Hot Wall Epitaxy(HWE)법에 의한 CdGa2Se4단결정 박막 성장과 열처리 효과

Abstract

The stochiometric mix of evaporating materials for the <TEX>$CdGa_2Se_4$</TEX> single crystal thin films was prepared from horizontal furnace. To obtain the single crystal thin films, <TEX>$CdGa_2Se_4$</TEX> mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperature were <TEX>$630^{\circ}C$</TEX> and <TEX>$420^{\circ}C$</TEX>, respectively. The crystalline structure of single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD).The carrier density and mobility of <TEX>$CdGa_2Se_4$</TEX> single crystal thin films measured from Hall effect by van der Pauw method are <TEX>$8.27{\times}10^{17}\;cm^{-3},\;345\;cm^2/V{\cdot}s$</TEX> at 293 K. respectively. The temperature dependence of the energy band gap of the <TEX>$CdGa_2Se_4$</TEX> obtained from the absorption spectra was well described by the Varshni's relation, <TEX>$Eg(T)\;=\;2.6400\;eV\;-\;(7.721{\times}10^{-4}\;eV/K)T^2/(T+399\;K)$</TEX>. After the as-grown single crystal <TEX>$CdGa_2Se_4$</TEX> thin films were annealed in Cd-, Se-, and Ga -atmospheres, the origin of point defects of single crystal <TEX>$CdGa_2Se_4$</TEX> thin films has been investigated by PL at 10 K. The native defects of <TEX>$V_{Cd}$</TEX>, <TEX>$V_{Se}$</TEX>, <TEX>$Cd_{int}$</TEX>, and <TEX>$Se_{int}$</TEX> obtained by PL measurements were classified as donors or accepters. We concluded that the heat-treatment in the Cd-atmosphere converted single crystal <TEX>$CdGa_2Se_4$</TEX> thin films to an optical p-type. Also, we confirmed that Ga in <TEX>$CdGa_2Se_4/GaAs$</TEX> did not form the native defects because Ga in single crystal <TEX>$CdGa_2Se_4$</TEX> thin films existed in the form of stable bonds.