Hot wall epitaxy법에 의한 MgGa2Se4 단결정 박막 성장과 광학적 특성
Growth and optical properties for MgGa2Se4 single crystal thin film by hot wall epitaxy
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초록
단결정 성장을 위한 MgGa2Se4 다결정은 수평 전기로에서 합성하였으며, 결정구조는 rhombohedral이고 격자상수a0는 3.953 Å, c0는 38.890 Å였다. MgGa2Se4 단결정박막은 HWE(Hot Wall Epitaxy) 방법으로 반절연성 GaAs(100)기판에 성장시켰다. 단결정박막의 성장 조건은 증발원의 온도 610oC, 기판의 온도 400oC에서 진행되었으며 성장 속도는 0.5 μm/h였다. 단결정박막의 결정성은 이중 결정 x-선 회절곡선의 반폭치와 X-선 회절무늬의 ω-2θ로부터 구하여 최적 성장 조건을 알수 있었다. Hall 효과는 van der Pauw 방법에 의해 측정되었으며, 온도에 의존하는 운반자 농도와 이동도는 293 K에서 각각 6.21 × 1018/cm3, 248 cm2/v·s였다. MgGa2Se4/SI(Semi-Insulated) GaAs(100) 단결정 박막의 광흡수 스펙트럼을 10 K에서293 K까지 측정하였다. 광흡수 스펙트럼으로부터 구한 에너지 갭 Eg(T)는 varshni 공식 Eg(T) = Eg(0) = (αT2/T + β)을 잘 만족함을 알 수 있었다. 여기서 Eg(0) = 2.34 eV, α = 8.81 × 10−4 eV/K, β = 251K였다.
Abstract
A stoichiometric mixture of evaporating materials for MgGa2Se4 single crystal thin films was prepared from horizontal electric furnace. The crystal structure of these compounds has a rhombohedral structure with lattice constants a0 =3.953 Å, c0 = 38.890 Å. 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 the double crystal X-ray rocking curve and X-ray diffraction ω-2θ scans. The carrier density and mobility of MgGa2Se4 single crystal thin films measured from Hall effect by van der Pauw method were 6.21 × 1018 cm−3 and 248 cm2/v·s at 293 K, respectively. The optical absorption of MgGa2Se4 single crystal thin films was investigated in the temperature range from 10 K to 293 K. The temperature dependence of the optical energy gap of the MgGa2Se4 obtained from the absorption spectra was well described by the Varshni’s equation, Eg(T) = Eg(0) − (αT2/T + β). The constants of Varshni’s equation had the values of Eg(0) = 2.34 eV, α = 8.80 × 10−4 eV/K and β = 251 K, respectively.
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