Composition-induced structural modifications in the quaternary CuIn1-xGaxSe2 thin films: bond properties versus Ga content

摘要

In this paper the dependence of structural properties of the quaternary CuIn1-xGaxSe2 films with tetragonal structure on the Ga content has been systematically investigated by Raman scattering and x-ray diffraction spectra.The shift of the dominant A1 mode,unlike the lattice constants,does not follow the linear Vegard law with increasing Ga content z,whereas exhibits approximately polynomial change from 174cm-1 for CuInSe2 to 185cm-1 for CuGaSe2.Such behaviour should be indicative of presence of the asymmetric distribution of Ga and In on a microscopic scale in the films,due to Ga addition.The changes in the tetragonal distortion η lead to a significant variation in the anion displacement parameter U,which should be responsible for the evolution of bond parameters and resultant Raman bands with x.