The effect of cobalt doping on the structure and properties of copper oxide thin films: Evolution in surface morphology, p- to n-type carrier transition and enhancement optoelectronic behavior

This paper reports the preparation of CuO and cobalt (Co)-doped CuO (Co:CuO) thin films (TFs) by a convenient spray pyrolysis reactor. Co concentration (conc.) was varied in CuO TFs from 2 to 8[Formula: see text]at.% at the step of 2[Formula: see text]at.%. In the FESEM images of undoped films, aggregations of nanoparticles were found. The surface morphology of CuO turned into porous and spongy nanostructures for 6[Formula: see text]at.% Co-doping. In XRD analysis, CuO film showed a monoclinic crystal structure with ([Formula: see text]11) peak occurrence. The crystallite size of the films was found to be between 5[Formula: see text]nm and 12[Formula: see text]nm. In UV–vis spectroscopy, the optical transmittance of Co:CuO films increased in the visible region and then saturated in the NIR light region. The highest transmittance of about 96% was found for the 6 at.% Co:CuO film. The band gap of Co:CuO increased with Co doping. Urbach energy, refractive index, dielectric constants and dispersion energy parameters were estimated. Electrical resistivity and carrier concentration were found in the order of [Formula: see text]-cm and [Formula: see text] [Formula: see text]cm[Formula: see text], respectively. CuO films showed n-type conductivity for 4, 6 and 8[Formula: see text]at.% Co-doping. The figure of merit increased significantly with Co-doping up to 6[Formula: see text]at.%, indicating the enhancement in optoelectronic behavior.