Temperature effects on the optoelectronic properties of AgIn5S8 thin films

Polycrystalline AgIn5S8 thin films are obtained by the thermal evaporation of AgIn5S8 crystals onto ultrasonically cleaned glass substrates under a pressure of similar to 1.3 x 10(-3) Pa. The temperature dependence of the optical band gap and photoconductivity of these films was studied in the temperature regions of 300-450 K and 40-300 K, respectively. The heat treatment effect at annealing temperatures of 350, 450 and 550 K on the temperature dependent photoconductivity is also investigated. The absorption coefficient, which was studied in the incidence photon energy range of 1.65-2.55 eV, increased with increasing temperature. Consistently, the absorption edge shifts to lower energy values as temperature increases. The fundamental absorption edge which corresponds to a direct allowed transition energy band gap of 1.78 eV exhibited a temperature coefficient of -3.56 x 10(-4) eV/K. The 0 K energy band gap is estimated as 1.89 eV. AgIn5S8 films are observed to be photoconductive. The highest and most stable temperature invariant photocurrent was obtained at an annealing temperature of 550 K. The photoconductivity kinetics was attributed to the structural modifications caused by annealing and due to the trapping-recombination centers' exchange. (C) 2010 Elsevier B.V. All rights reserved.