Characterization of zinc doped copper oxide thin films synthesized by spray pyrolysis technique

Abstract

Copper oxide (CuO) thin films are deposited onto glass substrates at various substrate temperatures (Ts) 300, 350, 370 and 400 °C by spray pyrolysis technique (SPT).Zinc doped copper oxide (CuO: Zn)thin films are deposited at the Ts of 350 °C with various concentrations of Zn, varied from 1 to 6 at%. The effect ofTs and Zn doping on structure, morphology, optical and electrical properties ofCuO andCuO: Zn thin films has been investigated in the present work. In field emission scanning electron microscope images, nanoparticles are observed around the nucleation center. Energy dispersive X-ray analysis reveals thatCuO andCuO: Zn thin films are stoichiometric and typically comprised of Cu, O and Zn. X-ray diffraction analysis ofCuO andCuO: Zn thin films indicates that the thin films have monoclinic structure with the preferred orientation along (1 1 1) plane. Maximum value of crystallite size is found about 28.24 nm for 5 at% CuO: Zn thin film. UV-Vis-NIR spectroscopic investigation shows thatCuO andCuO: Zn thin films are highly transparent in NIR region. The maximum transmittance is about 87% for CuO thin films deposited at Ts= 350 °C with 5 at% of Zn concentration.The direct band gap ofCuOthin films are found to be from 1.81 to 2.64 eV. The direct band gapCuO: Zn thin films are found to be from 2.50 to 2.88eV.Refractive index ofCuO varies between 1.33 and 2.60 and that of CuO: Zn thin films varies between 1.19 and 2.62. Dielectric constant of CuO thin films decreases with increasing Ts up to 350 °C and that of CuO: Zn decreases with Zn concentration up to 5 at%. The highest optical conductivity is found for 5 at% CuO: Zn thin filmprepared at Ts = 350 °C. The lowest electrical resistivity at room temperature is about1.51x103 ohm-m for 5 at% CuO: Zn thin films prepared at Ts = 350 °C. For CuO thin films the activation energy (ΔE) decreases as the Ts increases.The value of ΔE is varied from 0.12 to 0.26 eV for CuO thin films.In lower temperature region, Zn concentration has no significant effect on ΔE for CuO: Zn thin films. In higher temperature region, ΔE decreases at 2 at% Zn concentration and then it is increased slowly with increasing Zn concentrations. The value of ΔE varies from 0.06 to 0.39 eV for CuO: Zn thin films in both lower and highertemperature regions.