Material losses and compositional changes in two-step processed CuInSe2 thin films

Material losses and the resulting compositional changes in two-step processed chalcopyrite thin films are widely discussed topics in literature. In this study, metallic precursors were selenized in H2Se/Ar at a wide range of processing temperatures between 300 degreesC and 600 degreesC. The composition of the resulting films at different stages of processing were analyzed by electron probe microanalysis (EPMA) and X-ray fluorescence (XRF). Comparison of EPMA and XRF data from identical selenized samples revealed a discrepancy in composition at temperatures at or above a critical point around 400 degreesC. In contrast to the loss of In indicated by EPMA measurements, XRF analysis revealed that the Cu and In K alpha (1,2) intensity values remained virtually constant, irrespective of the selenization conditions tie. no evidence of material losses). The use of more surface sensitive L alpha (1) line scans clearly revealed a segregation of In away and Cu towards the upper part of the layer with increasing selenization temperature. Based on these results the commonly reported compositional shift due to material losses is interpreted as a measurement artifact of the EPMA technique under typical measurement conditions for two-step processed chalcopyrite absorber films.