Structure, microstructure and determination of optical constants from transmittance data of co-doped Zn_0.90Co_0.05M _0.05O (MAl, Cu, Cd, Na) films

ZnO, Zn_0.95Co_0.05O and Zn_0.90Co _0.05M_0.05O (MAl, Cd, Na, Cu) single phase films have been successfully synthesized by ultrasonic spray pyrolysis technique. Structural analysis by X-ray diffraction show that all the films have hexagonal wurtzite structure with an average crystallite size in the range of 19-25 nm. SEM analysis revealed that Cd and Na preserve the shape of nanopetals observed with ZnO or CoZnO films, while the doping with Al or Cu promote the formation of dense films constituted of nanorods. By the application of Levenberg-Marquardt least square method, the experimental transmittance data were fitted perfectly with the transmittance data calculated via a combination of Wemple-DiDomenico model, absorption coefficient of an electronic transition and Tauc-Urbach model. The concentration of absorbing centres N_Co and oscillator strength f of d-d transition of Co²⁺ ions are calculated from Smakula's formula.