Phase identification and AES depth profile analysis of Cu(In,Ga)Se ₂ thin films

This work presents results related with phase identification and study of the homogeneity in the chemical composition of Cu(In,Ga)Se₂ (CIGS) thin films grown by a chemical reaction of the precursor species evaporated sequentially on a soda-lime glass substrate, in a two or three-stage process. For that, the CIGS samples were characterized through X-ray diffraction (XRD) and Auger Electron Spectroscopy (AES) depth profile measurements, respectively. The presence of secondary phases growing superficially was identified through small angle XRD measurements. Theoretical simulation of the XRD spectra, carried out with the help of the Powder-Cell package, confirmed this result. The results showed that the deposition conditions affect the homogeneity of the chemical composition of the CIGS films, as well as the phase in which these films grow. In general, the samples grown in a two stage process present a mixture of the Cu(In,Ga)Se₂ phase with the secondary In₂ Se₃ and Cu₂Se phases, whereas, the films grown in a three stage process do it, mainly, in the Cu(In,Ga)Se₂ phase with a tetragonal (chalcopyrite type) structure and better homogeneity. CIGS films with characteristics like those found for the three stage samples, have demonstrated good properties for its use as absorber layers in thin film solar cells.