| 초록 |
A stoichiometric mixture of evaporating materials for CuGaSe2 single crystal thin films was prepared from horizontal electric furnace. Using extrapolation method of X-ray diffraction patterns for the polycrystal CuGaSe2, it was found tetragonal structure whose lattice constant a0 and c0 were 5.615 Å and 11.025 Å, respectively. To obtain the single crystal thin films, CuGaSe2 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℃ and 450℃, respectively. 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 CuGaSe2 single crystal thin films measured with Hall effect by van der Pauw method are 5.01×1017 cm-3 and 245 cm2/V·s at 293K, respectively. The temperature dependence of the energy band gap of the CuGaSe2 obtained from the absorption spectra was well described by the Varshni's relation, Eg(T) = 1.7998 eV - (8.7489 × 10-4 eV/K)T2/(T + 335 K). After the as-grown CuGaSe2 single crystal thin films was annealed in Cu-, Se-, and Ga-atmospheres, the origin of point defects of CuGaSe2 single crystal thin films has been investigated by the photoluminescence(PL) at 10 K. The native defects of VCU, VSe, Cuint, and Seint obtained by PL measurements were classified as a donors or acceptors type. And we concluded that the heat-treatment in the Cu-atmosphere converted CuGaSe2 single crystal thin films to an optical n-type. Also, we confirmed that Ga in CuGaSe2/GaAs did not form the native defects because Ga in CuGaSe2 single crystal thin films existed in the form of stable bonds. |
