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. 41 (2002) pp. L 1279–L 1280
Part 2, No. 11B, 15 November 2002
©2002 The Japan Society of Applied Physics

An InAs-Based Intersubband Quantum
Cascade Laser
Keita OHTANI* and Hideo OHNO
(Received October 7, 2002; accepted for publication October 8, 2002)

Quantum cascade laser structures using InAs quantum wells are designed, grown by molecular beam epitaxy, and processed into lasers. Theintersubband transition is chosen to be bound-to-continuum and the
double plasmon waveguide is employed as a cladding structure. Lasing
at 10.1µm has been observed at 4K with a threshold current density of
5.2 kA/cm2. [DOI: 10.1143/JJAP.41.L1279]
KEYWORDS: quantum cascade laser, type-II quantum well, intersubband transition, molecular beam epitaxy
Laboratory for Electronic Intelligent Systems, Research Institute of Electrical Communication, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan* E-mail address: keita@riec.tohoku.ac.jp

Jpn. J. Appl. Phys. Vol. 41 (2002) pp. L 1285–L 1287
Part 2, No. 11B, 15 November 2002
©2002 The Japan Society of Applied Physics

Observation of Stark Spectra of Argon High
Rydberg States in Well-Defined Electric Fields
by Laser-Induced Fluorescence-Dip
Spectroscopy
Kazuki TAKIZAWA, Koichi SASAKI and Kiyoshi KADOTA(Received October 17, 2002; accepted for publication October 21, 2002)

We detected high Rydberg states of Ar which had energies close tothefirst ionization potential by laser-induced fluorescence-dip spectroscopy, and observed the Stark spectra of the high Rydberg states inwell-defined electric fields. The detection was carried out by a two-step high Rydberg states).
laser excitation technique (In the presence of electric fields, the Stark mixing made thenp forbidden transitions observable. It has been shown that the Stark
shift of the np state is a good measure for the determination of the electric field strength. A detection limit of 6 V/cm has been demonstrated,which is the most sensitive detection limit when the Stark effect of an inert gas useful for applications is used for the electric field measurement.
[DOI: 10.1143/JJAP.41.L1285]
KEYWORDS: Stark effect, Ar, Rydberg state, electric field measurement, LIF-dip spectroscopy
Department of Electronics, Nagoya University, Nagoya 464-8603, Japan

Jpn. J. Appl. Phys. Vol. 41 (2002) pp. L 1281–L 1284
Part 2, No. 11B, 15 November 2002
©2002 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol. 41 (2002) pp. L 1345–L 1347
Part 2, No. 12A, 1 December 2002
©2002 The Japan Society of Applied Physics

Nitrogen-Doped p-Type ZnO Layers Preparedwith H2O Vapor-Assisted
Metalorganic Molecular-Beam Epitaxy

Photo-Rubbing: A General Method to Induce
Durable Liquid-Crystal Pretilt Angle on PhotoAlignment Films

A. B. M. Almamun ASHRAFI*, Ikuo SUEMUNE**, Hidekazu KUMANO andSatoru TANAKA

Masayuki KIMURA, Shoichi NAKATA, Yutaka MAKITA, Yasuo MATSUKI,
Atsushi KUMANO, Yasumasa TAKEUCHI1 and Hiroshi YOKOYAMA2(Received October 10, 2002; accepted for publication October 18, 2002)(Received October 15, 2002; accepted for publication October 21, 2002)

Nitrogen (N) doping in ZnO is studied to realize reproducible p-typeconductivity. Undoped ZnO layers prepared on a-face of sapphire substrates with H 2O vapor-assisted growth showed n-type conductivity. However, N-doped ZnO (ZnO:N) layers grown in the similar manner
showed the type conversion to p-type conductivity. As-grown p-type
ZnO:N layers showed low net acceptor concentrations (N A–N D) of ~1014cm–3, but thermal annealing of the N-doped ZnO samples as well as
the optimization of growth parameters increased the NA–ND up to ~ 51016cm–3. Photoluminescence measurements showed consistent spectrawith the electrical properties by a clear conversion from neutral donorbound exciton emission in n-ZnO to neutral acceptor-bound exciton
emission in the p-ZnO layers. [DOI: 10.1143/JJAP.41.L1281]
KEYWORDS: H2O vapor, undoped ZnO, N doped p-ZnO, H passivation, neutral acceptor-bound exciton

A normal-incidence single-exposure scheme to obtain a stablepretilted alignment of nematic liquid crystals on photo-alignment polymer layers is proposed. The new scheme consists in periodically modulating the intensity of the normally incident linearly polarized near-ultraviolet light and unidirectionally scanning it on the photosensitive alignment
layer. By properly choosing the relative directions of scan and polarization, this scheme works for any types of photo-alignment materials regardless of the resultant alignment direction relative to the polarization
direction of the UV light. The pretilt appears in such a way that the nematic director is lifted up in the scan direction, similar to the case of theconventional cloth rubbing. This “photo-rubbing” method allows a fairly accurate control of the pretilt angle by way of the scan speed. [DOI:
10.1143/JJAP.41.L1345]
KEYWORDS: photo-alignment, surface alignment, pretilt angle,
liquid crystal, scanning, rubbing

Laboratory of Optoelectronics, Research Institute for Electronic Science, Hokkaido University, Kita
12, Nishi 6, Sapporo 060-0812, Japan* Corresponding author. E-mail address: mamun@es.hokudai.ac.jp** E-mail address: isuemune@es.hokudai.ac.jp

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JSAP International No.8 (July 2003)

Display Research Laboratories, JSR Corporation, 100 Kawajiri-cho, Yokkaichi, Mie 510-8552, Japan
1 International Center for Materials Research, 1-1 Minamiwatarida-cho, Kawasaki-ku, Kawasaki, Kanagawa 210-0855, Japan
2 Nanotechnology Research Institute, National Institute of Advanced Industrial Science andTechnology, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, JapanJpn. J. Appl. Phys. Vol. 41 (2002) pp. L 1419–L 1421
Part 2, No. 12B, 15 December 2002
©2002 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol. 42 (2003) pp. L 1–L 3
Part 2, No. 1A/B, 15 January 2003
©2003 The Japan Society of AppliedPhysics

A Metastable Precursor in the Oxidation ofSi(111)-(7 7)

Preparation of Freestanding GaN Wafers byHydride Vapor Phase Epitaxy with
Void-Assisted Separation

Hiroshi OKUYAMA, Takashi MIKI, Tetsuya ARUGA and
Mitsuaki NISHIJIMA(Received November 7, 2002; accepted for publication November 14, 2002)

We have studied the initial adsorption of O2 on Si(111) at 78K using
scanning tunneling microscope (STM). The dominant products at 78K appear darker than the unreacted Si adatoms, in contrast to the adsorption
at room temperature where the dominant products appear bright. The
dark site is found to be a precursor to the bright site. The reaction of the
precursor is very slow at 78K (τ > 64 h, τ : lifetime of the precursor), but
can be readily induced by the STM tip. We briefly discuss the chemical
configurations of the reaction products. [DOI: 10.1143/JJAP.41.L1419]
KEYWORDS: scanning tunneling microscope, silicon, oxygen, precursor, manipulation
Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan

Yuichi OSHIMA*, Takeshi ERI, Masatomo SHIBATA, Haruo SUNAKAWA1,**,
Kenji KOBAYASHI2, Toshinari ICHIHASHI2 and Akira USUI1,**(ReceivedNovember 11, 2002; acceptedfor publication December 3, 2002)

We have developed a novel technique for preparing large-scale freestanding GaN wafers. Hydride vapor phase epitaxy (HVPE) growth of
thick GaN layer was performed on a GaN template with a thin TiN filmon the top. After the cooling process of the HVPE growth, the thick GaN
layer was easily separated from the template by the assistance of many
voids generated around the TiN film. As a result, a freestanding GaN wafer was obtained. The wafer obtained had a diameter of 45 mm, and amirror-like surface. The-full-width-at-half-maximum (FWHM) of (0002)
and(10 0) peaks in the X-ray rocking curve profile were 60 and 92 arcsec, respectively. The dislocation density was evaluated at 5 106cm–3 byetch pit density measurement. [DOI: 10.1143/JJAP.42.L1]
KEYWORDS: freestanding GaN, HVPE, TiN, X-ray diffraction, etchpit, TEM
Advanced Research Center, Hitachi Cable, Ltd., 3550 Kidamari, Tsuchiura, Ibaraki 300-0026, Japan
1 Photonic and Wireless Devices Research Laboratories, NEC Corporation, 34 Miyukigaoka, Tsukuba, Ibaraki 305-8501, Japan
2 Fundamental Research Laboratories, NEC Corporation, 34 Miyukigaoka, Tsukuba, Ibaraki
305-8501, Japan* E-mail address: yuichi@arc.hitachi-cable.co.jp** Present address: Furukawa Co., Ltd., 1-25-13 Kannondai, Tsukuba, Ibaraki 305-0856, Japan.

Jpn. J. Appl. Phys. Vol. 41 (2002) pp. L 1422–L 1424
Part 2, No. 12B, 15 December 2002
©2002 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol. 42 (2003) pp. L 4–L 6
Part 2, No. 1A/B, 15 January 2003
©2003 The Japan Society of Applied Physics

Sign Inversion of Photocarrier in Poly
(3-octadecylthiophene) Associated with
Solid-Liquid Phase Transition

Growth of a Large GaN Single Crystal Using
the Liquid Phase Epitaxy (LPE) TechniqueKazuya TADA, Koichi MIYABE and Mitsuyoshi ONODA

Fumio KAWAMURA*, Tomoya IWAHASHI, Kunimichi OMAE, Masanori
MORISHITA, Masashi YOSHIMURA, Yusuke MORI and Takatomo SASAKI(Received October 30, 2002; accepted for publication November 8, 2002)(Received November 28, 2002; accepted for publication December 4, 2002)

In this paper, we have shown that the sign inversion of photocarrier in a fusible conjugated polymer, regiorandom poly(3-octadecylthiophene) associated with the solid-liquid phase transition. The transient
photocurrent by hole is clearly observed in the solid state, while it weakens to be below the noise level in the liquid state. On the other hand,
the transient photocurrent by a negative carrier can be clearly observed
not in the solid state but in the liquid state. The mobility has been foundin a narrow range from 10–6 to 10–5 cm2/ V·s for both positive and negative carriers, except for the temperature near the melting point. This indicates not only that the photocarrier in the liquid state is not ionic but
electronic one, but also that the same mechanism, i.e. interchain hopping of carrier, dominantly limits their transport. The drastic conformational change of polymer backbone induced by the thermal activationof side chain vibration, which is responsible for the thermochromism inpoly(3- alkylthiophene)s, may play a key role for this unique phenomenon. [DOI: 10.1143/JJAP.41.L1422]
KEYWORDS: conjugated polymers, photocarrier, mobility, sign
inversion, time-of-flight method, poly(3-alkylthiophene), phase transition, liquid state

We grew a 12 5 0.8mm GaN single crystal using the liquid
phase epitaxy (LPE) method with Na flux. This GaN single crystal wasgrown on a 3 µm-thick GaN thin film synthesized on sapphire using themetal organic chemical vapor deposition (MOCVD) method. It grew in apolyhedral form larger than the MOCVD-GaN substrate. Results indicatethat a MOCVD-GaN thin film on a sapphire substrate functions as a seed
crystal in Na flux. The use of mixed nitrogen gas containing 40% ammonia instead of pure N2 gas also enabled the growth of a 10 µm-thick
GaN homo-epitaxial film on an MOCVD-GaN film under 5 atm, the lowest reported pressure for growing GaN in Na flux. In this paper, we describe the liquid phase epitaxy (LPE) technique for growing bulk GaN
single crystals, as well as the results of photoluminescence (PL) measurements. We also compare the PL intensity of the bulk GaN obtainedin this study and the MOCVD-GaN. PL measurements revealed that thepeak intensity of GaN single crystal grown by LPE indicates 40 times
larger than MOCVD-GaN film. Also, dislocation density of bulk GaN
crystals could be drastically reduced by the LPE growth technique. [DOI:
10.1143/JJAP.42.L4]
KEYWORDS: GaN, LPE, single crystal, high pressure, bulk, highquality, photoluminescence

Department of Electrical Engineering, Himeji Institute of Technology, Shosha 2167, Himeji671-2201, Japan

Department of Electrical Engineering, Osaka University, 2-1 Yamadaoka, Suita 565-0871, Japan* E-mail address: fkawamura@ssk.pwr.eng.osaka-u.ac.jp

JSAP International No.8 (July 2003)

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Jpn. J. Appl. Phys. Vol. 42 (2003) pp. L 7–L 9Part 2, No. 1A/B, 15 January 2003
©2003 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol. 42 (2003) pp. L 90–L 91
Part 2, No. 2A, 1 February 2003
©2003 The Japan Society of Applied Physics

Free-Standing InAs/InGaAs Microtubes andMicrospirals on InAs (100)Efficient Second-Harmonic Generation of
340-nm Light in a 1.4-µm
Periodically Poled Bulk MgO:LiNbO3

Alexander VOROB’EV*, Victor PRINZ, Valerii PREOBRAZHENSKII and
Boris SEMYAGIN(Received December 11, 2002; accepted for publication December 12, 2002)

A new material system for creating InAs-based free-standing microand nanoobjects is proposed. For the first time, InAs/InGaAs microtubes
and microspirals were obtained, including tubes containing two-dimensional electron gas, ordered arrays of tubes, and tubes protruding overthe substrate edge. First measurements of the electrical conductivity of
InAs/InGaAs microtubes were performed. [DOI: 10.1143/JJAP.42.L7]
KEYWORDS: InAs, free-standing microobjects, semiconductor microtubes, AlSb, selective etching
Institute of Semiconductor Physics, Acad. Lavrentyev Ave. 13, 630090 Novosibirsk, Russia* E-mail address: alex@isp.nsc.ru
Present address: ATR Adaptive Communications Research Laboratories, 2-2-2 Hikaridai,‘‘Keihanna Science City’’, Kyoto 619-0288, Japan.

Kiminori MIZUUCHI*, Akihiro MORIKAWA, Tomoya SUGITA and
Kazuhisa YAMAMOTO(Received December 6, 2002; accepted for publication December 20, 2002)

Ultra-violet second-harmonic generation in a 1.4 µm periodicallypoled MgO:LiNbO3 is presented. Using a high-voltage multi-pulse application method, a first-order nonlinear grating with a period of 1.4 µm was
fabricated over 10-mm interaction length in a 2-mm thick MgO:LiNbO3
substrate. In a single pass configuration, cw 1.2mW of ultraviolet lightat 341.5 nm was successfully obtained for a fundamental power of 141
mW, corresponding to a normalized conversion efficiency of 5.4%/ W.
[DOI: 10.1143/JJAP.42.L90]
KEYWORDS: second-harmonic generation, quasi-phase matching,
periodically poled MgO:LiNbO3, ultraviolet, nonlinear, bulk
Storage Media Systems Development Center, Matsushita Electric Industrial Co., Ltd., 3-1-1
Yagumo-Nakamachi, Moriguchi, Osaka 570-8501, Japan* E-mail address: mizuuchi.kiminori@jp.panasonic.com

Jpn. J. Appl. Phys. Vol. 42 (2003) pp. L 87–L 89
Part 2, No. 2A, 1 February 2003
©2003 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol. 42 (2003)pp. L 92–L 94
Part 2, No. 2A, 1 February 2003
©2003 The Japan Society of Applied Physics

Spin-Polarized Electron Injection through an
Fe/InAs Junction

Nanoelectrode Lithography

Hiroshi OHNO, Kanji YOH1,*, Kazuhisa SUEOKA, Koichi MUKASA,
Atsushi KAWAHARAZUKA2 and Manfred E. RAMSTEINER2(Received December 17, 2002; accepted for publication January 6, 2003)

We report on the spin-polarized electron injection through an
Fe(100)/InAs(100) junction. The circularly polarized electroluminescenceof injected electrons from epitaxially grown Fe thin film into InAs(100) inan external magnetic field is measured to investigate the spin injection
efficiency. The obtained polarization of the electroluminescence is seen
to increase up to about – 12% at the temperature of 6.5K and the external magnetic field of 10 T. This result suggests that the efficient spin
injection is possible through the ferromagnetic metal/semiconductor(FM/SC) interface without a tunneling barrier despite the contradictoryarguments based on conductivity mismatch at the FM/SC interface. [DOI:
10.1143/JJAP.42.L87]
KEYWORDS: Fe/InAs junction, spin injection, spintronics, indium
arsenide, epitaxial growth, Zeeman splitting
Nanoelectronics Laboratory, Graduate School of Engineering, Hokkaido University, N13 W8, Kitaku, Sapporo 060-8628, Japan
1 Research Center for Interface Quantum Electronics (RCIQE), Hokkaido University, N13 W8,
Kita-ku, Sapporo 060-8628, Japan
2 Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin, Germany* E-mail address: yoh@rciqe.hokudai.ac.jp

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JSAP International No.8 (July 2003)

Atsushi YOKOO(Received December 5, 2002; accepted for publication December 28, 2002)

A new lithographic method is proposed and demonstrated that has
the potential to make nano-fabrication a more widely available technique. Nanoelectrode lithography works by transferring the pattern on ananoelectrode to a target via an electrochemical reaction. This technique
may provide a better throughput and flexibility than conventional lithographic techniques. This describes and proves the concept of nanoelectrode lithography. [DOI: 10.1143/JJAP.42.L92]
KEYWORDS: lithography, nanoelectrode, anodic oxidation, atomic
force microscope, nanoprint
NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato Wakamiya, Atsugi 243-0198,
Japan

Part2

Abstracts of Express Letters

Jpn. J. Appl. Phys. Vol. 42 (2003) pp. L 209–L 211
Part 2, No. 3A, 1 March 2003
©2003 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol. 42 (2003) pp. L 215–L 216
Part 2, No. 3A, 1 March 2003
©2003 The Japan Society of Applied Physics

Avalanche-Type High Sensitive Image Pickup
Tube Using an a-Se Photoconductive Target

Electrical Properties of Poly(dA)·Poly(dT) andPoly(dG)·Poly(dC) DNA Doped with Iodine
Molecules

Wug-Dong PARK and Kenkichi TANIOKA1(Received January 16, 2003; accepted for publication January 22, 2003)

The avalanche-type high sensitive image pickup tube using 8 µm
thick a-Se layer was fabricated. The avalanche multiplication factor ofphotogenerated carriers was increased with increasing a target voltage. The quantum efficiency in an avalanche mode (target voltage:
880V) was higher than that in a non-avalanche mode (target voltage:
500V). Also the relative sensitivity in an avalanche mode at long wavelength was increased up to 620nm by the increase of the photodetection efficiency. The dark current was suppressed under 0.3 nA at a target voltage of 820 V, and decay lag at the third field was 1.2%. [DOI:
10.1143/JJAP.42.L209]
KEYWORDS: image pickup tube, photoconductive target, avalanche multiplication, quantum efficiency, relative
sensitivity, amorphous selenium
Department of Electronic Engineering, Dongyang University, 1 Kyochon-Dong, Punggi-Up,
Youngju, Kyungbuk 750-711, Korea
1 Advanced Imaging Devices Research Division, NHK Science and Technical Research Laboratories, 1-10-11 Kinuta, Setagaya-ku, Tokyo 157-8510, Japan

Masateru TANIGUCHI, Hea-Yeon LEE, Hidekazu TANAKA andTomoji KAWAI*(Received December 16, 2002; accepted for publication January 22, 2003)

Electrical resistivity of Poly(dA)·Poly(dT) and Poly(dG)·Poly(dC) DNA
were measured in a vacuum on nano-gap electrodes separated by 30–
50 nm. The DNAs showed very low conductivity of less than 0.1 pA at
1V. On the other hand, I2-doped Poly(dA)·Poly(dT) and Poly(dG)·Poly(dC)DNA form conducting DNAs, the current of which increased with an increase in the doping time. Doped Poly(dG)·Poly(dC) DNA shows higher
current than doped Poly(dA)·Poly(dT) DNA. Time dependence of resistivity of Poly(dG)·Poly(dC) DNA doped with iodine molecules exhibited thatthe total current composes of both hole current and ion current. [DOI:
10.1143/JJAP.42.L215]
KEYWORDS: Poly(dA)·Poly(dT) DNA, Poly(dG)·Poly(dC) DNA, chemical doping, dc measurement, electron transport, ionic conduction
The Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki,
Osaka 567-0047, Japan* Corresponding author.

Jpn. J. Appl. Phys. Vol. 42 (2003) pp. L 212–L 214
Part 2, No. 3A, 1 March 2003
©2003 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol. 42 (2003) pp. L 261–L 263
Part 2, No. 3B, 15 March 2003
©2003 The Japan Society of Applied Physics

Plasma Induced Subsurface Reactions for
Anisotropic Etching of Organic Low DielectricFilm Employing N2 and H2 Gas Chemistry

Quantitative Detection of Small Amount of
Nitrogen in Czochralski-Grown Silicon Crystals
Haruhiko ONO* and Mitsuhiro HORIKAWA1

Hisao NAGAI, Mineo HIRAMATSU , Masaru HORI and Toshio GOTO

(Received January 20, 2003; accepted for publication February 5, 2003)(Received January 6, 2003;accepted for publication January 15, 2003)

We successfully detected small amounts of nitrogen with a concentration of 3
10 13cm –3 in a nitrogen-doped Czochralski-grown
Si crystal. O–N–O complexes (or shallow thermal donors) were observed through infrared spectroscopy of electronic transition betweenhydrogen-like levels of the complexes. This method is very sensitiveand shows promise as a means of quantitatively detecting nitrogenin Si wafers of 1012–1014 cm–3. We found that almost all the N wasin the form of O–N–O complexes when the N concentration is lessthan 11014 cm–3. Therefore, conventional methods that measure
localized vibrational modes due to N–N and N–N–O complexes cannot detect nitrogen of less than 1
1014 cm–3, not only because of
the detection limit but also the lack of such vibrational centers. [DOI:
10.1143/JJAP.42.L261]
KEYWORDS: nitrogen, Czochralski-grown, silicon, infrared absorption, electronic transition, concentration

1*

Subsurface reactions of organic low dielectric (low k) film exposed toplasmas with low ion bombardment energy were investigated by a realtime analysis of Fourier transform infrared attenuated total reflection (FTIR ATR). The exposure of N2 plasma resulted in the formation of a CN
layer composed of C(sp2)=N and C(sp3)–N bonds. After the N2 plasma
exposure, the surface was exposed to H2 plasma. C(sp1)≡N and C(sp2)=N
bonds were removed by the H radicals, while the C(sp 3)–N bond remained. It was found that the C(sp3)–N bond was the key chemical bondagainst H2 plasma exposure. Based on the analyses, a reaction model foranisotropic profile in organic low k film etching employing N–H plasmas
is proposed. [DOI: 10.1143/JJAP.42.L212]
KEYWORDS: low k, etching, FT-IR ATR, CN layer, N2/H2 plasma, VUVAS
Department of Quantum Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya
464-8603, Japan
1 Department of Electrical and Electronic Engineering, Meijo University, 1-501 Shiogamaguchi,
Tempaku-ku, Nagoya 468-8502, Japan* E-mail address: hori@nuee.nagoya-u.ac.jp

Silicon Systems Research Laboratories, NEC Corporation, 1120 Shimokuzawa, Sagamihara, Kanagawa 229-1198, Japan
1 Elpida Memory Inc., 1120 Shimokuzawa, Sagamihara, Kanagawa 229-1198, Japan* Temporary address: Japan Fine Ceramics Center, 2-4-3 Nishi-Shinbashi, Minato-ku, Tokyo
105-0003, Japan.
E-mail address: ono@tokyo.jfcc.or.jp

JSAP International No.8 (July 2003)

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Jpn. J. Appl. Phys. Vol. 42 (2003) pp. L 264–L 266
Part 2, No. 3B, 15 March 2003
©2003 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol. 42 (2003) pp. L 267–L 269
Part 2, No. 3B, 15 March 2003
©2003 The Japan Society of Applied Physics

In-Plane Orientation and Polarity of
ZnO Epitaxial Films on As-Polished Sapphire(α-Al2O3) (0001) Substrates Grown by Metal
Organic Chemical Vapor Deposition

Significant Enhancement of Bi3.45La0.75Ti3O12
Ferroelectricity Derived by Sol-Gel Method

1,2,*

1

2

Bao-ping ZHANG , Le-hong MANH , Katsuki WAKATSUKI , Kentaro
TAMURA1,3, Tsuyoshi OHNISHI4, Mikk LIPPMAA 4, Noritaka USAMI 5,
Masashi KAWASAKI 5, Hideomi KOINUMA3 and Yusaburo SEGAWA1,2(Received February 14, 2003; accepted for publication February 14, 2003)

We report the control of the in-plane orientation of ZnO epitaxial
films grown on as-polished sapphire (α-Al2O3) (0001) substrates by metal organic chemical vapor deposition (MOCVD). When passing certain
flows of Zn-precursor over the substrate before introducing oxygen-precursor at certain substrate temperatures, unit cells of the ZnO film show
the same inplane orientation as the substrate. Otherwise, 30° rotation
is observed between unit cells of ZnO and the substrate. In case of using dietylzinc (DEZn) and oxygen gas as precursors, the substrate temperature and the flow rate of DEZn, under which notwist ZnO films canbe obtained, are determined experimentally. Measurements by coaxial
impact collision ion scattering spectroscopy (CAICISS), however, demonstrate that the ZnO films all have +c polarity, regardless of their in-planeorientation. This is different from the results obtained by laser-molecularbeam epitaxy by which +c polarity on as-polished sapphire (0001) substrates are hardly obtained. Since the +c polarity film is preferable in applications of wurtzite semiconductors, our results reveal that MOCVD
technique is particularly important in future applications of ZnO-relatedoxides. [DOI: 10.1143/JJAP.42.L264]
KEYWORDS: ZnO, MOCVD, polarity, epitaxy, thin film, wide gap
semiconductor, X-ray diffraction, sapphire, CAICISS
1 Photodynamics Research Center, The Institute of Physical and Chemical Research (RIKEN),
519-1399 Aoba, Aramaki, Aoba-ku, Sendai 980-0845, Japan
2 Department of Physics, Graduate School of Science, Tohoku University, Aoba-ku, Sendai
980-8578, Japan
3 Materials and Structures Laboratory, Tokyo Institute of Technology, Midori-ku, Yokohama
226-8503, Japan
4 Institute of Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan
5 Institute for Materials Research, Tohoku University, Aoba-ku, Sendai 980-8577, Japan* E-mail address: bzhang@postman.riken.go.jp

Yoshihisa FUJISAKI1,2, Kunie ISEKI2 and Hiroshi ISHIWARA2(Received January 28, 2003; accepted for publication February 7, 2003)

The ferroelectricity of sol-gel derived 80-nm Bi3.45La0.75Ti3O12 (BLT)films was significantly enhanced by low-pressure baking during the solgel process. The ferroelectricity enhancement was caused by the lowpressure baking after the drying process in air and before the crystallization of the dried gel. The maximum remanent polarization (Pr) was
27.2 µC/cm2, which was achieved after baking at 1.3 kPa oxygen pressure. The coercive field of 54.3 kV/cm was also achieved at the sametime. This Pr value is 2.3 times larger than the value attainable with theusual 1-atm baking process. The saturation property of the same capacitor proved that +/– 2V operation is possible. It was also found that theenhanced polarization is fatigue-free up to 1010 switching cycles. [DOI:
10.1143/JJAP.42.L267]
KEYWORDS: BLT, renament polarization, sol-gel, low pressure,bake
1 Research and Development Association of Future Electron Devices, Hatsumei-Kaikan Build. 5F,
2-9-14 Toranomon, Minato-ku, Tokyo 105-0001, Japan
2 Frontier Collaborative Research Center, Tokyo Institute of Technology, 4259 Nagatsuda,
Midori-ku, Yokohama 226-8503, Japan

Jpn. J. Appl. Phys. Vol. 42 (2003) pp. L 347–L 349
Part 2, No. 4A, 1 April 2003
©2003 The Japan Society of Applied Physics

High Mobility Thin Film Transistors withTransparent ZnO Channels
Junya NISHII1,2, Faruque M. HOSSAIN1,3, Shingo TAKAGI1,3, Tetsuya AITA3,
Koji SAIKUSA3, Yuji OHMAKI2, Isao OHKUBO3, Shuya KISHIMOTO2,
Akira OHTOMO1, Tomoteru FUKUMURA1, Fumihiro MATSUKURA2,
Yuzo OHNO2, Hideomi KOINUMA3,*, Hideo OHNO2 andMasashi KAWASAKI1,*,**(Received February 10, 2003; accepted for publication February 20, 2003)

We have fabricated high performance ZnO thin film transistors (TFTs)
using CaHfOx buffer layer between ZnO channel and amorphous silicon–nitride gate insulator. The TFT structure, dimensions, and materials set
are identical to those of the commercial amorphous silicon (a-Si) TFTs in
active matrix liquid crystal display, except for the channel and buffer layers replacing a-Si. The field effect mobility can be as high as 7 cm2/ V–1·
s–1 for devices with maximum process temperature of 300°C. The process temperature can be reduced to 150°C without much degrading theperformance, showing the possibility of the use of polymer substrate.
[DOI: 10.1143/JJAP.42.L347]
KEYWORDS: ZnO, CaHfOx , TFT, pulsed laser deposition, field effect mobility
1 Institute for Materials Research, Tohoku University, Aoba-ku, Sendai 980-8577, Japan
2 Research Institute of Electrical Communication, Tohoku University, Aoba-ku, Sendai 980-8577,
Japan
3 Materials and Structures Laboratory, Tokyo Institute of Technology, Midori-ku, Yokohama
226-8503, Japan* Also at Combinatorial Materials Exploration and Technology (COMET), National Institute forMaterials Science, Tsukuba 305-0044, Japan.
** E-mail address: kawasaki@imr.tohoku.ac.jp

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JSAP International No.8 (July 2003)

Part2

Abstracts of Express Letters

Jpn. J. Appl. Phys. Vol. 42 (2003) pp. L 350–L 352
Part 2, No. 4A, 1 April 2003
©2003 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol. 42 (2003) pp. L 404–L 405
Part 2, No. 4B, 15 April 2003
©2003 The Japan Society ofApplied Physics

Direct Synthesis of fct-FePt Nanoparticles by
Chemical RoutePreparation of Ferroelectric Thin films Using
Sol-Gel Solutions Dissolved in Supercritical
Carbon Dioxide

Balachandran JEYADEVAN, Kiyoshi URAKAWA, Akira HOBO,
Nallasamy CHINNASAMY, Kozo SHINODA, Kazuyuki TOHJI,
David D. Julianto DJAYAPRAWIRA1, Masakiyo TSUNODA1 andMigaku TAKAHASHI1(Received February 18, 2003; accepted for publication February 25, 2003)

Direct synthesis of fct-FePt nanoparticles was achieved by reducing platinum and iron acetylacetonates in tetraethylene glycol (TEG)
at 300°C. The particle diameter was between 5 and 10 nm. The X-ray
diffraction profile of the as-prepared FePt particles exhibited the superlattice reflections (001) and (110), which signified the tetragonality.
The Hk of 31 kOe measured at room temperature (RT) from hysteresis
loss analysis confirmed the presence of FePt particles with fractionallyordered fct structure which posses substantially high anisotropy. However, the RT coercivity was only 370 Oe due to strong magnetostaticinteraction of the particles. [DOI: 10.1143/JJAP.42.L350]
KEYWORDS: FePt, nanoparticles, fct-FePt, L10 phase, super latticereflections, polyol process, direct synthesis, coercive
field, hysteresis loss analysis
Department of Geoscience and Technology, Tohoku University, Aoba-ku, Sendai 980-8579, Japan
1 Department of Electronic Engineering, Tohoku University, Aoba-ku, Sendai 980-8579, Japan

Takeshi KIJIMA* and Hiroshi ISHIWARA(Received March 4, 2003; accepted for publication March 17, 2003)

A novel method to form ferroelectric thin films is presented,
in which sol-gel solutions such as Bi2SiO5-added Bi4Ti3O12 (BIT) andBi2SiO5-added SrBi2Ta2O9 (SBT) were dissolved in supercritical CO2 andejected onto Pt-coated Si substrates in the atmosphere. The surface
morphology of the deposited films was excellent even after crystallization annealing at 700°C for 30 min, and the remnant polarization values were 10 µC/cm2 and 7 µC/cm2 for BIT- and SBT-based films with70 nm in thickness, respectively. It was also found that the leakage
current depended on the post-annealing conditions; with increase ofoxygen pressure during the annealing, the leakage current density wasdecreased to about 1.0 10–7A/cm2. [DOI: 10.1143/JJAP.42.L404]
KEYWORDS: ferroelectric film, supercritical carbon dioxide, sol-gel
solution, Bi4Ti3O12, SrBi2Ta2O9
Frontier Collaborative Research Center, Tokyo Institute of Technology, 4259 Nagatsuta, Midoriku, Yokohama 226-8503, Japan* Present address: Technology Platform Research Center, Seiko Epson Corporation, 281 Fujimi,
Fujimi-machi, Nagano 399-0293, Japan

Jpn. J. Appl. Phys. Vol. 42(2003) pp. L 401–L 403
Part 2, No. 4B, 15 April 2003
©2003 The Japan Society of Applied Physics

Jpn. J. Appl. Phys. Vol. 42 (2003) pp. L 406–L 409
Part 2, No. 4B, 15 April 2003
©2003 The Japan Societyof Applied Physics

Molecular Beam Epitaxy of High Magnesium
Content Single-Phase Wurzite MgxZn1–xO
Alloys (x 0.5) and Their Application to
Solar-Blind Region Photodetectors

Ferroelectric Nematic Monolayer

Tsuyoshi TAKAGI, Hiroshi TANAKA, Shizuo FUJITA1,* and Shigeo FUJITA

Ferroelectricity is desirable for realizing fast-response liquid crystal
devices. Existing ferroelectric liquid crystals are improper with the spontaneous polarization Ps being indirectly induced by the broken centrosymmetry of molecular arrangement. We found that Langmuir monolayers of certain dialkylated nematic compound exhibit a laterally polarized
two-dimensional ferroelectric nematic. The Ps is comparable to that ofchiral smectic liquid crystals, and shows a fast linear electro-optic switching with a microsecond response. Estimates of electrostatic energy suggest that the ferroelectricity may be driven by the direct dipolar interactions. [DOI: 10.1143/JJAP.42.L406]
KEYWORDS: intrinsic ferroelectricity, nematic liquid crystal, achiralmolecule, spontaneous polarization, Langmuir monolayer, dipolar interaction, two-dimensionality(Received March 6, 2003; accepted for publication March 12, 2003)

A series of single-phase wurzite MgxZn1–xO alloys from x = 0 to 0.5
were successfully obtained by molecular beam epitaxial growth on sapphire substrates, resulting in artificial tuning of band gap energy E gfrom 3.3 to 4.5 eV which covers UV-A, UV-B, and solar-blind spectral
regions. The problem of phase separation ever reported in the growthof MgxZn1–xO with higher Mg content, e.g., x > 0.4 and Eg > 3.9 eV, hasbeen overcome by using a ZnO buffer layer. The Mg0.5Zn0.5O layers havebeen applied to a planar geometry Schottky type metal-semiconductormetal photodetector, exhibiting the photoresponse for the wavelength
shorter than 270 nm which correspond to the solar-blind region. [DOI:
10.1143/JJAP.42.L401]
KEYWORDS: MgZnO, MBE, ZnO buffer layer, solar-blind spectral
region, UV photodetector
Department of Electronic Science and Engineering, Kyoto University, Sakyo-ku, Kyoto 606-8501,
Japan
1 International Innovation Center, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan* E-mail address: fujita@iic.kyoto-u.ac.jp

Yuka TABE1,2, Takahiro YAMAMOTO1, Isa NISHIYAMA1,
Makoto YONEYA1 and Hiroshi YOKOYAMA1,2(Received February27, 2003; accepted for publication March 11, 2003)

1 Yokoyama Nano-structured Liquid Crystal Project, ERATO, Japan Science and Technology Corporation, 5-9-9 Tokodai, Tsukuba, Ibaraki 300-2635, Japan
2 Nanotechnology Research Institute, National Institute of Advanced Industrial Science andTechnology, 1-1-1 Umezono, Tuskuba, Ibaraki 305-8568, Japan

JSAP International No.8 (July 2003)

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