Electrical transport of sprayed In2S3:Ag thin films

Silver doped indium sulfide (In2S3:Ag) thin layers were prepared by spray pyrolysis. The Ag concentration varies in the range of 0-6 at%. The X-ray diffraction (XRD) indicates the presence of cubic phase of beta-In2S3 and the crystallite size values exhibit a maximum at an Ag concentration of 4%. In addition, morphological analysis by atomic force microscopy (AFM) shows that the film surface is continuous, compact, free of cracks and depends on the Ag concentration. This observation is remarkable by evolution of surface roughness values. The films reveal a semiconductor behavior. This is observed because the electrical conductance increases with the increase of measurement temperature and the analysis of the Nyquist diagram shows the appearance of half circles, whose radius decreases by increasing the temperature from 300 K to 600 K. The electrical equivalent circuit of undoped In2S3 and In2S3:Ag 4% at 460 K and 470 K contains two components connected in serial. The first is composed of a resistance R1, an inductance L and a constant phase element CPE1 in parallel and the other covers R2 and a constant phase element CPE2 that are connected in parallel. Inductive and capacitive effects exist in these materials and they depend on frequency. For Ag concentration equal or greater than 4%, the equivalent circuit is a parallel association of a resistor with a constant phase element. The activation energy is minimum for an Ag concentration of 4%.