X-ray and XPS studies of evaporated Cu x S thin films

Abstract

The structural changes in CuxS films have been monitored by x-ray diffraction and correlated to the chemical changes taking place on the CuxS surface, the latter monitored by XPS. The results show: evaporated CuxS films contained chalcocite, free copper phases, and probably a third phase (of sulfur); resistivity is related to the amounts of free Cu and S in the film; air heat treatments converted chalcocite to Cu deficient phases and resulted in the disappearance of the sulfide and predominance of CuSO4⋅nH2O and CuO; argon heat treatment tended to react Cu and S to form CuxS; Cd is detected on the surface of CuxS deposited onto CdS and is significantly increased in amount by heat treatments. These results can be related to chemical processes occurring on CuxS/CdS and CuxS/(Zn,Cd)S solar cells. For the CdS cell, oxides and sulfates of Cu and Cd are found on the CuxS surface and the sulfates are enhanced by the heat treatment in moist air. CuO and CuSO4 are formed in the absence of Cd, and dominate the CuxS surface.