Structural properties of Ge doped CuGaSe 2 films studied by Raman and Photoluminescence spectroscopy

Abstract

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.