The effect of annealing on the physical properties of thermally evaporated CuIn2n+1S3n+2 thin films (n=0, 1, 2 and 3)

In this study, the annealing effect on structural, electrical and optical properties of CuIn2n+1S3n+2 thin films (n=0, 1, 2 and 3) are investigated. CuIn2n+1S3n+2 films were elaborated by vacuum thermal evaporation and annealed at 150 and 250 degrees C during 2 h in air atmosphere. XRD data analysis shows that CuInS2 and CuIn3S5 (n = 0 and 1) crystallize in the chalcopyrite structure according to a preferential direction (112), CuIn5S8 and CuIn7S11 (n=2 and 3) crystallize in the cubic spinel structure with a preferential direction (311). The optical characterization allowed us to determine the optical constants (refractive indexes 2.2-3.1, optical thicknesses 250-500 nm, coefficients of absorption 10(5) cm(-1), coefficients of extinction <1, and the values of the optical transitions 1.80-2.22 eV) of the samples of all materials. We exploited the models of Cauchy, Wemple-DiDomenico and Spitzer-Fan for the analysis of the dispersion of the refractive index and the determination of the optical and dielectric constants. (C) 2013 Elsevier Ltd. All rights reserved.