A comparative study of the structural and optical properties of transition metals (M = Fe, Co, Mn, Ni) doped ZnO films deposited by spray-pyrolysis technique for optoelectronic applications

Abstract

A comparative study of the functional properties of transition metals (M = Fe, Co, Mn and Ni) doped ZnO nanostructured films has been performed for applications in optoelectronics and optical devices. Pristine and M-doped ZnO (M = Fe, Co, Mn, Ni) nanostructured films were prepared by spray pyrolysis procedure. The surfaces' morphology, elemental analysis, bonds’ vibrations, structural and optical properties of the samples are studied by a scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), FT-IR spectrophotometry, X-ray diffraction and UV–visible–NIR spectrophotometry, respectively. The structural analysis shows that all samples possess hexagonal wurtzite structures. The Rietveld refinement results reveal noticeable variations in the lattice parameters of the M-doped ZnO nanostructures as compared with those of the pristine one. Due to M-doping, clear deviations in the crystallite size, micro-strain and dislocation density as well as the crystallinity nature are noticed in the host ZnO nanostructures. The UV–visible–NIR spectra analysis reveals that the optical bandgap of the pristine ZnO films varies from 3.36 eV to 3.13 eV, 3.20 eV, 3.30 eV and 3.58 eV due to doping with Fe, Co, Mn and Ni respectively. The effect of M-doping on the Urbach energy and refractive index of the ZnO nanostructures has been explored. To the best of our knowledge, this is the first time that a comparative study on the functional properties of four sprayed transition metals doped in ZnO nanostructures has been reported. These unique findings introduce the sprayed M-doped ZnO nanostructures for new applications in optoelectronics and optical devices.