Chalcogen incorporation in Cu(InGa)(SeS)2 coevaporated thin films

Thin films of Cu(InGa)(SeS)₂ have been deposited by elemental coevaporation. Characterization of the relative incorporation of S and Se in the film as a function of the S/(S+Se) content in the vapor shows that S is preferentially incorporated in a Cu-rich film, whereas Se is preferentially incorporated into a Cu-poor film. In most cases, a film with a single phase can not be deposited. Cu-rich films have a CuS layer on top of a chalcopyrite layer. Many Cu-poor films have a layered chalcopyrite structure with a composition that approximates the vapor composition on the bottom, and a composition richer in Se at the surface. Mechanisms for this vertically segregated behavior are discussed with respect to relative S and Se incorporation.