Effect of Co doping in tailoring the crystallite size, surface morphology and optical band gap of CuO thin films prepared via thermal spray pyrolysis

Abstract

In this paper, we reported the nonmagnetic semiconductor to half metal transition behavior of Co doped CuO (CCO) thin films with p-to n-type characteristics for the first time. The thin films are prepared using a thermal spray pyrolysis technique with variations of Co doping concentration from 0 to 8 at.% in the steps of 2 at.%. Subsequently, the surface morphological, structural, optical, electrical properties and electronic band structures by density functional theory (DFT) have been studied intensively. The surface morphology of the CCO thin films is significantly influenced by Co doping concentrations and agglomerated spherical grains are formed, as indicated by field emission scanning electron microscopy (FESEM). The quantitative analysis is carried out by the energy dispersive X-ray (EDX) analysis that confirms the presence of Cu, O and Co atoms. X-ray diffraction (XRD) reveals all the deposited CCO thin films are belong to monoclinic structure with mixed phases, and average crystallite size shrinkages from 28.67 to 18.96 nm with Co doping concentrations. The optical transmittance and the band gap decrease noticeably from 85% to 58%, and 3.00 to 1.98 eV, respectively. Several significant optical parameters such as Urbach energy, steepness parameter, electron–phonon interaction, refractive index, dielectric constant and static dielectric constant is examined. Enhancement of Cu-O bond length is determined and found similarities between the Rietveld refinement and DFT studies. With the spin polarized density of state (DOS), polarized value lies between 0 and above 1 which confirms that semiconductor to half metal phase transition. Using the Hall Effect measurement, p- to n-type conductivity is determined, and finally a lower resistivity and mobility is found to be 07.83×10−3 Ω cm and 0.003 cm2V−1s−1, respectively at 8 at.% CCO thin film. Thus, the above results depict that 8 at.% of CCO thin films may have potential application in the field of spintronic and optoelectronic devices.