Growth and optical properties for MgGa2Se4 single crystal thin film by hot wall epitaxy

A stoichiometric mixture of evaporating materials for $MgGa_2Se_4$ single crystal thin films was prepared from horizontal electric furnace. The crystal structure of these compounds has a rhombohedral structure with lattice constants $a_0=3.953\;{\AA}$, $c_0=38.890\;{\AA}$. To obtain the single crystal thin films, $MgGa_2Se_4$ 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 $610^{\circ}C$ and $400^{\circ}C$, respectively. The crystalline structure of the single crystal thin films was investigated by the double crystal X-ray rocking curve and X-ray diffraction ${\omega}-2{\theta}$ scans. The carrier density and mobility of $MgGa_2Se_4$ single crystal thin films measured from Hall effect by van der Pauw method were $6.21{\times}10^{18}\;cm^{-3}$ and 248 $cm^2/v{\cdot}s$ at 293 K, respectively. The optical absorption of $MgGa_2Se_4$ 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 $MgGa_2Se_4$ obtained from the absorption spectra was well described by the Varshni's equation, $E_g(T)=E_g(0)-({\alpha}T^2/T+{\beta})$. The constants of Varshni's equation had the values of $E_g(0)=2.34\;eV$, ${\alpha}=8.81{\times}10^{-4}\;eV/K$ and ${\beta}=251\;K$, respectively.

Hot wall epitaxy법에 의한 MgGa2Se4 단결정 박막 성장과 광학적 특성

단결정 성장을 위한 $MgGa_2Se_4$ 다결정은 수평 전기로에서 합성하였으며, 결정구조는 rhombohedral이고 격자상수 $a_0$는 3.953 ${\AA}$, $c_0$는 38.890 ${\AA}$였다. $MgGa_2Se_4$ 단결정박막은 HWE(Hot Wall Epitaxy) 방법으로 반절연성 GaAs(100)기판에 성장시켰다. 단결정박막의 성장 조건은 증발원의 온도 $610^{\circ}C$, 기판의 온도 $400^{\circ}C$에서 진행되었으며 성장 속도는 0.5 ${\mu}m/h$였다. 단결정박막의 결정성은 이중 결정 x-선 회절곡선의 반폭치와 X-선 회절무늬의 ${\omega}-2{\theta}$로부터 구하여 최적 성장 조건을 알 수 있었다. Hall 효과는 van der Pauw 방법에 의해 측정되었으며, 온도에 의존하는 운반자 농도와 이동도는 293 K에서 각각 $6.21{\times}10^{18}/cm^3$, 248 $cm^2/v{\cdot}s$였다. $MgGa_2Se_4$/SI(Semi-Insulated) GaAs(100) 단결정 박막의 광흡수 스펙트럼을 10 K에서 293 K까지 측정하였다. 광흡수 스펙트럼으로부터 구한 에너지 갭 $E_g(T)$는 varshni 공식 $E_g(T)=E_g(0)=({\alpha}T^2/T+{\beta})$을 잘 만족함을 알 수 있었다. 여기서 $E_g(0)=2.34\;eV$, ${\alpha}=8.81{\times}10^{-4}\;eV/K$, ${\beta}=251\;K$였다.