Printed with permission of The Institute of Pure and Applied Physics (IPAP)

JAPANESE JOURNAL OF APPLIED PHYSICS [Part2]

Abstracts of Express Letters
Jpn. J. Appl. Phys. Vol.45 (2006) pp. L1057-L1060
Part 2, No. 40, 25 October 2006
©2006 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol. 45 (2006) pp. L1084-L1086
Part 2, No. 41, 25 October 2006
©2006 The Japan Society of Applied Physics

Current-Induced Magnetization Switching in
MgO Barrier Based Magnetic Tunnel Junctions
with CoFeB/Ru/CoFeB Synthetic Ferrimagnetic
Free Layer

Ultra-High Efficiency White Light Emitting
DiodesJun Hayakawa1,2,*, Shoji Ikeda2, Young Min Lee2, Ryutaro Sasaki2,
Toshiyasu Meguro2, Fumihiro Matsukura2, Hiromasa Takahashi1,2 andHideo Ohno2(Received September 13, 2006; accepted September 21, 2006; published online October 6, 2006)

We report the intrinsic critical current density (Jc0) in current-induced
magnetization switching and the thermal stability factor (E / kBT, where
E , k B, and T are the energy potential, the Boltzmann constant, andtemperature, respectively) in MgO based magnetic tunnel junctions witha Co40Fe40B20(2nm)/Ru(0.7–2.4nm)/Co40Fe40B20(2nm) synthetic ferrimagnetic (SyF) free layer. We show that Jc0 and E / kBT can be determined byanalyzing the average critical current density as a function of coercivity
using the Slonczewski’s model taking into account thermal fluctuation.
We find that high antiferromagnetic coupling between the two CoFeB
layers in a SyF free layer results in reduced Jc0 without reducing highE / kBT. [DOI : 10.1143/JJAP.45.L1057]
Keywords: current-induced magnetization switching, synthetic freelayer, magnetic tunnel junction, MgO barrier, CoFeB
1 Advanced Research Laboratory, Hitachi, Ltd., 1-280 Higashi-koigakubo, Kokubunji, Tokyo
185-8601, Japan
2 Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan* E-mail address: j-hayaka@rd.hitachi.co.jp

Jpn. J. Appl. Phys. Vol.45 (2006) pp. L1061-L1063
Part 2, No. 40, 25 October 2006
©2006 The Japan Society of Applied Physics

An Organic Light Emitting Device Employing
Transparent Rutile TiO2 as an Anode
Masaki Nakano, Tomoteru Fukumura*, Hidemi Toyosaki, Kazunori
Ueno and Masashi Kawasaki(Received July 19, 2006; accepted September 15, 2006; published online October 6, 2006)

Organic light emitting devices (OLEDs) using a transparent semiconductor rutile TiO2 film on r-sapphire substrate as an anode showsfine surface emission. The OLED structure is TiO 2 /poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS)/N,N’-Di-[(1naphthalenyl)-N,N’-diphenyl]-(1,1’-biphenyl)-4,4’-diamine (α-NPD)/tris(8hydroxyquinoline) aluminum (Alq 3)/LiF/Al. The obtained maximum
luminance and current efficiency are 1340cd/m2 at 21.0V and 1.6cd/A
at 15.0 V, respectively. Current efficiency and turn-on voltage of the
OLEDs systematically depend on the resistivity of the TiO2 anode. This
trend can be explained by dependence of hole injection efficiency on theresistivity. [DOI : 10.1143/JJAP.45.L1061]
Keywords: organic light emitting device, TiO 2, anode, oxide
semiconductor, hole injection, Alq3
Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan* E-mail address: fukumura@imr.tohoku.ac.jp

14

JSAP International No.16 (July 2007)

Yukio Narukawa*, Junya Narita1, Takahiko Sakamoto1,
Kouichiro Deguchi1, Takao Yamada1 and Takashi Mukai(Received September 14, 2006; accepted September 25, 2006; published online October 13, 2006)

We fabricated the high luminous efficiency white light emitting
diode (LED) and the high power white LED by using the patterned
sapphire substrates and an indium–tin oxide (ITO) contact as a p-type
electrode. The high luminous efficiency white LED was the yellow
YAG-phosphors-coated small-size (240 × 420 µm2) high efficiency blue
LED with the quantum efficiency of 63.3% at a forward-bias current of
20mA. The luminous flux (Φ), the forward-bias voltage (Vf), the correlated color temperature (Tcp), the luminous efficiency (ηL), and the wallplug efficiency (WPE) of the high luminous efficiency white LED are
8.6 lm, 3.11 V, 5450 K, 138 lm/W, and 41.7%, respectively. The luminous efficiency is 1.5 times greater than that of a tri-phosphor fluorescent lamp (90 lm/W). The high power white LED was fabricated fromthe larger-size (1 × 1mm2) blue LED with the output power of 458mW
at 350 mA. Φ, Vf, Tcp, ηL, and WPE of the high power white LED are
106lm, 3.29V, 5200K, 91.7lm/W, and 27.7%, respectively, at 350mA.
The WPE is greater than that of a fluorescent lamp (25%) in the visible
region. Moreover, the luminous flux of the high power white LED
reaches to 402lm at 2A, which is equivalent to the total flux of a 30W
incandescent lamp. [DOI : 10.1143/JJAP.45.L1084]
Keywords: GaN, InGaN, LED, YAG, white LED, blue LED
Nitride Semiconductor Research Laboratory, Nichia Corporation, 491 Oka, Kaminaka, Anan,
Tokushima 774-8601, Japan
1 Light Emitting Diode Front-End Engineering Department, Nichia Corporation, 491 Oka,
Kaminaka, Anan, Tokushima 774-8601, Japan* E-mail address: narukawa@hq.nichia.co.jp

Jpn. J. Appl. Phys. Vol.45 (2006) pp. L1087-L1089
Part 2, No. 41, 25 October 2006
©2006 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol.45 (2006) pp. L1114-L1117
Part 2, No. 42, 25 November 2006
©2006 The Japan Society of Applied Physics

Cr-Doping Effects to Electrical Properties
of BiFeO3 Thin Films Formed by Chemical
Solution Deposition

Characterization of Direct Immobilized Probe
DNA on Partially Functionalized Diamond
Solution-Gate Field-Effect Transistors

Sushil K. Singh*, Keisuke Sato1, Kenji Maruyama1 and Hiroshi Ishiwara

Jung-Hoon Yang1,2, Kwang-Soup Song1,2,3, Shouma Kuga1 and Hiroshi
Kawarada1,2,3,*(Received July 25, 2006; accepted September 13, 2006; published online October 13, 2006)

Cr-doped BiFeO 3 (BFO) thin films were formed by depositing
sol–gel solutions on Pt / Ti / SiO2 / Si(100) structures. Cr-doping up to
6 at % was effective in suppressing leakage current in the high electric field region and in increasing the remanent polarization. In a 3at%
Cr-doped 350-nm-thick BFO film, the remanent polarization as large as
100 µC/cm2 and the coercive field of 260 kV/cm were observed whenpolarization vs electric field hysteresis loops were drawn at a frequencyof 100kHz with the maximum electric field of 750kV/cm.
[DOI : 10.1143/JJAP.45.L1087]
Keywords: BiFeO3 film, Cr-doping, chemical solution deposition(CSD), ferroelectric properties
Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology,
4259 Nagatsuda, Midori-ku, Yokohama 226-8503, Japan
1 Fujitsu Laboratories Ltd., 10-1 Morinosato-Wakamiya, Atsugi, Kanagawa 243-0197, Japan* E-mail address: singh@neuro.pi.titech.ac.jp

Jpn. J. Appl. Phys. Vol.45 (2006) pp. L1111-L1113
Part 2, No. 42, 25 November 2006
©2006 The Japan Society of Applied Physics

30-nm-Gate AlGaN/GaN Heterostructure
Field-Effect Transistors with a Current-Gain
Cutoff Frequency of 181GHz
Masataka Higashiwaki1,*, Takashi Mimura1,2 and Toshiaki Matsui1(Received September 29, 2006; accepted September 30, 2006; published online October 20, 2006)

We fabricated Al0.4Ga0.6N(8 nm)/GaN heterostructure field-effecttransistors (HFETs) with a gate length (L G) of 30 nm on a sapphire
substrate. The AlGaN/GaN HFETs, which had a 2-nm-thick SiN passivation and gate-insulating layer formed by catalytic chemical vapor
deposition, showed a maximum drain current density of 1.49 A/mm, apeak extrinsic transconductance of 402mS/mm, a current-gain cutoff
frequency (f T) of 181 GHz, and a maximum oscillation frequency of
186 GHz. From a delay time analysis of f T for the HFETs with L G=30–150nm, the electron velocity overshoot was not observed even when LG
was decreased to 30nm.
[DOI : 10.1143/JJAP.45.L1111]
Keywords: GaN, heterostructure field-effect transistor (HFET), catalytic chemical vapor deposition (Cat-CVD), current-gain
cutoff frequency (fT), maximum oscillation frequency(fmax), millimeter wave
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* E-mail address: mhigashi@nict.go.jp(Received September 20, 2006; accepted October 2, 2006; published online October 20, 2006)

Amino groups were functionalized directly on the diamond surface
after treating 0.5 monolayer of oxidation for detection of DNAs. Also,
immobilization of probe DNAs was carried out directly on the partiallyaminated diamond without linker molecules. Specific hybridization with
21-mer DNA at a concentration of 100nM could be clearly detected by
two methods, fluorescence microscopy and diamond solution-gate fieldeffect transistors (SGFETs). DNA hybridization was confirmed using Cy-5labeled target DNA on a micropatterned diamond surface. The changes
in gate potential by the negative charge of immobilized or hybridized
DNA were measured on SGFETs and hybridization efficiency on the functionalized diamond surface was estimated as about 40%.
[DOI : 10.1143/JJAP.45.L1114]
Keywords: diamond, functionalization, DNA detection, direct
immobilization, SGFETs, micropattern
1 Department of Electronical Engineering and Bioscience, School of Science and Engineering,
Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555, Japan
2 Nanotechnology Research Center and Institute of Biomedical Engineering,
Waseda University, 513 Waseda Tsurumaki-cho, Shinjuku-ku, Tokyo 162-0041, Japan
3 Consolidated Research Institute for Advanced Science and Medical Care, Waseda University,
513 Waseda Tsurumaki-cho, Shinjuku-ku, Tokyo 162-0041, Japan* Corresponding author. E-mail address: kawarada@waseda.jp

Jpn. J. Appl. Phys. Vol.45 (2006) pp. L1136-L1138
Part 2, No. 43, 25 November 2006
©2006 The Japan Society of Applied Physics

Growth of a Two-Inch GaN Single Crystal
Substrate Using the Na Flux Method
Fumio Kawamura, Hidekazu Umeda, Masanori Morishita, Minoru
Kawahara, Masashi Yoshimura, Yusuke Mori, Takatomo Sasaki andYasuo Kitaoka1(Received October 6, 2006; accepted October 13, 2006; published online October 27, 2006)

We succeeded in growing a GaN single crystal substrate with diameter of about two inches using the Na flux method. Our success is dueto the development of a new apparatus for growing large GaN single
crystals. The crystal grown in this study has a low dislocation density of
2.3 × 105 cm-2. The secondary ion mass spectrometry (SIMS) techniquedemonstrates that the Na element is difficult to be taken in the crystal
in both the “+” and “-” c directions, resulting in a Na concentrationof 4.2 × 1014cm-3 in the crystal. Our success in growing a two-inch GaN
substrate with a low impurity content and low dislocation density shouldpave the way for the Na flux method to become a practical application.
[DOI : 10.1143/JJAP.45.L1136]
Keywords: GaN, single crystal, 2 inch, liquid phase epitaxy, LPE
Division of Electrical, Electronic and Information Engineering, Graduate School of Engineering,Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
1 Frontier Research Center, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan

JSAP International No.16 (July 2007)15

Jpn. J. Appl. Phys. Vol.45 (2006) pp. L1139-L1141
Part 2, No. 43, 25 November 2006
©2006 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol.45 (2006) pp. L1171-L1174
Part 2, No. 44, 25 November 2006
©2006 The Japan Society of Applied Physics–

Layer-by-Layer Growth of AlN on ZnO(0001)
Substrates at Room Temperature

Organic Thin-Film Transistors with Conductive
Metal–Oxides as Source–Drain Electrodes

Kohei Ueno1, Atsushi Kobayashi1, Jitsuo Ohta1,2 and Hiroshi Fujioka1,2,*

Musubu Ichikawa*, Li You, Shuhei Tatemichi, Toshiki Koyama andYoshio Taniguchi(Received October 5, 2006; accepted October 7, 2006; published online October 27, 2006)–

We have grown AlN layers on atomically flat ZnO(0001) substrates
by pulsed laser deposition at room temperature (RT) and investigatedtheir structural properties. The reflection high-energy electron-diffraction (RHEED) intensity monitoring and atomic force microscopy (AFM)
observations have revealed that the RT growth of AlN films proceeds bya layer-by-layer mode from the initial stage of the growth, and that thesurfaces of the AlN films possess atomically-flat terraces separated bystraight steps. We have also found that the AlN/ZnO heterointerfaces are
atomically abrupt. [DOI : 10.1143/JJAP.45.L1139]
Keywords: AlN, ZnO, epitaxial growth, crystal growth, pulsed laser
deposition, molecular-beam epitaxy
1 Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo
153-8508, Japan
2 Kanagawa Academy of Science and Technology (KAST), 3-2-1 Sakado, Takatsu-ku,
Kawasaki 213-0012, Japan* E-mail address: hfujioka@iis.u-tokyo.ac.jp

Jpn. J. Appl. Phys. Vol.45 (2006) pp. L1168-L1170
Part 2, No. 44, 25 November 2006
©2006 The Japan Society of Applied Physics

Enhancement-Mode AlGaN/AlN/GaN HighElectron Mobility Transistor with Low
On-State Resistance and High Breakdown
Voltage*

Yuji Ohmaki , Masashi Tanimoto, Shiro Akamatsu and Takashi Mukai(Received October 14, 2006; accepted October 16, 2006; published online November 2, 2006)

A low on-resistance and high-breakdown-voltage enhancementmode (E-mode) AlGaN/AlN/GaN high electron mobility transistor (HEMT)
was fabricated without the recessed-gate process. A thin AlGaN barrier
layer (4.5 nm) was used for the normally-off operation. In order todecrease the on-state resistance, two different techniques are used. One
is the side-ohmic contact, which has a low contact resistance, due to thedirect contact with the two-dimensional electron gas (2DEG). The otheris SiO2 passivation, which induces the sheet carriers and decreases the
sheet resistance. As a result, an on-state resistance of 1.9mΩ · cm2 andan off-state breakdown voltage of 610V were achieved for the E-mode
HEMT within a threshold voltage of approximately -0.1V.
[DOI : 10.1143/JJAP.45.L1168]
Keywords: GaN, thin AlGaN, high electron mobility transistor(HEMT), normally-off, enhancement-mode, SiO 2
passivation, side ohmic, on-state resistance, off-state
breakdown voltage
Nitride Semiconductor Research Laboratory, Nichia Corporation, 491 Oka, Kaminaka, Anan,
Tokushima 774-8601, Japan* E-mail address: yuji.omaki@nichia.co.jp

16

JSAP International No.16 (July 2007)(Received September 20, 2006; accepted October 17, 2006; published online November 2, 2006)

We demonstrated that bottom contact (BC) configuration organic
thin-film transistors (OTFTs) easily get higher performance by using
conductive metal oxide (CMO) as source and drain electrodes. Although
BC-OTFTs are more advantageous than top contact (TC) configuration in
the viewpoint of device fabrications, it is also well-known that BC-OTFTs
show poor performance compared with TC-OTFTs with the same active
material. We found out that using CMO like indium tin oxide as contact
electrodes enhanced performance of BC-OTFTs without any special
surface treatments. This manner was truly effective for most organic
semiconducting materials, for example, pentacene, polythiophene, andso on. [DOI : 10.1143/JJAP.45.L1171]
Keywords: organic transistor, organic TFT, bottom contact, pentacene, ITO
Department of Functional Polymer Science, Faculty of Textile Science and Technology, Shinshu
University, 3-15-1 Tokita, Ueda, Nagano 386-8567, Japan* Corresponding author. E-mail address: musubu@shinshu-u.ac.jp

Jpn. J. Appl. Phys. Vol.45 (2006) pp. L1190-L1192
Part 2, No. 45, 25 November 2006
©2006 The Japan Society of Applied Physics

Optical Observation of Carrier Accumulationin Single-Walled Carbon Nanotube Transistors
Taishi Takenobu1,2,*, Yuji Murayama1, Masashi Shiraishi3 andYoshihiro Iwasa1,2(Received September 30, 2006; accepted October 16, 2006; published online November 10, 2006)

Electric-field-induced spectral changes in single-walled carbon nanotubes were studied using a thin-film transistor configuration. As a function of electric field, the optical spectra displayed continuous intensity
modulations. This is the direct evidence of carrier accumulation, and theamount of accumulated carriers was quantitatively consistent with thecarrier density in the nanoscale wire-form field-effect transistor model.
[DOI : 10.1143/JJAP.45.L1190]
Keywords: single-walled carbon nanotube, field-effect device, thinfilm, optical properties
1 Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
2 CREST, Japan Science and Technology Agency, Kawaguchi, Saitama 330-0012, Japan
3 Department of Materials Engineering Science, Graduate School of Engineering Science,
Osaka University, Toyonaka, Osaka 560-8531, Japan* E-mail address: takenobu@imr.tohoku.ac.jp

Abstracts of Express Letters

Jpn. J. Appl. Phys. Vol.45 (2006) pp. L1223-L1225
Part 2, No. 46, 25 December 2006
©2006 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol.45 (2006) pp. L1286-L1288
Part 2, No. 49, 25 December 2006
©2006 The Japan Society of Applied Physics

CW Operation of the First-Order AlInGaN
405nm Distributed Feedback Laser Diodes

Room-Temperature Stimulated Emission from
AlN at 214nm

Shingo Masui, Kazutaka Tsukayama, Tomoya Yanamoto, Tokuya Kozaki,
Shin-ichi Nagahama and Takashi Mukai(Received November 7, 2006; accepted November 23, 2006; published online December 8, 2006)(Received October 14, 2006; accepted November 2, 2006; published online November 17, 2006)

The first-order AlInGaN 405 nm distributed feed-back (DFB) laser
diodes were grown on the free-standing GaN substrates by a metalorganic chemical vapor deposition method. The first-order diffractive grating was formed into an n-type cladding layer. As a result, we
succeeded in demonstrating the first-order AlInGaN based 405nm DFB
laser diodes under cw operation. The threshold current and the slope
efficiency were 22 mA and 1.44 W/A under cw operation at 25 °C,
respectively. The single longitudinal mode emission was maintained up toan output power of 60mW. The fundamental transverse mode operation
with a single longitudinal mode was observed in the temperature range
from 15 to 85°C at an output power of 20mW.
[DOI : 10.1143/JJAP.45.L1223]
Keywords: AlInGaN, laser diode, fist-order, DFB, 405nm, EB

Maxim Shatalov, Mikhail Gaevski, Vinod Adivarahan and Asif Khan*

We report the first ever room temperature (RT) stimulated emission
at 214nm using high quality AlN layers that were grown over patterned
sapphire substrates by pulsed lateral epitaxial overgrowth (PLOG)
process. The PLOG process yielded fully coalesced layers with total thicknesses in excess of 10µm resulting in a reduction in the threading dislocation density by several orders. The stimulated emission was achieved
at 214nm under pulsed optical pumping at RT. The RT threshold opticalpower density was approximately 9MW/cm2 and the stimulated edgeemission signal was strongly polarized with E || c.
[DOI : 10.1143/JJAP.45.L1286]
Keywords: AlN, nitride, stimulated emission, lasing, polarization,
MOCVD, lateral overgrowth
Department of Electrical Engineering, University of South Carolina, 301 S. Main Street,
Columbia, South Carolina 29208, U.S.A* E-mail address: asif@engr.sc.edu

LD Development Department, Nichia Corporation, 491 Oka, Kaminaka, Anan, Tokushima774-8601, Japan

Jpn. J. Appl. Phys. Vol.45 (2006) pp. L1322-L1324
Part 2, No. 50, 25 December 2006
©2006 The Japan Society of Applied Physics
Jpn. J. Appl. Phys. Vol.45 (2006) pp. L1244-L1246
Part 2, No. 47, 25 December 2006
©2006 The Japan Society of Applied Physics

Controlling Polarization of 1.55-µm
Columnar InAs Quantum Dots with Highly
Tensile-Strained InGaAsP Barriers on InP(001)
Kenichi Kawaguchi1,2,*, Nami Yasuoka1,2, Mitsuru Ekawa1,2, Hiroji Ebe3,
Tomoyuki Akiyama4, Mitsuru Sugawara1,2,4 and Yasuhiko Arakawa3,5(Received October 5, 2006; accepted November 8, 2006; published online November 24, 2006)

The optical polarization properties of columnar InAs quantum dots
(QDs) on InP substrate grown by metalorganic vapor-phase epitaxy
were investigated. The polarization of photoluminescence was foundto strongly depend on the strain in QDs as well as the shape of QDs.
We successfully changed the polarization properties from a transverseelectric-dominant to a transverse-magnetic-dominant regime by controlling the height of coupled QDs based on the stacking number and bycontrolling strain within QDs based on the thickness of 3.7%-tensilestrained barriers. Highly strained side barriers were required to change
the polarization of QDs, which is considered to be due to wetting layers
acting in maintaining biaxial-compressive strain in QDs. Polarizationinsensitive QDs with the 1.55-µm telecom region were obtained, which
promises to provide polarization-insensitive semiconductor optical amplifiers. [DOI : 10.1143/JJAP.45.L1244]
Keywords: quantum dot, polarization, tensile-strained barrier,stacking

Domain Nucleation and Annihilation in
Uniformly Magnetized State under Current
Pulses in Narrow Ferromagnetic Wires
Yoshihiko Togawa1,*, Takashi Kimura1,2, Ken Harada1,3, Tetsuya Akashi3,4,
Tsuyoshi Matsuda1,3, Akira Tonomura1,3 and Yoshichika Otani1,2(Received November 24, 2006; accepted November 26, 2006; published online December 15, 2006)

We investigate the current-driven magnetization dynamics in narrow
Permalloy wires by means of Lorentz microscopy and electron holography. Current pulses are found to transform the magnetic structure in
the uniformly magnetized state below the Curie temperature. A variety
of magnetic states including reversed magnetic domains are randomly
obtained in low probability. The dynamics of vortices found in mostof observed magnetic states seems to play a key role in triggering themagnetization reversal. [DOI : 10.1143/JJAP.45.L1322]
Keywords: current-driven magnetization dynamics, magnetic
domain nucleation, annihilation, Lorentz microscopy,
electron holography
1 Frontier Research System, the Institute of Physical and Chemical Research (RIKEN), Hirosawa,
Wako, Saitama 351-0198, Japan
2 Institute for Solid State Physics, The University of Tokyo, Kashiwanoha, Kashiwa, Chiba
277-8581, Japan
3 Advanced Research Laboratory, Hitachi, Ltd., Akanuma, Hatoyama, Saitama 350-0395,
Japan
4 Hitachi High-Tech Fielding Co., Yotsuya, Shinjuku-ku, Tokyo 160-0004, Japan* Corresponding author. E-mail address: yoshihiko.togawa.tq@hitachi.com

1 Fujitsu Limited and Fujitsu Laboratories, Limited, 10-1 Morinosato-Wakamiya, Atsugi,
Kanagawa 243-0197, Japan
2 Optoelectronic Industry and Technology Development Association (OITDA),
1-20-10 Sekiguchi, Bunkyo-ku, Tokyo 112-0014, Japan
3 Nanoelectronics Collaborative Research Center (NCRC), Institute of Industrial Science (IIS),The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan
4 QD Laser Inc., 1-14-17 Kudankita, Chiyoda-ku, Tokyo 102-0073, Japan
5 Research Center for Advanced Science and Technology (RCAST), The University of Tokyo,
4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan* E-mail address: k_kawaguchi@jp.fujitsu.com

JSAP International No.16 (July 2007)17

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L1-L3
Part 2, No. 1, 25 January 2007
©2007 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L7-L9
Part 2, No. 1, 25 January 2007
©2007 The Japan Society of Applied Physics

Reversible Resistance Switching of GeTi Thin
Film Used for Non-Volatile Memory

Nonlinear Optical Properties of theLanthanum-Modified Lead Zirconate
Titanate Ferroelectric Thin Films Using Z-Scan
TechniqueJie Shen1,2,*, Cheng Xu1,2, Bo Liu1, Zhitang Song1, Liangcai Wu1,
Songlin Feng1, and Bomy Chen3(Received November 24, 2006; accepted December 4, 2006; published online December 22, 2006)

Reversible resistance switching behavior was observed in a simple
proto-type non-volatile memory cell using GeTi thin film. The film
prepared by magnetic sputtering at room temperature was amorphous. The reversible switching phenomenon appeared when applying
a property external bias voltage on the cell. The ratio of the high resistance state (off-state) to the low resistance state (on-state) was 10–102.
Because of the electric-pulse-induced resistance switching property of
GeTi and its simple binary constitution compatible with the semiconductor industry, the application prospect of GeTi as a storage medium
for data recording can be predicted. [DOI : 10.1143/JJAP.46.L1]
Keywords: non-volatile memory, GeTi, electric-pulse-induced,
reversible resistance switching, new storage medium
1 Laboratory of Nanotechnology, Shanghai Institute of Microsystem andInformation 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

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L4-L6
Part 2, No. 1, 25 January 2007
©2007 The Japan Society of Applied Physics

Electrical Spin Injection from Out-of-Plane
Magnetized FePt/MgO Tunneling Junction
into GaAs at Room Temperature
Asawin Sinsarp*, Takashi Manago1, Fumiyoshi Takano, andHiro Akinaga(Received November 27, 2006; accepted December 6, 2006; published online December 22, 2006)

We have succeeded in demonstrating zero-magnetic-field spin injection in metal–insulator–semiconductor (MIS) structure at room temperature using FePt / MgO/GaAs-based light-emitting diode heterojunction
with out-of-plane magnetization. The spin polarization was investigatedby spin-polarized electroluminescence (EL). The lower estimate injected
at remanence was 1.5% and that injected at 1T was reached up to
11.5%. The spin injection efficiency was estimated at least 29%. The
bias dependence of the EL circular polarization showed that it decreases
with increasing bias voltage for both at 1T and at remanence.
[DOI : 10.1143/JJAP.46.L4]
Keywords: spin injection, perpendicular magnetization, tunneling
junction, spin-polarized light-emitting diode, FePt, MgO,
GaAs
Nanotechnology Research Institute (NRI), National Institute of Advanced Industrial Science andTechnology (AIST), 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan
1 Department of Electronics and Computer Science, Faculty of Science Engineering, Tokyo
University of Science, Yamaguchi, 1-1-1 Daigaku-dori, Sanyo-onoda, Yamaguchi 756-0884,
Japan* E-mail address: asawin.sinsarp@aist.go.jp

Wenjian Leng 1,*, Chuanren Yang 1, Jihua Zhang 1, Hongwei Chen 1,
Wencheng Hu1, Hong Ji1, Jinlong Tang1, Wenfeng Qin1, Junjian Li1,2,
Hui Lin1,2, and Lifeng Gao3

(Received October 27, 2006; accepted December 8, 2006; published online December 22, 2006)

Lanthanum-modified lead zirconate titanate (Pb,La)(Zr,Ti)O3 (PLZT)
ferroelectric thin films with perovskite structure were fabricated onquartz substrates by rf magnetron sputtering at 650 °C. Their opticalfundamental constants (the band gap, linear refractive index, andabsorption coefficient) were obtained through optical transmittancemeasurements with the envelope method. The nonlinear optical properties of the PLZT films were investigated by the Z-scan technique. The
films display strong nonlinear optical effects. A negative nonlinear refractive index n2 is determined to be 1.21×10-6 esu in the films. These results
show that the PLZT ferroelectric thin films are promising materials fornonlinear optics. [DOI : 10.1143/JJAP.46.L7]
Keywords: (Pb,La)(Zr,Ti)O3, rf magnetron sputtering, nonlinear
optical properties, Z-scan technique
1 State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic
Science and Technology of China, Chengdu 610054, People’s Republic of China
2 School of Optoelectronic Information, University of Electronic Science and Technology ofChina, Chengdu 610054, People’s Republic of China
3 Institute of Optics and Electronics, Chinese Academy of Sciences, Chengdu 610209,
People’s Republic of China* E-mail address: lngwen_dhj@yahoo.com

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L10-L12
Part 2, No. 1, 25 January 2007
©2007 The Japan Society of Applied Physics

Ultra High Efficiency Green Organic
Light-Emitting Devices
Daisaku Tanaka1, Hisahiro Sasabe1, Yan-Jun Li1, Shi-Jian Su1,
Takashi Takeda1, and Junji Kido1,2,*(Received November 24, 2006; accepted November 26, 2006; published online December 22, 2006)

We developed ultra high efficiency green organic light-emitting
devices (OLEDs) using a novel electron transport material containing
dipyridylphenyl moieties and green phosphorescent emitter, fac tris(2phenylpyridine)iridium, Ir(ppy)3. An OLED with a simple structure ofglass/indium–tin oxide/polymer buffer layer/arylamine derivative as ahole transport layer/Ir(ppy)3-doped dicarbazolylbiphenyl as an emitter
layer/dipyridylphenyl derivative as an electron transport layer/LiF/Al exhibited low drive voltages, which were 2.5 V at 100 cd/m2 and 2.9 V at
1000 cd / m2. High external quantum efficiencies of 29% at 100cd / m2
and 26% at 1000 cd / m2 were also observed, which lead to the ultrahigh power efficiencies of 133 lm/W at 100 cd / m2 and 107 lm/W at
1000cd / m2. [DOI : 10.1143/JJAP.46.L10]
Keywords: organic light-emitting device, iridium complex, dipyridylphenyl, electron transport layer, high efficiency
1 Optoelectronic Industry and Technology Development Association (OITDA), Bunkyo-ku,
Tokyo 112-0014, Japan
2 Department of Polymer Science and Engineering, Yamagata University, Yonezawa,
Yamagata 992-8510, Japan* Corresponding author. E-mail address: kid@yz.yamagata-u.ac.jp

18

JSAP International No.16 (July 2007)

Abstracts of Express Letters

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L25-L27
Part 2, No. 2, 25 January 2007
©2007 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L61-L63
Part 2, No. 3, 25 January 2007
©2007 The Japan Society of Applied Physics

Multilevel Data Storage Characteristics ofPhase Change Memory Cell with Doublelayer
Chalcogenide Films (Ge2Sb2Te5 and Sb2Te3)

Continuous Wave Laser Oscillation of
Stoichiometric YbAG Crystal*

Feng Rao , Zhitang Song, Min Zhong, Liangcai Wu, Gaoming Feng,
Bo Liu, Songlin Feng, and Bomy Chen1(Received December 7, 2006; accepted December 9, 2006; published online January 9, 2007)

Phase change memory (PCM) cells with monolayer chalcogenide
film (Ge2Sb2Te5 or Sb2Te3) and doublelayer chalcogenide films (Ge2Sb2Te5
and Sb2Te3) were successfully fabricated. The PCM cell with doublelayer
structure like W/Ge2Sb2Te5(30nm)/Sb2Te3(60nm) / TiN / Al shows superior
performances to monolayer ones, which is mostly referred to the reduction of set voltage value and reset voltage value, and the ability of multilevel data storage. Theoretical simulations of the temperature distributionof the PCM cell with the doublelayer structure were also investigated.
[DOI : 10.1143/JJAP.46.L25]
Keywords: phase change memory (PCM), multilevel data storage,
Sb2Te3, Ge2Sb2Te5
Nanotechnology Laboratory, Shanghai Institute of Micro-System and Information Technology,
Chinese Academy of Sciences, Shanghai 200050, China
1 Silicon Storage Technology, Inc., 1171 Sonora Court, Sunnyvale, CA 94086, U.S.A.
* E-mail address: fengrao@mail.sim.ac.cn

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L57-L60
Part 2, No. 3, 25 January 2007
©2007 The Japan Society of Applied Physics

Synthesis and Characterization of Pt/Co–O/Pt
Trilayer Exhibiting Large Reproducible
Resistance Switching
Hisashi Shima, Fumiyoshi Takano, Yukio Tamai1, Hiro Akinaga, andIsao H. Inoue2(Received November 15, 2006; accepted December 5, 2006; published online January 12, 2007)

The resistance switching in Pt / Co–O / Pt trilayers has been successfully demonstrated. The trilayers were prepared by radio-frequency
magnetron sputtering. The partial pressure of oxygen during sputteringand the post thermal process for the trilayer are crucial to realize thereproducible resistance switching. By adjusting oxygen partial pressure aswell as post-annealing temperature and time, large resistance switching
was steadily obtainable in both the as deposited and post-annealed
Pt / Co–O/Pt trilayers. The resistance switching ratio exceeds 103, being
sufficiently large for the resistance random access memory (RRAM).
Co–O is regarded as a very promising oxide for RRAM having compatibilities with the conventional complementary metal–oxide semiconductor
process. [DOI : 10.1143/JJAP.46.L57]
Keywords: ReRAM, Co oxide, magnetron sputtering, non-volatilememory, CMOS compatibility, Pt electrode, oxide thinfilm

Shinichi Matsubara*, Masahiro Inoue, Sakae Kawato, andTakao Kobayashi(Received December 8, 2006; accepted December 16, 2006; published online January 12, 2007)

Continuous wave laser oscillation of the stoichiometric microchip
YbAG crystal was realized at 1076 nm wavelength. The 200-µm-thick
YbAG crystal was pumped by the Ti:sapphire laser at 937nm. Maximum
output power of 100mW was obtained at room temperature with slope
efficiency of 38% and maximum optical-to-optical efficiency of 29% for
the incident pump power. [DOI : 10.1143/JJAP.46.L61]
Keywords: stoichiometric Yb material, YbAG crystal, quasi-threelevel, cw laser oscillation, room temperature
Graduate School of Engineering, University of Fukui, 3-9-1 Bunkyo, Fukui 910-8507, Japan* E-mail address: matubara@optele.fuee.fukui-u.ac.jp

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L64-L66
Part 2, No. 3, 25 January 2007
©2007 The Japan Society of Applied Physics

Surface Reaction Enhancement by UV
irradiation during Si Etching Process with
Chlorine Atom Beam
Seiji Samukawa*, Butsurinn Jinnai, Fumihiko Oda1, andYukihiro Morimoto1(Received December 12, 2006; accepted December 18, 2006; published online January 12, 2007)

We investigated the dependence of etching rate on irradiationof photons with a UV lamp during Si etching processes with chlorine
atom beam to understand the influence of UV photon irradiation in theplasma etching process. We found that UV from 220 to 380nm drastically enhanced Si surface reactions with a chlorine atom beam at lamp
power densities over 20mW/cm2. Additionally, we were able to control
the Si etching rate by changing the photon irradiation power density.
These results led us to speculate that the irradiation of UV photons from
220 to 380nm generates crystal defects on the Si surface and enhanceschemical reactions between Si and chlorine during Cl2 plasma etchingprocesses. [DOI : 10.1143/JJAP.46.L64]
Keywords: etching reaction, UV photon assisted reaction, neutralbeam etching, plasma etching, defect generation
Institute of Fluid Science, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
1 Fundamental Research Department, R&D Center, Lamp Company, Ushio Inc., 1194 Sazuchi,
Bessho-cho, Himeji, Hyogo 671-0224, Japan* E-mail address: samukawa@ifs.tohoku.ac.jp

Nanotechnology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 2, Tsukuba, Ibaraki 305-8568, Japan
1 Advanced Materials Research Laboratories, Sharp Corporation, Fukuyama, Hiroshima
721-8522, Japan
2 Correlated Electron Research Center, National Institute of Advanced Industrial Science andTechnology (AIST), Tsukuba Central 4, Tsukuba, Ibaraki 305-8562, Japan

JSAP International No.16 (July 2007)19

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L67-L69
Part 2, No. 3, 25 January 2007
©2007 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L97-L98
Part 2, No. 4, 25 February 2007
©2007 The Japan Society of Applied Physics

In-Situ Observation of the Fabrication
Process of a Single Shell Carbon Fullerene
Nano-Contact Using Transmission Electron
Microscope–Scanning Tunneling Microscope

Lead-Free Piezoelectric Ceramics with
Large Dielectric and Piezoelectric Constants
Manufactured from BaTiO3 Nano-Powder

1

1

2,3

Makoto Yoshida , Yoshihiko Kurui , Yoshifumi Oshima , andKunio Takayanagi1,3(Received December 1, 2006; accepted December 20, 2006; published online January 12, 2007)

A single shell carbon fullerene (SSF) was fabricated from an amorphous carbon agglomerate (a-C agglomerate) suspended between twogold electrodes. As the applied bias voltage to the a-C agglomerate wasincreased using a transmission electron microscope–scanning tunnelingmicroscope (TEM–STM) system, the transformation into the SSF via a
glassy carbon was observed. It was found that the SSF transformation
occurred above the bias voltage of 0.6V without a prominent loss of thenumber of carbon atoms. The size of the SSFs ranged from C60 to C620
having Ih or I symmetry. [DOI : 10.1143/JJAP.46.L67]
Keywords: single shell carbon fullerene, amorphous carbon
agglomerate, bias voltage, glassy carbon, size reduction,
TEM–STM1 Department of Physics, Tokyo Institute of Technology, Tokyo 152-8550, Japan
2 Department of Materials Science and Engineering, Tokyo Institute of Technology, Yokohama
226-8502, Japan
3 Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency, Kawaguchi, Saitama 332-0012, Japan

Tomoaki Karaki*, Kang Yan, Toshiyuki Miyamoto, and Masatoshi Adachi(Received December 26, 2006; accepted December 27, 2006; published online January 19, 2007)

Barium titanate (BaTiO3) ceramics with a density of more than
98% of the theoretical value were fabricated by two-step sintering
method from hydrothermally synthesized BaTiO 3 nano-particles of
100 nm. The average grain size was around 1.6 µm and the biggest
one was controlled less than 3µm. Dielectric constant εr33T of the poledsamples was 5000 and electromechanical coupling factor kp was 42%.
Large piezoelectric constants d33 = 460pC/N and d31 = -185pC/N were
measured by a d 33-meter and the resonance–antiresonance method,respectively. A high Poisson’s ratio σ = 0.38 was determined from theratio of overtone frequency and resonant frequency in the planar mode.
The high Poisson’s ratio and the large dielectric constants are most likely
the origin of the high d33 of the ceramics. The discovery of high d33 in
non-lead-based BaTiO3 ceramics with low cost process has importantpractical consequences in addition to scientific interest.
[DOI : 10.1143/JJAP.46.L97]
Keywords: lead-free, piezoelectric ceramics, barium titanate,piezoelectric constant, nano-particle, two-step sintering
Department of Intelligent Systems Design Engineering, Faculty of Engineering, Toyama Prefectural University, Imizu, Toyama 939-0398, Japan* E-mail address: chen@pu-toyama.ac.jp

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L93-L96
Part 2, No. 4, 25 February 2007
©2007 The Japan Society of Applied Physics

Acceptor Doped BiFeO3 Ceramics: A New
Material for Oxygen Permeation Membranes

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L120-L122
Part 2, No. 6, 25 February 2007
©2007 The Japan Society of Applied Physics

Kyle Brinkman*, Takashi Iijima, and Hitoshi Takamura1

Highly Manufacturable 90nm NOR FlashMulti-Level Cell Technology with WSix Gate

A new intermediate temperature mixed conducting material has
been fabricated based on acceptor doping of bismuth ferrite (BiFeO3).
Acceptor doping at levels of 5mol% with either Ca or Sr was found toincrease the maximum operating temperature of ceramics by more than
100°C as well as eliminate secondary phase formation often reported
in the pure BiFeO3 system. Mixed ionic and electronic conductivity wasconfirmed by measuring the oxygen permeation properties of doped
ceramics which exhibited flux’s on the order of 0.018 µmol/(cm2s) at
800°C over the oxygen partial pressure range 0.21atm (air) to 10-6atm(He). Ceramic membranes showed an increase in oxygen flux withdecreasing sample thickness indicating good surface catalysis propertiesof the system. [DOI : 10.1143/JJAP.46.L93]
Keywords: ionic conduction, oxygen separation membrane, point
defects, ceramics

Yun Heub Song*, Jeong Ho Park, Sang Eun Lee, Jun Young Lee, andJoong Shik Shin

(Received December 13, 2006; accepted December 23, 2006; published online January 19, 2007)

Research Center for Hydrogen Industrial Use and Storage, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 5, Tsukuba, Ibaraki 305-8565, Japan
1 Department of Materials Science, Graduate School of Engineering, Tohoku University,
Sendai 980-8579, Japan* E-mail address: kyle.brinkman@aist.go.jp(Received November 27, 2006; accepted January 18, 2007; published online February 2, 2007)

The multi-level cell (MLC) technology in flash memory has been
focused as one of solution for the enhancement of memory capacity andcost reduction. Recently, we had developed highly manufacturable 90nm
NOR flash MLC technology with WSix gate. This technology presents thecontrol of several critical parameters such as low resistance of word-line,
high transistor performance, narrow erase cell threshold voltage distribution, and high reliability characteristics. Here, tungsten silicide (WSix)
using dichlorosilane (DCS) gas chemistry is used as gate material in orderto reduce word-line resistance. Furthermore, the gate edge profile iscarefully controlled by optimizing a gate oxidation condition for narrowcell threshold voltage distribution. Finally, MLC reliability characteristic
was obtained by the advanced tunnel oxidation method.
[DOI : 10.1143/JJAP.46.L120]
Keywords: NOR flash, MLC, word-line resistance, DCS WSix, reliability
Flash Process Architecture Team, Memory Business, Samsung Electronics Co., Ltd., San \#24,
Nongseo-Ri, Giheung-Eup, Youngin-City, Gyunggi-Do 449-711, Korea* E-mail address: yunheub.song@samsung.com

20

JSAP International No.16 (July 2007)

Abstracts of Express Letters

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L126-L128
Part 2, No. 7, 25 February 2007
©2007 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L132-L134
Part 2, No. 7, 25 February 2007
©2007 The Japan Society of Applied Physics

High Power and High External Efficiency
m-Plane InGaN Light Emitting Diodes

Highly Efficient Continuous-Wave Laser
Oscillation in Microchip Yb:
YAG Laser at Room Temperature

Mathew C. Schmidt, Kwang-Choong Kim, Hitoshi Sato,
Natalie Fellows, Hisashi Masui, Shuji Nakamura, Steven P. DenBaars,
and James S. Speck(Received December 17, 2006; accepted January 25, 2007; published online February 9, 2007)–

High power and high efficiency nonpolar m-plane (1100) nitride lightemitting diodes (LEDs) have been fabricated on low extended defect bulk
m-plane GaN substrates. The LEDs were grown by metal organic chemical vapor deposition (MOCVD) using conditions similar to that of c-plane
device growth. The output power and external quantum efficiency (EQE)of the packaged 300 × 300µm2 was 23.7mW and 38.9%, respectively,
at 20 mA. The peak wavelength was 407 nm and <1nm redshift wasobserved with change in drive current from 1–20mA. The EQE shows aminimal drop off at higher currents. [DOI : 10.1143/JJAP.46.L126]
Keywords: GaN, nonpolar, m-plane, LED, high power, high efficiency

Shinichi Matsubara*, Tsutomu Ueda, Sakae Kawato, andTakao Kobayashi(Received November 2, 2006; accepted November 23, 2006; published online February 9, 2007)

Highly efficient continuous-wave laser oscillation in Yb:YAG microchip crystal has been realized at room temperature by high intensity
Ti:sapphire laser pumping. The maximum output power of 810 mW
was obtained at 1048nm wavelength oscillation. The optical-to-optical
efficiency was 81% for the incident pump power and 85% for theabsorbed pump power. These optical-to-optical efficiencies are close to
the quantum-defect-limit of 90%. [DOI : 10.1143/JJAP.46.L132]
Keywords: Yb:YAG, quasi-three-level, high-efficiency oscillation,high intensity pumping, room temperature
Graduate School of Engineering, University of Fukui, 3-9-1 Bunkyo, Fukui 910-8507, Japan* E-mail address: matubara@optele.fuee.fukui-u.ac.jp

Materials Department, and ERATO JST, UCSB Group, University of California, Santa Barbara, CA
93106, U.S.A.

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L135-L137
Part 2, No. 7, 25 February 2007
©2007 The Japan Society of Applied Physics
Jpn. J. Appl. Phys. Vol.46 (2007) pp. L129-L131
Part 2, No. 7, 25 February 2007
©2007 The Japan Society of Applied Physics

High Brightness Violet InGaN/GaN– Light–
Emitting Diodes on Semipolar (1011) Bulk
GaN Substrates
1,*

1

1

1

Anurag Tyagi , Hong Zhong , Natalie N. Fellows , Michael Iza ,James S. Speck1,2, Steven P. DenBaars1,2, and Shuji Nakamura1,2(Received December 16, 2006; accepted January 23, 2007; published online February 9, 2007)

We report the fabrication of violet InGaN/GaN light-emitting diodes––(LEDs) on semipolar (1011) GaN bulk substrates. The LEDs have a dimen2
sion of 300 × 300µm and are packaged in an epoxy resin. The output
power and external quantum efficiency (EQE) at a driving current of
20mA were 20.58mW and 33.91% respectively, with peak electroluminescence (EL) emission wavelength at 411nm. The LEDs show minimal
shift in peak EL wavelength with increasing drive current along with ahigh EQE. [DOI : 10.1143/JJAP.46.L129]––
Keywords: semipolar, (1011) plane, InGaN, light-emitting diode,GaN bulk substrate
1 Electrical and Computer Engineering and Materials Departments, University of California,
Santa Barbara, CA 93106, U.S.A.
2 NICP/ERATO JST, UCSB Group, University of California, Santa Barbara, CA 93106, U.S.A.
* E-mail address: anurag@ece.ucsb.edu

Readout Durability Improvement ofSuper-Resolution Near-Field Structure
Discs with PtOx–SiO2 Recording and GeNy
Interfacial Layers
Takayuki Shima*, Yuzo Yamakawa, and Junji Tominaga(Received November 15, 2006; accepted January 23, 2007; published online February 9, 2007)

Two dielectric materials were added to a super-resolution near-field
optical disc structure (super-RENS) to improve the readout durability.
PtOx–SiO2 (Pt8.4Si21.1O70.5) layers showed O2 desorption for temperatures
above 200°C and were usable as write-once recording layers. The GeNy
interfacial layers located between the Sb75Te25 and (ZnS)85(SiO2)15 layers
suppressed degradation in the reflected light intensity from the disc, i.e.,maintained the recorded structure as is, to at least 5× 104 readout cycles
using a recorded pattern designed to accelerate disc deterioration. The
carrier-to-noise ratio (CNR) obtained for 100-nm marks (laser wavelength:
405nm, numerical aperture: 0.65) was about 43dB. It was possible toreadout 2.6×105 cycles before the CNR decreased by 3dB. This represents an improvement of a factor of 70 over the readout durability of aconventional super-RENS structure. [DOI : 10.1143/JJAP.46.L135]
Keywords: super-RENS, readout durability, platinum oxide, germanium nitride, interfacial layer
Center for Applied Near-Field Optics Research (CAN-FOR), National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba, Ibaraki 305-8562, Japan* E-mail address: t-shima@aist.go.jp

JSAP International No.16 (July 2007)21

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L151-L153
Part 2, No. 8, 25 March 2007
©2007 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L157-L160
Part 2, No. 8, 25 March 2007
©2007 The Japan Society of Applied Physics

Injection and Population Inversion inElectrically Induced p–n Junction in Graphenewith Split Gates

Ultrafast All-Optical Refractive Index
Modulation in Intersubband Transition Switch
Using InGaAs/AlAs/AlAsSb Quantum Well

Maxim Ryzhii and Victor Ryzhii

Hiroshi Ishikawa, Hidemi Tsuchida, Kazi Sarwar Abedin1,
Takasi Simoyama, Teruo Mozume, Masanori Nagase, Ryoichi Akimoto,Tetsuya Miyazaki1, and Toshifumi Hasama(Received January 6, 2007; accepted February 2, 2007; published online February 16, 2007)

We study electron and hole injection processes in a forward biased
p–n junction electrically induced in a graphene heterostructure with split
gates and calculate the ac conductivity associated with the interband
and intraband transitions under the conditions of population inversion. It
is shown that the net conductivity can be negative in the terahertz rangeof frequencies, so that the electrically induced p–n junctions in graphene
heterostuctures might be used in sources of coherent terahertz radiation.
[DOI : 10.1143/JJAP.46.L151]
Keywords: graphene, split gates, two-dimensional electron–holesystem, p–n junction, injection, population inversion, ac
interband and intraband conductivity, terahertz radiation
Computer Solid State Physics Laboratory, University of Aizu, Aizu-Wakamatsu, Fukushima
965-8580, Japan

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L154-L156
Part 2, No. 8, 25 March 2007
©2007 The Japan Society of Applied Physics

Active Magnetic Regeneration Behaviorof Spherical Hydrogenated La(Fe0.86Si0.14)13
Fabricated by Rotating Electrode Process
Asaya Fujita, Sadayoshi Koiwai1, Shun Fujieda, Kazuaki Fukamichi2,
Tadahiko Kobayashi3, Hideyuki Tsuji3, Shiori Kaji3, andAkiko Takahashi Saito3(Received December 26, 2006; accepted January 30, 2007; published online February 16, 2007)

To verify effectiveness for a magnetic refrigerant, we have fabricated spheres of La(Fe0.86Si0.14)13 by a rotating electrode process (REP).
The Curie temperature of the spheres was increased up to around room
temperature by hydrogen absorption. Putting these spheres into an
active magnetic regenerator (AMR) test module, the temperature spanof 16K in the vicinity of room temperature was obtained in a steadystate. Consequently, it has been confirmed for the first time that theLa(Fe0.86Si0.14)13 spheres perform as an excellent material for the AMR.
[DOI : 10.1143/JJAP.46.L154]
Keywords: magnetocaloric effect, itinerant-electron metamagnetictransition, active magnetic regenerator (AMR), rotating
electrode process
Department of Materials Science, Graduate School of Engineering, Tohoku University, Sendai
980-8579, Japan
1 JST Research Fellow, JST Plaza Miyagi, Sendai 989-3204, Japan
2 Institute for Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai
980-8577, Japan
3 Corporate Research and Development Center, Toshiba Corporation, Kawasaki 212-8582,
Japan

22

JSAP International No.16 (July 2007)(Received January 12, 2007; accepted February 2, 2007; published online February 16, 2007)

Large, very fast phase modulation was observed in transverse electric(TE) probe light when an intersubband transition (ISBT) switch moduleusing an InGaAs/AlAs/AlAsSb quantum well was pumped by transverse
magnetic (TM) light. The phase shift amounted to 1.88rad for a pumppulse energy of 4pJ (fiber input), with very fast response. This phenomenon is explained by the change in plasma dispersion caused by the redistribution of electrons among subbands having different effective masses.
This phase modulation will enable us to realize various novel ultrafast
all-optical devices for signal processing. [DOI : 10.1143/JJAP.46.L157]
Keywords: intersubband transition, quantum well, phase modulation, refractive index, band nonparabolicity, effective
mass
National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki
305-8568, Japan
1 National Institute of Information and Communications Technology (NICT), Koganei, Tokyo
184-8795, Japan

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L161-L163
Part 2, No. 8, 25 March 2007
©2007 The Japan Society of Applied Physics

Direct Observation of Molecular Orbital at
Carbon Nanotube End
Masayuki Furuhashi1 and Tadahiro Komeda1,2(Received January 23, 2007; accepted January 29, 2007; published online February 16, 2007)

We report the appearance of superstructures in the topologicalimages of scanning tunneling microscopy of single wall carbon nanotubes in the regions near the cap. These structures are localized with
6–7nm from nanotubes ends and provide wavy pattern parallel to thearmchair direction. Our molecular orbital calculation indicates that thesuperstructure shows a good agreement with calculated lowest unoccupied molecular orbital state. We consider the observed structures are theappearance of real (or imaginary) part of the Bloch state, which occurs
as the result of the quantum interference between forward and backward waves. This suggests that the scattering of wave vector from k to -k
occurs in two-dimensional manner at the end of the tube.
[DOI : 10.1143/JJAP.46.L161]
Keywords: carbon nanotube, scanning tunneling microscopy,
superlattice, molecular orbital
1 Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai
980-8577, Japan
2 CREST, JST, Kawaguchi, Saitama 332-0012, JapanAbstracts of Express Letters

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L187-L189
Part 2, No. 9, 25 March 2007
©2007 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L192-L195
Part 2, No. 9, 25 March 2007
©2007 The Japan Society of Applied Physics

Continuous-Wave Operation of m-Plane
InGaN Multiple Quantum Well Laser Diodes

X-ray Induced Effects on Photocurrents in
Amorphous Se Films

Kuniyoshi Okamoto*, Hiroaki Ohta, Shigefusa F. Chichibu1,**,Jun Ichihara, and Hidemi Takasu

Koichi Shimakawa, Kenji Fukami, Hiroki Kishi, George Belev1, andSafa Kasap1(Received February 4, 2007; accepted February 6, 2007; published online February 23, 2007)(Received January 30, 2007; accepted February 4, 2007; published online February 23, 2007)

Continuous-wave (CW) operation of nonpolar m-plane InGaN/GaN
laser diodes (LDs) with the lasing wavelengths approximately 400 nm
was demonstrated. The threshold current was 36 mA (4.0 kA/cm2) for
the CW operation [28mA (3.1kA/cm2) for pulsed mode], being comparable to that of conventional c-plane violet LDs. Both the LDs with thestripes parallel to a- and c-axes showed TE mode operation, according
to the polarization selection rules of the transitions in strained InGaN.
The c-axis stripe LDs exhibited lower threshold current density, since thelowest energy transition is allowed. As is the case with the m-plane lightemitting diodes fabricated on the free-standing m-plane GaN bulk crystals [Okamoto et al.: Jpn. J. Appl. Phys. 45 (2006) L1197], the LDs shownin this paper did not have distinct dislocations, stacking faults, or macroscopic cracks. Nonpolar m-plane GaN-based materials are coming into
general use. [DOI : 10.1143/JJAP.46.L187]
Keywords: nonpolar, m -plane, InGaN, laser diode, GaN bulk
substrate, polarized light

Amorphous selenium (a-Se) is one of the X-ray photoconductors thatis available for use in recently developed direct conversion flat panel X-ray
image detectors for medical imaging. To obtain a better understandingof trapping and recombination effects in a-Se, we have studied light and
X-ray induced photocurrents in a-Se films. The residual photocurrent,
after X-ray exposure, decreases in sandwich cells whereas it increases in
coplanar cells. These effects are recovered over a time scale of hours. We
show that the results can be interpreted by using valence alternation pair(VAP) type charged defects. [DOI : 10.1143/JJAP.46.L192]
Keywords: amorphous selenium, X-ray image detector, X-ray
induced carriers, X-ray induced photocurrent, directconversion of X-ray image, ghosting image

Research and Development Headquarters, ROHM Co., Ltd., Kyoto 615-8585, Japan
1 Institute of Applied Physics and 21st Century Center-of-Excellence Office,
University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan* E-mail address: Kuniyoshi.Okamoto@dsn.rohm.co.jp** Present address: Institute of Multidisciplinary Research for Advanced Materials,
Tohoku University, 2-1-1 Katahira, Aoba, Sendai 980-8577, Japan

Department of Electrical and Electronic Engineering, Gifu University, Gifu 501-1193, Japan
1 Department of Electrical Engineering, University of Saskatchewan, S7N 5A9 Canada

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L196-L198
Part 2, No. 9, 25 March 2007
©2007 The Japan Society of Applied Physics

Electric Field Breakdown of Lateral Schottky
Diodes of DiamondTokuyuki Teraji*, Satoshi Koizumi, Yasuo Koide, and Toshimichi Ito1

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L190-L191
Part 2, No. 9, 25 March 2007
©2007 The Japan Society of Applied Physics

Demonstration of Nonpolar m-Plane
InGaN/GaN Laser Diodes
Mathew C. Schmidt, Kwang-Choong Kim, Robert M. Farrell, Daniel F.
Feezell, Daniel A. Cohen, Makoto Saito, Kenji Fujito1, James S. Speck,
Steven P. DenBaars, and Shuji Nakamura(Received January 29, 2007; accepted February 4, 2007; published online February 23, 2007)

The first nonpolar m-plane (1-100) nitride laser diodes (LDs) havebeen realized on low extended defect bulk m-plane GaN substrates. The
LDs were grown by metal organic chemical vapor deposition (MOCVD)
using conditions similar to that of c-plane device growth. Broad arealasers were fabricated and tested under pulsed conditions. Lasing
was observed at duty cycles as high as 10%. These laser diodes had
threshold current densities (Jth) as low as 7.5kA/cm2. Stimulated emission
was observed at 405.5nm, with a spectral line-width of 1nm.
[DOI : 10.1143/JJAP.46.L190]
Keywords: GaN, nonpolar, m-plane, laser diode(Received January 9, 2007; accepted February 6, 2007; published online February 23, 2007)

Current–voltage characteristics of Al lateral Schottky diodes fabricated on homoepitaxial diamond (100) films were analyzed. The currents
in reverse-bias voltages smaller and larger than 3V were well explainedby the image-force lowering mechanism modified by localized-fieldenhancement and the thermionic-field emission mechanism, respectively.
An electric field breakdown was observed when the maximum electricfield was in the range 1.08–1.46MV/cm. The breakdown electric field
became large with increasing the Schottky barrier height. These features
suggest that the electric field breakdown occurred at the electrode fringe
due to the field enhancement. [DOI : 10.1143/JJAP.46.L196]
Keywords: diamond, Schottky, breakdown, field enhancement
Sensor Materials Center, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki
305-0044, Japan
1 Department of Electrical, Electronic and Information Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan* E-mail address: TERAJI.Tokuyuki@nims.go.jp

Materials Department, and ERATO JST, UCSB Group, University of California, Santa Barbara, CA
93106, U.S.A.
1 Optoelectronics Laboratory, Mitsubishi Chemical Corporation, 1000 Higashi-Mamiana,
Ushiku, Ibaraki 300-1295, Japan

JSAP International No.16 (July 2007)23

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L218-L220
Part 2, No. 10, 25 March 2007
©2007 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L244-L246
Part 2, No. 11, 25 March 2007
©2007 The Japan Society of Applied Physics

Narrow-Bandwidth High-Brightness
External-Cavity Laser Diode Bar

Electro-Optic Properties ofLanthanum-Modified Lead Zirconate Titanate
Thin Films Epitaxially Grown by the Advanced
Sol–Gel Method

Yujin Zheng* and Hirofumi Kan(Received February 5, 2007; accepted February 14, 2007; published online March 2, 2007)

The spectral bandwidth and beam divergence of a high-power
laser diode bar were simultaneously suppressed with an external-cavity
configuration consisting of a micro-cylindrical lens and an off-axis volume
Bragg grating. We reduced the bandwidth from 1.7 to 0.32nm and thedivergence angle from 7.5 to 2.7° under operation at a peak current of
55A. The external-cavity laser diode bar achieved a peak power output
of 36.6W, or as much as 80% of the power radiated by a free-runninglaser diode bar without an external cavity. [DOI : 10.1143/JJAP.46.L218]
Keywords: laser diode bar, volume Bragg grating, external cavity,
bandwidth, divergence angle, output efficiency
Central Research Laboratory, Hamamatsu Photonics K.K., 5000 Hirakuchi, Hamamatsu,
Shizuoka 434-8601, Japan* E-mail address: y-zheng@crl.hpk.co.jp

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L221-L223
Part 2, No. 10, 25 March 2007
©2007 The Japan Society of Applied Physics

Sinusoidal Voltage-Controlled Oscillator
Based on a Liquid Crystal Cell as Variable
CapacitanceIsabel Pérez, José M. Sánchez-Pena*, Juan C. Torres,
Rodrigo Manzanares, José M. Otón1(Received December 27, 2006; accepted February 8, 2007; published online March 2, 2007)

A voltage-controlled oscillator (VCO) in Colpitts circuit configuration is demonstrated using a twisted-nematic (TN) liquid crystal (LC) cell
as a capacitance that can be varied as a function of applied voltage.
Oscillation frequencies in the range of kHz have been obtained for the
combination of inductance and capacitances used in the circuit. A theoretical study for the whole circuit is proposed and experimentally validated. Applications of this circuit include, among others, modulation anddemodulation frequency signal, phase locked-loops, and function generators. [DOI : 10.1143/JJAP.46.L221]
Keywords: liquid crystal cell, variable capacitance, feedback,voltage-controlled oscillator, communication systems
Departamento de Tecnología Electrónica, Universidad Carlos III, Avenida de la Universidad 30,
Leganés E28911, Madrid, Spain
1 Departamento de Tecnología Fotónica, Universidad Politécnica de Madrid, Ciudad Universitaria s / n, E28040, Madrid, Spain* E-mail address: jmpena@ing.uc3m.es

Kiyoshi Uchiyama*, Atsushi Kasamatsu**, Yohei Otani***, and Tadashi
Shiosaki(Received January 19, 2007; accepted February 15, 2007; published online March 9, 2007)

Epitaxially grown lanthanum-modified lead zirconate titanate (PLZT)
thin films were deposited on r-cut sapphire substrates using an advanced
sol–gel method. The methanol addition into sol–gel solutions brought
high quality epitaxial growth of PLZT thin films. This film showed highelectro-optic (EO) coefficients that were almost comparable to those ofbulk PLZTs. We believe this PLZT deposition technique will open the door
for the future data communication systems with integrated EO devices.
[DOI : 10.1143/JJAP.46.L244]
Keywords: lanthanum-modified lead zirconate titanate, PLZT,
electro-optic coefficients, epitaxial growth, thin films
Graduate School of Materials Science, Nara Institute of Science and Technology (NAIST), 8916-5
Takayama-cho, Ikoma, Nara 630-0192, Japan* E-mail address: uchiyama@ms.naist.jp** Present affiliation: Sumitomo Electric Industries, Ltd.
*** Present affiliation: Tokyo University of Science, Suwa.

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L263-L264
Part 2, No. 12, 25 April 2007
©2007 The Japan Society of Applied Physics

247nm Ultra-Violet Light Emitting Diodes
Jianyu Deng*, Yuriy Bilenko, Alex Lunev, Xuhong Hu,
Thomas M. Katona, Jianping Zhang, Michael S. Shur, and Remis Gaska(Received February 13, 2007; accepted February 28, 2007; published online March 16, 2007)

We report on AlGaN-based ultraviolet light emitting diodes withemission at the wavelengths as short as 247nm. Migration-enhanced
metal organic chemical vapor deposition technique allowed us to
improve the material quality. The phonon energy gap engineering
approach was used to optimize these UV sources and achieve continuous-wave regime at turn-on voltages lower than 8V at 20mA current.
Power levels of 0.3mW were achieved for the packaged devices driven
at 90mA DC current. In the pulse operation 9mW output power wasmeasured at 1.4A current. The peak to noise emission ratio was close to
400 at cw current in excess of 20mA. [DOI : 10.1143/JJAP.46.L263]
Keywords: AlGaN, deep ultra-violet, light emitting diode,sub-250nm, MEMOCVD
Sensor Electronic Technology, Inc., 1195 Atlas Rd., Columbia, SC 29209, U.S.A.
* E-mail address: deng@s-et.com

24

JSAP International No.16 (July 2007)

Abstracts of Express Letters

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L265-L267
Part 2, No. 12, 25 April 2007
©2007 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L281-L283
Part 2, No. 13, 25 April 2007
©2007 The Japan Society of Applied Physics

Photoinduced Phenomena in GeO2–GeS2
Glasses

Strong Intersubband Absorption in EuTe/PbTe
Double-Well Superlattices at Normal Incidence

Nobuaki Terakado and Keiji Tanaka

Akihiro Ishida, Martin Veis1, and Yoku Inoue(Received February 23, 2007; accepted February 26, 2007; published online March 16, 2007)(Received January 28, 2007; accepted March 7, 2007; published online March 23, 2007)

Composition dependences of glass-transition temperature, opticalgap, photodarkening, and photoinduced volume change in x GeO2–(100-x) GeS2 oxy-chalcogenide glasses have been studied comparatively.
The transition temperature and optical gap are nearly constant at 0 ≤ x<~80mol%, while the photodarkening and volume expansion appear
only at x <~60. Implications of these results are discussed.
[DOI : 10.1143/JJAP.46.L265]
Keywords: photoinduced phenomena, photodarkening,volume expansion, percolation, oxide, chalcogenide,oxy-chalcogenide, GeO2, GeS2

EuTe/PbTe double-well superlattices with two kinds of PbTe
quantum wells separated by monolayer EuTe were prepared on KCl(100)substrates by hot wall epitaxy. Strong intersubband absorptions as highas 2000cm-1 in absorption coefficient were observed for n-type samples
with a carrier concentration as high as 3×1018cm-3 at normal incidence.
The absorption was caused through the modulation of quantum-wellpotential along superlattice direction at L-point of the Brillouin zone.
Temperature dependence of the optical transmission properties was alsomeasured and the absorption peak showed a large tunability of 0.9cm-1K-1 caused by large temperature dependence of effective masses in PbTe.
[DOI : 10.1143/JJAP.46.L281]
Keywords: intersubband absorption, IV–VI semiconductor, superlattice, quantum well, optical property

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

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L268-L270
Part 2, No. 12, 25 April 2007
©2007 The Japan Society of Applied Physics

Photon Antibunching in the Emission from aSingle Organic Dye Nanocrystal
Sadahiro Masuo1,2, Akito Masuhara3, Takeaki Akashi1, Mai Muranushi1,
Shinjiro Machida1, Hitoshi Kasai3, Hachiro Nakanishi3,
Hidetoshi Oikawa3, and Akira Itaya1(Received February 6, 2007; accepted February 24, 2007; published online March 16, 2007)

We demonstrated that the emission from a single organic nanocrystal consisting of organic dye molecules shows photon antibunching.
That is, an assembling structure consisting of many chromophores canalso be made to behave as a single-photon source by controlling the size.
We found that most of single nanocrystals within a size range from 35
to 85nm show photon antibunching even when more than one exciton
in a crystal is generated by an intense single excitation pulse. On theother hand, single micrometer-sized crystals showed no antibunching.
The present results indicate that molecular assemblies can also be considered as candidates for new single-photon sources.
[DOI : 10.1143/JJAP.46.L268]
Keywords: nanocrystal, single-photon source, photon antibunching, quantum cryptography, photon correlation
measurement, coincidence measurement, emission,
perylenebisimide, molecular assembly

Department of Electrical and Electronic Engineering, Faculty of Engineering, Shizuoka University, 3-5-1 Johoku, Hamamatsu, Shizuoka 432-8561, Japan
1 Graduate School of Electronic Science and Technology, Shizuoka University, 3-5-1 Johoku,
Hamamatsu, Shizuoka 432-8561, Japan

Jpn. J. Appl. Phys. Vol.46 (2007) pp. L284-L286
Part 2, No. 13, 25 April 2007
©2007 The Japan Society of Applied Physics

AlGaN-Cladding-Free Nonpolar InGaN/GaN
Laser Diodes
Daniel F. Feezell*, Mathew C. Schmidt, Robert M. Farrell,
Kwang-Choong Kim, Makoto Saito, Kenji Fujito 1, Daniel A. Cohen,
James S. Speck, Steven P. DenBaars, and Shuji Nakamura(Received February 27, 2007; accepted March 9, 2007; published online March 23, 2007)

We demonstrate highly manufacturable nonpolar ( m -plane)
InGaN/GaN laser diodes without any Al-containing waveguide cladding layers. These devices utilize thick InGaN quantum wells to generatetransverse optical mode confinement and can be grown and fabricatedin a manner analogous to InGaN/GaN light emitting diodes. Pulsed lasing
operation was demonstrated, with threshold voltages and current densities of 6.7V and 3.7kA/cm2, respectively. [DOI : 10.1143/JJAP.46.L284]
Keywords: GaN, nonpolar, m-plane, laser diodeMaterials Department, University of California, Santa Barbara, CA 93106, U.S.A.
1 Optoelectronics Laboratory, Mitsubishi Chemical Corporation, 1000 Higashi-Mamiana,
Ushiku, Ibaraki 300-1295, Japan* E-mail address: feezell@engineering.ucsb.edu

1 Department of Macromolecular Science and Engineering, Kyoto Institute of Technology,
Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan
2 PRESTO, Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama
332-0012, Japan
3 Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1
Katahira, Aoba-ku, Sendai 980-8577, Japan

JSAP International No.16 (July 2007)25