Optical properties and complex refractive index of Co doped ZnO waveguide thin films elaborated by spray pyrolysis

Abstract CoxZn1-xO (x = 0.00, 0.04, 0.08 and 0.10) thin films were sprayed pyrolysis onto ordinary glass substrates. The micro Raman spectroscopy revealed the presence of wurtzite structure in all films. The UV-Vis investigation showed good optical transmittance in the visible region with the increase in the absorption bands related to internal Co+2 d-d transitions over Co concentration. The optical gap energy decreased by 0.34 eV as Co doping increased, contrary to Urbach energy which increased by 230 meV. The SEM observation indicated obvious modification in the morphology of the films. M-lines spectroscopy measured the ordinary refractive index which was found to increase by 0.0156 as the Co doping increased. Cobalt doping provoked the extinction of light coupling and propagation in the films manifested as an increase in full width at the half maximum of the guided peaks and a decrease in the reflected intensity. This was due to the increase in the extinction coefficient measured by UV-Vis spectroscopy.