Hot Wall Epitaxy(HWE)법에 의한 BaIn2S4 단결정 박막 성장과 광전도 특성
Growth and optical conductivity properties for BaIn2S4 single crystal thin film by hot wall epitaxy
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수평 전기로에서 BaIn2S4 다결정을 합성하여 HWE(Hot Wall Epitaxy) 방법으로 BaIn2S4 단결정 박막을 반절연성GaAs(100) 기판에 성장시켰다. BaIn2S4 단결정 박막의 성장 조건은 증발원의 온도 620oC, 기판의 온도 420oC였고 성장 속도는 0.5 μm/hr였다. 이때 이중결정 X-선 요동곡선(DCRC)의 반폭치(FWHM)도 128 arcsec로 가장 작아 최적 성장 조건임을알 수 있었다. Hall 효과는 van der Pauw 방법에 의해 측정되었으며, 온도에 의존하는 운반자 농도와 이동도는 293 K에서각각 6.13 × 1017 cm−3, 222 cm2/v · s였다. BaIn2S4/SI(Semi-Insulated) GaAs(100) 단결정 박막의 광흡수와 광전류 spectra를293 K에서 10 K까지 측정하였다. 광흡수 스펙트럼으로부터 band gap Eg(T)는 Varshni공식에 따라 계산한 결과 Eg(T) = 3.0581 eV − (3.9511 × 10−3 eV/K)T2/(T + 536 K)이었으며 광전류 스펙트럼으로부터 Hamilton matrix(Hopfield quasicubic mode) 법으로 계산한 결과 crystal field splitting energy Δcr값이 182.7 meV이며 spin-orbit energy Δso값은 42.6 meV임을 확인하였다. 10 K일 때 광전류 봉우리들은 n = 1, 24일때 A1-, B1-와 C24-exciton 봉우리임을 알았다.
Abstract
A stoichiometric mixture of evaporating materials for BaIn2S4 single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, BaIn2S4 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 620oC and 420oC, respectively. The crystalline structure of the single crystal thin films was investigated by double crystal X-ray diffraction (DCXD). The carrier density and mobility of BaIn2S4 single crystal thin films measured from Hall effect by van der Pauw method are 6.13 × 1017 cm−3 and 222 cm2/v · s at 293 K, respectively. The temperature dependence of the energy band gap of the BaIn2S4 obtained from the absorption spectra was well described by the Varshni's relation, Eg(T) = 3.0581 eV − (3.9511 × 10−3 eV/K)T2/(T + 536 K). The crystal field and the spin-orbit splitting energies for the valence band of the BaIn2S4 have been estimated to be 182.7 meV and 42.6 meV, respectively, by means of the photocurrent spectra and the Hopfield quasicubic model. These results indicate that the splitting of the Δso definitely exists in the Γ 5 states of the valence band of the BaIn2S4/GaAs epilayer. The three photocurrent peaks observed at 10 K are ascribed to the A1-, B1-exciton for n = 1 and C24-exciton peaks for n = 24.
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