Investigation of the Physical Properties of Sprayed Nanocrystalline In2S3 Films

In2S3 films have been grown on preheated glass substrate by spray pyrolysis. Indium chloride and thiourea in the molar ratio S:In = 2 were used as reagents. Substrate temperature was fixed at 613 K. These films adhered well to the substrate and were approximately 2 mu m thick. Structural, morphological, optical, and electrical properties of the as-grown In2S3 films were studied by use of x-ray diffraction (XRD) analysis, energy-dispersive spectroscopy, atomic force microscopy (AFM), optical absorption spectroscopy, and impedance spectroscopy. XRD revealed well crystallized films oriented in the (400) direction corresponding to the cubic beta-In2S3 phase. The surface of the films was smooth; average roughness was 5 nm. The AFM image revealed that the films were nanopolycrystalline and contained grains in the range 20-30 nm. Optical transmission in the visible and near-infrared regions was 80%. The direct band-gap energy was 2.62 eV. The electrical data were analyzed on the basis of the impedance Cole-Cole plots in the frequency range 0.1 Hz to 100 kHz at room temperature. Constant-phase elements were used in equivalent electrical circuits for fitting of experimental impedance data. The experimental results were fitted to the equivalent electrical circuit by use of Z-view software. The conductivity of grains and grain boundaries was estimated. The gas-sensing properties of the sample were investigated on the basis of the change in conductance as a result of adsorption and desorption of atmospheric oxygen.