Structural properties of Ge doped CuGaSe_2 films studied by Raman and Photoluminescence spectroscopy

摘要

The structural properties of Ge doped polycrystalline CuGaSe_2 films with potential applications in solar cell device technology have been studied by Raman spectroscopy at 300 K and by Photoluminescence (PL) spectroscopy at 300 K and 2 K. The films were intentionally doped with max. 200 keV Ge ions using one- and three-stage ion implantation processes. The Raman spectra of as grown films are dominated by the A_1-mode (breathing mode) of the CuGaSe_2 absorber at 184 cm~(-1). It was found, that in doped films the Raman mode intensities are reduced and the B_2-modes (TO at 249 cm~(-1) and LO at 273 cm~(-1)) take over. This implies an increase in structural disorder induced, probably, by bond reorientation effects that favor excitation of asymmetric lattice vibrations (B_2) instead of the symmetric ones (A_1). Moreover, it was found, that the Raman bands of doped films exhibit asymmetric broadening representative of a Fano line-shape. Changes were more pronounced in films doped at one-stage. The PL-emission of films subjected to one-stage process was enhanced, which supports an increase in structural disorder particularly for these films. On the contrary, for films doped in three-stages, the PL bands are less intensive and the Raman bands are less broadened.