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 μm 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 β-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.