Hot Wall Epitaxy(HWE) 방법에 의한 ZnIn2Se4 단결정 박막 성장과 광전기적 특성 연구

Abstract

ZnIn2Se4는 chalcopyrite 화합물 반도체로서 상온에서 띠간격이 1.82eV인 직접천이형 반도체이며 wide gap 재료로서, 청색발광소자, photoresister, tunable filter(비선형 광학재료 :전기광학필터), frequency doubler등에 이용되는 고감도의 광전도체이므로 광전기적 기본 물성, 광전도특성을 조사하여 카메라 노출계, 전자적인 카메라 셔터, 디지탈 자동조광기, 서브볼륨조절장치, 가스나 올리버너의 불釉蹄購 등에 이용되고자 한다.|A stoichiometric mixture of evaporating materials for ZnIn2Se4 single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, ZnIn2Se4 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 630 ℃ and 400 ℃, 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 ZnIn2Se4 single crystal thin films measured from Hall effect by van der Pauw method are 9.41×1016 electron/cm3 and 229 cm2/V․s at 293K, respectively. The temperature dependence of the energy band gap of the ZnIn2Se4 obtained from the absorption spectra was well described by the Varshni's relation, Eg(T) = 1.8622 eV - (5.23 × 10-4 eV/K)T2/(T + 775.5 K). The crystal field and the spin-orbit splitting energies for the valence band of the ZnIn2Se4 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 Γ5 states of the valence band of the ZnIn2Se4/GaAs epilayer. The three photocurrent peaks observed at 10 K are ascribed to the A1-, B1-exciton for n = 1 and C27-exciton peaks for n = 27. After the as-grown ZnIn2Se4 single crystalline thin films was annealed in Zn-, Se-, and In-atmospheres, the origin of point defects of ZnIn2Se4 single crystalline thin films has been investigated by the photoluminescence (PL) at 10 K. The native defects of VZn, VSe, Znint, and Seint obtained by PL measurements were classified as a donors or acceptors type. And we concluded that the heat-treatment in the Se-atmosphere converted ZnIn2Se4 single crystalline thin films to an optical p-type. Also, we confirmed that In in ZnIn2Se4/GaAs did not form the native defects because In in ZnIn2Se4 single crystalline thin films existed in the form of stable bonds.