Nonlinear Shift of the Raman A1 Mode inGa-Incorporated CuInSe2 Thin Films

Abstract

Composition dependence of quaternary CuIn1−xGaxSe2films on Ga content has been systematically investigated by Ramanscattering. The dominant A1 mode shifts from 174 cm−1 forCuInSe2 to 185 cm−1 for CuGaSe2 in an approximatelypolynomial curve other than a linear curve, indicating existence ofasymmetric distribution of Ga and In on a microscopic scale in films.With Ga content x>0.3, the significantly broadening andintensity decrease of A1 modes suggest the degradation ofcrystalline quality of chalcopyrite phase. Additionally, the quenchingof additional Raman band at 183 cm−1 for the Ga-rich filmsreveals that CuAu-ordered phase can coexist in nominal chalcopyriteCuInSe2 films but not in CuGaSe2, due to Ga inhibitioneffect.