Influence of nickel doping on the energy band gap, luminescence, and magnetic order of spray deposited nanostructured ZnO thin films

Abstract

We synthesized Ni doped ZnO thin films, ZnxNi1-xO (0.0≤x≤0.1), using spray pyrolysis deposition and performed a systematic study on their crystal structure, electronic, photoluminescent properties, and magnetic order. X-ray diffraction analysis showed that all nanostructured films under investigation are crystalized in a single phase wurtzite structure (space group P63mc), with a preferred orientation along (002) plane. The phase purity and the successful incorporation of Ni dopants into the ZnO lattice were also confirmed by the x-ray photoelectron spectroscopy (XPS), Ultra Violet-Visible, and Energy Dispersive X-ray spectroscopy measurements. The XPS results indicated that Ni ions are in 2 + oxidization state in all doped films. Photoluminescence (PL) spectroscopy showed strong emission peak in the UV region and multi-components emission peak in the visible luminescence, which is ascribed to deep-level emissions by different types of intrinsic defect states. Both XPS and PL spectroscopy clearly showed significant enhancement in the oxygen vacancy (VO) concentration by increasing the Ni doping. The saturation magnetization and coercivity also increase with Ni doping, indicating a strong correlation between the concentration of VO defects, and the observed magnetic order in the doped films. In addition, a red shift in the energy gap is found with Ni doping and is attributed to the sp–d exchange interaction, which is mediated by the VO defects in the ZnO lattice.