Influence of air/N2 treatment on the structural, morphological and optoelectronic traits of nanostructured ZnO:Mn thin films

Nanocrystalline ZnO:Mn thin films have been prepared by sol-gel dip-coating method. The content of Mn in sol was varied from 0 to 12 wt%. The influence of Mn concentration and annealing ambient (i.e. air and nitrogen) on the structural, morphological, optical and electrical properties of ZnO thin films were studied by using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV-visible spectroscopy and Hall Effect measurements. XRD results show that the films have hexagonal wurtzite structure and the crystallite size varies between 38 and 10 nm. The samples annealed in nitrogen indicate better crystallinity than those annealed in air. SEM results revealed that the surface smoothness of the films improved at higher content of Mn. AFM measurements exhibit that the RMS roughness of the samples reduces with Mn concentration. In comparison with air ambient, the electrical mobility improved with annealing in nitrogen. Meanwhile, it was found that introducing Mn decreased the electrical conductivity. The optical transparency and band gap of the doped films decreased with Mn doping. The band gap variation of the films due to Mn doping was discussed in details.