Insight of the role of F-impurity on the structural, electro-optical properties of ZnO: DFT and experiment

Abstract

A comprehensive study is performed to investigate the consequence of F doping on the structural, electronic, optoelectrical, and photoluminescence properties of ZnO. In the theoretical part, the density functional theory (DFT) is used to study the electronic and optical properties of F-doped ZnO. Whereas, the role of F on the structural, morphological, and optoelectrical characteristics of spray deposited ZnO thin films are studied by experimental means. Electronic band structures, density of states, and optical properties indicated that F is an efficient donor and broadened the direct band gap of F:ZnO system because of the well-known Burstein-Moss effect which matches the experimental data. Shifting of the Fermi level into conduction band (CB) fallouts the improvement of electrical conductivity and carrier concentrations of the doped system. The lattice constants of ZnO are increased due to F doping which is in accord with our experimental results. The existence of F1s in the films is confirmed by X-ray photoelectron spectroscopy (XPS) inspection. Surface morphology reveals the formation of nano-wall structures with different aspect ratios. Photoluminescence spectra show PL emissions for un-doped and 5% F-doped samples at 3.38 eV assigned to the near band edge (NBE) emission and weak peaks at 2.74 and 2.63 eV are attributed to emission from defect states. The optical band gap value first decreased up to 1% F content and then started to increase with increasing F concentration, which is well supported by the theoretical results. The findings from this study will be helpful for further investigation and selecting suitable areas of applications.