Surface morphology, optical conductivity, localized states and dielectric constants of sprayed nickel oxide films at different substrate temperatures

Thin films of nickel oxide (NiO) were deposited on glass substrates at a different temperature of growth using a spray pyrolysis technique. X-ray diffraction (XRD) and optical properties have been studied for the properties of the samples obtained. Analysis of XRD data show that at a low growth temperature, an amorphous form has been obtained, while at high growth temperature (Tsub 275 oC), single phase of the NiO formed which has a cubic structure. Optical properties were examined using spectral measurement at wavelength range of 300-2500nm. Optical constants (n and k) were calculated from corrected transmittance and corrected reflectance. The data obtained show that the direct transition (Eg) decreased from 3.738 to 3.146 eV and the indirect transition change from 2.790 to 2.049eV with increasing temperature. On the contrary, Urbach energy (band tail width), EU was found to be decreased from 0.65 to 0.36 eV. This behavior is believed to be associated with the increase of substrate temperatures. Optical conductivity, dielectric constants, optical density, skin depth, and electrical susceptibility were discussed as functions of substrate temperatures. From these results, NiO films has been categorized as an excellent material for optoelectronic applications and a potential candidate for solar cell applications because of its tune-ability for optimization.