http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
ZnO Nanorods and Periodicaly-Polarity-Inverted Structures for Photonic Devices
Sang Hyun Lee,Katsushi Fujii,Tsutomu Minegishi,Takafumi Yao 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.1
We control the morphology of ZnO nanorods and the crystal polarity of ZnO layers for applications to photonic devices. ZnO nanorods are grown through an aqueous reaction. The morphology of the ZnO nanorods is changed to porous by annealing folowed by wet chemical etching. The photoluminescence emision intensity from porous ZnO nanorods increases several timescomparedtothatfromas-grownnanorods. The enhancement of the emision intensity of the porous ZnO nanorods is explained in terms of an increase in the extraction eciency of emision. Periodicaly-polarity-inverted(PPI)ZnO structures are grown on paterned MgO buffers fabricated on c-Al2O3 substrates by using plasma-asisted molecular beam epitaxy, in which the paterned MgO consists of 8-nm-thick MgO and 1-nm-thick MgO. Zn-polar ZnO grows on the thick MgO buffer while O-polar ZnO on the thin MgO. Second harmonic generation for incident lightat 1060 nm under quasi-phase matching conditions is observed at 503 nm from the PPI structure, thus indicating the feasibility of using PPI ZnO structures for nonlinear optical devices.
조영지,장지호,하준석,Hyun-jae Lee,Katsushi Fujii,Takafumi Yao,Woong Lee,Takashi Sekiguchi,Jun-Mo Yang,Jungho Yoo 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.2
Remarkable reduction of the threading dislocation (TD) density has been achieved by insertinga GaN layer grown at an intermediate temperature (900 C) (IT-GaN layer), just prior to thegrowth of GaN at 1040 C by using a hydride vapor phase epitaxy. The variation in the dislocationdensity variation along the growth direction was observed by using cathodoluminescence (CL) andtransmission electron microscopy (TEM). A cross-sectional CL image revealed that the reductionof the TD density happened during the growth of IT-GaN layer. The TEM measurement providedthe proof that the TD reduction could be ascribed to the masking of the TD by stacking faults inthe IT-GaN layer.
Effect of Double-Layered n-Type GaN on the Photoelectrochemical Properties in NaOH Aqueous Solution
Kim, Eunsook,Bae, Hyojung,Ko, Younghee,Fujii, Katsushi,Park, Hyung-Jo,Jeong, Tak,Lee, Hyo-Jong,Oh, Tae-Sung,Ha, Jun-Seok The Electrochemical Society 2015 Journal of the Electrochemical Society Vol.162 No.1
<P>In this study, photoelectrochemical properties of a double-layered n-type GaN in NaOH aqueous solution were investigated. Several electrical properties such as impedance, photocurrent-voltage property, and photocurrent-time relationship were examined for comparison. After the measurement the electrical properties, the surface of GaN photoelectrodes were observed by field emission scanning electron microscope to confirm the electrolytic corrosion. The results of this study indicate that the double-layered n-GaN electrode increased the photocurrent density compared to the single-layered electrode. Moreover, the surface of the double-layered n-GaN electrode was more stable than that of the single-layered n-GaN, indicating that surface layer preserved the lower layer from photocorrosion, and also its depletion length was enough to help the movement of carriers. These results show that the double-layered n-GaN electrode has more advantages than the single-layered n-GaN electrode.</P>
ZnO를 이용한 GaN 자립형 기판의 제작에 관한 연구
김시영,정미나,이삼녕,장지호,이현재,Katsushi Fujii,Takenari Goto,Takafumi Yao,박승환,이웅,Takashi Sekiguchi 한국물리학회 2010 새물리 Vol.60 No.4
A new hydride vapor phase epitaxy (HVPE)-based approach to the fabrication of freestanding GaN (FS-GaN) substrates was investigated. For the direct formation of low-temperature GaN (LT-GaN) layers, the growth parameters (the polarity of ZnO, the growth temperature, and the V/III ratio) were optimized. The FS-GaN layer was achieved by gas etching (900℃, NH₃) in an HVPE reactor. The fabrication of a thin (80 ㎛) FS-GaN film on a FS-GaN (LT) seed substrate to improve the quality further is discussed. 간단한 공정을 이용한 자립형 GaN 기판 제작을 위하여 PAMBE(Plasma Assisted Molecular Beam Epitaxy)법으로 성장한 ZnO 희생층 상에, HVPE(Hydride Vapor Phase Epitaxy)법으로 GaN를 직접 성장하고, HVPE 반응로 안에서 기상 식각을 시도하여 GaN와 사파이어 기판을 분리하고 그 위에 고온에서 GaN 후막을 재 성장하는 방법을 제안하였다. ZnO-희생층 상에 저온 GaN를 직접 성장하기 위해서, ZnO-희생층의 극성, GaN의 성장 온도 및 V/III ratio를 최적화하였고, 설정된 조건에서 성장한 저온 GaN와 사파이어 기판을 고온 가스 식각을 (900℃, NH₃) 통하여 분리하였으며, 그위에 80 ㎛의 두께를 가지는 자립형 GaN 기판을 제작하여 결정성을 고찰 하였다.
Influence of Mg Flux on the Photoelectrochemical Properties of p-Type GaN for Hydrogen Production
Bae, Hyojung,Kim, Eunsook,Park, Jun-Beom,Fujii, Katsushi,Lee, Sanghyun,Lee, Hyo-Jong,Ryu, Sang-Wan,Lee, June Key,Ha, Jun-Seok American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.10
<P>This study investigates the effects of the doping flux of magnesium (Mg) on the photoelectrochemical (PEC) properties of p-type GaN. The Mg-doped GaN samples were deposited directly on c-plane Al2O3 substrates by metalorganic chemical vapor deposition (MOCVD). The Mg flux during growth was controlled by a mass flow controller at flows of 50, 100, 200, and 500 sccm. Optical property analysis revealed band-gaps for the films between 3.2 eV and 3.4 eV. The PEC properties of the films were examined by potentiostat with a three-electrode configuration. The photocurrent density of the 200 sccm sample was the highest, which would be attributed to vacancies or other intrinsic defects, such as interstitials and antisites, giving n-type conductivity.</P>
Bae, Hyojung,Park, Seung Hwan,Nakamura, Akihiro,Koike, Kayo,Fujii, Katsushi,Park, Hyung-Jo,Lee, Hyo-Jong,Oh, Tae-Sung,Ha, Jun-Seok The Electrochemical Society 2013 Journal of the Electrochemical Society Vol.160 No.11
<P>The effects of annealing with H<SUB>2</SUB> and N<SUB>2</SUB> on the photoelectrochemical (PEC) properties of annealed Nb-doped TiO<SUB>2</SUB> (ann-TNO) film were investigated. The photocurrent density of the ann-TNO film was 2 to 3 orders of magnitude higher than that of u-TiO<SUB>2</SUB> film. To understand this phenomenon, ann-TNO film was investigated by comparing u-TiO<SUB>2</SUB> and Nb-doped TiO<SUB>2</SUB> (TNO) films. An investigation was conducted using Hall effect estimation, photoluminescence (PL) analysis, and band-gap calculation.</P>
Bae, Hyojung,Rho, Hokyun,Min, Jung-Wook,Lee, Yong-Tak,Lee, Sang Hyun,Fujii, Katsushi,Lee, Hyo-Jong,Ha, Jun-Seok Elsevier 2017 APPLIED SURFACE SCIENCE - Vol.422 No.-
<P><B>Abstract</B></P> <P>Gallium nitride (GaN) nanowires are one of the most promising photoelectrode materials due to their high stability in acidic and basic electrolytes, and tunable band edge potentials. In this study, GaN nanowire arrays (GaN NWs) were prepared by molecular beam epitaxy (MBE); their large surface area enhanced the solar to hydrogen conversion efficiency. More significantly, graphene was grown by chemical vapor deposition (CVD), which enhanced the electron transfer between NWs for water splitting and protected the GaN NW surface. Structural characterizations of the prepared composite were performed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The photocurrent density of Gr/GaN NWs exhibited a two-fold increase over pristine GaN NWs and sustained water splitting up to 70min. These improvements may accelerate possible applications for hydrogen generation with high solar to hydrogen conversion efficiency.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Pristine GaN NWs were grown on n-type Si (111) substrates using radio-frequency plasma-assisted MBE. </LI> <LI> The graphene grown by CVD was coated on surface of GaN nanowires (Gr/GaN NWs). </LI> <LI> The photoelectrochemical properties of these structures were investigated. </LI> <LI> The saturated photocurrent density increased in Gr/GaN NWs than ref GaN NWs. </LI> <LI> We reported the reason for this difference. </LI> </UL> </P>