Effect of co doping on structural and optical properties of zno thin films prepared by chemical spray pyrolysis method

In this work, Zinc-cobalt oxide (Zn(1-x)CoxO) thin films, where x = 0, 4, 6 and 8 % have been successfully deposited on glass substrates by chemical spray pyrolysis (CSP) technique at substrate temperature of (400 °C) and thickness of about 300 nm. The structural and optical properties of these films have been studied using XRD, AFM, and UV-Visible spectroscopy. The XRD results showed that all films are polycrystalline in nature with Hexagonal structure and preferred orientation along (111),(002),(101),(102),(110) and (103) planes. The crystallite size was calculated using Scherrer’ formula and it is found that the undoped ZnO sample has maximum crystallite size (23.11nm). AFM results showed homogenous and smooth thin films. The absorbance and transmittance spectra have been recorded in the wavelength range of (300- 900) nm in order to study the optical properties. The optical energy gap for allowed direct electronic transition was calculated using Tauc equation. It is found that the band gap increases as the Co concentration increases and the band gap values were in the range of 3.27-3.32 eV. The optical constants including (absorption coefficient, real and imaginary parts of dielectric constant) were also calculated as a function of photon energy. Refractive index and extinction coefficient for Zinc-Cobalt Oxide thin films were estimated as a function of wavelength.