태양 전지 개발을 위한 ZnIn₂S₄ 단결정 박막 성장과 특성

유상하(Sangha You),홍광준(Kwangjoon Hong) 한국태양에너지학회 2002 한국태양에너지학회 학술대회논문집 Vol.- No.-

Hot Wall Epitaxy(HWE)법에 의한 MnAl₂S₄ 단결정 박막 성장과 광전도 특성

유상하,이기정,홍광준,문종대,You, Sangha,Lee, Kijeong,Hong, Kwangjoon,Moon, Jongdae 한국결정성장학회 2014 韓國結晶成長學會誌 Vol.24 No.6

수평 전기로에서 $MnAl_2S_4$ 다결정을 합성하여 HWE(Hot Wall Epitaxy)방법으로 $MnAl_2S_4$ 단결정 박막을 반절연성 GaAs(100)기판에 성장시켰다. $MnAl_2S_4$ 단결정 박막의 성장 조건은 증발원의 온도 $630^{\circ}C$, 기판의 온도 $410^{\circ}C$였고 성장 속도는 $0.5{\mu}m/hr$였다. 이때 $MnAl_2S_4$ 단결정 박막의 결정성의 조사에서 이중결정 X-선 요동곡선(DCRC)의 반폭치(FWHM)도 132 arcsec로 가장 작아 최적 성장 조건임을 알 수 있었다. $MnAl_2S_4$/SI(Semi-Insulated) GaAs(100) 단결정 박막의 광흡수를 293 K에서 10 K까지 측정하였다. 광흡수 스펙트럼으로부터 band gap $E_g(T)$는 Varshni 공식에 따라 계산한 결과 $E_g(T)=3.7920eV-(5.2729{\times}10^{-4}eV/K)T^2/(T+786K)$였다. $MnAl_2S_4$ 단결정 박막의 응용소자인 photocell로 사용할 수 있는 pc/dc 값이 가장 큰 광전도셀은 S 증기분위기에서 열처리한 셀로 $1.10{\times}10^7$이었으며, 광전도 셀의 감도(sensitivity)도 S 증기분위기에서 열처리한 셀이 0.93로 가장 좋았다. 또한 최대 허용소비전력(MAPD)값도 S 증기분위기에서 열처리한 셀이 316 mW로 가장 좋았으며, S 증기분위기에서 열처리한 셀의 응답시간은 오름시간 14.8 ms, 내림시간 12.1 ms로 가장 빠르게 나타나, $MnAl_2S_4$ 단결정 박막을 S 분위기에서 $290^{\circ}C$로 30분 열처리한 photocell이 상용화가 가능할 것으로 여겨진다. A stoichiometric mixture of evaporating materials for $MnAl_2S_4$ single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, $MnAl_2S_4$ mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperatures were $630^{\circ}C$ and $410^{\circ}C$, respectively. The crystalline structure of the single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). The temperature dependence of the energy band gap of the $MnAl_2S_4$ obtained from the absorption spectra was well described by the Varshni's relation, $E_g(T)=3.7920eV-5.2729{\times}10^{-4}eV/K)T^2/(T+786 K)$. In order to explore the applicability as a photoconductive cell, we measured the sensitivity (${\gamma}$), the ratio of photocurrent to dark current (pc/dc), maximum allowable power dissipation (MAPD) and response time. The results indicated that the photoconductive characteristic were the best for the samples annealed in S vapour compare with in Mn, Al, air and vacuum vapour. Then we obtained the sensitivity of 0.93, the value of pc/dc of $1.10{\times}10^7$, the MAPD of 316 mW, and the rise and decay time of 14.8 ms and 12.1 ms, respectively.

Growth and Temperature Dependence of The Photocurrent Spectra for HgCdTe Epilatyers

Seungnam Baek,Kwangjoon Hong,Sangha you,Sangyoul Lee,Seungpyung Choi,Hunsang Chung,Youngjin Shin 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.III

Hg$_{1-x}$Cd$_x$Te (MCT) was grown by hot wall epitaxy. Prior to the MCT growth, the CdTe (111) buffer layer was grown on the GaAs substrate at the temperature of 590 $^\circ$C for 15 min. When the thickness of the CdTe buffer layer was 5 $\mu$m or thicker, the full width at half maximum values obtained from the x-ray rocking curves were found to significantly decrease. After a good quality CdTe buffer layer was grown, the MCT epilayers were grown on the CdTe (111) /GaAs substrate at various temperatures in situ. The crystal quality for those epilayers was investigated by means of the x-ray rocking curves and the photocurrent experiment. The photoconductor characterization for the epilayers was also measured. The energy band gap of MCT was determined from the photocurrent measurement and the x composition rates from the temperature dependence of the energy band gap were turned out.

이동 무선랜 접속장치의 접속점 보안 천이 메커니즘과 유한상태머신

정병호,강유성,오경희,김상하,Chung ByungHo,Kang You Sung,Oh KyungHee,Kim SangHa 한국통신학회 2005 韓國通信學會論文誌 Vol.30 No.6C

무선랜 상에서 실시간 음성 서비스 제공에 대한 기대가 높아지면서, 무선랜 접속장치에 빠르고 안전한 이동성 지원 기술을 구현하는 문제는 최근 가장 활발히 연구되고 있는 분야 중 하나이다. 이동 단말이 새로운 접속장치로 이동하더라도 과거 접속장치로부터 제공 받던 보안 강도를 지속적으로 유지하면서 이동 지연시간을 최소화하는 문제는 매우 중요하다. 따라서 본 논문은 IEEE802.11i, 802.1x, 그리고 802.11f를 지원하는 무선랜에서 접속점 보안 천이시간을 시스템 성능 변수로 정의하고, 평균적 천이 지연시간의 최소화를 목적 함수로 하는 보안 메커니즘과 그 실현을 위한 유한 상태 머신을 제안한다. 실험 결과 제안된 보안 메커니즘이 기존의 802.1X인증 방식에 비하여 $79\%$ 까지의 성능 이득이 기대됨을 보인다 Recently with the high expectation of voice over WLAN service, to supped fast inter-AP security transition in WLAN AP is one of the most actively investigating issues. It is also very important to minimize inter-AP security transition latency, while maintaining constantly the secure association from old AP when a station transits to new AP. Hence, this paper first defines secure transition latency as a primary performance metric of AP system in WLAN supporting IEEE802.11i, 802.1x, and 802.11f, and then presents low latency inter-AP security transition mechanism and its security FSM whose objective is to minimize inter-AP transition latency. Experiment shows that the proposed scheme outperforms the legacy 802.1X AP up to $79\%$ with regard to the transition latency.

Determination of Diffusion and Perfusion by NMR Bipolar Gradients Pulse Technique

Kim, Namsoo,Baek, Changhyun,Shin, Yongjin,You, Sangha,Hong, Kwangjoon,Ryang, Kyungseung,Lee, Sangyoul,Cahill, Patrick T CHOSUN UNIVERSITY 1997 Basic Science and Engineering Vol.1 No.1

In Biologic tissues, intravoxel imcoherent motion(IVIM) include molecular diffusion of water, microcirculation of blood in the capillary network (perfusion), an nonuniform slow flow, such as cerebrospinal fluid(CSF) flow. Molecular diffusion is dependent an the physical properties of tissue, and microcirculation of blood or perfusion can also be considered an incoherent motion due to the pseudorandom organization of the capillary network at the voxel level. Perfusion imaging has the potential of characterizing tissues by their perfusion patterns, but also provides information as tissue function. IVIMs are quantified in each voxel on the basis of an apparent diffusion coefficient(ADC). Measure directly and individually both tissue diffusion and perfusion by use of a bipolar gradient pulse technique into NMR spin echo sequence. The diffusion coefficient(D) for water and acetone were 2.10 (x10-³mm²/sec) and 5.06(x10-³mm²/sec), respectively. The perfusion factor was linearly incremental for stepwise increases in flow velocities. A specially fabricated random flow phantom is used to support the validity of this theory.

The Growth and Photoconductive Characteristics of ?? Thin Films by the Hot Wall Epitaxy

Hong, Kwangjoon,Suh, Sangseok,Jeong, Junwoo,You, Sangha,Choi, Seungpyung,Lee, Koankio,Lee, Sangyoul,Kim, Haeyeon,Moon, Jongdae,Shin, Yongjin,Kim, Haesuk CHOSUN UNIVERSITY 1997 Basic Science and Engineering Vol.1 No.1

The CdS₁? Se? thin films were grown on the GaAs(100) wafers by a Hot Wall Epitaxy method (HWE). The temperatures the source and the substrate temperature are 580℃ and 440℃ respectively. The crystalline structure of thin films was investigated by double crystal X-ray diffraction (DCXD). Hall effect on the sample was measured by the van der Pauw method and studied on the carrier density and mobility dependence on temperature. In order to explore the applicability as a photoconductive cell, we measured the sensitivity(r), the ratio of photocurrent to darkcurrent(pc/dc), maximum allowable power dissipation (MAPD), spectral response and response time.

The Growth and Photoconductive Characteristics of ZnGa₂Se₄ Epilayers by the Hot Wall Epitaxy

Hong, Kwangjoon,Suh, Sangseok,Jeong, Junwoo,You, Sangha,Lee, Koankio,Choi, Seungpyung,Lee, Sangyoul,Kim, Haeyeon,Moon, Jongdae,Shin, Yongjin,Kim, Haesuk CHOSUN UNIVERSITY 1997 Basic Science and Engineering Vol.1 No.1

The stochiometric mix of evaporating materials for the ZnGa₂Se₄single crystal thin films were prepared from horizental furnace. The polycrystal structure obtaind from the power x-ray diffraction was defect chalcopyrite. The lattice costants a。and c。were a。=5.51 A, c。=10.98 A. To obtains the single crystal thin films, ZnGa₂Se₄mixed crystal were deposited on throughly etched Si(100) by the Hot Wall Epitaxy (HWE) system. The temperates of the source and the substrate were 590℃ and 450℃, respectively. The crystalline structure of single crystal thin films was investigated by the double crystal X-ray diffraction (DCXD). Hall effect on this sample was measured by the method of van der Pauw and studied on carrier density and mobility dependence on temperature. In order to explore the applicability as a photoconductive cell, we measured the sensitivity (r), the ratio of photocurrent to dark current (pc/dc), maximum allowable power dissipation (MAPD), spectral response and response time.