Annealing effect on physical properties of spin coated ZnO films

Abstract

ZnO thin films were deposited onto glass substrates using sol–gel spin coating technique from starting solutions having different precursor concentrations (0·1, 0·3 and 0·5M). The effects of precursor concentration and annealing temperature on the physical properties of the films were investigated. The X-ray diffraction studies confirm that all the films have preferential orientation along the (002) plane with hexagonal wurtzite structure. The optical transparency gradually decreases (from 95 to 80%) as the precursor concentration increases. The optical energy gap is in the range of 3·18–3·32 eV. The systematic study shows that the post-annealing process has significant impact on the quality of the films. The SEM images depict that the grain size decreases as the precursor concentration increases, and the AFM images show that the film annealed at 550°C has well defined uniform grains. The lowest dislocation density is observed for 0·3M annealed at 550°C.