Characterization of CuInSe2 thin films by XPS

Abstract The surface composition of CuInSe 2 thin films, made by co‐evaporation of the elements, has been shown to be strongly dependent on the bulk composition of the films. This is explained by the presence of a secondary phase, most likely Cu 2 Se, on the surface of Cu‐rich films. The fast variation of the surface concentration is also found for films that, according to the equilibrium pseudobinary phase diagram (Cu 2 SeIn 2 Se 3 ), should be single‐phase chalcopyrite. An explanation, suggesting the presence of a Cu‐rich compound also on the surface of films with a composition in the single phase regions, is proposed. Surface atomic concentrations have been shown to be modified in CuInSe 2 films by a 4.5 keV Ar + sputter etch. Heating in vacuum at the film deposition temperature restores the surface atomic concentrations to an as‐deposited condition, with the exception of the selenium concentration. The missing selenium atoms are substituted by oxygen atoms still remaining in the film after sputtering and heating.