PHOTOEMISSION-STUDY OF EVAPORATED CUINS(2) THIN-FILMS .1. SURFACE STOICHIOMETRY AND PHASE SEGREGATION

The surfaces of evaporated CuInS2 films were investigated by photoelectron spectroscopy (XPS) with respect to stoichiometry dependent features. The surface composition of In-rich CuInS2 films drastically exceeds the respective bulk value determined by energy dispersive x-ray fluorescence and displays the formation of an In-rich surface layer with a cation ratio of In/(In+Cu)=0.75(2). Sputter profiles obtained by Auger electron spectroscopy confirm the effect of In enrichment and Cu depletion on the surface. The altered surface region is estimated to extend approximately 0.1 mu m into the film. Films with a Cu-rich bulk composition also exhibited In-rich surfaces, but in addition the segregation of a CuS phase is concluded from XPS investigations. The interrelation of these observations is discussed using simple model considerations.