Influence of GaSe deposition temperature on the structural properties and in-depth compositional features of two-step grown Cu(In,Ga)Se2 thin films

In this study, Cu(In,Ga)Se-2 thin films were prepared by a classical two-stage growth process, which involved the selenization of thermally evaporated InSe/Cu/GaSe precursors. During the precursor-formation step the InSe and Cu were always deposited at 200degreesC, while the GaSe layers were deposited at temperatures between 200degreesC and 400degreesC. The respective precursors were simultaneously selenized under identical conditions in elemental Se vapor. In cases where the GaSe layers were deposited at low temperatures around 200degreesC, X-ray fluorescence (XRF) analysis revealed a large variation in element concentration with sample depth after selenization. In correspondence, X-ray diffraction (XRD) studies revealed the presence of separate CuInSe2 and CuGaSe2 phases in these specific samples. Optimum structural properties were obtained when the GaSe films were deposited at 300degreesC, followed by selenization. In general, these films were uniform and dense and XRD studies revealed single-phase Cu(in,Ga)Se-2 material. Even more importantly, XRF analysis revealed a remarkable improvement in in-depth compositional uniformity when the GaSe films were deposited at or above 300degreesC. An increase in GaSe deposition temperature to 400degreesC, however, resulted in a deterioration in the structural features of the Cu(in,Ga)Se-2 thin films. In contradiction with other reports, these results indicated that the in-depth composition uniformity and especially the Ga diffusion profile in two-step grown Cu(in,Ga)Se-2 thin films can be controlled. The crucial factor influencing the depth profile of these films is the GaSe deposition temperature during the precursor formation step. (C) 2003 Kluwer Academic Publishers.