Investigation on dispersive optical constants and electrical properties of CuIn₅S₈ thin films

Abstract

CuIn₅S₈ thin films were prepared by thermal evaporation under vacuum onto heated and no heated glass substrates. These films were characterized for their structural, optical and electrical properties by using X-ray diffraction (XRD), optical measurement and Hall-effect measurements. X-ray diffraction analysis of the deposited films revealed that the film deposited without heating the substrate was amorphous in nature and an amorphous-to-crystalline phase transition with could be obtained by heating the substrates above 100 °C. The optical constants of the deposited films were determined, in the spectral range 300–1800 nm, from the analysis of the transmission and reflection data. The energy bandgap values changed from 2.17 to 1.77 depending on the substrate temperature. The refractive index dispersion and extinction coefficient in the low absorption region are adequately described by the Wemple – Di Domenico single oscillator model. The values of the oscillator energy E₀, dispersion energy E_d, the high-frequency dielectric constant ε_∞ and the ratio of the carrier concentration to the effective mass were estimated according to the models of Wemple – Di Domenico and Spitzer - Fan. The resistivity values of the films increased from 0.826 to 1.495 10⁶ Ωcm and a transition from p-type conductivity to a highly compensated state is observed by increasing the substrate temperature