Annealing effect on optical properties of ZnO films fabricated by cathodic electrodeposition

(001)-oriented ZnO films on Zn substrates were synthesized by cathodic electrodeposition from an aqueous solution composed only of 0.05 M zinc nitrate at 65 °C. A bound exciton emission band around 3.34 eV along with three longitudinal optical (LO) phonon replicas and an intensive broad emission band around 2.17 eV were observed from the photoluminescence (PL) spectra of ZnO films prepared at more positive potential (− 0.6∼− 0.8 V). When more negative potential (− 1.0∼− 1.4 V) was applied, the ultraviolet emission band disappeared. These results indicate that more positive electrodeposition potential favors the high quality ZnO film growth. The PL spectra of the annealed ZnO films prepared at more positive electrodeposition potentials − 0.6∼− 1.0 V exhibit the ultraviolet emission at 3.35 eV and a negligibly weak emission from defects. Annealing resulted in the enhancement and sharpening of the excitonic emission band and decrease of the deep level emission. The bandgap (Eg) of the ZnO film prepared at − 1.0 V on indium tin oxide (ITO) substrate decreased from 3.56 to 3.29 eV due to the removing of Zn(OH)2 from the film after annealing.