room
Temperature

Visible Anisotropic Deformation of
Chalcogenide Glass by Illumination of Linearly
Polarized Light

Masaaki Nakayama, Shuh-ichi Ito, Kohji Mizoguchi1, Shingo Saito2, andKiyomi Sakai2

It has been discovered that illumination of linearly-polarizedbandgap light produces visible-scale anisotropic deformations in a covalent chalcogenide glass As2S3. X-ray diffraction and Raman-scattering
measurements for deforming As2S3 flakes detect no microscopic structural changes. Measurements of optical torque in deforming flakes andcomparative exposure experiments for crystalline As2S3 and amorphous
Se suggest that the anisotropic deformation occurs through radiation
force, photoinduced birefringence, and photoinduced fluidity.
[DOI : 10.1143/APEX.1.012006](Received November 1, 2007; accepted December 7, 2007; published online January 11, 2008)

We have investigated time-domain signals of terahertz (THz) radiation from coherent longitudinal-optical (LO) phonons in GaAs/AlAs
multiple quantum wells at room temperature, utilizing an optical gating
method with a photoconductive dipole antenna. It has been found thatan intense and monochromatic THz wave with a frequency of 8.7THz
is generated from coherent GaAs-like LO phonons under the condition that the energy spacing between the fundamental heavy-hole andlight-hole excitons is tuned to the LO-phonon energy. The pump-energy
and pump-power dependences of the THz-radiation intensity indicatethat the impulsive interference of the heavy-hole and light-hole excitons
dominates the generation process. [DOI : 10.1143/APEX.1.012004]
Department of Applied Physics, Graduate School of Engineering, Osaka City University,
Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan
1 Department of Physical Science, Graduate School of Science, Osaka Prefecture University,
Gakuen-cho, Naka-ku, Sakai 599-8531, Japan
2 National Institute of Information and Communications Technology, Koganei, Tokyo
184-8795, Japan

Appl. Phys. Express Vol.1, No.1 (2008) 012005

Development of Electrooptic Modulator for
Advanced Ground-Based Gravitational Wave
Telescopes Using Stoichiometric MgO-Doped
LiNbO3 Crystals
Noriaki Ohmae*, Kohei Takeno1, Shigenori Moriwaki, and Norikatsu
Mio(Received November 2, 2007; accepted November 20, 2007; published online January 11, 2008)

We have developed an electrooptic modulator (EOM) using stoichiometric MgO-doped LiNbO3 (MgO-doped SLN) crystals, and evaluated this EOM for the phase control of a high-power laser whose poweris over 100W. We succeeded in the phase modulation of a 100W laser
without a decrease in phase modulation index, due to a nonlinear opticaleffect, which can occur when a high-power laser beam enters the EOM.
We also estimated wavefront distortions caused by passing through the
EOM with a Shack – Hartmann wavefront sensor, and found that theadditional wavefront distortion was negligible. Thus, we confirmed that
MgO-doped SLN crystals are a suitable material for use in a high-power
laser system. [DOI : 10.1143/APEX.1.012005]
Department of Advanced Materials Science, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa,
Chiba 277-8561, Japan
1 National Institute of Advanced Industrial Science and Technology, 1-2-1 Namiki, Tsukuba,
Ibaraki 305-8564, Japan* E-mail address: kk66109@mail.ecc.u-tokyo.ac.jp

Keiji Tanaka(Received November 2, 2007; accepted November 25, 2007; published online January 11, 2008)

Department of Applied Physics, Graduate School of Engineering, Hokkaido University, Kita-ku,
Sapporo 060-8628, Japan

Appl. Phys. Express Vol.1, No.1 (2008) 012007

Kerr-Lens Mode-Locked Diode-Pumped
Yb:YAG Laser with the Transverse Mode
Passively Stabilized
Sadao Uemura* and Kenji Torizuka(Received November 5, 2007; accepted November 27, 2007; published online January 11, 2008)

We have developed a Kerr-lens mode-locked diode-pumped Yb:YAG
laser in which the transverse mode is passively stabilized. The modelocking scheme can be used for various diode-pumped Yb-doped bulk
lasers. The pulse duration is as short as 100 fs, which is to our knowledge the shortest pulse ever produced from an Yb:YAG laser. The center
wavelength and laser output power are 1051nm and 151mW, respectively. [DOI : 10.1143/APEX.1.012007]
Photonics Research Institute, National Institute of Advanced Industrial Science and Technology(AIST), Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan* E-mail address: s.uemura@aist.go.jp

Appl. Phys. Express Vol.1, No.1 (2008) 012008

Realization of All-fiber Tunable Filter andHigh Optical Power Blocker Using Thinned
Fiber Bragg Gratings Coated with Carbon
Nanotubes
Kien T. Dinh*, Yong-Won Song1, Shinji Yamashita1, and Sze Y. Set2

(Received November 13, 2007; accepted December 7, 2007; published online January 11, 2008)

We propose and create a novel structure formed with thinned fiber
Bragg gratings and carbon nanotubes utilizing their optical absorption
characteristics. We show that the reflection band of the fiber Bragg gratings can be shifted by controlling the in-line optical power. We use thestructure to realize two applications namely an all-fiber tunable filter anda high-optical-power blocker. [DOI : 10.1143/APEX.1.012008]
Graduate School of Frontier Sciences, University of Tokyo, Tokyo 113-8656, Japan
1 Department of Electronics Engineering, University of Tokyo, Tokyo 113-8656, Japan
2 Alnair Laboratories Corporation, Tokyo 154-0005, Japan* E-mail address: kien@sagnac.t.u-tokyo.ac.jp

16        JSAP International   No.18 (July 2008)

Applied Physics Express

Appl. Phys. Express Vol.1, No.1 (2008) 012009

Appl. Phys. Express Vol.1, No.1 (2008) 014002

Propagation of Terahertz Pulses on Coplanar
Strip-lines on Low Permittivity Substrates anda Spectroscopy Application

Behavior of Catalyst Particle at Tip of Carbon
Nanotube during Field Emission

Shinji Yanagi, Masayuki Onuma, Jiro Kitagawa, and Yutaka Kadoya*

Tadashi Fujieda*, Makoto Okai, Kishio Hidaka, Hiroaki Matsumoto1, andHiroshi Tokumoto2(Received November 22, 2007; accepted December 9, 2007; published online January 17, 2008)(Received November 1, 2007; accepted November 25, 2007; published online January 11, 2008)

The authors have investigated the propagation characteristics ofthe terahertz electrical pulses on the coplanar strip-lines (CPSs) made on
low permittivity substrates. By the use of a commercially available plastic
whose permittivity is about 2.3 in 1 – 3 THz, the radiation loss could
be made low, and the total attenuation of about 0.2 neper/mm wasachieved at 1THz. As a result, the spectra reaching 3THz with a dynamic
range of about 60dB were realized even after the 1mm propagation.
Using the CPS device, a spectroscopy of biotin powder is demonstrated
over a frequency range up to 2THz. [DOI : 10.1143/APEX.1.012009]

A catalyst particle at the tip of a multi-walled carbon nanotube(MWNT) during field emission inside a transmission electron microscope
was observed in-situ. The particle streamed from the tip like a liquid
as the emission current abruptly increased from 20 to 40 µA. This wasdue to the temperature rise at the tip of the MWNT, resulting from theincreased emission current and dipole moment in the particle caused by
the electric field. Maintenance of this high emission current led to anelectrical discharge, which severely damaged the MWNT electron emitter.
Under high emission currents, in particular, the catalyst particle caused
an unstable emission. [DOI : 10.1143/APEX.1.014002]

Graduate School of Advanced Sciences of Matter, Hiroshima University, 1-3-1 Kagamiyama,
Higashihiroshima, Hiroshima 739-8530, Japan* E-mail address: kd@hiroshima-u.ac.jp

Appl. Phys. Express Vol.1, No.1 (2008) 013001

Tunneling Current – Voltage Characteristics ofGraphene Field-Effect Transistor
Victor Ryzhii1,3, Maxim Ryzhii1,3, and Taiichi Otsuji2,3(Received November 2, 2007; accepted November 25, 2007; published online December 28, 2007)

We develop an analytical device model for a graphene field-effecttransistor. Using this model, we calculate its current – voltage characteristics at sufficiently high gate voltages when a n–p–n (p–n–p) lateral junction is formed in the transistor channel and the source – drain current isassociated with the interband tunneling through this junction.
[DOI : 10.1143/APEX.1.013001]
1 Computer Solid State Physics Laboratory, University of Aizu, Aizu-Wakamatsu, Fukushima
965-8580, Japan
2 Research Institute for Electrical Communication, Tohoku University, Sendai 980-8577, Japan
3 CREST, Japan Science and Technology Agency, Tokyo 107-0075, Japan

Appl. Phys. Express Vol.1, No.1 (2008) 014001

Growth of Single-Walled Carbon Nanotubes
from Ceramic Particles by Alcohol Chemical
Vapor Deposition
Huaping Liu1,*, Daisuke Takagi1, Hiroshi Ohno1, Shohei Chiashi1,
Tomohito Chokan1, and Yoshikazu Homma1,2,**(Received October 27, 2007; accepted December 10, 2007; published online January 11, 2008)

Al2O3 ceramic nano-particles, which were regarded as an inactive catalyst in the growth of carbon nanotubes in the past, have been
prepared as the catalyst for single-walled carbon nanotube (SWCNT)
growth using an alcohol chemical vapor deposition method. Dense
SWCNTs have been successfully synthesized, indicating that Al2O3 serves
as an efficient catalyst. Moreover, it was found that many SWCNTs werealso grown from irregular large Al2O3 particles ranging from several
tens of nanometers to hundreds of nanometers, which has never been
observed in the case of metallic catalyst particles. These results give moreinsights into the role of catalyst in SWCNT growth.
[DOI : 10.1143/APEX.1.014001]

Materials Research Laboratory, Hitachi, Ltd., Hitachi, Ibaraki 319-1292, Japan
1 Hitachi High-Tech Manufacturing and Service Corporation, Hitachinaka, Ibaraki 312-0033,
Japan
2 Nanotechnology Research Center, Research Institute for Electronic Science, Hokkaido
University, Sapporo 001-0021, Japan* E-mail address: tadashi.fujieda.yv@hitachi.com

Appl. Phys. Express Vol.1, No.1 (2008) 014003

Vapor – Liquid – Solid Growth of Small- andUniform-Diameter Silicon Nanowires at Low
Temperature from Si2H6
Saeed Akhtar1, Koichi Usami1, Yoshishige Tsuchiya1,2, Hiroshi Mizuta2,3,
and Shunri Oda1,2,*(Received November 12, 2007; accepted December 7, 2007; published online January 11, 2008)

We report 350°C as a critical growth temperature for overcoming
the aggregation of gold (Au) in the synthesis of high-density silicon
nanowires (SiNWs) with controlled diameters in a vapor – liquid – solid(VLS) mechanism by the low-temperature decomposition of Si2H6.
Low-temperature growth is considered essential for preserving the initial
distribution of Au droplets (8±5nm) during SiNW nucleation with small(12nm) and uniform (±5nm) diameters. Au – Si eutectics increase in sizewith aggregation at high temperatures, resulting in SiNWs with large andrandom diameters. The crystal quality, defect formation, and morphologyof the wires, grown in the (111) direction, are size dependent.
[DOI : 10.1143/APEX.1.014003]
1 Quantum Nanoelectronics Research Center, Tokyo Institute of Technology, 2-12-1
O-okayama, Meguro-ku, Tokyo 152-8552, Japan
2 Solution Oriented Research for Science and Technology, JST, Kawaguchi, Saitama 332-0012,
Japan
3 School of Electronics and Computer Science, Southampton University, Highfield,
Southampton SO17 1BJ, U.K.
* E-mail address: soda@pe.titech.ac.jp

1 Department of Physics, Tokyo University of Science, Shinjuku, Tokyo 162-8601, Japan
2 CREST, Japan Science and Technology Agency, Chiyoda, Tokyo 102-0075, Japan* E-mail address: hliu@rs.kagu.tus.ac.jp** E-mail address: Homma@rs.kagu.tus.ac.jp

JSAP International   No.18 (July 2008)        17Appl. Phys. Express Vol.1, No.1 (2008) 014004

Appl. Phys. Express Vol.1, No.1 (2008) 015001

Highly Sensitive Detection of Carbon
Monoxide at Room Temperature Using
Platinum-Decorated Single-Walled Carbon
Nanotubes

Development of 4H – SiC Epitaxial GrowthTechnique Achieving High Growth Rate andLarge-Area Uniformity

Winadda Wongwiriyapan, Satoshi Inoue, Tatsuya Ito1, Ryotaro(Received November 1, 2007; accepted November 25, 2007; published online January 11, 2008)

Shimazaki1, Toru Maekawa1, Kengo Suzuki1, Hiroshi Ishikawa1,
Shin-ichi Honda, Kenjiro Oura2, and Mitsuhiro Katayama*(Received November 13, 2007; accepted December 3, 2007; published online January 11, 2008)

We demonstrated highly sensitive detection of carbon monoxide (CO)down to 1ppm at room temperature using platinum-decorated singlewalled carbon nanotubes (Pt-SWNTs). The obtained sensitivity to CO was
3 – 4 orders higher than the values reported for functionalized SWNTs,
and was achieved by the controlled deposition of Pt nanoparticles on
SWNTs. For 1 – 10 ppm of CO, the sensor response linearly increased
with CO concentration, affording the quantitative detection of CO in a
low-concentration range. Furthermore, Pt-SWNTs exhibited detection
selectivity to CO against H2. The sensing mechanism was attributed toelectron donation to the SWNTs as a result of CO oxidation on the Pt
catalyst surface. [DOI : 10.1143/APEX.1.014004]
Division of Electrical, Electronic and Information Engineering, Graduate School of Engineering,Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
1 New Cosmos Electric Co., Ltd., 3-6-25 Mitsuya-naka, Yodokawa-ku, Osaka 532-0036,
Japan
2 Research Center for Ultrahigh Voltage Electron Microscopy, Osaka University, 7-1
Mihogaoka, Ibaraki, Osaka 567-0047, Japan* E-mail address: katayama@nmc.eei.eng.osaka-u.ac.jp

Masahiko Ito*, Liutauras Storasta, and Hidekazu Tsuchida
A vertical hot-wall epi-reactor that makes it possible to simultaneously achieve a high growth rate and large-area uniformity has beendeveloped. A maximum growth rate of 250 µm/h is achieved with amirror-like morphology at 1650°C. Under a modified epi-reactor setup,a thickness uniformity of 1.1% and a doping uniformity of 6.7 % for a
65-mm-radius area are achieved while maintaining a high growth rateof 79 µm/h. A low doping concentration of ~1× 1013cm-3 is obtained fora 50-mm-radius area. The low-temperature photoluminescence (LTPL)
spectrum shows the predominance of free exciton peaks with only few
impurity-related peaks and the L1 peak below detection limit. The deeplevel transient spectroscopy (DLTS) measurement for an epilayer grown
at 80 µm/h shows low trap concentrations of Z1/2: 1.2 × 1012 and EH6/7:
6.3 × 1011cm-3. A 280-µm-thick epilayer with a RMS roughness of 0.2nm
and a carrier lifetime of ~1 µs is obtained.
[DOI : 10.1143/APEX.1.015001]
Central Research Institute of Electric Power Industry, 2-6-1 Nagasaka, Yokosuka, Kanagawa
240-0196, Japan* E-mail address: m-ito@criepi.denken.or.jp

Appl. Phys. Express Vol.1, No.1 (2008) 015002
Appl. Phys. Express Vol.1, No.1 (2008) 014005

Local Synthesis of Tungsten Oxide
Nanowires by Current Heating of Designed
Micropatterned Wires
Keisuke Nagato1,2,*, Yusuke Kojima1, Keigo Kasuya3, Hiroki Moritani1,
Tetsuya Hamaguchi1, and Masayuki Nakao1(Received December 4, 2007; accepted December 15, 2007; published online January 17, 2008)

We locally synthesized tungsten oxide nanowires at predetermined positions by current heating of designed micropatterned wires.
The current wires were fabricated from tungsten thin film and had
two different widths in the same wire, and the narrower sections were
heated more than the wider sections due to the difference in electric
resistance. The temperature of the narrower sections was controlled
to be optimal for nanowire synthesis in an O2 atmosphere in a vacuum
chamber. We demonstrated the synthesis of nanowires over an areaof approximately 1×1 µm2 and successfully synthesized nanowires on aregular 20 by 20 array with narrow sections with 10 µm pitch.
[DOI : 10.1143/APEX.1.014005]
1 Department of Engineering Synthesis, School of Engineering, The University of Tokyo, 7-3-1
Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
2 Research Fellow of the Japan Society for the Promotion of Science, 8 Ichibancho, Chiyodaku, Tokyo 102-8472, Japan
3 Central Research Laboratory, Hitachi, Ltd., 1-280 Higashi-koigakubo, Kokubunji, Tokyo
185-8601, Japan* E-mail address: nagato@hnl.t.u-tokyo.ac.jp

18        JSAP International   No.18 (July 2008)

High Mobility Titanium-Doped In2O3 Thin
Films Prepared by Sputtering/Post-Annealing
Technique
Ryota Hashimoto, Yoshiyuki Abe1, and Tokio Nakada(Received November 1, 2007; accepted December 15, 2007; published online January 17, 2008)

High-electron-mobility Ti-doped In2O3 (ITiO) thin films were preparedon soda-lime glass substrates by rf magnetron sputtering followed by apost-annealing process. Both carrier concentration and electron mobility
were considerably improved by annealing in a vacuum at 530 °C. A highest
electron mobility of 105cm2 V-1 s-1 with a resistivity of 1.95 × 10-4 Ω cm
was obtained for an annealed ITiO thin film. The ITiO thin film exhibited
an optical transmission of approximately 80 % at wavelengths ranging
from 400 to 1800nm. Post-annealing in a vacuum is one of the effective
methods for improving the electrical properties of ITiO thin films without
sacrificing optical transmission. [DOI : 10.1143/APEX.1.015002]
Department of Electrical Engineering and Electronics, Aoyama Gakuin University, 5-10-1
Fuchinobe, Sagamihara, Kanagawa 229-8558, Japan
1 Ichikawa Research Laboratory, Sumitomo Metal Mining Co., Ltd., Nakakokubun, Ichikawa,
Chiba 272-8588, Japan

Applied Physics Express

Appl. Phys. Express Vol.1, No.1 (2008) 015003

Appl. Phys. Express Vol.1, No.1 (2008) 015005

Photoluminescence from Epitaxial Films of
Perovskite-type Alkaline-earth Stannates

Molecular Layer-by-Layer Growth of C60 Thin
Films by Continuous-Wave Infrared Laser
Deposition

Kazushige Ueda*, Tsuyoshi Maeda, Kensuke Nakayashiki, KatsuhikoGoto, Yutaka Nakachi, Hiroshi Takashima1, Kenji Nomura2, Koichi
Kajihara2,**, and Hideo Hosono2(Received November 20, 2007; accepted December 18, 2007; published online January 17, 2008)

The epitaxial films of the recently developed calcium and strontium stannates phosphors with perovskite or its related structure were
fabricated by the pulsed-lased deposition method. The films were all
highly transparent in the visible region, and showed intense luminescence of several colors under ultraviolet excitation. Light scattering at
the substrates' surfaces varied the appearance of photoluminescence. In
combination with epitaxial-film-growth technologies for many perovskite
functional materials, the obtained results provide a promise for future
developments of multifunctional optoelectronic devices.
[DOI : 10.1143/APEX.1.015003]
Kyushu Institute of Technology, 1-1 Sensui, Tobata, Kitakyushu 804-8550, Japan
1 National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba,
Ibaraki 305-8568, Japan
2 ERATO-SORST, Japan Science and Technology Agency (JST), in Frontier Collaborative
Research Center (FCRC), Tokyo Institute of Technology, 4259 Nagatsuta, Midori, Yokohama
226-8503, Japan* E-mail address: kueda@che.kyutech.ac.jp** Present address: Department of Applied Chemistry, Graduate School of Urban
Environmental Sciences, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji, Tokyo
192-0397, Japan.

Appl. Phys. Express Vol.1, No.1 (2008) 015004

Exciton-derived Electron Emission from (001)
Diamond p – n Junction Diodes with Negative
Electron Affinity
Daisuke Takeuchi1,*, Toshiharu Makino1, Sung-Gi Ri1, Norio Tokuda1,
Hiromitsu Kato1, Masahiko Ogura1, Hideyo Okushi1,2, and Satoshi
Yamasaki1,3(Received November 27, 2007; accepted December 18, 2007; published online January 17, 2008)

Electron emission current was observed from a hydrogen-terminated n-layer diamond surface of forward biased diamond p – n junction
diodes, while there was no electron emission from the same surface after
oxidization, suggesting that the phenomenon is related to negative electron affinity (NEA) of the hydrogen-terminated diamond surface. Sinceelectrons in the n-layer flow toward to the p-layer due to forward bias,
they cannot directly contribute to the emission current from the n-layer
surface. In view of our previous result that the exciton-derived photoelectron emission was observed from the NEA diamond surface by total
photoelectron yield spectroscopy, the phenomenon can be explained aselectron emission due to exciton diffusion at the forward bias.
[DOI : 10.1143/APEX.1.015004]
1 Nanotechnology Research Institute, National Institute of Advanced Industrial Science andTechnology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan
2 Sensor Materials Center, National Institute for Materials Science (NIMS), 1-1 Namiki,
Tsukuba, Ibaraki 305-0044, Japan
3 Graduate School of Pure and Applied Science, University of Tsukuba, Tsukuba, Ibaraki
305-8577, Japan* E-mail address: d.takeuchi@aist.go.jp

Seiichiro Yaginuma1,2, Kenji Itaka2,3, Masamitsu Haemori4, Masao
Katayama1,3, Keiji Ueno5, Tsuyoshi Ohnishi6, Mikk Lippmaa6, Yuji
Matsumoto1,3, and Hideomi Koinuma2,3,4,*(Received November 30, 2007; accepted December 18, 2007; published online January 17, 2008)

The observation of reflection high energy electron diffraction (RHEED)
oscillations has been proved to be a key to open the nano-world ofmaterials, since it definitely verifies that the film growth proceeds inlayer-by-layer mode with each layer thickness controllable by simply
counting the number of oscillations. This enabled the fabrication of
nano-engineered hetero-junctions and devices as commonly practiced
for conventional semiconductors and metals. Here we report on the firstobservation of clear RHEED intensity oscillation in thin film fabrication ofa π-conjugated molecular solid. The observation has been achieved bycoupling a novel deposition method using a continuous-wave infraredlaser for evaporation and a high sensitive RHEED detector, in addition to
the combinatorial optimization of film deposition parameters that facilitated our preceding first success in the layer-by-layer growth of oxidethin films. Some details of system design and experimental conditions arepresented to discuss the key factors for atomically controlled film growthof molecular solids. [DOI : 10.1143/APEX.1.015005]
1 Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midoriku, Yokohama 226-8503, Japan
2 Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa,
Chiba 277-8568, Japan
3 CREST, Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama
332-0012, Japan
4 National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan
5 Department of Chemistry, Saitama University, 255 Shimo-Okubo, Sakura-ku, Saitama
338-8570, Japan
6 Institute for Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa,
Chiba 277-8581, Japan* E-mail address: koinuma@k.u-tokyo.ac.jp

Appl. Phys. Express Vol.1, No.1 (2008) 015006

Selective-Area Growth of GaN Nanocolumns
on Si(111) Substrates Using Nitrided Al
Nanopatterns by RF-Plasma-Assisted
Molecular-Beam Epitaxy
Shunsuke Ishizawa1,2, Katsumi Kishino1,2,*, and Akihiko Kikuchi1,2(Received December 5, 2007; accepted December 9, 2007; published online January 17, 2008)

The selective-area growth of GaN nanocolumns using predeposited
Al nanopatterns (a 300-nm-period triangular lattice of 85-nm-diameter
Al nanodots) on Si(111) substrates by rf-plasma-assisted molecular-beam
epitaxy (rf-MBE) was demonstrated. GaN nanocolumns were grown at
the edge of each nitrided Al dot after nitridation, forming a nanotubular
structure in the growth temperature range from 941 to 966 °C. The
size fluctuation of the sidewall thickness in the nanotubular structure
was less than that of the diameters of nanocolumns grown on the Si
surface outside the nitrided Al nanopatterns. At a high growth temperature of 966 °C, nanocolumn growth on the Si surface was completely
suppressed. [DOI : 10.1143/APEX.1.015006]
1 Department of Electrical and Electronics Engineering, Sophia University, Tokyo 102-8554,
Japan
2 CREST, Japan Science and Technology Agency, Saitama 332-0021, Japan* E-mail address: kishino@katsumi.ee.sophia.ac.jp

JSAP International   No.18 (July 2008)        19Appl. Phys. Express Vol.1, No.1 (2008) 015007

Appl. Phys. Express Vol.1, No.2 (2008) 021102

Thermal Stability of Giant Thermoelectric
Seebeck Coefficient for SrTiO3/SrTi0.8Nb0.2O3
Superlattices at 900K

Improvement of Al-Polar AlN Layer Quality by
Three-Stage Flow-Modulation Metalorganic
Chemical Vapor Deposition

Kyu Hyoung Lee1,*, Yoriko Mune2, Hiromichi Ohta1,2,**, and Kunihito
Koumoto1,2

Misaichi Takeuchi1,2,3,*, Shin Ooishi2, Takumi Ohtsuka2, Tomohiro
Maegawa2, Takahiro Koyama4, Shigefusa F. Chichibu4, and Yoshinobu
Aoyagi1,2,3(Received December 5, 2007; accepted December 15, 2007; published online January 17, 2008)(Received December 10, 2007; accepted January 9, 2008; published online February 1, 2008)

Herein we report the carrier transport properties of [(SrTiO3)x /(SrTi0.8Nb0.2O3)1]20 (x=0 – 50) superlattices at high temperatures (T=300 –
900K). Significant structural changes were not observed in the superlattices after annealing at 900K in a vacuum. The Seebeck coefficient of
the [(SrTiO3)20 / (SrTi0.8Nb0.2O3)1]20 superlattice, which was 300 µ V·K-1
at room temperature, gradually increased with temperature andreached 450 µV·K-1 at 900K, which is ~3 times larger than that of bulk
SrTi0.8Nb0.2O3. These observations provide clear evidence that the superlattice is stable and exhibits a giant Seebeck coefficient even at hightemperature. [DOI : 10.1143/APEX.1.015007]
1 CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama
332-0012, Japan
2 Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8603,
Japan* Present address: Advanced Materials Laboratory, Samsung Advanced Institute of Technology,
P.O. Box 111, Suwon, Korea.
** E-mail address: h-ohta@apchem.nagoya-u.ac.jp

Appl. Phys. Express Vol.1, No.2 (2008) 021101

Study on Injection Efficiency in InGaN/GaN
Multiple Quantum Wells Blue Light Emitting
DiodesLai Wang, Jiaxing Wang, Hongtao Li, Guangyi Xi, Yang Jiang, Wei
Zhao, Yanjun Han, and Yi Luo*

(Received December 6, 2007; accepted December 28, 2007; published online January 25, 2008)

The dependence of the electrical efficiency on the injection current
was studied in detail in InGaN / GaN multiple quantum wells (MQWs) blue
light emitting diodes. When the InGaN quantum well thickness increased
from 2 to 3.5nm, or the Al component in p-AlGaN changed from 0.1
to 0.2, it was found that the electrical efficiency decreased dramatically,
while a thin Mg-doped GaN layer inserted between p-AlGaN and MQWs
with optimized Mg concentration can enhance the electrical efficiency
effectively. Analysis shows that the injection efficiency was dramaticallyaffected by the interface states due to the strong stress at the interface
between p-AlGaN blocking layer and MQWs active region and the capability of electrons arriving at the interface.
[DOI : 10.1143/APEX.1.021101]
State Key Laboratory on Integrated Optoelectronics/Tsinghua National Laboratory for
Information Science and Technology, Department of Electronic Engineering, Tsinghua University,
Beijing 100084, P. R. China* E-mail address: luoy@tsinghua.edu.cn

Improvement of Al-polar AlN layer quality was accomplished bythree-stage flow-modulation metalorganic chemical vapor deposition(FM-MOCVD). In this method, the unit of the FM-MOCVD sequence wascomposed of three stages; Stage I for simultaneous source supply, StageII for trimethylaluminum supply, and Stage III for ammonia supply, whichwere cyclically repeated. The AlN quality revealed by X-ray diffraction
strongly depended on the time of Stage I. A growth model was proposedconsidering the surface coverage of the islands nucleated during Stage
I. Exciton fine structures were eventually observed by low-temperature
cathodoluminescence reflecting the tremendously improved crystalline
quality. [DOI : 10.1143/APEX.1.021102]
1 Nanoscience Development and Support Team, RIKEN, 2-1 Hirosawa, Wako, Saitama
351-0198, Japan
2 Department of Electronics and Applied Physics, Tokyo Institute of Technology, 4259
Nagatsuta, Midori-ku, Yokohama 226-8503, Japan
3 Ritsumeikan University, 1-1-1 Noji-Higashi, Kusatsu, Shiga 525-8577, Japan
4 Center for Advanced Nitride Technology (CANTech), Institute of Multidisciplinary Research
for Advanced Materials (IMRAM), Tohoku University, 2-1-1 Katahira, Aoba, Sendai
980-8577, Japan* E-mail address: Misa.Takeuchi@riken.jp

Appl. Phys. Express Vol.1, No.2 (2008) 021103

AlGaN/GaN Heterostructure Field-EffectTransistors on 4H-SiC Substrates with CurrentGain Cutoff Frequency of 190GHz
Masataka Higashiwaki1,*, Takashi Mimura1,2, and Toshiaki Matsui1(Received December 26, 2007; accepted December 28, 2007; published online February 1, 2008)

We report on state-of-the-art AlGaN/GaN heterostructure fieldeffect transistor (HFET) technology in the scope of millimeter-wave applications. 60-nm-long-gate HFETs having 4- and 6-nm-thick Al0.4Ga0.6N
barrier layers and SiN passivation layers formed by catalytic chemical
vapor deposition (Cat-CVD) were fabricated on 4H-SiC substrates. Bothstructures had low sheet resistances of 200 – 220Ω / sq that were due tonot only high mobilities of 1900 – 2000cm2/(V·s) but also high electron
densities of (1.4–1.7)×1013cm-2, which were provided by the high-Alcomposition barrier layers and the Cat-CVD SiN. The devices with the 4and 6-nm-thick barriers had maximum drain current densities of 1.4 and1.6A/mm and peak extrinsic transconductances of 448 and 424mS/mm,
respectively. Maximum fT and fmax reached 190 and 251GHz, respectively. [DOI : 10.1143/APEX.1.021103]
1 National Institute of Information and Communications Technology, 4-2-1 Nukui-Kitamachi,
Koganei, Tokyo 184-8795, Japan
2 Fujitsu Laboratories Ltd., 10-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0197, Japan* Present address: Department of Electrical and Computer Engineering, University ofCalifornia, Santa Barbara, Santa Barbara, CA 93106, U.S.A.
E-mail address: mhigashi@ece.ucsb.edu

20        JSAP International   No.18 (July 2008)

Applied Physics Express

Appl. Phys. Express Vol.1, No.2 (2008) 021104

Appl. Phys. Express Vol.1, No.2 (2008) 021301

GaN-Based Trench Gate Metal Oxide
Semiconductor Field-Effect Transistor
Fabricated with Novel Wet Etching

Tunnel Magnetoresistance Effect in Magnetic
Tunnel Junctions Using a Co2MnSi(110)Electrode

Masahito Kodama*, Masahiro Sugimoto1, Eiko Hayashi, Narumasa
Soejima, Osamu Ishiguro, Masakazu Kanechika, Kenji Itoh, Hiroyuki
Ueda, Tsutomu Uesugi, and Tetsu Kachi

Masashi Hattori, Yuya Sakuraba, Mikihiko Oogane, Yasuo Ando, andTerunobu Miyazaki(Received December 20, 2007; accepted December 28, 2007; published online February 1, 2008)(Received December 21, 2007; accepted January 24, 2008; published online February 15, 2008)

A novel method for fabricating trench structures on GaN was–developed. A smooth non-polar (1100) plane was obtained by wet
etching using tetramethylammonium hydroxide (TMAH) as the etchant.
–
A U-shape trench with the (1100) plane side walls was formed withdry etching and the TMAH wet etching. A U-shape trench gate metaloxide semiconductor field-effect transistor (MOSFET) was also fabricated using the novel etching technology. This device has the excellent
normally-off operation of drain current – gate voltage characteristics withthe threshold voltage of 10 V. The drain breakdown voltage of 180 V
was obtained. The results indicate that the trench gate structure can beapplied to GaN-based transistors. [DOI : 10.1143/APEX.1.021104]

Magnetic tunnel junctions (MTJs) with half-metallic electrodes
are expected to show a large tunnel magnetoresistance (TMR) ratio,according to Julliere's model. A Co2MnSi Heusler alloy is theoretically
expected to possess a half-metallic electronic state. Experimentally, at
low temperature, Co2MnSi(100)/Al-oxide/CoFe junctions exhibited alarge TMR ratio. We fabricated MTJs with high-quality (110)-oriented
Co2MnSi electrodes and investigated the TMR effects. We obtained a
TMR ratio of about 40 % at room temperature and 120 % at 2K, respectively. However, we observed degradation of the energy gap of Co2MnSi
in the minority spin band from the conductance – voltage characteristics.
We infer that the interface of Co2MnSi(110) possesses no half-metallic
property. [DOI : 10.1143/APEX.1.021301]

Toyota Central R&D Laboratories, Inc., Nagakute-cho, Aichi 480-1192, Japan
1 Toyota Motor Corp., 543 Kirigahora, Nishihirose-cho, Toyota, Aichi 470-0309, Japan* E-mail address: kodama@mosk.tytlabs.co.jp

Department of Applied Physics, Graduate School of Engineering, Tohoku University, Aoba-ku,
Sendai 980-8579, Japan

Appl. Phys. Express Vol.1, No.2 (2008) 021201

Epitaxial Lift-Off of InGaAs/InAlAs
Metamorphic High Electron Mobility
Heterostructures and Their van der Waals
Bonding on AlN Ceramic Substrates
Yonkil Jeong, Masanori Shindo, Masashi Akabori*, and Toshi-kazu
Suzuki**Appl. Phys. Express Vol.1, No.2 (2008) 021302

Enhanced Interlayer Coupling andMagnetoresistance Ratio in Fe3Si/FeSi2
Superlattices
Kaoru Takeda, Tsuyoshi Yoshitake*, Yoshiki Sakamoto, Tetsuya Ogawa,
Daisuke Hara, Masaru Itakura, Noriyuki Kuwano, Toshinori Kajiwara1,
and Kunihito Nagayama2(Received January 8, 2008; accepted January 18, 2008; published online February 8, 2008)(Received November 28, 2007; accepted December 24, 2007; published online January 25, 2008)

We have carried out epitaxial lift-off (ELO) of In 0.57Ga 0.43 As/
In0.56Al0.44As metamorphic high electron mobility heterostructures andtheir van der Waals bonding (VWB) on AlN ceramic substrates. Usinga metamorphic heterostructure with an AlAs sacrificial layer and an
InGaAs graded buffer grown on GaAs(001), thin film Hall-bar devices
on AlN ceramic substrates were successfully fabricated by ELO and
VWB. The Hall-bar devices exhibit very high electron mobilities, such as11000cm2/(V s) at room temperature (RT) and 84000 cm2/(V s) at 12K.
The RT mobility is the highest ever reported for ELO devices. This is thefirst report on ELO for metamorphic devices.
[DOI : 10.1143/APEX.1.021201]
Center for Nano Materials and Technology, Japan Advanced Institute of Science and Technology(JAIST), 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan* Present address: Institute of Bio- and Nanosystems (IBN-1), Research Centre Juelich, 52425
Juelich, Germany.
** E-mail address: tosikazu@jaist.ac.jp[Fe3Si / FeSi2]20 superlattices were prepared on Si(111) at an elevatedsubstrate temperature of 300°C, and the magnetoresistance ratio andinterlayer coupling strengths were enhanced by approximately 100 and
34 %, respectively, as compared to those of superlattices deposited atroom temperature. While the elevated substrate temperature degraded
the interface sharpness, the crystalline orientation and the crystallinity of
the Fe3Si layers were apparently enhanced. The latters strongly influenceon the interlayer coupling and the magnetoresistance ratio. This implies
that quantum well states are tightly formed under the well-ordered crystalline planes, and the spin diffusion lengths are improved due to theenhanced crystallinity. [DOI : 10.1143/APEX.1.021302]
Department of Applied Science for Electronics and Materials, Kyushu University, 6-1 Kasuga,
Fukuoka 816-8580, Japan
1 Department of Electrical Engineering, Fukuoka Institute of Technology, Higashi-ku, Fukuoka
811-0295, Japan
2 Department of Aeronautics, Kyushu University, Nishi-ku, Fukuoka 819-0395, Japan* E-mail address: yoshitake@asem.kyushu-u.ac.jp

JSAP International   No.18 (July 2008)        21Appl. Phys. Express Vol.1, No.2 (2008) 021401

Appl. Phys. Express Vol.1, No.2 (2008) 021403

Quantitative Evaluation of Silicon
Displacement Induced by Arsenic Implantation
Using Silicon Isotope Superlattices

Improved Room-Temperature 1.6 µm
Electroluminescence from p-Si/β-FeSi2/n-Si
Double Heterostructures Light-Emitting
DiodesYasuo Shimizu, Masashi Uematsu, Kohei M. Itoh*, Akio Takano1,
Kentarou Sawano2, and Yasuhiro Shiraki2(Received November 21, 2007; accepted December 28, 2007; published online January 25, 2008)

We established a new method for evaluating quantitatively thesilicon atomic displacement as a function of the depth from the surface
induced by arsenic implantation into a silicon wafer. A simulation basedon a convolution integral was developed successfully to reproduce theexperimental depth profiles of isotopes in the arsenic-implanted 28Si / 30Si
isotope superlattices, from which the average distance of the silicondisplacements due to the collisions with implanted arsenic is obtained.
We show that it takes the average displacement of ~0.5nm to make thestructure appear amorphous by transmission electron microscopy.
[DOI : 10.1143/APEX.1.021401]
Department of Applied Physics and Physico-Informatics, Keio University, 3-14-1 Hiyoshi,
Kohoku-ku, Yokohama 223-8522, Japan
1 NTT Advanced Technology Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa
243-0124, Japan
2 Research Center for Silicon Nano-Science, Advanced Research Laboratories, Musashi
Institute of Technology, 8-15-1 Todoroki, Setagaya-ku, Tokyo 158-0082, Japan* E-mail address: kitoh@appi.keio.ac.jp

Appl. Phys. Express Vol.1, No.2 (2008) 021402

Room-temperature Transport Properties ofHigh Drift Mobility Two-dimensional Electron
Gas Confined in a Strained Si Quantum Well
Maksym Myronov, Kentarou Sawano, Kohei M. Itoh1, and Yasuhiro
Shiraki(Received December 1, 2007; accepted December 18, 2007; published online January 25, 2008)

The drift mobility, carrier density and conductivity of the two-dimensional electron gas (2DEG) confined in the tensilely strained 15 nm Si
quantum well (QW) of SiGe heterostructures were obtained by mobility
spectrum analysis at room-temperature. The highest 2DEG drift mobilityof 2900 cm2 V-1s-1 with carrier density of 1 × 1011cm-2 were observedin the Si QW with -0.9 % tensile strain. However, the increase of strain
up to -1.08 % resulted in the decline of 2DEG drift mobility down to2670 cm2,V-1s-1 and the pronounced increase of carrier density up to
4.4 × 1011cm-2. Nevertheless, the pronounced enhancement of 2DEG
conductivity was observed. [DOI : 10.1143/APEX.1.021402]
Advanced Research Laboratories, Musashi Institute of Technology, 8-15-1 Todoroki, Setagayaku, Tokyo158-0082, Japan
1 Department of Applied Physics and Physico-Informatics, Keio University, Yokohama
223-8522, Japan

Mitsushi Suzuno, Shigemitsu Murase, Tomoaki Koizumi, and Takashi
Suemasu(Received January 21, 2008; accepted January 27, 2008; published online February 15, 2008)

We have epitaxially grown p-Si / β-FeSi2 / n-Si double heterostructures
light-emitting diodes (LEDs) on Si(111) substrates by molecular-beam
epitaxy. The 1.6 µm electroluminescence intensity measured at room
temperature (RT) was improved significantly for LEDs constructed using
a thick β-FeSi2 active layer (190nm) embedded in heavily-doped Si p – ndiodes formed on floating-zone Si(111) substrates. The external quantum
efficiency was increased up to approximately 0.02 % at RT.
[DOI : 10.1143/APEX.1.021403]
Institute of Applied Physics, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba, Ibaraki 305-8573,
Japan

Appl. Phys. Express Vol.1, No.2 (2008) 021501

Un-stability of Sputtered Ge2Sb2Te5 Films inElectrical Phase Changes
Akira Saitoh, Toshiaki Donuma, and Keiji Tanaka(Received December 11, 2007; accepted December 22, 2007; published online January 25, 2008)

Microscopic structures of amorphous Ge2Sb2Te5 films, electricallyphase-changed using co-planar electrodes, have been studied throughelectrical and structural investigations. Microscope images show a structured phase-change region consisting of a narrow channel, banks on
both sides, and rough peripheral regions. The room-temperature resistivity is ~10-3Ω·cm, which has a metallic temperature dependence.
Micro-Raman scattering spectra at the channel and the bank exhibit
peaks due to crystalline Te and tellurides. X-ray diffraction patterns fromthe films, which contain many channels, present crystalline peaks ascribable to cubic GeTe and other compounds. These observations suggestthat the Ge2Sb2Te5 melt is liable to phase-separate under electrical selfheating. [DOI : 10.1143/APEX.1.021501]
Department of Applied Physics, Graduate School of Engineering, Hokkaido University, Sapporo
060-8628, Japan

Appl. Phys. Express Vol.1, No.2 (2008) 021701

Improvement of Superconductive Propertiesof Mesoscopic Nb Wires by Ti Passivation
LayersKohei Ohnishi1, Takashi Kimura1,2, and Yoshichika Otani1,2(Received December 17, 2007; accepted December 28, 2007; published online February 1, 2008)

We have investigated superconductive properties of nano-scale
Nb wires fabricated by a simple lift-off process with magnetron sputtering. The superconductive properties of the Nb wires were remarkably improved by employing highly plasma resistant electron-beam resist
ZEP520A combined with a thin Ti passivation layer. This optimized fabrication process yielded a 300-nm-wide Nb wire with the same transition
temperature as that of the reference Nb film. Thereby, a highly transparent Nb/Cu junction was successfully fabricated.
[DOI : 10.1143/APEX.1.021701]
1 Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba
277-8581, Japan
2 Frontier Research System, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan

22        JSAP International   No.18 (July 2008)

Applied Physics Express

Appl. Phys. Express Vol.1, No.2 (2008) 021702

Appl. Phys. Express Vol.1, No.2 (2008) 021802

MgB2 Thin Films Fabricated by a Precursor
and Post-annealing Method Have a High Jc in
High Magnetic Fields

Improvement of Hole Mobility in Organic
Field-Effect Transistors Based on Octylsubstituted Oligo-p-phenylenevinylene
by Thermal Treatment at Smectic Liquid
Crystalline Phase

Akiyoshi Matsumoto, Yuki Kobayashi, Ken-ichiro Takahashi, Hiroaki
Kumakura, and Hitoshi Kitaguchi(Received December 26, 2007; accepted January 15, 2008; published online February 1, 2008)

The critical current densities (Jc) of MgB2 thin films deposited on
α-Al2O3 fabricated by a precursor and post-annealing process have been
investigated in high magnetic fields of up to 30T. Jc values of 2.8×105,
3.0×104, and 3.7×103A/cm2 were obtained at 4.2K in external magnetic
fields of 10, 20, and 26T respectively, applied parallel to the film surface.
These values were comparable to those seen for Nb3Sn in fields up to
18T, and surpassed them in fields over 18T. The superconducting transition temperature was Tconset=29.6K and Tczero=28.5K. Grain connectivity was estimated to be 38.4 %. The Hc2(0) estimated from the resistivity measurements was 45 T. Transmission electron microscope (TEM)
observations of the microstructures suggested that grains 10 – 20 nm
in size exist that show no epitaxial growth relationship to the sapphire
substrate. Jc enhancements in fields up to ~26T are due to the strong
grain boundary pinning associated with the small grains and the small
size of MgO precipitates. [DOI : 10.1143/APEX.1.021702]
National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan

Hiroaki Nakamura*, Masatoshi Saito, Tadashi Kusumoto, Takeshi
Yasuda1,2, and Tetsuo Tsutsui1(Received December 7, 2007; accepted December 15, 2007; published online January 25, 2008)

Organic field-effect transistors based on octyl-subustituted oligo-pphenylenevinylene have been studied. We have succeeded in improving
field-effect hole mobilities by thermal treatment at liquid crystalline phasecharacterized as a highly ordered smectic phase. The field-effect mobilityof the device as vacuum-evaporated was calculated to be 6.9 × 10-3cm2
V-1 s-1 whereas the mobility was enhanced to 1.7 × 10-1cm2 V-1 s-1 after
annealing the device at 100°C for 12h. From the surface morphologyof the films observed by using atomic force microscope, the enhancement is found to be attributed to reduction of defect density in the film
because of the thermal movement of liquid-crystal molecules. [DOI :10.1143/APEX.1.021802]
Central Research Laboratories, Idemitsu Kosan Co., Ltd., Sodegaura, Chiba 299-0293, Japan
1 Department of Applied Science for Electronics and Materials, Graduate School ofEngineering Sciences and Institute for Material Chemistry and Engineering, Kyushu
University, Kasuga, Fukuoka 816-8580, Japan
2 PRESTO, Japan Science and Technology Agency, Chiyoda-ku, Tokyo 102-0075, Japan* E-mail address: hiroaki.nakamura@si.idemitsu.co.jp

Appl. Phys. Express Vol.1, No.2 (2008) 021801

Characterization of Depletion Layer using
Photoluminescence Technique
Vipul Singh*, Anil K. Thakur, Shyam S. Pandey, Wataru Takashima, andKeiichi Kaneto(Received November 19, 2007; accepted December 18, 2007; published online January 25, 2008)

The depletion layer formed at the interface of aluminum (Al) withpoly(3-hexylthiophene-2, 5-diyl) (P3HT) has been studied, using the bias
dependent photoluminescence (PL) spectra in indium tin oxide (ITO)/
P3HT/Al sandwiched cells. A quenching in the PL intensity has been
observed under the reverse bias conditions, which has been attributed tothe increase in the depletion layer width. A direct relationship between
the depletion layer width and the PL quenching has been derived andexplained. [DOI : 10.1143/APEX.1.021801]
Graduate School of Life Sciences and Systems Engineering, Kyushu Institute of Technology, 2-4
Hibikino, Wakamatsu-ku, Kitakyushu 808-0196, Japan* E-mail address: vipulsingh79@gmail.com

Appl. Phys. Express Vol.1, No.2 (2008) 021803

Complementary Two-input NAND Gates with
Low-voltage-operating Organic Transistors on
Plastic Substrates
Jong Ho Na1,*, Masatoshi Kitamura2, and Yasuhiko Arakawa1,2(Received November 19, 2007; accepted January 9, 2008; published online February 1, 2008)

We fabricated two-input NAND gates composed of p-channel pentacene and n-channel C60 transistors. The logic devices were prepared on
flexible polymer substrates through a shadow mask process. Correct
NAND logic functionality was demonstrated at a wide voltage rangeof 2 – 7V. From voltage transfer characteristics of the NAND gates, we
obtained impressive signal gains up to 120 and large noise margins in
the given voltage range. [DOI : 10.1143/APEX.1.021803]
1 Research Center for Advanced Science and Technology, University of Tokyo, 4-6-1 Komaba,
Meguro-ku, Tokyo 153-8904, Japan
2 Institute for Nano Quantum Information Electronics, University of Tokyo, 4-6-1 Komaba,
Meguro-ku, Tokyo 153-8904, Japan* E-mail address: pions@iis.u-tokyo.ac.jp

JSAP International   No.18 (July 2008)        23Appl. Phys. Express Vol.1, No.2 (2008) 021804

Appl. Phys. Express Vol.1, No.2 (2008) 022001

Whitening of Polymer Light-Emitting Diodes
by Dispersing Vapor of an Orange Fluorescent
Dye into a Blue-Emitting Polymer Film

Waveguide-Integrated Si Nano-Photodiodewith Surface-Plasmon Antenna and its
Application to On-chip Optical ClockDistribution

Toshiko Mizokuro*, Claire Heck, Nobutaka Tanigaki, Takashi Hiraga, andNorio Tanaka1(Received December 28, 2007; accepted January 11, 2008; published online February 1, 2008)

Whitening of polymer light-emitting diodes (PLEDs) based on theblue-emitting poly(9,9-dioctylfluorene) (PDOF) films was possible bydispersing vapor of an orange fluorescent dye 4-(dicyanomethylene)2-methyl-6-(4-dimethylaminostyryl)-4H -pyran (DCM) into the film bymeans of the solution-free vapor transportation method (VTM). Devices
prepared with this method showed good color stability with bias voltage
increase, while those formed with conventional spin-coating, where dyes
and polymers were mixed in a solution (solution-mixed), showed color
change from yellow to white-yellow. The maximum luminance of the
PLED formed by the VTM was higher than that formed by conventional
spin-coating process. [DOI : 10.1143/APEX.1.021804]
Photonics Research Institute, National Institute of Advanced Industrial Science and Technology,
1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, Japan
1 Dainichiseika Color and Chemicals Manufacturing Co., Ltd., 1-9-4 Horinouchi, Adachi-ku,
Tokyo 123-8555, Japan* E-mail address: chem42@ni.aist.go.jp

Appl. Phys. Express Vol.1, No.2 (2008) 021805

Highly Efficient Phosphorescent Organic
Light-Emitting Diodes Using Alkyl-Substituted
Iridium Complexes as a Solution-Processible
Host Material
Toshimitsu Tsuzuki* and Shizuo Tokito(Received January 11, 2008; accepted January 24, 2008; published online February 15, 2008)

We fabricated highly efficient organic light-emitting diodes (OLEDs)
using the solution processible iridium complexes which have long alkyl
or cycloalkyl substituents in an ancillary ligand as a host material and ared phosphorescent iridium complex as an emitting guest by spin coating
method. The OLEDs emitted red phosphorescence from the guest andthe luminance reached around 10,000cd/m2. The efficiency of the OLED
improved after we added an electron transport material (ETM) to theemitting layer. The OLED using a mixture of the alkyl substituted iridium
complex and ETM as the host showed an external quantum efficiency of
10 %. [DOI : 10.1143/APEX.1.021805]
Science and Technical Research Laboratories, NHK, Setagaya-ku, Tokyo 157-8510, Japan* E-mail address: tsuzuki.t-hq@nhk.or.jp

24        JSAP International   No.18 (July 2008)

Junichi Fujikata*, Koichi Nose, Jun Ushida, Kenichi Nishi, Masao
Kinoshita, Takanori Shimizu, Toshihide Ueno, Daisuke Okamoto, Akiko
Gomyo, Masayuki Mizuno, Tai Tsuchizawa1, Toshifumi Watanabe1, Koji
Yamada1, Seiichi Itabashi1, and Keishi Ohashi(Received November 21, 2007; accepted December 24, 2007; published online January 25, 2008)

We developed a waveguide-integrated Si nano-photodiode (PD) witha surface plasmon (SP) antenna for on-chip optical clock distribution. Theinterfacial periodic nano-scale metal – semiconductor – metal Schottky
electrodes were shown to function as an SP optical antenna and also as
an optical coupler between a SiON waveguide and a very thin Si-absorption layer. Furthermore, a very high speed response of 17ps as well as
enhanced photoresponsivity was achieved for a 10-µm coupling length.
By using this technology, we fabricated a prototype of a large-scaleintegration (LSI) on-chip optical clock system and demonstrated 5GHz of
optical clock circuit operation connected with a 4-branching H-tree structure. [DOI : 10.1143/APEX.1.022001]
MIRAI-Selete, 34 Miyukigaoka, Tsukuba, Ibaraki 305-8501, Japan
1 NTT Microsystem Integration Labs., 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa
243-0198, Japan* E-mail address: fujikata.jyunichi@selete.co.jp

Appl. Phys. Express Vol.1, No.2 (2008) 022002

Semiconductor Waveguide Optical Isolator
Incorporating Ferromagnetic Epitaxial MnSb
for High Temperature Operation
Tomohiro Amemiya*, Yusuke Ogawa1, Hiromasa Shimizu2, Hiro
Munekata1, and Yoshiaki Nakano**(Received November 26, 2007; accepted December 9, 2007; published online January 25, 2008)

A 1.5-µ m nonreciprocal-loss waveguide optical isolator having
improved transverse-magnetic-mode (TM-mode) isolation ratio wasdeveloped. The device consisted of an InGaAlAs/InP semiconductor
optical amplifier waveguide covered with a ferromagnetic epitaxial MnSb
layer. Because of the high Curie temperature (Tc = 314 °C) and strong
magneto-optical effect of MnSb, the nonreciprocal propagation of
11 – 12dB/mm has been obtained at least up to 70°C.
[DOI : 10.1143/APEX.1.022002]
Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba,
Meguro-ku, Tokyo 153-8904, Japan
1 Imaging Science and Engineering Laboratory, Tokyo Institute of Technology, 4259-G2-13
Nagatsuta, Midori-ku, Yokohama 226-8502, Japan
2 Department of Electrical and Electronic Engineering, Tokyo University of Agriculture andTechnology, 2-24-16 Nakacho, Koganei, Tokyo 184-8588, Japan* E-mail address: ametomo@hotaka.t.u-tokyo.ac.jp** E-mail address: nakano@ee.t.u-tokyo.ac.jp

Applied Physics Express

Appl. Phys. Express Vol.1, No.2 (2008) 022003

Appl. Phys. Express Vol.1, No.2 (2008) 022005

New Precise Fabrication Technology for
Lenticular Lens Sheet with Black Stripe
Patterns by Using Photo-Sensitive Material
with Surface Modifier

Generation of Periodic Sawtooth Optical
Intensity by Phase-Shifting Mask

Atsushi Nagasawa*, Katsuya Fujisawa1, and Toshiyuki Watanabe2(Received December 6, 2007; accepted December 22, 2007; published online January 25, 2008)

We have developed a new precise fabrication technology of alenticular lens sheet with black stripe patterns for a rear-projection television. The black stripe patterns have to be accurately aligned to cylindrical lenses on the lenticular lens sheet and be able to absorb ambient
light. Our proposed technology utilized a photo-sensitive material with asurface modifier which controls surface free energy for surface modification. Using this material, we could obtain two patterned areas which had
different surface free energies. Furthermore, fabrication of black stripe
patterns on the lenticular lens sheet was carried out by a self-alignment
method. This lenticular lens sheet with black stripe patterns had similar
optical properties compared with a conventional one.
[DOI : 10.1143/APEX.1.022003]
Technology Research Association for Advanced Display Materials (TRADIM), 2-24-16
Nakamachi, Koganei, Tokyo 184-0012, Japan
1 Kuraray Co., Ltd., 41 Miyukigaoka, Tsukuba, Ibaraki 305-0841, Japan
2 Department of Organic and Polymer Materials Chemistry, Tokyo University of Agriculture
and Technology, 2-24-16 Nakamachi, Koganei, Tokyo 184-0012, Japan* E-mail address: a.nagasawa@tradim.or.jp

Appl. Phys. Express Vol.1, No.2 (2008) 022004

Single-Mode Vertical-Cavity Surface-Emitting
Lasers with a Deep-Etched Half-Ring-Shaped
Holey Structure
Hung-Pin D. Yang, Fang-I Lai1, and Jim Y. Chi(Received December 10, 2007; accepted January 5, 2008; published online January 25, 2008)

A single-mode oxide-confined vertical-cavity surface-emitting laser(VCSEL) with deeply-etched half-ring-shaped holey structure for fiberoptic applications is demonstrated. Single fundamental mode continuous-wave output power of 2.6mW has been achieved in the 850nm
range, with a threshold current of approximately 1 mA. Side-mode
suppression ratio (SMSR) larger than 26dB has been measured. Contrary
to the previously reported surface relief methods, the deep-etched(approximately 2.2 µm in depth) holey structure in this paper provides
another approach to achieve single-mode operation of the VCSEL with alarger oxide aperture. [DOI : 10.1143/APEX.1.022004]

Shogo Ura*, Kenji Kintaka1, Hideyuki Awazu, Kenzo Nishio, Yasuhiro
Awatsuji, and Junji Nishii2(Received December 19, 2007; accepted January 11, 2008; published online February 1, 2008)

A new simple interference exposure method using a phase-shiftingmask was discussed on the basis of Fourier synthesis for fabricating
blazed gratings. Phase-shifting mask was designed with 244nm exposure-light wavelength to launch multiple diffraction beams so that resultant interference pattern fit to required optical intensity profile. Finesurface-relief pattern on SiO2 mask for 3-µm-period sawtooth opticalintensity profile was fabricated by electron-beam direct-writing lithography with 30nm scanning step and relief height of 65nm. Sawtoothlike intensity profile was demonstrated with theoretically predictedinterference visibility. [DOI : 10.1143/APEX.1.022005]
Department of Electronics, Graduate School of Science and Technology, Kyoto Institute ofTechnology, Kyoto 606-8585, Japan
1 Photonics Research Institute, National Institute of Advanced Industrial Science andTechnology, Tsukuba, Ibaraki 305-8568, Japan
2 Photonics Research Institute, National Institute of Advanced Industrial Science andTechnology, Ikeda, Osaka 563-8577, Japan* E-mail address: ura@kit.ac.jp

Appl. Phys. Express Vol.1, No.2 (2008) 022006

Three-Dimensional Profiling of Refractive
Index Distribution inside Transparent
Materials by Use of Nonresonant Four-Wave
Mixing Microscopy
Keisuke Isobe, Takehito Kawasumi, Takayuki Tamaki, Shogo Kataoka,
Yasuyuki Ozeki, and Kazuyoshi Itoh
(Received December 10, 2007; accepted January 15, 2008; published online February 8, 2008)

We propose that four-wave mixing (FWM) microscopy can beapplied to three-dimensional mapping of refractive index (RI) structure
inside transparent samples. We derive an analytical relationship between
the RI and the intensity of the FWM signal that is due to nonresonant optical nonlinearity. By using the relationship, the RI profile can bedirectly and quantitatively obtained from the intensity distribution of the
FWM signal. We experimentally demonstrate the RI profiling of a phasegrating fabricated in a non-alkali glass.
[DOI : 10.1143/APEX.1.022006]
Department of Material and Life Science, Graduate School of Engineering, Osaka University,
2-1 Yamadaoka, Suita, Osaka 565-0871, Japan

Electronics and Optoelectronics Research Laboratories, Industrial Technology Research Institute,
Chutung 31015, Hsinchu, Taiwan 31015, R.O.C.
1 Department of Electrical Engineering, Yuan Ze University, Chung-Li, Taiwan 32003, R.O.C.

JSAP International   No.18 (July 2008)        25Appl. Phys. Express Vol.1, No.2 (2008) 022007

Appl. Phys. Express Vol.1, No.2 (2008) 022009

Generation of High Efficiency 2 µm Laser
Pulse from a Periodically Poled 5mol % MgODoped LiNbO3 Optical Parametric Oscillator

Octave Spanning High Quality Super
Continuum Generation Using 10nJ and 104fs
High Energy Ultrashort Soliton Pulse

Ravi Bhushan*, Hidetsugu Yoshida, Koji Tsubakimoto, Hisanori Fujita,
Masahiro Nakatsuka, Noriaki Miyanaga, Yasukazu Izawa, Hideki
Ishizuki1, and Takunori Taira1(Received December 21, 2007; accepted January 24, 2008; published online February 15, 2008)(Received December 17, 2007; accepted January 21, 2008; published online February 8, 2008)

We report on an optical parametric oscillator (OPO) based on a large
aperture periodically poled 5 mol % MgO-doped LiNbO3 (PPMgLN). A
high average power Q-switched Nd:YAG laser operating at 1.064 µm
producing 10ns pulses at a repetition rate of 10Hz was used to pump
the OPO. Total output pulse energy of 126 mJ at 2 µ m with 62 %slope efficiency was achieved at relatively low pump power intensity.
Temperature tuning behavior of the quasi-phase matched OPO was also
observed. [DOI : 10.1143/APEX.1.022007]
Institute of Laser Engineering, Osaka University, 2-6 Yamada-oka, Suita, Osaka 565-0871,
Japan
1 Laser Research Center for Molecular Science, Institute for Molecular Science, 38
Nishigonaka, Myodaiji, Okazaki, Aichi 444-8585, Japan* E-mail address: bhushan@ile.osaka-u.ac.jp

Appl. Phys. Express Vol.1, No.2 (2008) 022008

Cylindrical Vector Laser Beam Generated by
the Use of a Photonic Crystal Mirror
Yuichi Kozawa, Shunichi Sato, Takashi Sato1, Yoshihiko Inoue1, Yasuo
Ohtera2, and Shojiro Kawakami1,3(Received December 12, 2007; accepted January 21, 2008; published online February 15, 2008)

A concentrically patterned photonic crystal mirror with polarization selectivity fabricated by the autocloning technique was used forthe generation of radially and azimuthally polarized beams from an Nd:
YAG laser cavity. By adopting the photonic crystal mirror as the output
coupler of the cavity, both radially and azimuthally polarized beams wereobtained with similar output power as that of an unpolarized beam
generated by a conventional, non-polarization-selective output coupler.
[DOI : 10.1143/APEX.1.022008]
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1
Katahira, Aoba-ku, Sendai 980-8577, Japan
1 Photonic Lattice, Inc., Aoba Incubation Square, Aramaki aza Aoba, Aoba-ku, Sendai
980-0845, Japan
2 Biomedical Engineering Research Organization, Tohoku University, 6-6-11 Aramaki aza
Aoba, Aoba-ku, Sendai 980-8579, Japan
3 Sendai Foundation of Applied Information Technology, Aoba Incubation Square, Aramaki
aza Aoba, Aoba-ku, Sendai 980-0845, Japan

26        JSAP International   No.18 (July 2008)

Norihiko Nishizawa* and Masaru Hori1

Octave spanning high quality super continuum is generated in all
fibre system. A 10nJ and 104 fs high energy ultrashort soliton pulse isgenerated from 1ps fiber chirped pulse amplification laser using large
mode area photonic crystal fibre. The conversion efficiency from 1ps
pulse into ultrashort soliton pulse is 33 %. A 1.05 – 2.20 µm over one
octave spanning high quality super continuum with ±5dB uniformity is
generated using the high energy soliton pulse and highly nonlinear fiber.
[DOI : 10.1143/APEX.1.022009]
Division of Advanced Science and Biotechnology, Graduate School of Engineering, Osaka
University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
1 Department of Electronical Engineering and Computer Science, Graduate School ofEngineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan* E-mail address: nishizawa@mls.eng.osaka-u.ac.jp

Appl. Phys. Express Vol.1, No.2 (2008) 023001

Nearly Temperature-Independent Saturation
Drain Current in a Multi-Mesa-Channel
AlGaN/GaN High Electron Mobility Transistor
Takahiro Tamura*, Junji Kotani, Seiya Kasai, and Tamotsu Hashizume**(Received December 8, 2007; accepted January 21, 2008; published online February 15, 2008)

We fabricated a multi-mesa-channel (MMC) structure by forminga periodic trench just under a gate electrode to improve the uniformityof effective electric field in the channel in an AlGaN/GaN high electron
mobility transistor (HEMT). A unique performance, i.e., a nearly temperature-independent saturation drain current, was observed in the MMC
device in a wide temperature range. A two-dimensional (2D) potential calculation indicates that the mesa-side gate effectively modulates
the potential, resulting in a field surrounding 2D electron gas. Such asurrounding-field effect and a relatively lower source access resistance
may be related to a unique current behavior in the MMC HEMT.
[DOI : 10.1143/APEX.1.023001]
Research Center for Integrated Quantum Electronics and Graduate School of Information
Science and Technology, Hokkaido University, N13, W8, Kita-ku, Sapporo 060-8628, Japan* E-mail address: tamura@rciqe.hokudai.ac.jp** E-mail address: hashi@rciqe.hokudai.ac.jp

Applied Physics Express

Appl. Phys. Express Vol.1, No.2 (2008) 024001

Appl. Phys. Express Vol.1, No.2 (2008) 024003

Coulomb Blockade Oscillations in Narrow
Corrugated Graphite Ribbons

Electrostatic Imprint Process for Glass

Hisao Miyazaki1,2, Shunsuke Odaka1,3, Takashi Sato4, Sho Tanaka4,
Hidenori Goto2,4, Akinobu Kanda2,4, Kazuhito Tsukagoshi1,2,5,*, Youiti
Ootuka4, and Yoshinobu Aoyagi1,2,3(Received November 8, 2007; accepted December 22, 2007; published online January 25, 2008)

We report Coulomb blockade oscillations in an atomically thingraphite ribbon fabricated by the micromechanical cleavage technique.
Aperiodic current oscillations as a function of the gate voltage indicate the formation of multiple Coulomb islands inside the thin graphiteribbon. We conclude that the Coulomb islands originate from puddlesof electrons and holes caused by the inhomogeneous interface between
the ribbon and the substrate. [DOI : 10.1143/APEX.1.024001]
1 RIKEN, Wako, Saitama 351-0198, Japan
2 CREST, Japan Science and Technology Agency, Kawaguchi, Saitama 332-0012, Japan
3 Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology,
Midori-ku, Yokohama 226-8502, Japan
4 Institute of Physics and Tsukuba Research Center for Interdisciplinary Materials Science,
University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan
5 National Institute of Advanced Industrial Science and Technology, Umezono, Tsukuba,
Ibaraki 305-8568, Japan* E-mail address: tsuka@riken.jp

Appl. Phys. Express Vol.1, No.2 (2008) 024002

Performance Estimation of Graphene FieldEffect Transistors Using Semiclassical Monte
Carlo Simulation
Naoki Harada*, Mari Ohfuti, and Yuji Awano(Received November 16, 2007; accepted December 28, 2007; published online February 1, 2008)

A semiclassical Monte Carlo simulation was run to estimate theperformances of a monolayer and a bilayer (with vertical electric fieldof 1V/nm applied) graphene-channel field-effect transistor (FET). The
vertical field produces a band gap of 0.16 eV and gives semiconductive properties in the bilayer graphene. Electrons in monolayer graphene
show a notable velocity overshoot of up to 7.6×107cm/s. A sub-0.1ps
transit time is also expected in a 65-nm channel device. The performanceof a bilayer graphene-channel FET is inferior to a monolayer graphene
one, but comparable with that of an InP high electron mobility transistor(HEMT). This lower performance may be attributed to the electron effective mass produced by the vertical field. [DOI : 10.1143/APEX.1.024002]

Hideki Takagi, Shin-ichi Miyazawa, Masaharu Takahashi, and Ryutaro
Maeda(Received November 27, 2007; accepted January 5, 2008; published online February 1, 2008)

In usual thermal imprint process, mold patterns are transferred byapplying mechanical pressures at elevated temperatures. We have developed a new imprint process for glass, which utilizes electrostatic force asa driving force for deformation. In the method, high dc voltage is applied
between a mold and a glass specimen so that the mold becomes ananode. This method enables glass forming at lower temperatures withsmaller mechanical force compared to usual thermal imprint process. In
addition, this method is suitable for small patterns less than 1 µm. It is
expected that this method realizes large-area and high-efficiency nanoforming process for glass. [DOI : 10.1143/APEX.1.024003]
Advanced Manufacturing Research Institute, National Institute of Advanced Industrial Scienceand Technology (AIST), Tsukuba, Ibaraki 305-8564, Japan

Appl. Phys. Express Vol.1, No.2 (2008) 025001

Nitrogen – Oxygen Complexes Associatedwith Shallow Thermal Donors in Silicon
Haruhiko Ono(Received December 10, 2007; accepted January 27, 2008; published online February 15, 2008)

A structural model is described for the shallow thermal donors(STDs), which typically consist of seven identical absorption peaks thatare caused by electronic transition. In the STD family, attention was paid
to the 247 cm-1 peak that appears to strongly depend on the condition of both the crystal growth and the annealing. We examined NO
configuration and the six kinds of NO+Oi configuration. Semi-empiricalmolecular orbital calculations for these complexes suggested that not
only the complex with the C2v symmetry but also the asymmetric NO+Oi
complexes could simultaneously exist in the Si crystal. We concluded thatthe 247cm-1 peak, which was highly unstable and behaved oddly during
annealing, might be the NO complex and that the other six STD peaks
might correspond to the six kinds of NO+Oi complexes.
[DOI : 10.1143/APEX.1.025001]
Kanagawa Industrial Technology Center, Ebina, Kanagawa 243-0435, Japan

Nanotechnology Research Center, Fujitsu Laboratories Ltd., Atsugi, Kanagawa 243-0197, Japan* E-mail address: harada.naoki@jp.fujitsu.com

JSAP International   No.18 (July 2008)        27Appl. Phys. Express Vol.1, No.2 (2008) 027001

Appl. Phys. Express Vol.1, No.2 (2008) 027003

Point Spread Function for the Calculationof Acid Distribution in Chemically Amplified
Resists for Extreme Ultraviolet Lithography

Extremely Small Proximity Effect in 30keV
Electron Beam Drawing with Thin Calixarene
Resist for 20 × 20nm2 Pitch Dot Arrays

Takahiro Kozawa1,2,*, Akinori Saeki1,2, and Seiichi Tagawa1,2,**Sumio Hosaka1,3,*, Zulfakri Mohamad2, Masumi Shira2, Hirotaka Sano2,
You Yin1, Akihira Miyachi3, and Hayato Sone1(Received November 15, 2007; accepted December 15, 2007; published online January 25, 2008)

The process simulator is a key technology in extreme ultraviolet(EUV) lithography, which is regarded as the ultimate in projection lithography. The requirement for the accuracy of process simulators has
become increasingly strict with the shrinkage of feature size. In chemically amplified EUV resists, acid generators decompose through a reaction with thermalized electrons (~25meV). This sensitization mechanismof EUV resists is analogous to that induced by an electron beam (EB).
However, the acid distribution in EUV resists is different from that in EB
resists because of the multispur effect, which is caused by the charged
intermediates narrowly distributed around the absorption points of EUV
photons. In this work, the authors formulate a proposed point spreadfunction for the EUV lithography process based on chemically amplified
resists. [DOI : 10.1143/APEX.1.027001]
1 The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki,
Osaka 567-0047, Japan
2 CREST, Japan Science and Technology Agency, c/o Osaka University, 8-1 Mihogaoka, Ibaraki,
Osaka 567-0047, Japan* E-mail address: kozawa@sanken.osaka-u.ac.jp** E-mail address: tagawa@sanken.osaka-u.ac.jp

Appl. Phys. Express Vol.1, No.2 (2008) 027002

Hyper Rheology Measurement by Emission
and Collision of Micro-Fluid Particles
Hideaki Kutsuna and Keiji Sakai(Received December 11, 2007; accepted January 11, 2008; published online February 8, 2008)

We introduce a system to measure the mechanical properties of
fluids under high shear deformation rates of up to 106s -1. The newly
developed micro-fluid emission nozzle remarkably extended the varietyof liquids to, for example, organic solvents, strong alkalis and acids, andviscous fluids. The dynamic behavior of a fluid after the head-on collisionof the two emitted particles was observed by the stroboscopic method.
The surface tension and viscosity were determined from the resonant
frequency and decay constant of the resonant oscillation by comparison
with numerical simulation. An approximate theory to describe the largeamplitude oscillation is also presented. [DOI : 10.1143/APEX.1.027002]
Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505,
Japan(Received December 6, 2007; accepted January 21, 2008; published online February 15, 2008)

We studied proximity effect in 30keV electron beam (EB) drawing
with calixarene resist for patterned media and quantum devices. Using
about 15-nm-thick calixarene resist on Si substrate in conventional EB
drawing system, the proximity effect has been studied by forming andobserving 20-, 25-, 30-, and 40-nm-pitch resist dot arrays and measuringexposure dosage intensity distribution (EID) function. As a result, theproximity effect is negligible small due to comparing with some dot
sizes in center, side and corner of 2 µm square with 25×25nm2 pitch dot
arrays. In addition, the proximity effect parameter η in EID function isless than 0.3. It is clear that the EB drawing and calixarene resist system
is very suitable for forming ultrahigh packed dot arrays pattern. We
demonstrated 20×20nm2 pitch resist dot arrays (about 1.6Tb / in.2) witha dot diameter of about 14nm and the same size as everywhere in thepattern. [DOI : 10.1143/APEX.1.027003]
1 Department of Production Science Technology, Graduate School of Engineering, Gunma
University, 1-5-1 Tenjin, Kiryu, Gunma 376-8515, Japan
2 Department of Nano Material Systems, Graduate School of Engineering, Gunma University,
1-5-1 Tenjin, Kiryu, Gunma 376-8515, Japan
3 Advanced Technology Research Center (ATEC), Gunma University, 1-5-1 Tenjin, Kiryu,
Gunma 376-8515, Japan* E-mail address: hosaka@el.gunma-u.ac.jp

Appl. Phys. Express Vol.1, No.2 (2008) 027004

Dependence of Acid Generation Efficiency on
Molecular Structures of Acid Generators upon
Exposure to Extreme Ultraviolet Radiation
Ryo Hirose, Takahiro Kozawa*, Seiichi Tagawa**, Toshiyuki Kai1, andTsutomu Shimokawa1(Received  January 15, 2008; accepted January 24, 2008; published online February 15, 2008)

The trade-off between resolution, sensitivity, and line edge roughness (LER) is the most serious problem for the development of sub-30nm
resists based on chemical amplification. Because of this trade-off, theincrease in acid generation efficiency is essentially required for highresolution patterning with high sensitivity and low LER. In this study,
we investigated the dependences of acid generation efficiency on themolecular structure and concentration of acid generators upon exposure to extreme ultraviolet (EUV) radiation. The acid generation efficiency(the number of acid molecules generated by a single EUV photon) was
obtained within the acid generator concentration range of 0 – 30wt %for five types of ionic and nonionic acid generators.
[DOI : 10.1143/APEX.1.027004]
The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki,
Osaka 567-0047, Japan
1 JSR Corp., 100 Kawajiri-cho, Yokkaichi, Mie 510-8552, Japan* E-mail address: kozawa@sanken.osaka-u.ac.jp** E-mail address: tagawa@sanken.osaka-u.ac.jp

28        JSAP International   No.18 (July 2008)

Applied Physics Express

Appl. Phys. Express Vol.1, No.2 (2008) 028001

Appl. Phys. Express Vol.1, No.3 (2008) 031301

Longitudinal and Transverse Coupling of
the Beam Temperature Caused by the Laser
Cooling of 24Mg+

Ferroelectric Polarization Reversal by
a Magnetic Field in Multiferroic Y-type
Hexaferrite Ba2Mg2Fe12O22

Mikio Tanabe*, Takehiro Ishikawa, Masao Nakao, Hikaru Souda,
Masahiro Ikegami1, Toshiyuki Shirai1, Hiromu Tongu1, and Akira Noda1

Kouji Taniguchi, Nobuyuki Abe1, Shintaro Ohtani1, Hiroshi Umetsu1,
and Taka-hisa Arima(Received November 27, 2007; accepted December 18, 2007; published online February 1, 2008)(Received January 20, 2008; accepted February 6, 2008; published online February 29, 2008)

A laser-cooling experiment of a 40keV 24Mg+ beam was carried out
in the small laser-equipped storage ring (S-LSR). A laser co-propagatingwith the beam and an induction accelerator were utilized in the experiment. The lowest longitudinal temperature achieved in the present
experiment was 3.6K for 3 × 104 ions stored in the ring. It was foundthat the number of stored ions is related to the temperature at the final
equilibrium state of the laser cooling. This relation shows that the longitudinal temperature of the laser-cooled beam linearly couples with thetransverse one through intra-beam scattering.
[DOI : 10.1143/APEX.1.028001]

Coexistence of the ferroelectric polarization and spontaneous
magnetization has been found in Y-type hexaferrite Ba2Mg2Fe12O22.
The reversal of magnetization by a small magnetic field below ~0.02T
accompanies an electric polarization reversal through the clamping offerrimagnetic and ferroelectric domain walls. This behavior can be potentially used as a magnetically rewritable ferroelectric memory and an electrically rewritable magnetic memory. [DOI : 10.1143/APEX.1.031301]

Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
1 Advanced Research Center for Beam Science, Institute for Chemical Research, Kyoto
University, Gokasho, Uji, Kyoto 611-0011, Japan* E-mail address: tanabe@kyticr.kuicr.kyoto-u.ac.jp

Appl. Phys. Express Vol.1, No.3 (2008) 031201

Synthesis and Thermoelectric Properties ofSilicon Clathrates Sr8AlxGa16-xSi30 with theType-I and Type-VIII Structures
Kengo Kishimoto*, Naoya Ikeda, Koji Akai1, and Tsuyoshi Koyanagi(Received January 14, 2008; accepted February 21, 2008; published online March 14, 2008)

Nominal composition Sr 8 Al x Ga 16-x Si 30 (0≤ x ≤16) samples wereprepared by powder metallurgy. The samples with x=0–7 exhibited the–type-I clathrate structure (Pm3n, No.223), while the samples with x =–8–13 almost exhibited the type-VIII clathrate structure (I43m, No.217).
These samples possessed the electrical conductivities and Seebeck coefficients typical of n-type degenerated semiconductors. The results on
their thermoelectric properties indicate that the type-VIII SrAlGaSi clathrate would be a more efficient thermoelectric material than the type-I
SrAlGaSi clathrate. For example, the type-VIII Sr8Al9Ga7Si30 sample
had a maximum power factor of 11 µWcm-1 K-2 at 1000K and a room
temperature Hall mobility of 24 cm2 V-1 s-1, while those of the type-I
Sr8Al6Ga10Si30 sample were 7 µWcm-1 K-2 and 5cm2 V-1 s-1, respectively.
[DOI : 10.1143/APEX.1.031201]

Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai
980-8577, Japan
1 Department of Physics, Graduate School of Science, Tohoku University, Sendai 980-8577,
Japan

Appl. Phys. Express Vol.1, No.3 (2008) 031302

Determination of Penetration Depth ofTransverse Spin Current in Ferromagnetic
Metals by Spin Pumping
Tomohiro Taniguchi1,2, Satoshi Yakata3, Hiroshi Imamura2, and Yasuo
Ando3(Received February 7, 2008; accepted February 21, 2008; published online March 14, 2008)

Spin pumping in nonmagnetic / ferromagnetic metal multilayers is
studied both theoretically and experimentally. We show that the line
widths of the ferromagnetic resonance (FMR) spectrum depend on the
thickness of the ferromagnetic metal layers, which must not be in resonance with the oscillating magnetic field. We also show that the penetration depths of the transverse spin current in ferromagnetic metals canbe determined by analyzing the line widths of their FMR spectra. The
obtained penetration depths in NiFe, CoFe, and CoFeB were 3.7, 2.5,
and 12.0nm, respectively. [DOI : 10.1143/APEX.1.031302]
1 Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
2 Nanotechnology Research Institute (NRI), National Institute of Advanced Industrial Scienceand Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan
3 Department of Applied Physics, Graduate School of Engineering, Tohoku University, Sendai
980-8579, Japan

Graduate School of Science and Engineering, Yamaguchi University, Ube, Yamaguchi 755-8611,
Japan
1 Media and Information Technology Center, Yamaguchi University, Ube, Yamaguchi
755-8611, Japan* E-mail address: kkishi@yamaguchi-u.ac.jp

JSAP International   No.18 (July 2008)        29Appl. Phys. Express Vol.1, No.3 (2008) 031501

Appl. Phys. Express Vol.1, No.3 (2008) 031702

Microcrystalline Si1-xGex Solar Cells Exhibiting
Enhanced Infrared Response with Reduced
Absorber Thickness

Time Resolution Improvement ofSuperconducting NbN Stripline Detectors forTime-of-Flight Mass Spectrometry

Takuya Matsui1,*, Chia-Wen Chang1, Tomoyuki Takada1,2, Masao
Isomura2, Hiroyuki Fujiwara1, and Michio Kondo1

Koji Suzuki*, Shigehito Miki1, Shigetomo Shiki, Zhen Wang1, andMasataka Ohkubo(Received January 25, 2008; accepted February 14, 2008; published online March 7, 2008)(Received January 25, 2008; accepted February 14, 2008; published online March 7, 2008)

Thin film p – i – n junction solar cells incorporating hydrogenatedmicrocrystalline Si1-xGex (µc-Si1-xGex:H) absorber i layers (1 µm) have been
fabricated by plasma-enhanced chemical vapor deposition in the composition range of 0≤x≤0.35. By increasing Ge content from x=0 to 0.15 – 0.2,
short-circuit current density increases by ~5mA/cm2 with spectral sensitivities extending into the infrared wavelengths (>600 nm). However,solar cell parameters for larger Ge contents (x>0.2) are lowered by theincreased charge carrier recombination in the µc-Si1-xGex:H i layer. As aresult, a 6.3 % efficient solar cell is obtained at x=0.2, exhibiting infrared
response even higher than that of double-thickness µc-Si:H solar cells.
The solar cell shows excellent performance stability under prolonged
light soaking. [DOI : 10.1143/APEX.1.031501]

We have applied superconducting stripline detectors (SSLDs) for
time-of-flight mass spectrometry (TOF-MS) as molecule detectors. Two
SSLDs, which consist of 7-nm-thick niobium nitride (NbN) striplines withdifferent linewidths of 200 or 300nm on a MgO substrate, were fabricated to investigate the effects of kinetic inductance on time resolution. We have observed ultrafast ion detection signals with risetimesof 360 – 640ps, and successfully obtained mass spectra for a peptide,
Angiotensin I, and a protein, bovine serum albumin (BSA) at an energyof 17.5keV. It has been confirmed that the response time is governed by
the kinetic inductance of the nano-striplines.
[DOI : 10.1143/APEX.1.031702]

1 Research Center for Photovoltaics, National Institute of Advanced Industrial Science andTechnology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan
2 Department of Electrical and Electronic Engineering, Tokai University, 1117 Kitakaname,
Hiratsuka, Kanagawa 259-1292, Japan* E-mail address: t-matsui@aist.go.jp

Appl. Phys. Express Vol.1, No.3 (2008) 031701

Rare-Earth-Dependent Magnetic Anisotropy
in REBa2Cu3Oy
Atsushi Ishihara, Shigeru Horii*, Tetsuo Uchikoshi1, Tohru S. Suzuki1,
Yoshio Sakka2, Hiraku Ogino, Jun-ichi Shimoyama, and Kohji Kishio

Research Institute of Instrumentation Frontier, National Institute of Advanced Industrial Scienceand Technology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan
1 National Institute of Information and Communications Technology, Kobe 651-2492, Japan* E-mail address: suzuki-ssm@aist.go.jp

Appl. Phys. Express Vol.1, No.3 (2008) 031703

Effect of c-Axis-Correlated Disorders on the
Vortex Diagram of the Pinning State
Masafumi Namba, Satoshi Awaji, Kazuo Watanabe, Tsutomu Nojima1,
Satoru Okayasu2, Masashi Miura3, Yusuke Ichino3, Yutaka Yoshida3,
Yoshiaki Takai3, Tomoya Horide4, Paolo Mele4,5, and Kaname
Matsumoto5(Received January 24, 2008; accepted February 17, 2008; published online March 7, 2008)(Received January 24, 2008; accepted February 21, 2008; published online March 14, 2008)

We report magnetic anisotropies (Δχ) depending on rare earth (RE)element in the paramagnetic REBa2Cu3Oy (RE123) system as an important finding of magneto-scientific grain-orientation. The c-axis-oriented
RE123 powder samples using static or rotating magnetic fields were
fabricated at room temperature to clarify Δχ. Their easy axes of magnetization were mainly dominated by second-order Stevens factors, whereas|Δχ| largely depended on y and RE elements. Especially for heavy RE
elements, |Δχ| reached the order of 10-4, indicating that appropriate
choice of RE directly leads to a drastic reduction of required magnetic
fields for grain-orientation of RE123. [DOI : 10.1143/APEX.1.031701]

The introduction of the c-axis-correlated disorder is a promising technique for the improvement of the critical current density Jc for B//c of
REBa2Cu3Oy (RE123) films and tapes. In order to understand the vortex
pinning mechanism with the different variety of the c-axis-correlateddisorder, the angular dependence of Jc was measured in detail for an
Y123 film with BaZrO3 nano-rods, a Sm123 film with fine nano-particles
and edge dislocations and an Y123 film with columnar defects introduced by the heavy-ion irradiation parallel to the c-axis. We found thatthe vortex pinning state for the variety of the c-axis-correlated pinningis similar in low fields below the matching field, but it shows different
behaviors in high fields above the matching field. It is considered that theinterstitial vortices interacted with the c-axis-correlated disorders throughthe vortex interaction may play an important role for the appearance ofthe c-axis-correlated pinning behavior in a high-field region above thematching field. [DOI : 10.1143/APEX.1.031703]

Department of Applied Chemistry, University of Tokyo, Tokyo 113-8656, Japan
1 Nano Ceramics Center, National Institute for Materials and Science, Tsukuba, Ibaraki
305-0047, Japan
2 WPI Center for Materials Nanoarchitectonics, National Institute for Materials and Science,
Tsukuba, Ibaraki 305-0047, Japan* E-mail address: tholy@mail.ecc.u-tokyo.ac.jp

High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku
University, Sendai 980-8577, Japan
1 Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
2 Japan Atomic Energy Agency, Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan
3 Nagoya University, Nagoya 464-8603, Japan
4 Kyoto University, Kyoto 606-8501, Japan
5 Kyushu Institute of Technology, Kitakyushu 804-8550, Japan

30        JSAP International   No.18 (July 2008)

Applied Physics Express

Appl. Phys. Express Vol.1, No.3 (2008) 032001

Appl. Phys. Express Vol.1, No.3 (2008) 032003

Reduction of Viewing-Angle Dependent Color
Shift in a Reflective Type Cholesteric Liquid
Crystal Color Filter

Second Harmonic Generation with High
Conversion Efficiency and Wide Temperature
Tolerance by Multi-Pass Scheme

Won-Gun Jang*, Tae Won Beom1, Hao Cui1, Jong Rak Park1, Seong Jin
Hwang2, Young Jin Lim2, and Seung Hee Lee2

Tetsuro Mizushima*, Hiroyuki Furuya, Shinichi Shikii, Koichi Kusukame,
Kiminori Mizuuchi, and Kazuhisa Yamamoto(Received January 3, 2008; accepted January 24, 2008; published online February 22, 2008)(Received January 21, 2008; accepted February 17, 2008; published online March 7, 2008)

The reflective type color filter for the liquid crystal displays (LCDs)
was produced using cholesteric liquid crystal monomers whose phaseis characterized by the unique optical features of selective reflection.
Periodic micrometer scale hemi-spherical photoresist (PR) patterns wereformed on glass substrates by thermal reflow method after photolithography. Cholesteric color filter films for red, green, and blue light reflections were then produced and the viewing angle dependence was investigated and compared with that of reflected light on the non-patterned
substrates. Computer simulations using “LightTools” were also carriedout, and it was confirmed that the color shifts were much smaller on
the patterned substrates by bare eyes and Commission Internationale
de'Eclairage (CIE) chromaticity coordination analysis qualitatively.
[DOI : 10.1143/APEX.1.032001]

We proposed a multi-pass second harmonic generation scheme inwhich condensed fundamental light passed through a nonlinear crystal
many times. The multi-pass scheme was realized by using a wide periodically-poled MgO:LiNbO3, concave mirrors and condensing optics. The
total wavelength conversion efficiency of the multi-pass scheme wasincreased because non-converted fundamental light which had passed
through the nonlinear crystal was re-injected and condensed into thenonlinear crystal and converted. Moreover the total temperature tolerance of the multi passes was widened because the fundamental beam
passes had different phase-matching temperature and compensated formiss conversions of other passes. In this work, continuous-wave 5 W
green light (532nm) with 66 % conversion efficiency and wide temperature tolerance were obtained. [DOI : 10.1143/APEX.1.032003]

Korea Photonics Technology Institute, Wolchul-dong, Buk-gu, Gwangju 500-460, Korea
1 Department of Photonic Engineering, Chosun University, 375 Seosok-dong, Dong-gu,
Gwangju 501-759, Korea
2 BK-21 Polymer BIN Fusion Research Team, Research Center of Industrial Technology, Schoolof Advanced Materials Engineering, Chonbuk National University, Chonju, Chonbuk561-756, Korea* E-mail address: wgjang@kopti.re.kr

AV Core Technology Development Center, Matsushita Electric Industrial Co., Ltd., 3-1-1
Yagumo-naka-machi, Moriguchi, Osaka 570-8501, Japan* E-mail address: mizushima.tetsuro@jp.panasonic.com

Appl. Phys. Express Vol.1, No.3 (2008) 032002

Lowering Threshold by Energy Transfer
between Two Dyes in Cholesteric Liquid
Crystal Distributed Feedback Lasers
Koji Sonoyama, Yoichi Takanishi*, Ken Ishikawa, and Hideo Takezoe(Received December 7, 2007; accepted February 8, 2008; published online February 29, 2008)

Lowering lasing threshold based on the Förster-type energy transfer
process has been studied in distributed feedback (DFB) lasers of cholesteric liquid crystals (CLCs) containing two dyes. We found that the lasing
threshold in the energy transfer process was lowered to less than half ofthat in direct excitation processes. This effect is attributed to the suppression of self-absorption of a dye (acceptor). This provides a method forlowering threshold in CLC-DFB lasers containing multiple dyes particularly with a small Stokes shift. [DOI : 10.1143/APEX.1.032002]
Department of Organic and Polymeric Materials, Tokyo Institute of Technology, 2-12-1-S8-42
O-okayama, Meguro-ku, Tokyo 152-8552, Japan* Present address: Department of Physics, Kyoto University, Kitashirakawa-oiwake-cho, Sakyoku, Kyoto 606-8502, Japan.

Appl. Phys. Express Vol.1, No.3 (2008) 032004

Green Photoluminescence from GaInN
Photonic Crystals
Hitoshi Kitagawa1,2,*, Toshihide Suto1,2, Masayuki Fujita1,**, Yoshinori
Tanaka1, Takashi Asano1, and Susumu Noda1,3,***(Received December 21, 2007; accepted February 21, 2008; published online March 14, 2008)

We have investigated green-emitting GaInN two-dimensional
photonic crystals with air holes that penetrate through the active layer.
At room temperature, the observed photoluminescence intensity fromthe photonic crystal is approximately three times that of a sample withno photonic crystal structure. This is due to the low surface recombination velocity (1.4 × 103cm/s) of GaInN at the air hole edges and a higher
degree of light extraction by the diffraction effect.
[DOI : 10.1143/APEX.1.032004]
1 Department of Electronic Science and Engineering, Kyoto University, Kyotodaigaku-katsura,
Nishikyo-ku, Kyoto 615-8510, Japan
2 Process Technology DVLPMT. Center ALPS Electric Co., Ltd., Sendai 981-3208, Japan
3 Photonics and Electronics Science and Engineering Center, Kyoto University, Kyotodaigakukatsura, Nishikyo-ku, Kyoto 615-8510, Japan* E-mail address: kitagawa@qoe.kuee.kyoto-u.ac.jp** E-mail address: fujita@qoe.kuee.kyoto-u.ac.jp*** E-mail address: snoda@kuee.kyoto-u.ac.jp

JSAP International   No.18 (July 2008)        31Appl. Phys. Express Vol.1, No.3 (2008) 034001

Appl. Phys. Express Vol.1, No.3 (2008) 034003

Position-Controlled Si Nanocrystals in a
SiO2 Thin Film Using a Novel Amorphous Si
Ultra-Thin-Film “Nanomask” due to a BioNanoprocess for Low-Energy Ion Implantation

Optical and Conductive Characteristics ofMetallic Single-Wall Carbon Nanotubes withThree Basic Colors; Cyan, Magenta, andYellow

Yuji Nakama*, Shinji Nagamachi1, Jun Ohta, and Masahiro Nunoshita

Kazuhiro Yanagi*, Yasumitsu Miyata, and Hiromichi Kataura(Received January 22, 2008; accepted February 4, 2008; published online February 22, 2008)(Received February 1, 2008; accepted February 8, 2008; published online February 29, 2008)

A nano-size and position controlling technique of silicon-nanocrystal(Si-NC) assemblies in a SiO2 thin film has been investigated by using
low-energy ion implantation (0.6keV) through a novel amorphous silicon(a-Si) ultra-thin-film “nanomask”. This a-Si nanomask was developed on
the basis of a self-assembled bio-nanoprocess with proteins “ferritin”. Si
NCs were synthesized from the excess Si+ ions implanted in a SiO2 matrix
by annealing with a Nd:YAG pulsed laser. As a result, almost ordered
Si-NC assemblies with very small and uniform size (3.0±0.3nm) and interparticle separation (5 to 6nm) were obtained by the transcription of thea-Si nanomask pattern. [DOI : 10.1143/APEX.1.034001]

We present protocols to prepare high-purity metallic single-wallcarbon nanotubes (SWCNTs) with three basic colors, cyan, magenta, andyellow, through density gradient centrifugations. Addition of deoxycholate sodium salts as a co-surfactant could improve separation capability
for metallic SWCNTs in centrifugations. We applied the improved separation protocols to the SWCNTs with different average diameters (1.34, 1.0,
and 0.84nm), and obtained the metallic SWCNTs with cyan, magenta,
and yellow colors. Their optical / conductive characteristics were revealed,
and conductive color films were formed from the metallic SWCNTs.
[DOI : 10.1143/APEX.1.034003]

Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5
Takayama, Ikoma, Nara 630-0101, Japan
1 Ion Engineering Research Institute Corporation, 2-8-1 Tudayamate, Hirakata, Osaka
573-0128, Japan* E-mail address: n-yuuji@ms.naist.jp

JST/CREST, Nanotechnology Research Institute, National Institute of Advanced Industrial Scienceand Technologies (AIST), Tsukuba, Ibaraki 305-8562, Japan* E-mail address: k-yanagi@aist.go.jp

Appl. Phys. Express Vol.1, No.3 (2008) 034002

Carbon Nanotubes from a Divided Catalyst:
the Carbon Transmission Method

High-Quality Carbon Nanotube Growth at
Low Temperature by Pulse-Excited Remote
Plasma Chemical Vapor Deposition

Takeshi Hikata, Kazuhiko Hayashi, Tomoyuki Mizukoshi1, Yoshiaki
Sakurai1, Itsuo Ishigami1, Takaaki Aoki2, Toshio Seki2, and Jiro Matsuo2

Yuichi Yamazaki, Naoshi Sakuma, Masayuki Katagiri, Mariko Suzuki,
Tadashi Sakai, Shintaro Sato1, Mizuhisa Nihei1, and Yuji Awano1

Appl. Phys. Express Vol.1, No.3 (2008) 034004(Received January 23, 2008; accepted February 4, 2008; published online February 22, 2008)(Received January 24, 2008; accepted February 17, 2008; published online March 7, 2008)

We have fabricated carbon nanotubes (CNTs) using a catalyzed
growth technique that we call the carbon transmission method (CTM).
We could control independently functions for carbon source gas supply
and CNT growth by using a foil barrier (Ag) penetrated by pure Fe fibers.
CNTs grew on one end of the Fe fibers, formed from diffused carbon
that originates in carbon source gas at the other end of the fibers. Long
CNTs with length over 100 µm were obtained on the end of the Fe fibers
in the carbon transmitted side. [DOI : 10.1143/APEX.1.034002]

Carbon nanotube (CNT) growth at temperatures below 400°C by
pulse-excited remote plasma chemical vapor deposition was demonstrated. Reduction of plasma power was carried out in order to decrease
the amount of all particles, ions, electrons, and radicals. In addition,a biased plate-type screening electrode was introduced to removal of
charged particles, ions, and electrons. The negative bias below 50 V
was most effective for growth rate. High-quality CNT growth with thegrowth rate of 98 nm/min was successfully obtained at 400 °C. The
results suggest that both removal of charged particles and control of theamount of radicals are important for high-quality CNT growth at temperatures below 400°C. [DOI : 10.1143/APEX.1.034004]

Sumitomo Electric Industries, Ltd., Osaka 554-0024, Japan
1 Technology Research Institute of Osaka Prefecture, Osaka 594-1157, Japan
2 Faculty of Engineering Quantum Science and Engineering Center, Kyoto University, Kyoto
606-8501, JapanMIRAI – Selete, 1 Komukai-Toshiba-cho, Saiwai-ku, Kawasaki 212-8582, Japan
1 MIRAI – Selete, 10-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0197, Japan

32        JSAP International   No.18 (July 2008)

Applied Physics Express

Appl. Phys. Express Vol.1, No.3 (2008) 034005

Appl. Phys. Express Vol.1, No.3 (2008) 034007

Real-Time Observation of Growth of Tungsten
Oxide Nanowires with a Scanning Electron
MicroscopeInter-Layer Screening Length to Electric Fieldin Thin Graphite Film

Keigo Kasuya*, Takeshi Ooi**, Yusuke Kojima, and Masayuki Nakao(Received January 30, 2008; accepted February 14, 2008; published online March 7, 2008)

We observed the growth process of tungsten oxide nanowires inreal-time with a field emission scanning electron microscope (SEM). The
observation was performed by a new in-situ observation system designed
to perform two functions: heating of tungsten film and local supply of
O2 gas. The nanowires grew after the nucleation on the surface. Their
length extended with time keeping the direction constant. The growthrate decreased with exponential. [DOI : 10.1143/APEX.1.034005]
Department of Engineering Synthesis, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo
113-8656, Japan* Present address: Central Research Laboratory, Hitachi Ltd., 1-280 Higashi-koigakubo,
Kokubunji, Tokyo 185-8601, Japan. E-mail address: keigo.kasuya.bp@hitachi.com** Present address: Komatsu Ltd., 1200 Manda, Hiratsuka, Kanagawa 254-8567, Japan

Appl. Phys. Express Vol.1, No.3 (2008) 034006

Adsorption Properties of a Gold-Binding
Peptide Assessed by its Attachment to a
Recombinant Apoferritin Molecule
Kazutaka Ishikawa1, Kiyohito Yamada1,2, Shinya Kumagai2, KenIchi Sano3,4, Kiyotaka Shiba3,4, Ichiro Yamashita1,2,4, and Mime
Kobayashi1,4,*(Received January 10, 2008; accepted February 21, 2008; published online March 14, 2008)

The adsorption properties of a recombinant apoferritin protein fused
to a gold-binding peptide were characterized. The results of quartz
crystal microbalance measurements showed that the fusion protein preferentially adsorbs to gold surfaces. Scanning electron microscopy also
revealed that the protein selectively adsorbed onto a nanometer-scale
gold pattern on a SiO2 surface fabricated by electron-beam lithography.
Our results indicate that nanodots and nanowires synthesized using abiotemplate can be selectively placed onto a gold surface by geneticallymodifying the outer surface of the biotemplate. This technique represents an important step toward biotemplate-mediated fabrication of ananometer-scaled device that utilizes gold electrodes.
[DOI : 10.1143/APEX.1.034006]
1 Graduate School of Materials Science, Nara Institute of Science and Technology, Ikoma,
Nara 630-0192, Japan
2 Advanced Technology Research Laboratories, Matsushita Electric Industrial Co., Ltd.,
Hikaridai, Seika, Kyoto 619-0237, Japan
3 Department of Protein Engineering, Cancer Institute, Japanese Foundation for Cancer
Research, Koto-ku, Tokyo 135-8550, Japan
4 Core Research for Evolutional Science and Technology, Japan Science and Technology
Agency, Kawaguchi, Saitama 332-0012, Japan* E-mail address: mime@ms.naist.jp

Hisao Miyazaki1,2, Shunsuke Odaka1,3, Takashi Sato4, Sho Tanaka4,
Hidenori Goto2,4, Akinobu Kanda2,4, Kazuhito Tsukagoshi1,2,5,*, Youiti
Ootuka4, and Yoshinobu Aoyagi1,2,3(Received January 19, 2008; accepted February 21, 2008; published online March 14, 2008)

Electric conduction in thin graphite film was tuned by two gate electrodes to clarify how the gate electric field induces electric carriers in thingraphite. The graphite was sandwiched between two gate electrodes
arranged in a top and bottom gate configuration. A scan of the top gate
voltage generates a resistance peak in ambiploar response. The ambipolar peak is shifted by the bottom gate voltage, where the shift ratedepends on the graphite thickness. The thickness-dependent peak shift
was clarified in terms of the inter-layer screening length to the electricfield in the double-gated graphite film. The screening length of 1.2nm
was experimentally obtained. [DOI : 10.1143/APEX.1.034007]
1 RIKEN, Wako, Saitama 351-0198, Japan
2 CREST, Japan Science and Technology Agency, Kawaguchi, Saitama 332-0012, Japan
3 Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology,
Midori-ku, Yokohama 226-8502, Japan
4 Institute of Physics and Tsukuba Research Center for Interdisciplinary Materials Science,
University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan
5 Advanced Industrial Science and Technology, Higashi, Tsukuba, Ibaraki 305-8568, Japan* E-mail address: tsuka@riken.jp

Appl. Phys. Express Vol.1, No.3 (2008) 035001

A Heterojunction Photodiode Operating at
Inorganic Nanosheet Interfaces
Hisako Sato, Kentaro Okamoto1, Kenji Tamura2, Hirohisa Yamada2,
Kazuko Saruwatari, Toshihiro Kogure, and Akihiko Yamagishi1,2,*(Received November 12, 2007; accepted February 4, 2008; published online February 22, 2008)

A heterojunction photodiode was fabricated by forming two contact
regions on a glass substrate: one side was a cast film of perovskite-type
niobate [(CH3)3NHSr2Nb3O10] as a n-type photosemiconductor and theother side a cast film of Zn-saponite (Na0.96[Si7.18Al0.64]Zn6.20O20(OH)2) asa p-type semiconductor under oxygen atmosphere. Diode-type current –voltage characteristics were obtained under the illumination of light(340 nm) and oxygen atmosphere (1atm) at 25 – 100 °C. The interfacial structure was studied by means of focused ion-beam and transmission electron microscopy techniques, confirming the contact of the twodifferent nanosheets on a nanometer scale. The results are discussed on
the basis of the nanosheet band structures.
[DOI : 10.1143/APEX.1.035001]
Graduate School of Science, The University of Tokyo, Tokyo 113-0013, Japan
1 Faculty of Science, Ochanomizu University, Tokyo 112-8610, Japan
2 Photocatalytic Materials Center, National Institute for Materials Science, Tsukuba, Ibaraki
305-0044, Japan* E-mail address: yamagishi.akihiko@ocha.ac.jp

JSAP International   No.18 (July 2008)        33Appl. Phys. Express Vol.1, No.3 (2008) 035002

Appl. Phys. Express Vol.1, No.3 (2008) 035004

Influence of Substrates on Initial Growth of
Diamond-Like Carbon Films

Nitrogen Gas Flow Driven Unintentional
Incorporation of Al during the Growth of
Dilute Nitride Semiconductor by PlasmaAssisted Molecular Beam Epitaxy

Nobuto Yasui1,2, Hiroshi Inaba1, and Naoto Ohtake3(Received November 24, 2007; accepted February 11, 2008; published online February 29, 2008)

We investigated the influence of substrate materials on bonding
structure of diamond-like carbon (DLC) films, fabricated by filteredcathodic vacuum arc, by using X-ray photoelectron spectroscopy andsecondary ion mass spectroscopy. Two kinds of substrate materials, Si
and NiFe, were evaluated. The results showed that sp3 ratio of DLC films
on NiFe was lower than that on Si by approximately 10 %, and implies
that the diffusion of Ne and Fe into DLC films inhibits sp3 bonding
formation. [DOI : 10.1143/APEX.1.035002]
1 Production Engineering Research Laboratory, Hitachi, Ltd., Yokohama 244-0817, Japan
2 Department of Mechanical Sciences and Engineering, Tokyo Institute of Technology, Tokyo
152-8552, Japan
3 Graduate School of Engineering, Nagoya University, Nagoya 464-8603, Japan

Appl. Phys. Express Vol.1, No.3 (2008) 035003

Near-Surface Defects in Boron-Doped
Diamond Schottky Diodes Studied From
Capacitance Transients

Shudong Wu, Masakazu Kato, Masayuki Uchiyama, Kotaro Higashi,
Fumitaro Ishikawa, and Masahiko Kondow(Received January 30, 2008; accepted February 8, 2008; published online February 29, 2008)

We report the unintentional incorporation of Al during the growthof molecular beam epitaxy using RF plasma source, driven by N2 gas
flow. The concentrations of N, Al, O, and C within GaNAs/GaAs/AlAs
structure are investigated by secondary ion mass spectrometry. In spite of
the closed shutter of Al cell, we observe Al incorporation with a concentration up to 1×1018cm-3 in GaNAs layer and characteristically in thebottom side GaAs. Its concentration is solely dependent on N2 gas flow
rate. Remarkably, the operation of the RF plasma has no impact on that.
C and O show their concentrations corresponding to the extrinsic Al. The
complex interactions between those elements predict a possible origin ofmaterial deteriorations and difficulty for the precise doping control.
[DOI : 10.1143/APEX.1.035004]
Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871,
Japan

Pierre Muret, Julien Pernot, Tokuyuki Teraji1, and Toshimichi Ito2

(Received January 17, 2008; accepted January 31, 2008; published online February 29, 2008)

Appl. Phys. Express Vol.1, No.3 (2008) 036001

Transient capacitance spectroscopy of deep energy levels (DLTS) in
the band gap of boron-doped homoepitaxial diamond displays two typesof defect when temperature is raised from 250 to 650K. The first trap is
a strongly attractive center for holes while the second one is repulsive,with respective activation energies of 1.57 and 1.15eV. Concentration
profile is non-monotonic for the first trap and changes when the diode
undergoes repetitive temperature cycles. Analysis of all the data showsthat the deep centers found in this study come from structural defects,
eventually associated with a charged impurity.
[DOI : 10.1143/APEX.1.035003]

Difference in Reaction Schemes in Photolysis
of Triphenylsulfonium Salts between 248nm
and Dry/Wet 193nm Resists

Institut Néel, Centre National de la Recherche Scientifique and Université Joseph Fourier BP166,
38042 Grenoble Cedex 9, France
1 Sensor Materials Center, National Institute for Materials Science, 1-1 Namiki, Tsukuba,
Ibaraki 305-0044, Japan
2 Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871,
Japan

Yoshinori Matsui*, Hidekazu Sugawara, Shu Seki, Takahiro Kozawa,
Seiichi Tagawa**, and Toshiro Itani1(Received January 11, 2008; accepted February 17, 2008; published online March 7, 2008)

Chemically amplified (CA) resists are important in the semiconductor industry because of their high orders of magnitude of sensitivity
enhancement. The key components of CA resists are a polymer with anacid labile group and a photoacid generator (PAG) that produces an acidupon exposure to radiation. Although the photolysis of PAGs has been
intensively studied, the difference in reaction schemes between 248 and
193nm resists had not been clarified. In this work, we have focused on
the reaction of Ph2S•+, which is one of the major intermediates in thephotolysis of triphenylsulfonium triflate. It was revealed that the difference in reaction schemes between 248 and 193nm resists is caused by
the ion molecular reactions of a polymer radical cation produced by electron transfer from the polymer to Ph2S•+.
[DOI : 10.1143/APEX.1.036001]
The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki,
Osaka 567-0047, Japan
1 Semiconductor Leading Edge Technologies, Inc., 16-1 Onogawa, Tsukuba, Ibaraki 305-8569,
Japan* Present address: NEC Electronic Corporation, 1120 Shimokuzawa, Sagamihara, Kanagawa
229-1198, Japan. E-mail address: yoshinori.matsui@necel.com** E-mail address: tagawa@sanken.osaka-u.ac.jp34        JSAP International   No.18 (July 2008)

Applied Physics Express

Appl. Phys. Express Vol.1, No.3 (2008) 037001

Appl. Phys. Express Vol.1, No.3 (2008) 038001

Correlation Imaging of Magnetic Recorded
Patterns and Grain Structures of Perpendicular
Magnetic-Recording Media

Enhanced Transfection Efficiency in LaserInduced Stress Wave-Assisted Gene Transfer
at Low Laser Fluence by Increasing Pressure
ImpulseYoshio Takahashi(Received January 7, 2008; accepted February 8, 2008; published online February 29, 2008)

An observation technique to image polycrystalline and magnetic
structures at the same sub-micron area of perpendicular magneticrecording media has been developed. The granular grain structures andmagnetically recorded bit patterns were imaged by transmission electron
microscopy and magnetic force microscopy, respectively. The small guidemarks fabricated on a disk sample with a focused ion beam apparatus
were used for aligning the images with each other. By applying this technique to analyze the magnetically recorded CoCrPtSiO thin film layers ofa hard disk medium, the correlation between the positions of the clustered grains and the percolation of the magnetic bit patterns could be
discussed. [DOI : 10.1143/APEX.1.037001]
Central Research Laboratory, Hitachi, Ltd., Kokubunji, Tokyo 185-8601, Japan

Appl. Phys. Express Vol.1, No.3 (2008) 037002

New Technique of Manipulating a Protein
Crystal Using Adhesive Material
Tomoya Kitatani1,2, Shigeru Sugiyama1,2, Hiroyoshi Matsumura1,2,3,
Hiroaki Adachi1,2,3, Hiroshi Y. Yoshikawa1,2, Syou Maki1,2, Satoshi
Murakami2,3,4, Tsuyoshi Inoue1,2,3, Yusuke Mori1,2,3, and Kazufumi
Takano1,2,3,*(Received January 31, 2008; accepted February 17, 2008; published online March 7, 2008)

We have developed Crystal Catcher, a new device for manipulating
protein crystals. Crystal Catcher directly captures a crystal with an adhesive. The easy and stable removal of a protein crystal from a drop has
been achieved using the Crystal Catcher. The crystal picked up on the
Crystal Catcher is positioned in the cryostream on a goniometer andflash-cooled. Various protein crystals can be captured and mounted
without causing significant damage. This new approach will replacenylon loops for picking up protein crystals.
[DOI : 10.1143/APEX.1.037002]
1 Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871,
Japan
2 CREST, Japan Science and Technology Agency, 2-1 Yamadaoka, Suita, Osaka 565-0871,
Japan
3 SOSHO Inc., 1-6-18 Honmachi, Chuo-ku, Osaka 541-0053, Japan
4 Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki,
Osaka 567-0047, Japan* E-mail address: ktakano@mls.eng.osaka-u.ac.jp

Shinta Takano, Shunichi Sato1,*, Mitsuhiro Terakawa, Hiroshi Asida1,
Hideyuki Okano2, and Minoru Obara(Received December 21, 2007; accepted February 11, 2008; published online February 29, 2008)

To improve transfection efficiency in gene delivery based on nanosecond pulsed laser-induced stress waves, we examined different typesof transparent materials, a poly(ethylene terephthalate) sheet, poly(vinyl
alcohol) gel, and water, which were placed on a laser target for plasma
confinement. We found that the use of water was most effective formaintaining a large pressure impulse during multipulse laser irradiation
and, as a result, high transfection efficiency was demonstrated in rat
skin in vivo at a relatively low laser fluence of 0.7J / cm2. At this fluence,steady laser transmission through quartz fibers was confirmed, allowing
endoscopic application of our gene delivery technique.
[DOI : 10.1143/APEX.1.038001]
Department of Electronics and Electrical Engineering, Keio University, 3-14-1 Hiyoshi, Kohokuku, Yokohama 223-8522, Japan
1 Division of Biomedical Information Sciences, National Defense Medical College ResearchInstitute, 3-2 Namiki, Tokorozawa, Saitama 359-8513, Japan
2 Department of Physiology, Keio University School of Medicine, 35 Shinanomachi, Shinjukuku, Tokyo 160-8582, Japan* E-mail address: shunsato@ndmc.ac.jp

Appl. Phys. Express Vol.1, No.4 (2008) 041101

Compositional Dependence of Nonpolar
m-Plane InxGa1-xN/GaN Light Emitting Diodes
Hisashi Yamada*, Kenji Iso, Makoto Saito, Hisashi Masui, Kenji Fujito1,
Steven P. DenBaars, and Shuji Nakamura(Received February 12, 2008; accepted March 3, 2008; published online March 21, 2008)

Characteristics of m-plane InGaN/GaN light emitting diodes (LEDs)
with various indium compositions were investigated. X-ray diffraction revealed that indium compositions in the InGaN multi quantum
wells (MQWs) on m-plane substrate were 2 – 3 times lower than thoseon c-plane substrate. The optical polarization ratio for m-plane LEDs
increased from 0.27 to 0.89 with increasing emission wavelength from
383 to 476nm due to compressively strained InGaN QWs. The output
power of electroluminescence decreased above 400nm although polarization-related internal electric fields were eliminated.
[DOI : 10.1143/APEX.1.041101]
Materials Department, University of California, Santa Barbara, CA 93106, U.S.A.
1 Optoelectronics Laboratory, Mitsubishi Chemical Co., Ltd., 1000 Higashi-Mamiana, Ushiku,
Ibaraki 300-1295, Japan* E-mail address: yamadah7@sc.sumitomo-chem.co.jp

JSAP International   No.18 (July 2008)        35Appl. Phys. Express Vol.1, No.4 (2008) 041102

Appl. Phys. Express Vol.1, No.4 (2008) 041202

Hydrogen Sensing Characteristics ofa Pd/AlGaN/GaN Schottky Diode

Enhancement-Mode ZnO Thin-Film Transistor
Grown by Metalorganic Chemical Vapor
Deposition

Tsung-Han Tsai, Huey-Ing Chen1, Kun-Wei Lin, Ching-Wen Hung, ChiaHao Hsu, Tzu-Pin Chen, Li-Yang Chen, Kuei-Yi Chu, Chung-Fu Chang,and Wen-Chau Liu*
(Received February 29, 2008; accepted March 12, 2008; published online April 11, 2008)

In this paper, the interesting hydrogen sensing properties of a
Pd-gate AlGaN/GaN Schottky diode are investigated. A significantly low
detection limit of 850ppb H2/air gas can be observed with increasing thetemperature to 423K. The experimental results indicate that hydrogenmolecules cause great influences on the diode breakdown voltage. Also,
the diode exhibits an ultrahigh sensing response of 2.04 × 105 at 423K
when exposure to a 9660ppm H2/air gas. The transient response timeand reversibility of the studied device can be improved by increasing theoperating temperature. [DOI : 10.1143/APEX.1.041102]
Institute of Microelectronics, Department of Electrical Engineering, National Cheng-Kung
University, 1 University Road, Tainan, Taiwan 70101, R.O.C.
1 Department of Chemical Engineering, National Cheng-Kung University, 1 University Road,
Tainan, Taiwan 70101, R.O.C.
* E-mail address: wcliu@mail.ncku.edu.tw

Appl. Phys. Express Vol.1, No.4 (2008) 041201

Enhanced Conversion Efficiencies of
Cu2ZnSnS4-Based Thin Film Solar Cells byUsing Preferential Etching Technique
Hironori Katagiri, Kazuo Jimbo, Satoru Yamada, Tsuyoshi Kamimura,Win Shwe Maw, Tatsuo Fukano1,*, Tadashi Ito1, and Tomoyoshi
Motohiro1(Received November 12, 2007; accepted March 7, 2008; published online April 4, 2008)

Cu2ZnSnS4 (CZTS) thin film solar cells have been fabricated byco-sputtering technique using three targets of Cu, SnS, and ZnS. CZTSbased thin film solar cells over 6.7 % efficiency were obtained for the
first time by soaking the CZTS layer on the Mo coated soda-lime glass
substrate in deionized water (DIW) after forming the CZTS layer. It was
found that DIW-soaking had the effect of preferential etching, which
eliminated selectively metal oxide particles in the CZTS layer, by electronprobe X-ray micro analysis. [DOI : 10.1143/APEX.1.041201]
Department of Electrical and Electronic Systems Engineering, Nagaoka National College ofTechnology, 888 Nishikatakai, Nagaoka, Niigata 940-8532, Japan
1 Materials Department, Toyota Central Research and Development Laboratories Inc.,
Nagakute, Aichi 480-1192, Japan* E-mail address: e0987@mosk.tytlabs.co.jp

36        JSAP International   No.18 (July 2008)

Jungyol Jo*, Ogweon Seo1, Hyoshik Choi, and Byeonggon Lee2
(Received January 23, 2008; accepted March 21, 2008; published online April 11, 2008)

We developed a method to control threshold voltage and on/off
ratio of ZnO thin-film transistor (TFT) grown by metalorganic chemical
vapor deposition (MOCVD). ZnO usually shows oxygen deficiency, whichshows up as n-type defects of zinc interstitial or oxygen vacancy. In orderto reduce these defects, we allowed sufficient oxidation time during
growth. Instead of one long oxidation step, we repeated thin-layer
growth and oxidation, until desired thickness is achieved. By using thismethod, we could obtain high quality ZnO TFT by MOCVD. Our ZnO TFT
grown at 450 °C showed 15cm2/(Vs) mobility and 107 on/off ratio, with
+5 V threshold voltage, which enables enhancement mode TFT operation. [DOI : 10.1143/APEX.1.041202]
Department of Electrical and Computer Engineering, Ajou University, Suwon 443-749, Korea
1 Nano Fabrication Technology Center, Samsung Advanced Institute of Technology, Suwon
440-600, Korea
2 CDA Co., Ltd., Yangjaedong, Seoul 137-893, Korea* E-mail address: jungyol@ajou.ac.kr

Appl. Phys. Express Vol.1, No.4 (2008) 041203

Enhanced Temperature Characteristics of
InGaAs/InAlGaAs Multi-Quantum-Well Lasers
on Low-In-Content InGaAs Ternary Substrates
Takeshi Fujisawa*, Masakazu Arai, Takaaki Kakitsuka, Takayuki
Yamanaka, Yasuhiro Kondo, and Hiroshi Yasaka(Received February 14, 2008; accepted March 21, 2008; published online April 11, 2008)

Temperature characteristics of multi-quantum-well lasers on InGaAs
ternary substrates are investigated. By using InAlGaAs barriers andlow-In-content InGaAs substrates, the characteristic temperature of
the laser can reach as high as 150K between 25 and 85°C due to theenhancement of the material gain. Calculated characteristic temperatures
are in good agreement with those obtained by experiment, showing thevalidity of the results presented here. [DOI : 10.1143/APEX.1.041203]
Photonics Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa
243-0198, Japan* E-mail address: fujisawa@aecl.ntt.co.jp

Applied Physics Express

Appl. Phys. Express Vol.1, No.4 (2008) 041301

Appl. Phys. Express Vol.1, No.4 (2008) 041501

X-ray Magnetic Circular Dichroism andPhotoemission Study of the Diluted
Ferromagnetic Semiconductor Zn1-xCrxTe

Reduction of Optical Loss in HydrogenatedAmorphous Silicon/Crystalline Silicon
Heterojunction Solar Cells by High-Mobility
Hydrogen-Doped In2O3 Transparent
Conductive Oxide

Yukiaki Ishida1,*, Masaki Kobayashi1, Jong-Il Hwang1, Yukiharu Takeda2,
Shin-ichi Fujimori2, Tetsuo Okane2, Kota Terai2, Yuji Saitoh2, Yasuji
Muramatsu2, Atsushi Fujimori1,2, Arata Tanaka3, Hidekazu Saito4, andKoji Ando4

Takashi Koida*, Hiroyuki Fujiwara, and Michio Kondo(Received January 28, 2008; accepted February 24, 2008; published online March 21, 2008)(Received February 22, 2008; accepted March 1, 2008; published online March 21, 2008)

We have performed X-ray magnetic circular dichroism (XMCD) andvalence-band photoemission studies of the diluted ferromagnetic semiconductor Zn1-xCrxTe. XMCD signals due to ferromagnetism and paramagnetism and/or superparamagnetism were observed at the Cr 2p
absorption edge. Comparison with atomic multiplet calculations suggeststhat the magnetically active component of the Cr ion was divalent under
the tetrahedral crystal field with tetragonal distortion along the crystalline a-, b-, and c-axes. In the valence-band spectra, spectral weight near
the Fermi level was strongly suppressed, suggesting the importance ofJahn – Teller effect and the strong Coulomb interaction between the Cr
3d electrons. [DOI : 10.1143/APEX.1.041301]

Hydrogen-doped In2O3 (IO:H) films with high electron mobility andimproved near-infrared transparency have been applied as a transparent
conducting oxide (TCO) electrode in hydrogenated amorphous silicon(a-Si:H)/crystalline silicon heterojunction solar cells. The incorporation of
IO:H, instead of conventional Sn-doped In2O3, improved the short-circuitcurrent density (J sc) and the resulting conversion efficiency. Detailed
optical analysis of the solar cells revealed that the improvement in Jsc isdue to the reduction of reflection loss at the TCO/a-Si:H interface andless optical absorption in the TCO layer. [DOI : 10.1143/APEX.1.041501]

1 Department of Physics, University of Tokyo, Bunkyo, Tokyo 113-0033, Japan
2 Synchrotron Radiation Research Center, Japan Atomic Energy Agency, Sayo, Hyogo
679-5148, Japan
3 Graduate School of Advanced Sciences of Matter, Hiroshima University, Higashihiroshima,
Hiroshima 739-8530, Japan
4 Nanoelectronics Research Institute, National Institute of Advanced Industrial Science andTechnology (AIST), Tsukuba Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan* E-mail address: ishida@spring8.or.jp

Appl. Phys. Express Vol.1, No.4 (2008) 041302

Spin-Transfer Switching and Thermal Stability
in an FePt/Au/FePt Nanopillar Prepared by
Alternate Monatomic Layer Deposition
Kay Yakushiji*, Shinji Yuasa, Taro Nagahama, Akio Fukushima, Hitoshi
Kubota, Toshikazu Katayama, and Koji Ando

(Received February 14, 2008; accepted March 12, 2008; published online April 4, 2008)

We fabricated a current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) nanopillar with a 1-nm-thick FePt free layer having
perpendicular anisotropy using the alternate monatomic layer deposition
method. Nanopillars consisting of [Fe (1monolayer (ML))/Pt (1ML)]n (n:the number of the alternation period) ferromagnetic layers and an Au
spacer layer showed spin-transfer induced switching at room temperature. An average critical switching current density (Jc0) of 1.1 × 107A/
cm2 with a large thermal stability parameter (Δ) of 60 was obtained in a
nanopillar with a free-layer thickness of 1.02nm (n=3) and a pillar diameter of 110nm. The ultrathin free-layer with high perpendicular anisotropy is effective to obtain both large Δ and small Jc.
[DOI : 10.1143/APEX.1.041302]
Nanoelectronics Research Institute, National Institute of Advanced Industrial Science andTechnology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan* E-mail address: k-yakushiji@aist.go.jp

Research Center for Photovoltaics, National Institute of Advanced Industrial Science andTechnology (AIST), Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan* E-mail address: t-koida@aist.go.jp

Appl. Phys. Express Vol.1, No.4 (2008) 041601

Optically Controlled Bimorph Cantilever ofPoly(vinylidene difluoride)
Yasuhiro Mizutani, Yukitoshi Otani, and Norihiro Umeda(Received February 8, 2008; accepted February 29, 2008; published online March 21, 2008)

Optically driven actuators are a non-contact method for the remoteapplication of light energy. We propose a new optically driven actuatorthat employs bimorph poly(vinylidene difluoride) (PVDF) cantilevers. PVDF
is an effective polymer from which to prepare actuators since it has bothpyroelectric and piezoelectric properties. We have produced a bimorph
cantilever from a PVDF film with a thin Ag electrode on one side. A
bending model of the PVDF cantilever has been established and its
bending characteristics have been experimentally measured. The mechanism can be explained by taking into consideration the model and its
dielectric breakdown. [DOI : 10.1143/APEX.1.041601]
Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan

Appl. Phys. Express Vol.1, No.4 (2008) 041602

Microstructure Analysis of Solid-State
Reaction in Synthesis of BaTiO3 Powder Using
Transmission Electron Microscope
Keisuke Kobayashi, Toshimasa Suzuki, and Youichi Mizuno(Received February 13, 2008; accepted February 29, 2008; published online March 21, 2008)

The kinetics and mechanism of the solid-state reaction in BaTiO3
powder synthesis were investigated microstructurally. An equimolar
mixture of BaCO3 and TiO2 (rutile) powders calcinated at 600 and 800°C
in air was observed by using transmission electron microscopy (TEM).
During the reaction, layered BaTiO3 was formed over the TiO2 particles
with a structurally and compositionally sharp interface. The crystallographic orientation relationship between TiO2 and BaTiO3 was universally–observed as [001]TiO2 //[110]BTO, (100)TiO2 //(111)BTO. The perovskite phase
BaTiO3 was formed by inward diffusion of barium and oxygen ions into
the rutile lattice, maintaining a topotaxial relationship with the rutile
structure. [DOI : 10.1143/APEX.1.041602]
Material Development Department, Taiyo Yuden Co., Ltd., 5607-2 Nakamuroda, Takasaki,
Gunma 370-3347, Japan

JSAP International   No.18 (July 2008)        37Appl. Phys. Express Vol.1, No.4 (2008) 041701

Appl. Phys. Express Vol.1, No.4 (2008) 042001

Annealing Effect of 80K-Class
Superconductivity of Ca-Doped B2S2CuO6+δ in
Bi-2201 Phase

Photon Correlation in GaAs Self-Assembled
Quantum Dots

Ryozo Yoshizaki1,2,*, Tetsuya Nakajima1, Masayoshi Tange1,**, andHiroshi Ikeda1,2(Received January 15, 2008; accepted March 1, 2008; published online March 28, 2008)

Annealing effect on magnetic properties of superconductivity isinvestigated for the crystals of Bi1.9CaySr1.9-yCuO6+δ (0≤y≤1.8) in Bi-2201
phase. It is found that carrier density is reduced with Ca doping in
Ca-poor region of y≤0.8. In contrast, the excess oxygen δ is saturated
with doping at about the optimal Tc in Ca-rich region of y>0.8. The
results indicate possible oxygen deficiencies with Ca doping, which gives
a new aspect to a model for the appearance of 80K-class superconductivity. [DOI : 10.1143/APEX.1.041701]
1 Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki
305-8571, Japan
2 Cryogenics Division, Research Facility Center for Science and Technology, University ofTsukuba, Tsukuba, Ibaraki 305-8571, Japan* E-mail address: yoshizak@ims.tsukuba.ac.jp** Present address: Department of Materials Science and Engineering, Faculty of Engineering,
Iwate University, Morioka 020-8551, Japan

Appl. Phys. Express Vol.1, No.4 (2008) 041801

Grain Size Increase and Field-Effect Mobility
Enhancement of Pentacene Thin Films
Prepared in a Low-Pressure H2 Ambient
Takamichi Yokoyama*, Chang Bum Park, Kosuke Nagashio, Koji Kita,
and Akira Toriumi(Received February 6, 2008; accepted March 3, 2008; published online March 21, 2008)

Pentacene films were grown by thermal evaporation in different gas
atmospheres at a relatively low vacuum of about 3Pa, and the effectsof the gas ambient on the performance of thin film transistors (TFTs)
were investigated. The TFT mobility of film deposited in H2 was twice
the typical value of 0.3cm2/(V·s) for film deposited in vacuum, while themobility values of films deposited in N2 and O2 were almost the sameas that of vacuum-deposited film. No significant changes in on/off ratio,
threshold voltage, or hysteresis behavior were observed in pentacene
TFTs prepared by evaporation in gas ambient. The improved mobility of
pentacene film prepared in H2 can be explained by an increase in grain
size of the first layer on the SiO2 / Si substrate.
[DOI : 10.1143/APEX.1.041801]
Department of Materials Engineering, School of Engineering, The University of Tokyo, 7-3-1
Hongo, Bunkyo, Tokyo 113-8656, Japan* E-mail address: yokoyama@adam.t.u-tokyo.ac.jp38        JSAP International   No.18 (July 2008)

Takashi Kuroda1,2,*, Marco Abbarchi1,3, Takaaki Mano1, Kenji
Watanabe1, Masakazu Yamagiwa1, Keiji Kuroda1, Kazuaki Sakoda1,
Giyuu Kido1, Nobuyuki Koguchi1, Carmine Mastrandrea3, Lucia Cavigli3,
Massimo Gurioli3, Yoshihiro Ogawa4, and Fujio Minami4(Received February 19, 2008; accepted March 12, 2008; published online April 4, 2008)

We report on photon coincidence measurement in a single GaAs
self-assembled quantum dot (QD) using a pulsed excitation light source.
At low excitation, when a neutral exciton line was present in the photoluminescence (PL) spectrum, we observed nearly perfect single photon
emission from an isolated QD at 670nm wavelength. For higher excitation, multiple PL lines appeared on the spectra, reflecting the formation of exciton complexes. Cross-correlation functions between theselines showed either bunching or antibunching behavior, dependingon whether the relevant emission was from a biexciton cascade or acharged exciton recombination. [DOI : 10.1143/APEX.1.042001]
1 National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
2 PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama
332-0012, Japan
3 European Laboratory for Non-Linear Spectroscopy, and Dipartimento di Fisica, Università diFirenze, Via Sansone 1, 50019, Sesto Fiorentino, Firenze, Italy
4 Department of Physics, Tokyo Institute of Technology, O-okayama, Meguro, Tokyo
152-8551, Japan* E-mail address: kuroda.takashi@nims.go.jp

Appl. Phys. Express Vol.1, No.4 (2008) 042002

Terahertz-Wave Generation Using a
4-Dimethylamino-N-methyl-4-stilbazolium
tosylate Crystal Under Intra-Cavity Conditions
Takayuki Shibuya1,2, Takuya Akiba1, Koji Suizu1, Hirohisa Uchida3, Chiko
Otani2, and Kodo Kawase1,2(Received February 28, 2008; accepted March 12, 2008; published online April 4, 2008)

We succeeded in generating terahertz waves using differencefrequency generation (DFG) in an organic 4-dimethylamino-N-methyl4-stilbazolium tosylate (DAST) crystal under intra-cavity conditions. We
constructed a dual wavelength output optical parametric oscillator (OPO)
with two potassium titanium oxide phosphate (KTP) crystals for the DFG
pumping source, and placed the DAST crystal inside the OPO cavity to
act as a nonlinear wavelength conversion element. Our experimental
measurements confirmed that intra-cavity generation was possible andthat the output level was approximately the same as that of normal excitation using the external OPO output. [DOI : 10.1143/APEX.1.042002]
1 Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
2 RIKEN, Aramaki-Aoba, Aoba-ku, Sendai 980-0845, Japan
3 Daiichi Pure Chemicals Co., Ltd., Koyodai, Ryugasaki, Ibaraki 301-0852, Japan

Applied Physics Express

Appl. Phys. Express Vol.1, No.4 (2008) 042003

Appl. Phys. Express Vol.1, No.4 (2008) 045002

Frequency Increase of Resonant Tunneling
Diode Oscillators in Sub-THz and THz Range
Using Thick Spacer Layers

Super-High Brightness and High-SpinPolarization PhotocathodeNaomichi Kishimoto1, Safumi Suzuki1, Atsushi Teranishi,1 and Masahiro
Asada1,2,*(Received February 14, 2008; accepted March 18, 2008; published online April 11, 2008)

We obtained frequency increase of resonant tunneling diode (RTD)
oscillators using thick spacer layers at the collector in sub-terahertz
range. This is attributed to reduction of parasitic capacitance due to theincrease of spacer layer thickness. The oscillation frequency increased
from 325 to 425GHz by the change of spacer layer thickness from 5 to
45nm in reasonable agreement with theoretical calculation. Frequency
switching with bias direction was also obtained for an RTD having an
asymmetric structure with the thickness of the collector and emitter
spacer layers of 30 and 5nm, respectively. The oscillation frequency was
394 GHz under forward bias, whereas 336 GHz under reverse bias inwhich the role of the emitter and collector spacers was exchanged.
[DOI : 10.1143/APEX.1.042003]
1 Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology,
2-12-1-S9-3 O-okayama, Meguro-ku, Tokyo 152-8552, Japan
2 CREST, Japan Science and Technology Agency, 2-12-1-S9-3 O-okayama, Meguro-ku, Tokyo
152-8552, Japan* E-mail address: asada@pe.titech.ac.jp

Xiuguang Jin, Naoto Yamamoto1, Yasuhide Nakagawa1, Atsushi Mano1,
Takanori Kato, Masatoshi Tanioku, Toru Ujihara, Yoshikazu Takeda, Shoji
Okumi1, Masahiro Yamamoto1, Tsutomu Nakanishi1, Takashi Saka2,
Hiromichi Horinaka3, Toshihiro Kato4, Tsuneo Yasue5, and Takanori
Koshikawa5(Received December 18, 2007; accepted February 29, 2008; published online March 28, 2008)

Using a newly developed transmission-type photocathode, an electron beam of super-high brightness [(1.3±0.5)×107A·cm-2·sr-1] wasachieved. Moreover, the spin-polarization was as high as 90 %. We
fabricated a transmission-type photocathode based on a GaAs – GaAsP
strained superlattice on a GaP substrate in order to enhance the brightness and polarization greatly. In this system, a laser beam is introduced
through the transparent GaP substrate. The beam is focused on the
superlattice active layer with a short focal length lens. Excited electrons are generated in a small area and extracted from the surface. The
shrinkage of the electron generation area improved the brightness. In
addition, a GaAs layer was inserted between the GaP substrate and the
GaAsP buffer layer to control the strain relaxation process in the GaAsP
buffer layer. This design for strain control was key in achieving highpolarization (90 %) in the transmission-type photocathode.
[DOI : 10.1143/APEX.1.045002]

Appl. Phys. Express Vol.1, No.4 (2008) 045001

Time-Resolved Investigation of Nanosecond
Crystal Growth in Rapid-Phase-Change
Materials: Correlation with the Recording
Speed of Digital Versatile Disc Media
Yoshimitsu Fukuyama1, Nobuhiro Yasuda1, Jungeun Kim1, Haruno
Murayama1, Yoshihito Tanaka1,2, Shigeru Kimura1, Kenichi Kato1,2,
Shinji Kohara1, Yutaka Moritomo1,3, Toshiyuki Matsunaga4, Rie Kojima4,
Noboru Yamada4, Hitoshi Tanaka1,2, Takashi Ohshima1,2, and Masaki
Takata1,2,5,*(Received December 19, 2007; accepted February 24, 2008; published online March 21, 2008)

The crystallization process in digital versatile disc (DVD) media wasinvestigated using a time-resolved X-ray diffraction apparatus coupledwith in situ photoreflectivity measurement. The time profiles of crystallization were found to be consistent with the changes in photoreflectivity. The phase changes were characterized by the start and end
time; 90±1 and 273±1ns for Ge2Sb2Te5, and 85±1 and 206±1ns forAg3.5In3.8Sb 75.0Te17.7, respectively. The faster crystallization time inAg3.5In3.8Sb75.0Te17.7 is ascribed to its characteristic crystallization process;its X-ray diffraction profile shows a significant sharpening during the
crystallization process, whereas the peak width of Ge2Sb2Te5 remained
unchanged. The present findings suggest that crystal growth control isanother key for designing faster phase-change materials.
[DOI : 10.1143/APEX.1.045001]
1 Japan Synchrotron Radiation Research Institute/SPring-8, 1-1-1 Kouto, Sayo-cho, Sayo-gun,
Hyogo 679-5198, Japan
2 SPring-8/RIKEN, 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan
3 The Graduate School of Pure and Applied Sciences, University of Tsukuba, Tennodai,
Tsukuba, Ibaraki 305-8571, Japan
4 Matsushita Electric Industrial Co., Ltd., 3-1-1 Yagumo-Nakamachi, Moriguchi, Osaka
570-8501, Japan
5 Department of Advanced Materials Science, School of Frontier Sciences, The University ofTokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan* E-mail address: takatama@spring8.or.jp

Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603,
Japan
1 Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602,
Japan
2 Electrical and Electronics Engineering, Daido Institute of Technology, 10-3 Takiharu-cho,
Minami-ku, Nagoya 457-8530, Japan
3 Graduate School of Engineering, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku,
Sakai 599-8531, Japan
4 Daido Steel Co., Ltd., 2-30 Daido-cho, Minami-ku, Nagoya 457-8545, Japan
5 Fundamental Electronics Research Institute, Academic Frontier Promotion Center, Osaka
Electro-Communication University, 18-8 Hatsu-cho, Neyagawa, Osaka 572-8530, Japan

Appl. Phys. Express Vol.1, No.4 (2008) 045003

Self-Separation of a Thick AlN Layer froma Sapphire Substrate via Interfacial Voids
Formed by the Decomposition of Sapphire
Yoshinao Kumagai1,*, Jumpei Tajima1, Masanari Ishizuki1,2, Toru
Nagashima3, Hisashi Murakami1, Kazuya Takada3, and Akinori Koukitu1(Received March 4, 2008; accepted March 21, 2008; published online April 11, 2008)

A technique for separating a thick AlN layer grown by hydride vapor
phase epitaxy (HVPE) on a (0001) sapphire substrate was developed. Byheat treatment at 1450°C in a gas flow containing H2 and NH3, many
voids could be formed at the interface between a thin (100nm) AlN layergrown at 1065 °C and the sapphire substrate due to the preferential
decomposition of sapphire. During the cooling process after the subsequent growth of a thick (85 µm) AlN layer, the thick AlN layer separated
from the sapphire substrate with the aid of the interfacial voids. The
freestanding AlN substrate thus obtained had a smooth (0001) surface,a dislocation density of 1.1 × 109cm-2, and an optical transparency forwavelengths above 208.1nm. [DOI : 10.1143/APEX.1.045003]
1 Department of Applied Chemistry, Graduate School of Engineering, Tokyo University ofAgriculture and Technology, 2-24-16 Naka-cho, Koganei, Tokyo 184-8588, Japan
2 Research and Development Division, Tokuyama Corporation, Shibuya Konno Bldg., 3-3-1
Shibuya, Shibuya-ku, Tokyo 150-8383, Japan
3 Tsukuba Research Laboratories, Tokuyama Corporation, 40 Wadai, Tsukuba, Ibaraki
300-4247, Japan* E-mail address: 4470kuma@cc.tuat.ac.jp

JSAP International   No.18 (July 2008)        39Appl. Phys. Express Vol.1, No.4 (2008) 045004

Appl. Phys. Express Vol.1, No.4 (2008) 046002

Determination of the Twist Angle of GaN Filmby High Resolution X-ray Diffraction

Discharge Characteristics of Microwave andHigh-Frequency In-Liquid Plasma in Water

Hongtao Li, Yi Luo*, Lai Wang, Guangyi Xi, Yang Jiang, Wei Zhao, andYanjun Han

Shinfuku Nomura, Hiromichi Toyota, Shinobu Mukasa, Yoshiyuki
Takahashi, Tsunehiro Maehara, Ayato Kawashima1, and Hiroshi
Yamashita

As an azimuthal scan method, ϕ -scans preformed by X-ray diffraction are usually used to determine the twist angle in GaN films. However,both twist and tilt contribute to full width at half maximum (FWHM) of
ϕ -scan curves. So far no model has been proposed to distinguish thecontributions of tilt and twist to FWHM of these curves. A geometricalmodel is presented to distinguish their contributions, which is very important to precisely determine the dislocation densities in GaN. Based on thismodel, FWHM of ϕ -scans can be expressed as a simple explicit functionof the original twist angle and an additional twist angle induced by tilt.
These twist angles are then simply and effectively determined for various
GaN films according to this simple function, and are in good agreementwith those deduced from ω-scan data fitting.
[DOI : 10.1143/APEX.1.045004](Received January 31, 2008; accepted March 12, 2008; published online April 4, 2008)(Received March 5, 2008; accepted March 21, 2008; published online April 11, 2008)

State Key Laboratory on Integrated Optoelectronics/Tsinghua National Laboratory for
Information Science and Technology, Department of Electronic Engineering, Tsinghua University,
Beijing 100084, China* E-mail address: luoy@tsinghua.edu.cn

Appl. Phys. Express Vol.1, No.4 (2008) 046001

Gas-Temperature-Dependent Characteristics
of Cryo-Dielectric Barrier Discharge Plasma
under Atmospheric Pressure
Yuri Noma, Jai Hyuk Choi, Sven Stauss, Takaaki Tomai, and Kazuo
Terashima(Received January 21, 2008; accepted March 7, 2008; published online March 28, 2008)

In the present work, cryo-dielectric barrier discharge (DBD) plasma
was generated continuously below room temperature down to liquid
nitrogen temperature (296 to 78K) under atmospheric pressure using
parallel indium – tin-oxide (ITO)-coated electrodes. Gas-temperaturedependent optical emission spectroscopy (OES) measurements anddischarge pattern observation of cryo-DBD plasma were performed. In
the case of helium gas, the discharge mode of cryo-DBD plasma changed
from filamentary mode to glow mode as the gas temperature decreased.
When introducing a small amount of nitrogen in helium gas, the filamentary discharge mode persisted upon decreasing the gas temperature,
although the discharge pattern changed from concentric rings (296K) toa hexagon-like pattern (78K). [DOI : 10.1143/APEX.1.046001]
Department of Advanced Materials Science, Graduate School of Frontier Sciences, The
University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 227-8561, Japan

The plasma in water is generated by applying high-frequency (HF)
irradiation of 27.12MHz or microwave (MW) radiation of 2.45GHz froman electrode. The electrode is heated by joule heating by the HF or MW
irradiation, and vapor bubbles are generated simultaneously. The plasma
is then ignited inside the bubbles on the electrode. The glow discharge
plasma can be maintained in spite of atmospheric pressure due to thecooling effect of the liquid itself. The electron temperature of the plasma
generated by the 27.12MHz radiation is higher than that generated by
the 2.45GHz radiation. [DOI : 10.1143/APEX.1.046002]
Graduate School of Science and Engineering, Ehime University, 3 Bunkyo-cho, Matsuyama
790-8577, Japan
1 Department of Environmental Science for Industry, Ehime University, 3-5-7 Tarumi,
Matsuyama 790-8566, Japan

Appl. Phys. Express Vol.1, No.4 (2008) 047001

Enhancement of Acid Production in
Chemically Amplified Resist for Extreme
Ultraviolet Lithography
Hiroki Yamamoto, Takahiro Kozawa*, Seiichi Tagawa**, Hiroto Yukawa1,
Mitsuru Sato1, and Junichi Onodera1(Received November 27, 2007; accepted February 29, 2008; published online March 21, 2008)

The trade-off among sensitivity, resolution, and line edge roughness(LER) is the most serious problem for the realization of extreme ultraviolet(EUV) lithography. A solution to this problem is the enhancement of acidgeneration efficiency per unit volume. In chemically amplified EUV resists,
not the acid generators but the polymer mainly absorbs EUV photons.
The secondary electrons generated by EUV absorption sensitize the acidgenerators. Therefore, an increase in the polymer absorption coefficientis expected to lead to the enhancement of acid production. The incorporation of fluorine atoms is a promising way for the increase in theabsorption coefficient of EUV resists. However, fluorinated compounds
decrease the acid generation efficiency by interfering with the reactionof acid generators with low-energy electrons. We investigated which
effect prevails in acid generation. Using a spectroscopic method, it was
confirmed that the incorporation of fluorine atoms leads to an increasein acid generation efficiency per unit volume.
[DOI : 10.1143/APEX.1.047001]
The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki,
Osaka 567-0047, Japan
1 Tokyo Ohka Kogyo Co., Ltd., 1590 Tabata, Samukawa, Koza, Kanagawa 253-0114, Japan* E-mail address: kozawa@sanken.osaka-u.ac.jp** E-mail address: tagawa@sanken.osaka-u.ac.jp

40        JSAP International   No.18 (July 2008)

Applied Physics Express

Appl. Phys. Express Vol.1, No.4 (2008) 047002

Organic Contaminant Detection of Silicon
Wafers Using Negative Secondary Ions
Induced by Cluster Ion Impacts
Kouichi Hirata*, Yuichi Saitoh1, Atsuya Chiba1, and Kazumasa Narumi2(Received January 24, 2008; accepted March 7, 2008; published online March 28, 2008)

Emission yields of carbon and hydrogenated carbon cluster
secondary ions CpHq± (p≥1, q≥0) originating from organic contaminants
on a silicon wafer are compared between monoatomic (0.5-MeV/atomC1+) and cluster ion (0.5-MeV/atom C8+) impacts using time-of-flight(TOF) secondary ion mass spectrometry. CpHq- for the cluster ion impact
exhibits the highest emission yield per incident atom among CpHq± withthe same p number. The highest relative CpHq- emission yield for thecluster ion impact reaches ~20 and ~60 times higher in comparison withthose of CpHq- and CpHq+ with the same p number for the impact ofthe monoatomic ion with the same velocity, respectively. Combination ofnegative secondary ion TOF measurements with cluster impact ionization
is a promising tool for highly sensitive detection of organic-contaminants
on silicon wafers. [DOI : 10.1143/APEX.1.047002]
National Metrology Institute of Japan, National Institute of Advanced Industrial Science andTechnology (AIST), Tsukuba, Ibaraki 305-8565, Japan
1 Department of Advanced Radiation Technology, Takasaki Advanced Radiation ResearchInstitute (TARRI), Japan Atomic Energy Agency (JAEA), Takasaki, Gumma 370-1292, Japan
2 Advanced Science Research Center, Japan Atomic Energy Agency (JAEA), Takasaki, Gumma
370-1292, Japan* E-mail address: k.hirata@aist.go.jp

Appl. Phys. Express Vol.1, No.4 (2008) 049201

Erratum: “Local Synthesis of Tungsten Oxide
Nanowires by Current Heating of Designed
Micropatterned Wires”
Keisuke Nagato1,2,*, Yusuke Kojima1, Keigo Kasuya3, Hiroki Moritani1,
Tetsuya Hamaguchi1, and Masayuki Nakao1(Received January 29, 2008; accepted March 11, 2008; published online March 28, 2008)[DOI : 10.1143/APEX.1.049201]
1 Department of Engineering Synthesis, School of Engineering, The University of Tokyo, 7-3-1
Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
2 Research Fellow of the Japan Society for the Promotion of Science, 8 Ichibancho, Chiyodaku, Tokyo 102-8472, Japan
3 Central Research Laboratory, Hitachi, Ltd., 1-280 Higashi-koigakubo, Kokubunji, Tokyo
185-8601, Japan* E-mail address: nagato@hnl.t.u-tokyo.ac.jp

JSAP International   No.18 (July 2008)        41