Effects of Cobalt Doping on Optical Properties of ZnO Thin Films Deposited by Sol–Gel Spin Coating Technique

Cobalt (Co) doped Zinc Oxide (ZnO) thin films, containing different amount of Cobalt nanoparticles as the Co doping source, deposited by the sol–gel spin coating method onto glass via annealing temperature at 400˚C, have been investigated by optical characterization method. The effect of Co incorporation on the surface morphology was clearly observed from scanning electron microscopy (SEM) images. Optical conductivity and optical constants such as absorption coefficient, reflectivity, extinction coefficient, and refractive index as a function of photon energy were calculated, and it was found that the doping with Co led to decrease absorption coefficient, extinction coefficient, refractive index and bandgap energy, while the optical conductivity increased at higher photon energies. The optical band gap depends on the Co doping level and on the particle size and crystallinity of the films and is in the range of 3.05– 3.17 eV. The optical band gap widening is proportional to the one-third power of the carrier concentration.