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 amountof Cobalt nanoparticles as the Co doping source, deposited by the sol–gel spin coatingmethod onto glass via annealing temperature at 400˚C, have been investigated by opticalcharacterization method. The effect of Co incorporation on the surface morphology wasclearly observed from scanning electron microscopy (SEM) images. Opticalconductivity and optical constants such as absorption coefficient, reflectivity, extinctioncoefficient, and refractive index as a function of photon energy were calculated, and itwas found that the doping with Co led to decrease absorption coefficient, extinctioncoefficient, refractive index and bandgap energy, while the optical conductivityincreased at higher photon energies. The optical band gap depends on the Co dopinglevel 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 thecarrier concentration.