Structural, optical, and conducting properties of crystalline ZnO:Co thin films grown by reactive electron beam deposition

Abstract

Abstract We deposited an undoped ZnO and 6 different Co doped ZnO (ZnO:Co) thin films on fused silica (SiO 2 ) substrates with ~100 nm thickness at substrate temperature of 125 °C using a Reactive Electron Beam Deposition technique. Energy-Dispersive X-ray Spectroscopy (EDS) was used to analyze the elemental composition rates of films. Elemental Co concentration varies from 4.62 to 28.77 at. %. The surface morphologies and grain sizes of thin films were investigated by Scanning Electron Microscope (SEM). The crystal and phase structures of the ZnO:Co thin films were characterized using X-ray diffraction (XRD). The films have single crystal and polycrystalline structures due to Co concentrations. Theoretical crystallite size and strain calculations were performed by applying the Scherrer and Williamson–Hall (W–H) methods. The grain sizes are 2–4 times greater than the crystalline sizes for ZnO:Co films. Optical properties of the films were studied by absorbance measurements using a UV–vis spectrophotometer. The analysis of the optical absorption spectra indicated that the energy band gap of the bulk ZnO film increased from 3.22 eV to maximum 4.17 eV upon Co deposition. Co 2+ ion replaces Zn 2+ ion in the structure without causing any remarkable defect for its hexagonal Wurtzite structure. Electrical conducting properties were investigated by using a Four Point Probe (FPP) technique. The conductivity depends on crystalline quality and Co concentration.