Laser radiation effect on microstructural, linear, and nonlinear optical characteristics of Sn0.04Co0.06O2 nanostructured films

Abstract

The influence of He-Ne laser radiation on linear and nonlinear optical characteristics of Co-doped SnO2 (Sn0.04Co0.06O2) thin film was studied before and after irradiation. 22 mW (633 nm) He-Ne laser beam was employed to irradiate the film with different exposure times (Texpo. = 1, 2, 5, 15, 20, 40, and 60 min). As grown and irradiated films were examined by X-ray diffraction (XRD), an atomic force microscope (AFM) was integrated with UV-VIS–NIR spectrophotometer. XRD pattern analysis showed that the crystallite size decreased as the exposure increased to 5 min, however, a further increase in Texpo from 15 to 60 min increased the crystallite size. Analysis of AFM micrographs shows that the roughness of the surface and root mean square roughness of the film depend on the increase in the laser exposure time. The optical studies of irradiated films show that the optical energy gap Eg decreases as the exposure time increases to 5 min and then raises as the film is irradiated for up to 60 min. This reduction was attributed to the elimination of the additional oxygen from the film, and the increase of Eg is explained by the Burstein–Moss effect. Swanepoel’s envelope method is used to calculate the linear optical parameters of the irradiated film from the light transmission spectrum, such as refractive index n, and extinction coefficient k. The results reveal that the global behavior of n and k increases with exposure time. The oscillator parameters of the irradiated film of different exposure times were evaluated from the single-oscillator Wemple–DiDomenico model, which was then used to calculate the nonlinear optical parameters such as n2 the nonlinear refractive index, and χ(3) the third-order nonlinear optical susceptibility. It is concluded that the He-Ne laser irradiation with different exposure times enhances the optoelectronic properties of Sn0.04Co0.06O2 nanocrystalline semiconductor thin film