Influence of Fluorine and Nitrogen Co-Doping on the Structural and Morphological Properties of Sol-Gel ZnO Films

The structural, vibrational, optical and morphological properties of ZnO:N:F films, obtained by the sol-gel method, were investigated. The effect of single (fluorine, nitrogen) and F, N co-doping and thermal treatments (300–600 °C) on the properties of ZnO films was analyzed. X-ray Diffraction (XRD) revealed that ZnO:N:F films crystallized in a polycrystalline wurtzite structure. F and N incorporation changed lattice parameters, crystallite sizes, texture coefficients (TC) and residual stress. TC (002) of ZnO:N:F films increased with annealing, reaching 1.94 at 600 °C lower than the TC (002) of ZnO and ZnO:N films. The shifting of the characteristic absorption bands and/or the appearance of new IR lines were detected for ZnO:N:F samples. The highest transmittance (90.98%) in the visible spectral region was found for ZnO:F films. ZnO:N:F films possessed optical transparency up to 88.18% and their transmittance decreased at the higher annealings. The optical band gap (Eg) values of ZnO:N:F films were changed with fluorine and nitrogen concentrations. The formation of the wrinkle-like structures on the surface of ZnO and ZnO:N films was depicted in Field Emission Scanning Electron Microscopy (FESEM) images. The F, N dual doping modified ZnO morphology and suppressed wrinkle formation.