Hot Wall Epitaxy(HWE) 방법에 의한 CdIn2S4 단결정 박막 성장과 광전기적 특성 연구

Abstract

A stoichiometric mixture of evaporating materials for CdIn2S4 single crystal thin films was prepared from horizontal furnace. To obtain the single crystal thin films, CdIn2S4 mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by hot wall epitaxy(HWE) system. The source and substrate temperatures were 630 ℃ and 420 ℃, respectively. The crystalline structure of single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction(DCXD). The carrier density and mobility of CdIn2S4 single crystal thin films measured from Hall effect by van der Pauw method are 9.01×1016 cm-3 and 219 cm2/V·sec at 293 K, respectively. From the optical absorption measurement, the temperature dependence of energy band gap on CdIn2S4 single crystal thin films was found to be Eg(T)=2.7116 eV-(7.74×10-4 eV/K)T2/(T＋434 K). The crystal field and the spin-orbit splitting energies for the valence band of the CdIn2S4 have been estimated to be 0.1291 eV and 0.0248 eV, 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 Γ5 states of the valence band of the CdIn2S4/GaAs epilayer. The three photocurrent peaks observed at 10 K are ascribed to the A1-, B1-, and C1-exciton peaks for n=1. After the as-grown CdIn2S4 single crystal thin films was annealed in Cd-, S-, and In-atmospheres, the origin of point defects of CdIn2S4 single crystal thin films has been investigated by the photoluminescence(PL) at 10 K. The native defects of VCd, VS obtained by PL measurements were classified as a donors or acceptors type. And we concluded that the heat-treatment in the S-atmosphere converted CdIn2S4 single crystal thin films to an optical n-type. Also, we confirmed that In in CdIn2S4/GaAs did not form the native defects because In in CdIn2S4 single crystal thin films existed in the form of stable bonds.