Variation of optical band gap in anodically grown nanocrystalline ZnO thin films at room temperature—effect of electrolyte concentrations

Zinc oxide thin films were deposited by electrochemical oxidation of Zinc at room temperature using high purity Zn as anode, Pt cathode, a calomel reference electrode and an aqueous electrolytic solution of oxalic acid. A range of 0.3, 0.1, 0.05, and 0.01 M electrolyte concentrations were used during anodization. Glancing angle X-ray diffraction and field emission scanning electron microscope were used to determine the crystallinity and the surface morphology respectively of the deposited ZnO thin films. The variation of the molar concentration of the electrolyte during anodic oxidation had a significant effect on the optical band gap of ZnO thin film. There was an increase in band gap with the decreasing concentrations of oxalic acid and a highest bandgap of 4.20 eV was obtained by using 0.05 M oxalic acid electrolyte. An apparent blue shift of band gap was further confirmed by Photoluminescence spectra.