Growth of CuInSe 2 thin films by high vapour Se treatment of co-sputtered Cu-In alloy in a graphite container

Abstract

The crystallization of CuInSe 2 thin films by high Se vapour selenization of co-sputtered Cu-In alloy precursor within a partially closed graphite container is reported. X-ray diffusion (XRD) analysis of the Cu-In alloy films displayed mainly the CuIn 2 and Cu 11In 9 phases. A three-fold volume expansion was recorded in all the selenized CuInSe 2 films at 500–550°C. Large and densely packed crystals with sizes of about 5 μm were exhibited by the films irrespective of whether they were Cu-rich or In-rich. Single phase chalcopyrite CuInSe 2 structure with preferential orientation in the (112) direction were obtained. Films with a wide range of compositions (Cu/In of 0.43–1.2 and Se/(Cu+In) of 0.92–1.47) were fabricated. All the films where Se rich, with the exception of samples with very high Cu content. The measured film resistivities varied from 10 −1 to 10 5 Ω-cm in consistence with the increasing Cu content of the alloy precursor during deposition. The alloy films with very high In content yielded the CuIn 2Se 3.5 or CuIn 3Se 5 compound as determined from XRD and EDX analyses. A study of the reaction mechanism performed between 250 and 550°C indicated that the crystal growth was assisted by the formation of the CuSe flux agent. The development of a suitable window layer to test the photovoltaic properties of these films is currently in progress.