Spray pyrolyzed surface-modified ZnO thin films via cobalt doping: Optical, structural and morphological properties

ZnO thin film was doped with cobalt (Co) at concentration of 0.02 M, 0.08 M and 0.14 M. The deposition temperature of 400(degrees) C with precursor flow rate of 3 ml/min at the substrate to nozzle distance of 15 cm was used for spray pyrolysis technique. The structural property, measured by X-ray diffractometer (XRD), of the film showed seven diffraction peaks matched with the hexagonal structure with preferred orientation along (101) plane. Surface morphology, obtained using scanning electron microscope (SEM), showed uniform evenly distributed grains with hexagonal structure in the samples. SEM micrographs revealed that Co doped ZnO films increased in average grain size as Co concentrations increased. The EDX measurement indicated presence of Zn and O for undoped film and Zn, O and Co for doped films. The optical property of the films was obtained using UV/Vis spectrophotometer. The obtained result revealed decrease in energy band gap from 3.43 eV to 3.30 eV as the concentration of the doping atom (Co) increased. Red-shift in absorption of the films was observed as the concentration of Co increased which is in agreement with photoluminescence (PL) measurement. Also, electrical characterization showed increase in electrical conductivity as the dopant concentrations increased this resulted in decrease of activation energy from 0.271 to 0.184 eV. The concentration of the dopant were found to have substantial impact on properties of the ZnO film. This suggests that increase in Co concentration in ZnO could be adopted as a method of enhancing the electrical conductivity in semiconductor for solar devices.