Study of the Effect of Annealing Temperature on the Structural and Optical Properties of ZnO Thin Films Prepared by Sol-Gel Method via Spin Coating

Abstract

This study investigated the effect of annealing temperatures  (As -prepared, 350°C, 450°C, 550°C, and 650°C) on the properties of zinc oxide (ZnO) thin films prepared by sol-gel spin coating on glass substrates. X-ray diffraction (XRD) analysis confirmed a hexagonal wurtzite structure with an increase in grain size from 15 nm to 22 nm and a decrease in both residual stress and dislocation density with increasing annealing temperature. UV-Vis-NIR spectrophotometry measurements showed high transmittance in the visible region, a red shift in the transmittance edge, a decrease in film thickness from 333 nm to 280 nm, and an increase in refractive index, a decrease in the optical energy gap from 3.31 eV to 3.22 eV with increasing annealing temperature. while Urbach energy (E_U) exhibited non-linear behavior,  reduced at 550 °C. Wemple-DiDomenico model fitting supported the improved crystallinity and reduced defects with increasing annealing temperature. Finally, the results showed an increase  in free carrier density, increase plasma frequency with increasing annealing temperature.