Composition Control in the Growth of Cu(InGa)(SeS)2 by the Reaction of Cu-In-Ga PRECURSORS in H2Se and H2S

The two-reaction selenization/sulfization of metallic Cu-ln-Ga precursors is a commercially viable process for the manufacture of Cu(InGa)(SeS)₂ films. In this work, the reaction pathways in single-reaction selenization and sulfization processes are studied, as well as composition profile development in two-reaction processes. Sputter-deposited precursor films were annealed at 450degC to characterize the starting intermetallic composition, or reacted in either H₂Se or H₂S at 450degC to observe changes in phase composition as the reaction progressed. The key observation was the formation of an initial Cu₉(In_0.64Ga_0.36 )₄ intermetallic that is depleted incongruently to form Cu₉Ga₄ during selenization, and Cu₁₆In ₉ during sulfization. In studying the two-reaction selenization/sulfization process, a 2times2 matrix of reaction times was examined. Samples were selenized for either 15 or 30 minutes at 450degC, followed by sulfization at 550degC for either 15 or 30 minutes. Samples selenized for 15 minutes exhibited uniform Ga through the depth of the film, while those selenized for 30 minutes exhibited the commonly observed back-contact Ga accumulation