Effect of annealing temperature on the properties of transition metal doped zinc oxide – A review

A review on the effect of post-annealing temperature on the structural, morphological and optical properties of transition metal (TM= Co, Ni, Cu, Y, and Cd) doped zinc oxide (ZnO) mainly prepared by sol-gel and spin coating method is reported. The deposited thin films were annealed at different temperature ranging from 300 °C to 800 °C. XRD analysis showed that both ZnO and TM doped ZnO flms were in hexagonal wurtzite crystalline structure, with preferred orientation of (002). The average crystallite size indicated an increasing pattern as the annealing temperature increased. The surface morphology was investigated via AFM and SEM which revealed that the shape of the grains changed with the change in temperature. ZnO and TM doped ZnO exhibited transmittance spectra from 70% to 90% in the visible range, and the optical band gap showed increasing and decreasing patterns when the annealing temperature increased.