The Influence of Substrate Temperatures and Thickness on Optical and Electrical Conductivity of CuIn(Se0.25S0.75)2

Abstract

Effect of thickness and substrate temperatures on optical and electrical properties of CuIn(Se0.25S0.75)2 had been studied. The films were deposited by a thermal evaporation method. Structure of samples was examined by XRD. Transmission of compositions was measured in wavelength range (200 ≤ λ ≤ 1100 nm). Transmittance decreases with increasing both of substrate temperatures (Ts) and thickness (d). Energy band gaps (Eg) decrease with increasing Ts whilst increase with increasing d. Urbach energy gaps of polycrystalline films increase with the increase of Ts and d. On the other hand, optical constants such as absorption coefficient, refractive index and extinction coefficient as a function of photon energy or wavelength of all films were calculated. Single-oscillator Wemple and DiDomenico model (WDD) was used to determine oscillator energy (Eo), dispersion energy (Ed), and the ratio of free carrier concentration to electron effective mass (N/m*). Moreover, static refractive index (n0), high-frequency dielectric constant at an infinite wavelength (e∞) and lattice dielectric constant (eL) can be obtained. The effect of thickness and (Ts) on electrical conductivity (σ) at room temperature was investigated. σ decreases with increasing both substrate temperatures and thickness.