Control of composition in co-evaporated Cu(InGa)(SeS)2 thin films

Cu(InGa)(SeS)2 thin films have been prepared using multi source thermal co-evaporation. The incorporation of the volatile chalcogen species Se and S into the films depends on the fluxes of the evaporated species during growth and the relative [Cu]/[In+Ga] and [Ga]/[In+Ga] compositions. The dependence of the relative Se and S incorporation in Cu(InGa)(SeS)2 on the substrate temperature is characterized with various [S]/[Se+S] flux rate ratios for substrate temperatures of 300, 450, and 550°C. The relative chalcogen incorporation is the same at 450 – 550°C for both Cu-excess and Cu-deficient growth. However, at 300°C the relative [S]/[Se+S] incorporation changes. The chalcogen incorporation is compared to predictions from equilibrium thermodynamics and to an empirical kinetic model. Deposition processes with sequential layers including Cu-excess and Cu-poor fluxes have inhomogeneous composition and microstructural models for these processes are proposed.