Thickness induced microstructure, electronic structure and optoelectronic properties of Cu2S films deposited by radio frequency magnetron sputtering

This study addresses the influence of film thickness on the microstructure, electronic structure, and optoelectronic properties of Cu<inf>2</inf>S films. To this end, thickening Cu<inf>2</inf>S films are deposited on the soda lime glass substrate by varying the deposition time (t) from 60 to 420 min at room temperature (303 K) using radio frequency magnetron sputtering, and a range of experimental techniques are then used to characterize these films. Though films deposited at t of 60-360 min are found to have a pure Cu<inf>2</inf>S phase, an additional Cu<inf>1.8</inf>S phase is detected for the film deposited at 420 min. The valence state of Cu is found to be +1 in all these films, though the binding energy positions of the core level 2p electrons are found to shift systematically and are correlated to the thickness-induced compositional changes in these films. Sulfur is found to exist in two valence states in all these films: S^-2 bound with Cu<inf>2</inf>S and elemental or nonstoichiometric S^-n, the overall S^-n/S^-2 ratio being found to reduce with increasing film thickness. This microstructural adjustment in the thickening film is found to alter the electronic structure and optoelectronic properties of these films, measured using a wide range of experimental techniques. In the end, the principle behind the microstructure alteration of this thickening film is proposed.