Hot Wall Epitaxy(HWE)법에 의한 CdGa2Se4 단결정 박막의 성장과 가전자대 갈라림에 대한 광전류 연구
Photocurrent study on the splitting of the valence band and growth of CdGa2Se4 single crystalthin film by hot wall epitaxy
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CdGa2Se4 단결정 박막을 수평 전기로에서 합성한 CdGa2Se4 다결정을 증발원으로하여, hot wall epitaxy(HWE) 방법으로 증발원과 기판(반절연성-GaAs(100))의 온도를 각각 630oC, 420oC로 고정하여 성장하였다. 이때 단결정 박막의 결 정성은 광발광 스펙트럼과 이중결정 X-선 요동곡선(DCRC)으로 부터 구하였다. Hall 효과는 van der Pauw 방법에 의해 측 정되었으며, 293 K에서 운반자 농도와 이동도는 각각 8.27 × 1017cm.3, 345 cm2/V·s였다. CdGa2Se4/SI(Semi-Insulated) GaAs (100) 단결정 박막의 광흡수와 광전류 spectra를 293 K에서 10 K까지 측정하였다. 광흡수 스펙트럼으로부터 band gap Eg(T) 는 Varshni 공식에 따라 계산한 결과 Eg(T) = 2.6400 eV . (7.721 × 10.4eV/K)T2/(T + 399 K)였다. 광전류 스펙트럼으로부터 Hamilton matrix(Hopfield quasicubic mode)법으로 계산한 결과 crystal field splitting 에너지 Δcr값이 106.5 meV이며 spinorbit 에너지 Δso값은 418.9 meV임을 확인하였다. 10 K일 때 광전류 세 봉우리들은 A1-, B1-와 C11-exciton 봉우리임을 알 았다.
Abstract
Single crystal CdGa2Se4 layers were grown on a thoroughly etched semi-insulating GaAs (100) substrate at 420oC with the hot wall epitaxy (HWE) system by evaporating the polycrystal source of CdGa2Se4 at 630oC. 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 single crystal CdGa2Se4 thin films measured with Hall effect by van der Pauw method are 8.27 × 1017 cm.3, 345 cm2/V·s at 293 K, respectively. The photocurrent and the absorption spectra of CdGa2Se4/SI (Semi-Insulated) GaAs (100) are measured ranging from 293 K to 10 K. The temperature dependence of the energy band gap of the CdGa2Se4 obtained from the absorption spectra was well described by the Varshni’s relation, Eg(T) = 2.6400 eV . (7.721 × 10.4 eV/K)T2/(T + 399 K). Using the photocurrent spectra and the Hopfield quasicubic model, the crystal field energy (Δcr) and the spin-orbit splitting energy (Δso) for the valence band of the CdGa2Se4 have been estimated to be 106.5 meV and 418.9 meV at 10 K, respectively. The three photocurrent peaks observed at 10 K are ascribed to the A1-, B1-, and C11-exciton peaks.Iat
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