Hot wall epitaxy(HWE)법에 의한 AgGaSe2 단결정 박막 성장과 열처리 효과
Growth and effect of thermal annealing for AgGaSe2 single crystal thin film by not wall epitaxy
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AgGaSe2 단결정 박막을 수평 전기로에서 합성한 AgGaSe2 다결정을 증발원으로하여, hot wall epitaxy(HWE) 방법으로 증발원과 기판(반절연성-GaAs(100))의 온도를 각각 630oC, 420oC로 고정하여 성장하였다. 이때 단결정 박막의 결정성은 광발광 스펙트럼과 이중결정 X-선 요동곡선(DCRC) 으로 부터 구하였다. AgGaSe2의 광흡수 스펙트럼으로부터 구한 온도에 의존하는 에너지 밴드갭 Eg(T)는 Varshni 공식에 fitting한 결과 Eg(T) = 1.9501 eV - (8.79 × 10-4 eV/K)T2/(T + 250 K)를 잘 만족하였다. 성장된 AgGaSe2 단결정 박막을 Ag, Ga, Se 분위기에서 각각 열처리하여 10 K에서 photoluminescience (PL) spectrum을 측정하여 점 결함의 기원을 알아보았다. PL 측정으로 부터 얻어진 VAg, VSe, Agint, 그리고 Seint는 주개와 받개로 분류되어졌다. AgGaSe2 단결정 박막을 Ag 분위기에서 열처리하면 p형으로 변환됨을 알 수 있었다. 또한, Ga 분위기에서 열처리하면 열처리 이전의 PL 스펙트럼을 보이고 있어서, AgGaSe2 단결정 박막에서 Ga은 안정된 결합의 형태로 있기 때문에 자연 결함의 형성에는 관련이 없음을 알았다.
Abstract
A stoichiometric mixture of evaporating materials for AgGaSe2 single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, AgGaSe2 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 630oC and 420oC, respectively. The temperature dependence of the energy band gap of the AgGaSe2 obtained from the absorption spectra was well described by the Varshni뭩 relation, Eg(T) = 1.9501 eV - (8.79 ?10-4 eV/K)T2/(T + 250 K). After the as-grown AgGaSe2 single crystal thin films was annealed in Ag-, Se-, and Ga-atmospheres, the origin of point defects of AgGaSe2 single crystal thin films has been investigated by the photoluminescence (PL) at 10 K. The native defects of VAg, VSe, Agint, and Seint obtained by PL measurements were classified as a donors or acceptors type. And we concluded that the heat-treatment in the Ag-atmosphere converted AgGaSe2 single crystal thin films to an optical p-type. Also, we confirmed that Ga in AgGaSe2/GaAs did not form the native defects because Ga in AgGaSe2 single crystal thin films existed in the form of stable bonds.
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