Effect of annealing temperature on the optical properties of electrodeposited ZnO/MgO superlattice

Superlattice of ZnO/MgO thin films were successfully synthesized on Fluorine doped Tin Oxide (FTO) glass substrates by means of electrodeposition technique from MgSO(4 center dot)7H(2)O, citric acidic and NaOH. A Janway 6405 UV/visible spectrophotometer was used to obtain the spectra absorbance data. Optical properties of the films which include; transmittance, reflectance, energy band gap (E-g), refractive index (eta), optical conductivity and extinction coefficient were studied. The surface morphology of the deposited films was also studied using Scanning Electron Microscopy (SEM). We studied the effects of annealing temperature on the optical properties of the deposited thin films. Optical results indicate that absorbance decreased as annealing temperature of the films increased. The transmittance of the annealed thin films increased as the annealing temperature increased. Also, annealing slightly increases the refractive index of the films, with approximately 2.60 in UV and VIS regions. We also observed that annealing of the films increased the value of the refractive index. The annealing temperature was found to vary inversely with the optical conductivity of the films. The band gap energy between 2.70 eV and 3.02 eV was obtained for ZnO/MgO superlattices. Thickness of the deposited films ranges between 190 nm and 635 nm. Our result indicates that as temperature increased from 523 K to 673K, thickness of the deposited ZnO/MgO superlattice decreased from 635 nm to 285 nm.