Effect of oxygen on the surface morphology of CuGaS2 thin films

Since the effect of oxygen is very significant during the heat treatment of the thin films, we study the effect of this during the annealing of CuGaS₂ thin films by two different types. In this study, CuGaS₂ thin films were deposited by vacuum thermal evaporation of CuGaS₂ powder on heated glass substrates at 200 °C submitted to a thermal gradient. The films are annealed in air and under nitrogen atmosphere at 400 °C for 2 h. In order to improve our understanding of the influence of oxygen during two annealing types on device performance, we have investigated our CuGaS₂ material by X-ray diffraction, scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X-ray analysis (EDX) and spectrophotometry. A correlation was established between the surface roughness, growth morphology and optical properties, of the annealed CuGaS₂ thin films. It was found that annealing of CuGaS₂ film in nitrogen atmosphere leads to a decrease of the mean grain size and to an evolution of a (112) preferred film orientation. Annealing in air results in the growth of oxide phases such as CuO and modifies the films structure and their surface morphology.