Hot Wall Epitaxy(HWE)법에 의한 MnAl2S4 단결정 박막 성장과 광전도 특성
Growth and optical conductivity properties for MnAl2S4 single crystal thin film by hot wall epitaxy method
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초록
수평 전기로에서 MnAl2S4 다결정을 합성하여 HWE(Hot Wall Epitaxy)방법으로 MnAl2S4 단결정 박막을 반절연성 GaAs(100)기판에 성장시켰다. MnAl2S4 단결정 박막의 성장 조건은 증발원의 온도 630oC, 기판의 온도 410oC였고 성장속도는 0.5 μm/hr였다. 이때 MnAl2S4 단결정 박막의 결정성의 조사에서 이중결정 X-선 요동곡선(DCRC)의 반폭치(FWHM)도 132 arcsec로 가장 작아 최적 성장 조건임을 알 수 있었다. MnAl2S4/SI(Semi-Insulated) GaAs(100) 단결정 박막의 광흡수를 293 K에서 10 K까지 측정하였다. 광흡수 스펙트럼으로부터 band gap Eg(T)는 Varshni 공식에 따라 계산한 결과 Eg(T) =3.7920 eV − (5.2729 × 10−4 eV/K)T2/(T + 786 K)였다. MnAl2S4 단결정 박막의 응용소자인 photocell로 사용할 수 있는 pc/dc값이 가장 큰 광전도셀은 S 증기분위기에서 열처리한 셀로 1.10 × 107이었으며, 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,MnAl2S4 단결정 박막을 S 분위기에서 290oC로 30분 열처리한 photocell이 상용화가 가능할 것으로 여겨진다.
Abstract
A stoichiometric mixture of evaporating materials for MnAl2S4 single crystal thin films was prepared fromhorizontal electric furnace. To obtain the single crystal thin films, MnAl2S4 mixed crystal was deposited on thoroughlyetched semi-insulating GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperatureswere 630oC and 410oC, respectively. The crystalline structure of the single crystal thin films was investigated by thephotoluminescence and double crystal X-ray diffraction (DCXD). The temperature dependence of the energy band gap ofthe MnAl2S4 obtained from the absorption spectra was well described by the Varshni's relation, Eg(T) = 3.7920 eV − (5.2729 ×10−4 eV/K)T2/(T + 786 K). In order to explore the applicability as a photoconductive cell, we measured the sensitivity (γ),the ratio of photocurrent to dark current (pc/dc), maximum allowable power dissipation (MAPD) and response time. Theresults indicated that the photoconductive characteristic were the best for the samples annealed in S vapour compare within Mn, Al, air and vacuum vapour. Then we obtained the sensitivity of 0.93, the value of pc/dc of 1.10 × 107, the MAPDof 316 mW, and the rise and decay time of 14.8 ms and 12.1 ms, respectively.
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