Hot Wall Epitaxy(HWE)법에 의한 CuAlSe2단결정 박막의 성장과 가전자대 갈라짐에 대한 광전류 연구

Abstract

A stoichiometric mixture of evaporating materials for <TEX>$CuAlSe_{2}$</TEX> single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, <TEX>$CuAlSe_{2}$</TEX> 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 <TEX>$680^{\circ}C$</TEX> and <TEX>$410^{\circ}C$</TEX>, 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 <TEX>$CuAlSe_{2}$</TEX> single crystal thin films measured with Hall effect by van der Pauw method are <TEX>$9.24{\times}10^{16}cm^{-3}$</TEX> and <TEX>$295cm^{2}/V{\codt}s$</TEX> at 293 K, respectively. The temperature dependence of the energy band gap of the <TEX>$CuAlSe_{2}$</TEX> obtained from the absorption spectra was well described by the Varshni's relation, <TEX>$E_{g}(T)$</TEX> = 2.8382 eV - (<TEX>$8.68{\circ}10^{-4}$</TEX> eV/K)<TEX>$T^{2}$</TEX>/(T + 155 K). The crystal field and the spin-orbit splitting energies for the valence band of the <TEX>$CuAlSe_{2}$</TEX> 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 <TEX>${\Delta}so$</TEX> definitely exists in the <TEX>${\Gamma}_{5}$</TEX> states of the valence band of the <TEX>$CuAlSe_{2}$</TEX>. The three photocurrent peaks observed at 10 K are ascribed to the <TEX>$A_{1-}$</TEX>, <TEX>$B_{1-}$</TEX>, and <TEX>$C_{1-}$</TEX> exciton peaks for n = 1.