Hot Wall Epitaxy(HWE)법에 의한 MgGa2Se4 단결정 박막 성장과 가전자대 갈라짐에 대한 광전류 연구
Photocurrent study on the splitting of the valence band and growth of MgGa2Se4 single crystal thin film by hot wall epitaxy
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수평 전기로에서 MgGa2Se4 다결정을 합성하여 HWE(Hot Wall Epitaxy)방법으로 MgGa2Se4 단결정 박막을 반절연성 GaAs(100)기판에 성장시켰다. MgGa2Se4단결정 박막의 성장 조건은 증발원의 온도 610oC, 기판의 온도 400oC였고 성장 속도는 0.5 μm/hr였다. 이때 이중결정 X-선 요동곡선(DCRC)의 반폭치(FWHM)도 212 arcsec로 가장 작아 최적 성장 조건임을 알 수 있었다. MgGa2Se4/SI(Semi-Insulated) GaAs(100) 단결정 박막의 광흡수와 광전류 spectra를 293 K에서 10 K까지 측정하였다. 광흡수 스펙트럼으로부터 band gap Eg(T)는 varshni공식에 따라 계산한 결과 Eg(T) = 2.34 eV − (8.81 × 10−4eV/K)T2/(T + 251 K)이었으며 광전류 스펙트럼으로부터 Hamilton matrix(Hopfield quasicubic mode)법으로 계산한 결과crystal field splitting energy Δcr값이 190.6 meV이며 spin-orbit energy Δso값은 118.8 meV임을 확인하였다. 10 K일 때 광전류봉우리들은 n = 1, 27일때 A1-, B1-와 C27-exciton 봉우리임을 알았다.
Abstract
A stoichiometric mixture of evaporating materials for MgGa2Se4 single crystal thin films was prepared from horizontal electric furnace. To obtain the single crystal thin films, MgGa2Se4 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 610oC and 400oC, respectively. The crystalline structure of the single crystal thin films was investigated by double crystal X-ray diffraction (DCXD). The temperature dependence of the energy band gap of the MgGa2Se4 obtained from the absorption spectra was well described by the Varshni’s relation, Eg(T) = 2.34 eV − (8.81 × 10−4 eV/K)T2/(T + 251 K). The crystal field and the spin-orbit splitting energies for the valence band of the MgGa2Se4 have been estimated to be 190.6 meV and 118.8 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 MgGa2Se4/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.
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