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. 42 (2003) pp. L1293-L1295
Part 2, No. 11A, 1 November 2003
©2003 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol. 42 (2003) pp. L1296-L1298
Part 2, No. 11A, 1 November 2003
©2003 The Japan Society of Applied Physics

Impact of Vicinal Sapphire (0001) Substrates
on the High-Quality AlN Films by
Plasma-Assisted Molecular Beam Epitaxy

High-Power Continuous Wave Green
Generation by Single-Pass Frequency Doublingof a Nd:GdVO4 Laser in a Periodically Poled
MgO:LiNbO3 Operating at Room Temperature

Xu-Qiang SHEN*, Mitsuaki SHIMIZU and Hajime OKUMURA(Received September 2, 2003; accepted September 16, 2003; published October 22, 2003)

AlN films grown by plasma-assisted molecular beam epitaxy on vicinal sapphire (0001) substrates were investigated. High structural andoptical qualities were confirmed by high-resolution X-ray diffraction and
77K cathodoluminescence measurements. It was found that changing
the vicinal angles of sapphire substrates can easily control the surface
morphologies of AlN films. Spiral-growth features were greatly suppressed. Furthermore, well-ordered straight monatomic-layer steps andmulti-atomic-layer macro-steps were clearly observed by atomic force
microscopy. Surface diffusion and step incorporation kinetics during the
growth are the key-factors in determining the surface morphologies.
[DOI : 10.1143/JJAP.42.L1293]
KEYWORDS: AlN, vicinal sapphire (0001) substrate, surface diffusion,
step bunching, rf-MBE

Power Electronics Research Center, National Institute of Advanced Industrial Science and Technology (AIST), Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan* Corresponding author. E-mail address: xq-shen@aist.go.jp

Kiminori MIZUUCHI*, Akihiro MORIKAWA, Tomoya SUGITA,
Kazuhisa YAMAMOTO, Nicolaie PAVEL1, Ichiro SHOJI1 andTakunori TAIRA1, **(Received September 9, 2003; accepted September 11, 2003; published October 22, 2003)

Continuous-wave power of 0.89 W at 531 nm with 14.3% conversion efficiency is reported at room temperature from a 2-mm-thick periodically polled uncoated MgO:LiNbO3 by single-pass frequency doublingof a diode end-pumped Nd:GdVO4 laser; the corresponding internal
green power and conversion efficiency were 1.03 W and 16.5%, respectively. The MgO:LiNbO3 device of 6.95-µm domain period was fabricatedby using a high-voltage multi-pulse poling method; uniform periodicity and 50% duty cycle were obtained on the entire 10-mm-long crystal.
The sample exhibited an effective nonlinear coefficient of 14 pm/V (∼88%of the ideal nonlinear coefficient), resulting in a measured normalized
conversion efficiency of 2.7%/ W. To the authors best knowledge thisis the highest power ever obtained by quasi-phase matching process atroom temperature. [DOI : 10.1143/JJAP.42.L1296]
KEYWORDS: second-harmonic generation, quasi-phase matching, periodically poled MgO:LiNbO3, Nd:GdVO4 laser

Storage Media Systems Development Center, Matsushita Electric Industrial Co., Ltd.,
3-1-1 Yagumo-Nakamachi, Moriguchi, Osaka 570-8501, Japan
1 Laser Research Center, Institute for Molecular Science, 38 Nishigonaka, Okazaki 444-8585,
Japan* Author to whom correspondence should be addressed.
E-mail address: mizuuchi.kiminori@jp.panasonic.com** E-mail address: taira@ims.ac.jp

JSAP International No.10 (July 2004)15

Jpn. J. Appl. Phys. Vol. 42 (2003) pp. L1347-L1349
Part 2, No. 11B, 15 November 2003
©2003 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol. 42 (2003) pp. L1353-L1355
Part 2, No. 11B, 15 November 2003
©2003 The Japan Society of Applied Physics

Solid Phase Crystallization in Initial Growth
Region of Polycrystalline Silicon Layer During
Deposition at 180°C by Plasma Chemical Vapor
Deposition

Carrier Injection and Transport of Steady-State
High Current Density Exceeding 1000 A/cm2 in
Organic Thin Films*

Toshihiko TOYAMA, Riza MUHIDA, Tomokazu HARANO,
Tsuyoshi SUGANO, Masaya OKAJIMA and Hiroaki OKAMOTO(Received September 19, 2003; accepted September 29, 2003; published November 5, 2003)

Microstructures of low-temperature-grown polycrystalline Si (poly-Si)
have been studied by transmission electron microscope measurements.
Two poly-Si layers with different thicknesses in the n-i-p structure wereprepared by plasma chemical vapor deposition at 180°C. The ∼50-nmthick amorphous-rich layer is observed at the bottom of the 0.5-µmthick poly-Si layer. Meanwhile, in the first hundreds of nanometers in
the 2.4-µm-thick poly-Si layer, an increase in the crystalline fraction due
to crystalline columns grown onto the substrate n-layer is found. Solidphase crystallization during the deposition in the initial growth region
down to the substrate is discussed. [DOI : 10.1143/JJAP.42.L1347]
KEYWORDS: solid phase crystallization, microstructure, plasma chemical vapor deposition, silicon, thin film
Department of Systems Innovation, Graduate School of Engineering Science, Osaka University,
Toyonaka, Osaka 560-8531, Japan

Wataru YOKOYAMA, Hiroyuki SASABE1 and Chihaya ADACHI1,**(Received October 1, 2003; accepted October 8, 2003; published November 5, 2003)

We demonstrate carrier injection and transport of steady-state highcurrent density into organic thin films. The maximum current density
reaches J =1053A/cm2, the highest ever reported. We employ a 25 nmthick Copper phthalocyanine (CuPc) thin film sandwiched between an
indium-tin-oxide anode and a magnesium-silver alloy cathode with anactive electrode dot-size (S ) of S =2.0×10-5cm2 (radius: r =25 µm). We observed that the maximum current density depends on the organic materials used, and the device size and thickness. Decreasing the organic
layer thickness significantly changes the current density-voltage (J -V )characteristics, demonstrating that the rate-limiting step of the J -V characteristics changes from the carrier transport process to the carrier injection process. Our achievement of high current density exceeding 1000
A/cm2 in organic thin films is a first step towards the development of organic laser diodes that need extremely high excitation intensity.
[DOI : 10.1143/JJAP.42.L1353]
KEYWORDS: high current density, 1000A/cm2, OLED, organic laser diode, CuPc
Department of Photonics Materials Science, Chitose Institute of Science and Technology (CIST),
758-65 Bibi, Chitose, Hokkaido 066-8655, Japan
1 CREST Program, Japan Science and Technology Agency (JST), Japan* This paper was originally presented in the 50th Spring Meet. Japan Society of Applied Physics
and Related Societies, 2003. (Ext. Abstr., Paper No. 29p-A-8) W. Yokoyama, H. Sasabe and
C. Adachi.
** E-mail address: c-adachi@photon.chitose.ac.jp

Jpn. J. Appl. Phys. Vol. 42 (2003) pp. L1350-L1352
Part 2, No. 11B, 15 November 2003
©2003 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol. 42 (2003) pp. L1356-L1358
Part 2, No. 11B, 15 November 2003
©2003 The Japan Society of Applied Physics

29

Insulator-Coated Carbon Nanotubes
Synthesized by Pulsed Laser Deposition

Si Nuclear-Spin Decoherence Process
Directly Observed by Multiple Spin-Echoes
for Pure and Carrier-Less Silicon
1,2Shinji WATANABE and Susumu SASAKI(Received September 22, 2003; accepted September 28, 2003; published November 5, 2003)

We report on the 29Si nuclear spin decoherence time at room temperature for a pure (99.99999%, 7N) and carrier-less (p-type, doping level of 1015cm-3) silicon in which 29Si nuclei are naturally abundant(4.7%). Despite the experimental difficulties coming from the extremely
long spin-lattice relaxation time T 1 (of the order of 104 s), we have successfully observed a series of spin-echoes of which the time dependence
is characterized by the decoherence time T 2. We found that the decoherence process deviates from a single Gaussian or Lorentzian function but
is well-reproduced by a bi-exponential function with the shorter T 2S=15±
5 ms and the longer T 2L=200± 20 ms.
[DOI : 10.1143/JJAP.42.L1350]
KEYWORDS: 29Si, NMR, quantum computing, decoherece, multiple
spin-echoes, Carr-Purcell method
Graduate School of Science and Technology, Niigata University, 8050 Ikarashi 2 no-cho, Niigatashi, Niigata 950-2181, Japan
1 Department of Materials Science and Technology, Faculty of Engineering, Niigata University,
8050 Ikarashi 2 no-cho, Niigata-shi, Niigata 950-2181, Japan
2 Core Research for Evolutional Science and Technology, Japan Science and Technology Corporation (CREST-JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan

16

JSAP International No.10 (July 2004)

Takashi IKUNO1, Mitsuhiro KATAYAMA1,*, Kazunori KAMADA1,
Shin-ichi HONDA1, Jung-Goo LEE2, Hirotaro MORI2 and Kenjiro OURA1,2(Received September 18, 2003; accepted September 29, 2003; published November 5, 2003)

We present a method for synthesizing insulator-coated carbon nanotubes by pulsed laser deposition. Isolated multi-walled carbon nanotubes (MWNTs) were coated with an SiOx thin layer in a multishell form.
The product showed that a stoichiometric SiO2 thin layer was uniformly
wrapped around a MWNT, and reflected the shape of the MWNT. The
thickness of the SiO2 thin layer was precisely controlled in the range
from 2 to 28 nm. The insulating property of the product was verified using a template of vertically oriented carbon nanotubes.
[DOI : 10.1143/JJAP.42.L1356]
KEYWORDS: carbon nanotube, SiO2, insulator-carbon nanotube composites, coating, pulsed laser deposition
1 Department of Electronic Engineering, Graduate School of Engineering, Osaka University,
2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
2 Research Center for Ultrahigh Voltage Electron Microscopy, Osaka University, 7-1 Mihogaoka,
Ibaraki, Osaka 567-0047, Japan* Corresponding author. E-mail address: katayama@ele.eng.osaka-u.ac.jp

Abstracts of Express Letters

Jpn. J. Appl. Phys. Vol. 42 (2003) pp. L1405-L1407
Part 2, No. 12A, 1 December 2003
©2003 The Japan Society of Applied Physics

Japanese Journal of Applied Physics
Vol. 43, No. 1A/B, 2004, pp.L53-L55©2004 The Japan Society of Applied Physics

Patterning GaN Microstructures by
Polarity-Selective Chemical Etching

Room Temperature Layer by Layer Growth of
GaN on Atomically Flat ZnO

Hock M. NG*, Wolfgang PARZ, Nils G. WEIMANN and
Aref CHOWDHURY

Atsushi KOBAYASHI1, Hiroshi FUJIOKA1,2,*, Jitsuo OHTA1 andMasaharu OSHIMA1(Received September 22, 2003; accepted October 21, 2003; published November 18, 2003)(Received October 22, 2003; accepted November 6, 2003; published December 19, 2003)

We have demonstrated GaN microstructures formed by polarityselective chemical etching in KOH solution. It was found that KOH selectively etches N-polar GaN but not Ga-polar GaN. The polarity-patterned
GaN was grown by plasma-assisted molecular beam epitaxy. For intermediate etching times, hexagonal GaN pyramids were formed in the N-polar
regions. With prolonged etching, the N-polar GaN can be completely removed. A one-dimensional array of GaN stripes and a two-dimensional
array of hexagonal holes formed in a GaN matrix have been fabricated.
Extremely smooth vertical sidewalls have been achieved along with anetch depth of up to 4 µm. [DOI : 10.1143/JJAP.42.L1405]
KEYWORDS: GaN, polarity-selective chemical etching, microstructures, molecular beam epitaxy

We have grown GaN on atomically flat ZnO (000-1) substrates atroom temperature with pulsed laser deposition (PLD). We have foundthat atomically flat surfaces of ZnO (000-1) substrates with a clear stepand terrace structure have been obtained by annealing in a box madeof ceramic ZnO. We have also found that GaN grows epitaxially even atroom temperature on the step and terrace ZnO surface. Reflection highenergy electron diffraction (RHEED) observations have revealed that theGaN film grows in the layer by layer mode from the early stage of thefilm growth. X-ray reflectivity measurements have revealed that the heterointerface between GaN and ZnO is quite abrupt and its roughness isless than 0.5 nm. [DOI : 10.1143/JJAP.43.L53]
KEYWORDS: GaN, ZnO, epitaxial growth, layer by layer growth,
pulsed laser deposition

Bell Laboratories, Lucent Technologies, 600 Mountain Avenue, Murray Hill, New Jersey 07974,
U.S.A.
* E-mail address: hmng@lucent.com

1 Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo
113-8656, Japan
2 Kanagawa Academy of Science and Technology (KAST), 3-2-1 Sakado, Takatsu-ku, Kawasaki,
Kanagawa 213-0012, Japan* E-mail address: fujioka@sr.t.u-tokyo.ac.jp

Jpn. J. Appl. Phys. Vol. 42 (2003) pp. L1408-L1410
Part 2, No. 12A, 1 December 2003
©2003 The Japan Society of Applied Physics

Japanese Journal of Applied Physics
Vol. 43, No. 1A/B, 2004, pp.L100-L102©2004 The Japan Society of Applied Physics

Accumulation and Depletion Layer
Thicknesses in Organic Field Effect Transistors

Organic Field-Effect Transistor of (Thiophene/
Phenylene) Co-Oligomer Single Crystals with
Bottom-Contact Configuration

Manabu KIGUCHI1, Manabu NAKAYAMA1, Kohei FUJIWARA1,
Keiji UENO2, Toshihiro SHIMADA3 and Koichiro SAIKI1,3(Received October 9, 2003; accepted October 15, 2003; published November 18, 2003)

We present a simple but powerful method to determine the thicknesses of the accumulation and depletion layers and the distribution curveof injected carriers in organic field effect transistors. The conductivity oforganic semiconductors in thin film transistors was measured in situ andcontinuously with a bottom contact configuration, as a function of film
thickness at various gate voltages. Using this method, the thicknesses of
the accumulation and depletion layers of pentacene were determined tobe 0.9 nm (V G=–15 V) and 5 nm (V G=15 V), respectively.
[DOI : 10.1143/JJAP.42.L1408]
KEYWORDS: field effect transistor, accumulation layer, depletion layer, organic film
1 Department of Complexity Science & Engineering, Graduate School of Frontier Sciences,
The University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
2 Department of Chemistry, Faculty of Science, Saitama University, Sakura-ku, Saitama, Saitama
338-8570, Japan
3 Department of Chemistry, Graduate School of Science, The University of Tokyo, Bunkyo-ku,
Tokyo 113-0033, Japan

Kiyoshi NAKAMURA, Musubu ICHIKAWA, Rei FUSHIKI,
Taketomi KAMIKAWA1, Masamitsu INOUE, Toshiki KOYAMA andYoshio TANIGUCHI*(Received October 21, 2003; accepted November 20, 2003; published December 26, 2003)

A novel and simple fabrication technique of organic field-effect transistors (FETs) of organic single crystals with bottom-contact configuration
was proposed. The organic single crystal that was made by vapor phasegrowth was used as a FET semiconductor layer. The proposed fabrication process of the device is quite simple. That is, a single crystal is only
placed on an electrode-prepared substrate. The devices exhibited goodbottom-contact type FET characteristics, and the field-effect mobility
reached 0.15 cm2·V -1·s-1 in the best device, which was higher than thatof thin film transistors that were prepared by vacuum evaporation.
[DOI : 10.1143/JJAP.43.L100]
KEYWORDS: organic semiconductor, organic single crystal, organic
transistor
Department of Functional Polymer Science, Faculty of Textile Science and Technology,
Shinshu University, 3-15-1 Tokita, Ueda, Nagano 386-8567, Japan
1 Technology Platform Research Center, Seiko Epson Corporation, 281 Fujimi, Fujimi-machi,
Suwa-gun, Nagano 399-0293, Japan* Corresponding author. E-mail address: tany@giptc.shinshu-u.ac.jp

JSAP International No.10 (July 2004)

17

Japanese Journal of Applied Physics
Vol. 43, No. 1A/B, 2004, pp.L103-L104©2004 The Japan Society of Applied Physics

Japanese Journal of Applied Physics
Vol. 43, No. 2A, 2004, pp.L170-L172©2004 The Japan Society of Applied Physics

Improvement of Optical Properties of
Air-Exposed Regrowth Interfaces Embedded
in InAs Quantum Dots and GaAs/AlGaAs
Quantum Wells by Atomic Hydrogen

Structure and Dielectric Behavior of
Epitaxially Grown SrTiO3 Film between
YBa2Cu3O7-δ Electrodes

Jong Su KIM*, Mitsuo KAWABE and Nobuyuki KOGUCHI

Hiroshi TAKASHIMA, Ruiping WANG, Makoto OKANO, Akira SHOJI and
Mitsuru ITOH1(Received October 23, 2003; accepted November 13, 2003; published December 26, 2003)(Received November 6, 2003; accepted December 1, 2003; published January 9, 2004)

We report an atomic hydrogen cleaning effect on surface oxide andcontaminants on airexposed interfaces embedded in GaAs quantum well
(QW) and InAs quantum dot (QD). A partly grown GaAs QW and a GaAs
buffer layer for InAs QDs were air-exposed and hydrogen cleaned. After
this procedure, we directly regrew a GaAs QW and InAs QDs as an active
layer. Removal of surface oxide was monitored by reflection high-energy
electron diffraction. The cleaned surface showed β (2×4) reconstruction.
The photoluminescence properties of GaAs/AlGaAs QWs and InAs/GaAs
QDs showed no degradation compared with those of the reference samples, even though the air-exposed interfaces were included in the active
regions. [DOI : 10.1143/JJAP.43.L103]
KEYWORDS: atomic hydrogen etching/cleaning, GaAs quantum wells(QWs), InAs quantum dots (QDs), regrowth, photoluminescence (PL), molecular beam epitaxy (MBE)

To obtain a high insulating SrTiO3 layer, the parallel capacitors of epitaxially grown YBa2Cu3O7-δ / SrTiO3 / YBa2Cu3O7-δ have been fabricatedby a Chemical Mechanical Planarization method. The dielectric constantand tan δ of the SrTiO3 film at 2.2 K was 27000 and 0.027 at 10 kHz,
respectively. The temperature variation of the dielectric constant could
be well fitted by the formulae of Curie-Weiss and Barrett in the temperature ranges above 100 K and 30<T <100 K, respectively. The best-fit
parameters were coincident with those for SrTiO3 single crystals. In order
to examine the influence of degraded SrTiO3 layers at the YBa2Cu3O7-δ
/ SrTiO3 interfaces on the dielectric constant, a multilayer model involving two kind of SrTiO3 layers with different dielectric characteristics was
proposed. The results revealed that the degraded SrTiO3 layer is very thinand the dielectric constant of the SrTiO3 film was dominated by that ofsingle-crystal-like SrTiO3 layer.
[DOI : 10.1143/JJAP.43.L170]
KEYWORDS: STO film, YBCO, epitaxial growth, parallel capacitor, dielectric constant, Curie-Weiss law, Barrett formula

Nanomaterials Laboratory, National Institute for Materials Science, Tsukuba 305-0047, Japan* Corresponding author. E-mail address: Jongsu.KIM@nims.go.jp

National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba,
Ibaraki 305-8568, Japan
1 Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midoriku, Yokohama 226-8503, Japan

Japanese Journal of Applied Physics
Vol. 43, No. 1A/B, 2004, pp.L105-L107©2004 The Japan Society of Applied Physics

Japanese Journal of Applied Physics
Vol. 43, No. 2A, 2004, pp.L180-L182©2004 The Japan Society of Applied Physics

Fabrication of Organic Monolayer Modified
Ion-Sensitive Field Effect Transistors withHigh Chemical Durability

Improved External Efficiency InGaN-BasedLight-Emitting Diodes with Transparent
Conductive Ga-Doped ZnO as p-Electrodes

Daisuke NIWA, Takayuki HOMMA and Tetsuya OSAKA*

Ken NAKAHARA*, Kentaro TAMURA, Mitsuhiko SAKAI,
Daisuke NAKAGAWA, Norikazu ITO, Masayuki SONOBE,
Hidemi TAKASU, Hitoshi TAMPO 1, Paul FONS 1, Koji MATSUBARA 1,
Kakuya IWATA1, Akimasa YAMADA1 and Shigeru NIKI1(Received October 29, 2003; accepted November 15, 2003; published December 26, 2003)

Fabrication of ion-sensitive field effect transistor (FET) with modified
SiO2 gate by various organosilane monolayers was investigated. By precise control of the fabrication processes, the FETs modified with various
functional monolayers were successfully formed on the same substrate.
Each modified device indicates typical transistor property with a goodstability in aqueous solution. The transistor with amino monolayer modified gate showed good pH sensitivity of 58 mV/pH, whereas the profilesof transistor with the perfluoro-alkyl monolayer modified gate kept constant in any pH solutions. These monolayer-modified devices are expected to be applied as an ion-sensitive and a reference electrode for sensing
devices in the solution. [DOI : 10.1143/JJAP.43.L105]
KEYWORDS: organic monolayer, modification, field effect transistor,
durability, aqueous solution, pH responsibility, sensing
devices
Department of Applied Chemistry, Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555,
Japan* E-mail address: osakatet@waseda.jp(Received November 18, 2003; accepted December 8, 2003; published January 9, 2004)

Transparent conductive Ga-doped ZnO (ZnO:Ga) was fabricated toserve as p-contacts of InGaN-based light-emitting diodes (LEDs) using
molecular-beam epitaxy. As-grown ZnO:Ga films typically have resistivities of ρ =2-4×10-4 Ω·cm, and over 80% transparency in the near UV andvisible wavelength ranges. The current-voltage characteristics between
as-grown ZnO:Ga contacts and p-GaN layers were ohmic. The brightness
of LEDs fabricated with ZnO:Ga p-contacts was nearly double compared
to LEDs with conventional Ni/Au p-contacts. We obtained the external
efficiency as high as 20.8% in the case of the near UV LED. The forward
voltage at 20 mA was found not to increase even after the lamp LEDwith ZnO:Ga were kept for 80 h in high humidity and high temperatureenvironments. [DOI : 10.1143/JJAP.43.L180]
KEYWORDS: ZnO, GaN, InGaN, LED, MBE, external efficiency, transparent, reliability, ohmic contact
Optical Devices R&D Center, ROHM Co., Ltd., 21 Saiin Mizosaki-cho, Ukyo-ku, Kyoto 615-8585, Japan
1 Optoelectronic Materials and Devices Group, Photonics Research Institute, National Instituteof Advanced Industrial Science and Technology (AIST), Central 2, 1-1-1 Umezono, Tsukuba,
Ibaraki 305-8568, Japan* E-mail address: optical_device@rohm.co.jp

18

JSAP International No.10 (July 2004)

Abstracts of Express Letters

Japanese Journal of Applied Physics
Vol. 43, No. 2A, 2004, pp.L214-L216©2004 The Japan Society of Applied Physics

Japanese Journal of Applied Physics
Vol. 43, No. 2B, 2004, pp.L256-L257©2004 The Japan Society of Applied Physics

Influence of Small Amounts of Dispersed
Single-Walled Carbon-Nanotubes on
the Optical Properties of Poly-3-hexylthiophen

Optical Fuse by Carbon-Coated TeO2 Glass
Segment Inserted in Silica Glass Optical Fiber
CircuitJun TSUKAMOTO* and Junji MATA

Shin-ichi TODOROKI* and Satoru INOUE(Received November 21, 2003; accepted December 12, 2003; published January 16, 2004)(Received November 18, 2003; accepted December 19, 2003; published January 23, 2004)

We studied the dispersion of single-walled carbon-nanotubes(SWNTs) in poly-3-hexylthiophene (P3HT) and the influence of their dispersion on the optical properties of the polymer. The bundles of SWNTs
were found to be well dispersed in P3HT solution, being broken up into
finer ropes. We also found that dispersal of only a small amount (lessthan 1 wt%) of SWNTs in P3HT gives rise to a steep increase in opticalabsorbance close to the absorption edge, remarkable quenching of photoluminescence, and formation of oriented micro-domains. These results
suggest that an ordered structure in the conjugation of P3HT is formedby the incorporation of SWNTs. [DOI : 10.1143/JJAP.43.L214]
KEYWORDS: carbon-nanotubes, poly-3-hexylthiophene, absorbance,
conjugation, photoluminescence

Excessive-light-induced melt down was observed in a carbon-coated
TeO2 glass segment formed between a pair of optical fiber end-faces.
This structure was made by splicing single-mode silica fibers throughTeO2 glass melt to form a necked bridge, which was coated with carboncontaining paint after quenching it. Optical fusing action was induced
by 0.3-1.5 W of CW light (1.54 µm) and its output power dropped by
12 dB on average. Optical decoupling seems to be induced by not only
deformation but also crystallization of the glass bridge. Its quite a highinsertion loss of about 2 dB can be reduced by introducing some refractive index modulations into the present structure.
[DOI : 10.1143/JJAP.43.L256]
KEYWORDS: optical fiber, tellurium oxide glass, carbon, optical fuse,hybrid device

Electronic and Imaging Materials Research Laboratories, Toray Industries Inc., 3-2-1 Sonoyama,Otsu, Shiga 520-0842, Japan* E-mail address: jun_tsukamoto@nts.toray.co.jp

Advanced Materials Laboratory, National Institute for Materials Science, 1-1 Namiki, Tsukuba,
Ibaraki 305-0044, Japan* E-mail address: TODOROKI.Shin-ichi@nims.go.jp

Japanese Journal of Applied Physics
Vol. 43, No. 2A, 2004, pp.L233-L236©2004 The Japan Society of Applied Physics

Japanese Journal of Applied Physics
Vol. 43, No. 2B, 2004, pp.L306-L308©2004 The Japan Society of Applied Physics

Electrical and Optical Control of
Ferromagnetism in III-V Semiconductor
Heterostructures at High Temperature (∼100 K)

Contribution of Shape Anisotropy to
the Magnetic Configuration of (Ga, Mn)As

1,2

1

Ahsan M. NAZMUL , Shigeki KOBAYASHI , Satoshi SUGAHARA
Masaaki TANAKA1,2,*

1,2

and

Kohei HAMAYA*, Rai MORIYA1, Akira OIWA2, Tomoyasu TANIYAMA,
Yoshitaka KITAMOTO, Yohtaro YAMAZAKI and Hiroo MUNEKATA1(Received December 9, 2003; accepted December 25, 2003; published February 6, 2004)(Received December 5, 2003; accepted December 15, 2003; published January 16, 2004)

We demonstrate the electrical and optical control of ferromagnetismin semiconductor heterostructures at high temperatures of 100-117 K. The
heterostructures consist of Mn delta (δ )-doped GaAs and p-type AlGaAs.
We are able to isothermally change the paramagnetic state to the ferromagnetic state and vice versa , by applying a gate electric-field or bylight irradiation. The large modulation of T C (∆ T C ∼15K) at high temperatures (>∼100 K) demonstrated here may pave the way for functional device applications compatible with the present semiconductor technology.
[DOI : 10.1143/JJAP.43.L233]
KEYWORDS: ferromagnetism, delta doping, Mn, GaAs, magnetic
semiconductor, heterostructure, selective doping
1 Department of Electronic Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku,
Tokyo 113-8656, Japan
2 PRESTO, Japan Science & Technology Corporation, 4-1-8 Honcho, Kawaguchi, Saitama
332-0012, Japan* To whom correspondence should be addressed. E-mail address: masaaki@ee.t.u-tokyo.ac.jp

We report on an effect of shape anisotropy on the magnetic configuration of the magnetic semiconductor (Ga, Mn)As using magnetoresistance (MR) measurements. A substantial change in the MR curve occurs
for a wire sample with a width of 0.8 µm, in which the shape anisotropy
along the wire axis is more significant than the intrinsic magnetic anisotropy. Moreover, the magnetic configuration of the wire sample depends
on the hole concentration which has an influence on the cubic, uniaxial
and shape anisotropy, being reflected by the hole induced ferromagnetic
characteristics of (Ga, Mn)As. [DOI : 10.1143/JJAP.43.L306]
KEYWORDS: III-V magnetic semiconductors, (Ga, Mn)As, magnetic anisotropy, shape anisotropy
Department of Innovative and Engineered Materials, Tokyo Institute of Technology,
4259 Nagatsuta, Midori-ku, Yokohama 226-8502, Japan
1 Imaging Science and Engineering Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta,
Midori-ku, Yokohama 226-8503, Japan
2 PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi 332-0012, Japan* E-mail address: hamaya@iem.titech.ac.jp

JSAP International No.10 (July 2004)

19

Japanese Journal of Applied Physics
Vol. 43, No. 2B, 2004, pp.L312-L314©2004 The Japan Society of Applied Physics

Japanese Journal of Applied Physics
Vol. 43, No. 2B, 2004, pp.L317-L319©2004 The Japan Society of Applied Physics

Liquid Crystal Biaxiality at the Polymer
Alignment Surface Studied Using Infrared
Dichroism

Teflon Photonic Crystal Fiber as Terahertz
Waveguide

1,2

Xibin SHAO

1

and Tatsuo UCHIDA

Masahiro GOTO1, Alex QUEMA1, Hiroshi TAKAHASHI2, Shingo ONO1,2
and Nobuhiko SARUKURA1,2(Received December 22, 2003; accepted December 28, 2003; published February 6, 2004)(Received January 7, 2004; accepted January 11, 2004; published February 6, 2004)

Using infrared dichroism technique and wedge cell, we have investigated the surface order of nematic liquid crystal at the polymer alignment surface. The results show that the order parameter at surface ismuch lower than that of bulk, and a light biaxiality exists at the interface
between a liquid crystal and the alignment layer. The distribution of bothorder parameter and biaxiality parameter over the liquid crystal layer follows an exponent function. [DOI : 10.1143/JJAP.43.L312]
KEYWORDS: liquid crystals, order parameter, surface, biaxiality, infrared dichroism

We demonstrate the construction of reasonably long and non-polarization changing photonic fiber waveguide using Teflon which is areadily available and highly flexible material. Due to its relatively low loss
coefficient, the possibility of preparing longer photonic fiber waveguide,
which has the potential of guiding intense THz radiation, can be easily
attained. [DOI : 10.1143/JJAP.43.L317]
KEYWORDS: terahertz radiation, waveguide, photonic crystal fiber,polarization

1 Uchida Laboratory, Department of Electronics, Graduate School of Engineering,Tohoku University, Aoba-ku, Sendai 980-8579, Japan
2 Changchun Institute of Optics, Fine Machine & Physics, Changchun, China

1 Institute for Molecular Science (IMS), Myodaiji, Okazaki 444-8585, Japan
2 Department of Photo Science, The Graduate University for Advanced Studies, Shonan Village,
Hayama 240-0193, Japan

Japanese Journal of Applied Physics
Vol. 43, No. 2B, 2004, pp.L315-L316©2004 The Japan Society of Applied Physics

Japanese Journal of Applied Physics
Vol. 43, No. 3A, 2004, pp.L349-L351©2004 The Japan Society of Applied Physics

The First Observation of 1H-NMR Spectrum ofPentacene

Observation of Exciton Transition in 1.3-1.55µm
Band from Single InAs/InP Quantum Dots in
Mesa Structure

Mika NAGANO, Tetsuya HASEGAWA, Norikatsu MYOUJIN,
Jun YAMAGUCHI, Kenji ITAKA, Hiroki FUKUMOTO1,
Takakazu YAMAMOTO1 and Hideomi KOINUMA(Received January 6, 2004; accepted January 12, 2004; published February 6, 2004)

Despite much interest in pentacene as a promising organic semiconductors, its chemical properties have scarcely been elucidated. Even sucha fundamental data as 1H-NMR spectrum has not been reported yet due
to poor solubility of pentacene in various solvents. Here we report thefirst observation of 1H NMR spectrum of pentacene by using dimethyl
sulfoxide-d 6 as solvent and heating the sample to 80°C. Not only the signal assignment but also the easily oxidizable property of pentacene wasverified from the comparison between the spectra measured in degassed
and non-degassed solvents. [DOI : 10.1143/JJAP.43.L315]
KEYWORDS: pentacene, NMR, organic semiconductor

Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku,
Yokohama 226-8503, Japan
1 Chemical Resources Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku,
Yokohama 226-8503, Japan

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JSAP International No.10 (July 2004)

Kazuya TAKEMOTO*, Yoshiki SAKUMA1, Shinichi HIROSE, Tatsuya USUKI
and Naoki YOKOYAMA(Received January 9, 2004; accepted January 14, 2004; published February 13, 2004)

Single InAs/InP quantum dots from the O-band (1.3 µm) to the
C-band (1.55 µm) were produced in order to realize a quantum information device for optical telecommunication. Our single quantum dot inany band has a sharp and discrete exciton line. To obtain quantum dotswith intensive emissions, we applied a `double-cap’ growth technique tometalorganic chemical vapor deposition. To lower fabrication damage toquantum dots, we employed photolithography and wet chemical etching for fabricating 140-nm mesa structure with a quantum dot. Combination of the growth and the fabrication techniques is essential to thegood optical property. [DOI : 10.1143/JJAP.43.L349]
KEYWORDS: InAs/InP, single quantum dots, double-cap growth,
MOCVD, C-band, O-band
Fujitsu Laboratories Ltd., 10-1 Morinosato-Wakamiya, Atsugi 243-0197, Japan
1 National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047, Japan* E-mail address: kazuya.takemoto@jp.fujitsu.com

Abstracts of Express Letters

Japanese Journal of Applied Physics
Vol. 43, No. 3B, 2004, pp.L407-L410©2004 The Japan Society of Applied Physics

Japanese Journal of Applied Physics
Vol. 43, No. 4A, 2004, pp.L456-L459©2004 The Japan Society of Applied Physics

Band Structures of Wurtzite InN and Ga1-xInxN
by All-Electron GW Calculation

The Impact of Supercritical Fluoro-Compounds
on Lithography Use

Manabu USUDA*, Noriaki HAMADA1, Kenji SHIRAISHI2 andAtsushi OSHIYAMA2

Hideo NAMATSU(Received January 22, 2004; accepted February 13, 2004; published March 12, 2004)(Received November 6, 2003; accepted January 26, 2004; published March 5, 2004)

The experimentally reported bandgap of wurtzite-type InN dramatically decreased from 1.9 eV to 0.7-0.8 eV very recently. In this paper wereport first-principles electronic band-structure calculations of InN byusing the all-electron full-potential linearized augmented-plane-wave(FLAPW) method in both local-density approximation (LDA) and GW approximation (GWA), and provide the reliable theoretical bandgap of InN.
Our calculation suggests that InN is a narrow-gap semiconductor andstrongly supports the recently reported smaller bandgaps. Moreover, we
reproduce the bandgap change of Ga1-x Inx N ternary alloys as a functionof In content x . The present work supports the possibility of bandgap
control in the entire range of visible light, using nitrides alone.
[DOI : 10.1143/JJAP.43.L407]
KEYWORDS: InN, bandgap, GW calculation

This article describes the use of supercritical fluoro-compounds forsupercritical resist drying. In contrast to carbon dioxide, fluoro-compounds, which are heavier than water in liquid form, can displace therinse water on the resist due to the difference in specific gravity. The removal of rinse water from a sample surface by replacing it with a liquid
fluoro-compound, followed by the conversion of the compound to thesupercritical state, enables patterns to be formed without collapse andwithout the use of a surfactant. Furthermore, with the help of helium,
which can be released quickly from the chamber, the use of supercritical
fluoro-compounds like C2HF5 and SF6 also enable the very fast supercritical resist drying of water-rinsed resists for advanced lithography.
[DOI : 10.1143/JJAP.43.L456]
KEYWORDS: supercritical drying, supercritical fluid, fluoro-compounds, resist, advanced lithography

Synchrotron Radiation Research Center, Japan Atomic Energy Research Institute, Mikazuki,
Hyogo 679-5148, Japan
1 Department of Physics, Faculty of Science and Technology, Tokyo University of Science, Noda,
Chiba 278-8510, Japan
2 Institute of Physics, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan* E-mail address: m-usuda@spring8.or.jp

NTT Basic Research Laboratories, 3-1 Morinosato Wakamiya, Atsugi, Kanagawa 243-0198, Japan

Japanese Journal of Applied Physics
Vol. 43, No. 3B, 2004, pp.L424-L426©2004 The Japan Society of Applied Physics

Japanese Journal of Applied Physics
Vol. 43, No. 4A, 2004, pp.L460-L463©2004 The Japan Society of Applied Physics

InAs/AlGaSb Piezoresistive Cantilever for
Sub-Angstrom Scale Displacement Detection

Extraction of Trap Distribution in Organic
Semiconductors by Transient Photocurrent

Lionel F. HOULET1, Hiroshi YAMAGUCHI1, Sen MIYASHITA2 andYoshiro HIRAYAMA1,3

Akira OHNO*, Jun-ichi HANNA, David H. DUNLAP1,** andAaron CABRAL1(Received January 6, 2004; accepted January 30, 2004; published March 5, 2004)(Received February 12, 2004; accepted February 17, 2004; published March 12, 2004)

We report on the fabrication and characterization of 0.3-µm-thickpiezoresistive cantilevers based on the InAs/AlGaSb heterostructure. The
dependence of the displacement resolution on the cantilever size, whichranges from 20×10 to 2×1µm2, has been studied by a novel characterization method using an atomic force microscope. The results show that
downscaling the cantilevers improves their performances, and an optimum resolution of 0.26Å/Hz0.5 was obtained with a 3×1.5µm2 cantileverat a modulation frequency of 714 Hz. A finite-element simulator allowed
the calculation of the resonance frequencies and a maximum value of
20.5 MHz was obtained for the 3×1.5µm2 cantilever.
[DOI : 10.1143/JJAP.43.L424]
KEYWORDS: InAs/AlGaSb, cantilever, piezoresistivity, AFM, subangstrom

The mobility of photoinjected holes in smectic-B liquid crystals as
measured by time of flight shows an electric field dependence at low
fields. This dependence is suspect, for whether the mobility rises or falls
with field depends on the method by which the photocurrent transientsare analyzed. In the context of the multiple trapping model, a generalformalism is developed for analyzing the transients, in which the distribution of traps may be determined under the assumption that the Einstein relation between the mobility and the diffusion constant is obeyed.
For the smectic-B liquid crystal, this distribution is adequately describedby a Gaussian of depth 100 meV and width 50 meV.
[DOI : 10.1143/JJAP.43.L460]
KEYWORDS: transient photocurrent, time of flight method, liquid
crystal, smectic B phase, organic semiconductor

1 NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato Wakamiya, Atsugi,
Kanagawa 243-0198, Japan
2 NTT-AT, 3-1 Morinosato Wakamiya, Atsugi, Kanagawa 243-0198, Japan
3 SORST-JST, 3-1 Honcho, Kawaguchi, Saitama 332-0012, Japan

Imagining Science and Engineering Laboratory, Tokyo Institute of Technology, Nagatsuta-cho,
Midori-ku, Yokohama 226-8503, Japan
1 Department of Physics and Astronomy, University of New Mexico, Albuquerque, New Mexico
87131, U.S.A.
* E-mail address: akira@isl.titech.ac.jp** E-mail address: dunlap@unm.edu

JSAP International No.10 (July 2004)

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Japanese Journal of Applied Physics
Vol. 43, No. 4A, 2004, pp.L499-L500©2004 The Japan Society of Applied Physics

Japanese Journal of Applied Physics
Vol. 43, No. 4B, 2004, pp.L579-L581©2004 The Japan Society of Applied Physics

350.9 nm UV Laser Diode Grown on
Low-Dislocation-Density AlGaNNew Route to Fabricate Ferromagnetic
Semiconductors without Transition Metal
Elements

Kazuyoshi IIDA*, Takeshi KAWASHIMA, Atsushi MIYAZAKI,
Hideki KASUGAI, Syunsuke MISHIMA, Akira HONSHIO, Yasuto MIYAKE,
Motoaki IWAYA, Satoshi KAMIYAMA, Hiroshi AMANO andIsamu AKASAKI

Masayoshi SEIKE*, Kazuhide KENMOCHI, Kazunori SATO, Akira YANASE
and Hiroshi KATAYAMA-YOSHIDA(Received February 23, 2004; accepted March 8, 2004; published April 2, 2004)(Received February 17, 2004; accepted February 20, 2004; published March 19, 2004)

We demonstrated a UV-laser diode grown on low-dislocation-density AlGaN. The combination of a low-temperature-deposited AlN interlayer technology and heteroepitaxial lateral overgrowth yielded crack-freeand partially low-dislocation-density AlGaN on a grooved GaN substrate.
A ridge waveguide was fabricated in the low-dislocation-density region.
The lasing wavelength under pulsed current injection at room temperature was 350.9 nm, which is the shortest wavelength ever reported.
[DOI : 10.1143/JJAP.43.L499]
KEYWORDS: UV laser diode, dislocation, AlGaN, GaN, LT-AlN interlayer, heteroepitaxial lateral overgrowth
Faculty of Science and Technology, High-Tech Research Center, 21st-Century COE Program “NanoFactory”, Meijo University, 1-501 Shiogamaguchi, Tempaku-ku, Nagoya 468-8502 Japan* E-mail address: m0334001@ccmailg.meijo-u.ac.jp

We propose a new route for ferromagnetic diluted magnetic semiconductors by controlling the impurity-band width (W ) and the electroncorrelation energy (U ) in the partially occupied impurity band in thecondition of highly correlated electron system (U >W ). Based upon firstprinciples calculations of K2(S,Si) and K2(S,Ge), we demonstrate thattransparent, half-metallic and room-temperature ferromagnetic DMS
could be designed even without transition metal elements. The results
show that it is possible to fabricate the room-temperature ferromagnets
in K2(S,Si) and K2(S,Ge) around 8 at%-impurity concentration.
[DOI : 10.1143/JJAP.43.L579]
KEYWORDS: materials design, potassium sulfide, p-impurity band,ferromagnetism without transition metal elements
The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki,
Osaka 567-0047, Japan* E-mail address: seike@cmp.sanken.osaka-u.ac.jp

Japanese Journal of Applied Physics
Vol. 43, No. 4A, 2004, pp.L501-L503©2004 The Japan Society of Applied Physics

Japanese Journal of Applied Physics
Vol. 43, No. 4B, 2004, pp.L582-L584©2004 The Japan Society of Applied Physics

High Performance of Silicon Oxide Selective
Etching Using F2 Gas and Graphite Instead of
Perfluorinated Compound Gases

Sample-and-Hold Imaging for Fast Scanning in
Atomic Force Microscopy*

Mikio NAGAI, Masaru HORI and Toshio GOTO
(Received February 17, 2004; accepted February 19, 2004; published March 19, 2004)

We have demonstrated an environmentally benign SiO2 selectiveetching process in a magnetron plasma using a graphite target and F2
gas instead of perfluorinated compound (PFC) gases. The top electrodeof graphite was supplied with power from two different 13.56 MHz and
450 kHz RF sources. The amount of C-based species in the plasma wascontrolled by the 450 kHz RF source bias voltage. The F atom density
was controlled in the plasma by changing the amount of F2 feed gas.
High SiO2/resist selectivity and a vertical etching pattern profile were realized. Microtrenching was suppressed by the injection of high energy
electrons. [DOI : 10.1143/JJAP.43.L501]
KEYWORDS: etching, graphite, carbon, fluorine, CF, radical density,
microtrenching
Department of Quantum Engineering, School of Engineering, Nagoya University, Furo-cho,
Chikusa-ku, Nagoya, Aichi 464-8603, Japan* E-mail address: hori@nuee.nagoya-u.ac.jp

22

JSAP International No.10 (July 2004)

Takuji TAKAHASHI* and Shiano ONO(Received February 23, 2004; accepted March 8, 2004; published April 2, 2004)

We have proposed to use a sample-and-hold circuit for direct monitoring of cantilever deflection signals as a novel method for fast imaging in an intermittent contact mode atomic force microscopy (AFM).
This method enables us to construct a quasi-topographic image fromtip heights at moments when the tip taps on a sample surface. As a result, we obtained the tip height image well corresponding to the sample
topography at a scanning rate above 30 Hz/ line without any other customization on both a cantilever and a piezo scanner in a commercial
AFM system. [DOI : 10.1143/JJAP.43.L58]
KEYWORDS: atomic force microscopy, sample-and-hold circuit, fast
imaging, quality-factor
Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505,
Japan* E-mail address: takuji@iis.u-tokyo.ac.jp

Abstracts of Express Letters

Japanese Journal of Applied Physics
Vol. 43, No. 4B, 2004, pp.L585-L587©2004 The Japan Society of Applied Physics

Japanese Journal of Applied Physics
Vol. 43, No. 4B, 2004, pp.L591-L593©2004 The Japan Society of Applied Physics

Emission Characteristics of Extreme
Ultraviolet Radiation from CO2 Laser-Produced
Xenon Plasma

Observation of Revival Structure in
Femtosecond-Laser-Induced Alignment of N2
with High-Order Harmonic Generation

Hiroki TANAKA, Koji AKINAGA, Akihiko TAKAHASHI1 andTatsuo OKADA*

Masanori KAKU, Keita MASUDA and Kenzo MIYAZAKI*(Received March 1, 2004; accepted March 8, 2004; published April 2, 2004)(Received February 23, 2004; accepted March 3, 2004; published April 2, 2004)

We propose a CO2 laser-produced plasma as the extreme ultraviolet(EUV) light source for a future optical lithography system. The EUV radiation around 13.5 nm was generated by focusing the laser beam from atransversely-excited atmospheric CO2 laser (4 J, 50 ns full width at halfmaximum (FWHM)) on a Xe gas target and a Xe cryogenic target. The
EUV energy was measured by a Flying Circus II detecting system, and an
output energy of more than 3 mJ/pulse and an conversion efficiency ofmore than 0.1% per 2π sr at 13.5 nm were obtained. These values arecomparable to those of Nd:YAG laser-produced plasma, indicating thepotential scalability of the EUV light source using a CO2 laser produced
plasma. [DOI : 10.1143/JJAP.43.L585]
KEYWORDS: extreme ultraviolet lithography, extreme ultraviolet
sources, laser-produced plasmas, Xenon, CO2 laser

We report a new sensitive method using high-order harmonic generation to observe revival structure in fs-laser induced alignment of a rotational wave packet of molecules. Pump and probe fs-laser pulses witha time delay were focused collinearly into a pulsed N2 gas jet, so that thepump pulse induces alignment of a ground-state rotational wave packet, and the delayed probe pulse produces harmonic radiation from thealigning molecules. The harmonic signal observed as a function of timedelay has clearly demonstrated a typical time-dependent revival structurein the field-free alignment of molecules. [DOI : 10.1143/JJAP.43.L591]
KEYWORDS: revival structure, rotational wave packet, molecularalignment, high-order harmonic generation, femtosecond laser
Institute of Advance Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan* E-mail address: miyazaki@iae.kyoto-u.ac.jp

Department of Electrical and Electronic Systems Engineering, Graduate School of Information Science and Electrical Engineering, Kyushu University, 6-10-1 Hakozaki, Fukuoka 812-8581, Japan
1 Department of Health Sciences, School of Medicine, Kyushu University, 3-1-1 Maidashi,
Fukuoka 812-8582, Japan* Correspondence author. E-mail address: okada@ees.kyushu-u.ac.jp

Japanese Journal of Applied Physics
Vol. 43, No. 4B, 2004, pp.L588-L590©2004 The Japan Society of Applied Physics

High Tunnel Magnetoresistance at Room
Temperature in Fully Epitaxial Fe/MgO/Fe
Tunnel Junctions due to Coherent
Spin-Polarized Tunneling
Shinji YUASA1,2,*, Akio FUKUSHIMA1, Taro NAGAHAMA1, Koji ANDO1
and Yoshishige SUZUKI1(Received February 24, 2004; accepted March 10, 2004; published April 2, 2004)

We fabricated fully epitaxial Fe(001)/MgO(001)/Fe(001) magnetic
tunnel junctions (MTJs) and observed a magneto-resistance (MR) ratio of
88% at T = 293 K (146% at T = 20 K), the highest value yet reported.
The origin of the high MR ratio is not the diffusive tunneling of Julliere’s
model but the coherent spin-polarized tunneling in epitaxial MTJs, inwhich only the electrons with totally symmetric wave functions with respect to the barrier-normal axis can tunnel. The bias-voltage dependenceof the MR was very small, resulting in a high output voltage of 380 mV.
This high voltage will help overcome problems in the development ofhigh-density magnetoresistive random-access-memory (MRAM).
[DOI : 10.1143/JJAP.43.L588]
KEYWORDS: tunnel magnetoresistance, TMR effect, magnetic tunnel
junction, MRAM, epitaxial growth
1 NanoElectronics Research Institute, AIST, 1-1-1 Umezono, Tsukuba 305-8568, Japan
2 PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi, Saitama
332-0012, Japan* E-mail address: yuasa-s@aist.go.jp

JSAP International No.10 (July 2004)

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