Investigation of Cu(In,Ga)Se₂ polycrystalline growth: Ga diffusion and surface morphology evolution

We report a study of selenization and annealing treatment of copper indium gallium selenide (CIGS) film. Morphologies and composition of surface and cross section were observed by scanning electron microscopy (SEM) equipped with Energy Dispersive Spectroscopy (EDS). X-ray diffraction (XRD) and Raman spectra were used to investigate film structure. Depth profiles of element distributions were detected by Auger electron spectroscopy (AES). A double-layer structure was formed in the film by selenizing metallic precursor at 450 C. Further annealing at 600 C in pure argon enhanced gallium diffusion from the bottom to the top of the film, while additional selenium in the annealing had a negative effect. A MoSe₂ layer was detected between CIGS and Mo layers with annealing in additional Se. The annealing treatment also significantly modified the film surface morphology. A large amount of triangular and polygon shaped islands were observed by SEM. That might be due to different nucleation kinetics for different crystal facets.