Influence of heat treatment on the structural, optical and electrical properties of Cd20Sn10Se70 thin films

The effect of annealing temperature (T-a) on the structural, optical, and electrical properties of thermally evaporated Cd20Sn10Se70 thin films has been investigated. Differential Thermal Analysis (DTA) was used to determine the glass transition temperature (T-g) of the prepared alloy. X-ray diffraction studies showed that the as-deposited film and the films that were annealed at T-a < T-g are of low crystallinity. On annealing above T-g, these films showed a polycrystalline nature. The surface morphology and microstructure of as-deposited and annealed films have been examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Their optical constants were calculated from the transmittance measurements in the range 200-2500 nm. The dispersion of refractive index was analyzed in terms of the single-oscillator Wemple-Di Domenico model. Analysis of the optical absorption data indicates that the optical band gap E-g of these films obeys Tauc's relation for the allowed direct transition. The optical band gap Eg as well as the activation energy for the electrical conduction Delta E were found to increase with increase of annealing temperature up to T-g, whereas above T-g there is a remarkable decrease in both E-g and Delta E. The obtained results were interpreted in terms of the Mott-Davis model and amorphous crystalline transformation. (C) 2014 Elsevier Ltd. All rights reserved.