Effect of air annealing on dispersive optical constants and electrical properties of SnSb2S4 thin films

SnSb2S4 thin films were prepared by thermal evaporation under vacuum onto no heated glass substrates. The as-deposited films were annealed in air for 1 h in the temperature range 70–350 °C. XRD data analysis shows that SnSb2S4 crystallizes in the orthorhombic structure according to a preferential direction (531). The optical properties of thin films were determined, in the spectral range 300–1800 nm, from the analysis of the experimental recorded transmittance and reflectance data. High absorption coefficients (105–106 cm−1) are reached in the energy range 2–2.5 eV. A decrease in optical band gap from 1.97 to 1.61 eV by increasing the air annealing temperature was observed. The Wemple–DiDomenico single oscillator model was applied to determine the optical constants such as oscillator energy E0 and dispersion energy Ed of the films after annealing. The electric free carrier susceptibility and the ratio of carrier concentration to the effective mass were estimated according to the model of Spitzer–Fan. The layers annealed at temperatures greater than 200 °C undergo abrupt changes in their electrical properties and a hysteresis phenomenon was observed.