Cobalt-doped zinc oxide thin solid films deposited by chemical spray techniques on silicon (1 0 0) substrates: The effects of the [Co]/[Zn] ratio on the morphological and physical properties

Undoped and cobalt-doped zinc oxide [ZnO:Co] thin solid films were deposited on Si(1 0 0) substrates applying the chemical spray technique (CST), using zinc acetate and cobalt chloride as precursors. The influence of both the dopant concentration in the starting solution and the substrate temperature on the composition, electrical and morphological properties of the ZnO:Co thin solid films were studied. The substrate temperature varied from 450 to 500 deg. C and the cobalt concentration in the starting solution was varied as a 3%, 8%, and 16% for each temperature. The minimum value of 5x10-3 Ω cm was found for the electrical resistivity. In consequence, with ZnO:Co thin films, the resistivity increased. X-ray diffraction studies exhibit the polycrystalline nature of the films with a homogeneous distribution of nanoparticles of similar size and morphology for various samples deposited at different substrate temperatures. The film composition and the dopant concentration were determined by Rutherford backscattering spectrometry; from these results showed that Co concentration increases with temperature. The scanning electron microscopy and high resolution transmission electron microscopy micrographs illustrated an evolution of morphological details as the Cobalt concentration solution increased.