Hot Wall Epitaxy(HWE)에 의한 CuAlSe2 단결정 박막 성장과 가전자대 갈라짐에 대한 광전류 연구
Photocurrent Study on the Splitting of the Valence band and Growth of CuAlSe2 Single Crystal Thin Film by Hot Wall Epitaxy
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Abstract
A stoichiometric mixture of evaporating materials for CuAlSe2 single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, CuAlSe2 mixed crystal was deposited on thoroughly etched semiinsulating GaAs(100) substrate by the hot wall epitaxy (HWE) system. The source and substrate temperatures were 680oC and 410oC, respectively. The crystalline structure of the single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). The carrier density and mobility of CuAlSe2 single crystal thin films measured with Hall effect by van der Pauw method are 9.24 ?1016 cm-3 and 295 cm2/V ?s at 293 K, respectively. The temperature dependence of the energy band gap of the CuAlSe2 obtained from the absorption spectra was well described by the Varshni's relation, Eg(T) = 2.8382 eV - (8.68 ?10-4 eV/K)T2/(T + 155 K). The crystal field and the spin-orbit splitting energies for the valence band of the CuAlSe2 have been estimated to be 0.2026 eV and 0.2165 eV at 10 K, respectively, by means of the photocurrent spectra and the Hopfield quasicubic model. These results indicate that the splitting of the Dso definitely exists in the G5 states of the valence band of the CuAlSe2. The three photocurrent peaks observed at 10 K are ascribed to the A1-, B1-, and C1-exciton peaks for n = 1.
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