(112) and (220)/(204)-oriented CuInSe2 thin films grown by co-evaporation under vacuum

CuInSe2 (CIS) layers were grown by co-evaporation in a molecular beam epitaxy system onto soda lime glass substrates by using both two-step and three step processes. The physical properties of the layers were investigated using X-ray diffraction (XRD) and optical spectroscopy. The sample atomic composition was assessed by energy dispersive analysis of X-rays. Cu-rich or In-rich CIS thin films were obtained exhibiting strong preferential (112) and (220)/(204) orientations in both cases. We performed thermal annealing at 450 °C under nitrogen, keeping Se overpressure to avoid Se desorption from the layer. The annealed layers all exhibit improved crystalline quality, with reduced stoichiometric discrepancy. The secondary phases like CuxSe1 − x or InxSe1 − x are no more observable by XRD measurements. Regarding the preferential orientation, thermal annealing of Cu-rich CIS layers favours the (112) orientation leading to a more (112) textured layer after annealing, whatever the initial preferential growth orientation was. In opposite, thermal annealing of In-rich samples increases the (220)/(204) texture of the sample.

► We have studied the thermal annealing effect of Cu-rich and In-rich CuInSe2. ► Thermal annealing improves the optical and crystalline quality. ► Secondary phase turned to CuInSe2 through a recrystallization process or evaporated. ► Thermal annealing of Cu-rich layers leads to an increase of the (112) texture. ► Thermal annealing of In-rich layers leads to an increase of the (220)/(204) texture.