Influence of deposition time on optoelectronic properties of Ni-doped SnO₂ thin films for NLO device applications

In this study, the influence of film thickness on the linear and nonlinear optical properties of Sn_1-xNi_xO₂ thin films deposited by the spray pyrolysis technique was systematically investigated using various characterization methods. X-ray diffraction study helps in noticing the difference in the crystallite size brought by the variation in thickness. High transparent films with polycrystalline nature, with a peak at (110) were observed. Oxidation sates of Sn, Ni and O were confirmed using the X-ray photoelectron spectroscopy. Granular surface was observed at higher thickness by using the Field emission scanning electron microscope technique. Energy dispersive x-ray confirmed the wt.% of the Tin, Nickel and Oxygen as deposited thin films. A decrease in transmittance from 80 % for low thickness to 71 % at high thickness thin film was observed and a band-gap in the range of 3.41eV was found for the deposited samples. The urbach energy found an enhancement with thickness indicating the increase in disorderness of the film. The photoluminescence spectra depicted the contribution of both dopant defects, and oxygen vacancies with 6 peaks. The 3rd order non-linear optical properties were confirmed using the Z-scan technique. All the Sn_1-xNi_xO₂ thin films of different thickness showed reverse saturable absorption and self-defocusing. The third-order non-linear susceptibility was found to range between (0.34−0.67)×10⁻⁶ and (0.44−1.65)×10⁻⁶ for 230 nm and 949 nm thickness respectively. Overall, the as deposited Sn_1-xNi_xO₂ thin films found promising application in optical limiting devices.