Structure And Optical Properties Of Cu And Ag Doped ZnO Films

ZnO is II-VI compound semiconductor with a wide direct band gap of 3.3 eV at room temperature, exciton binding energy of 60meV, and a hexagonal wurtzite structure of space group P63mc. Its lattice parameters are a=0.3249 nm and c=0.5206 nm. Due to their excellent physical and chemical properties, ZnO films have many realized and potential applications such as surface acoustic wave devices, ultraviolet photodetectors, gas sensors, light emitters, transition layer for GaN and transparent conductors for display, etc. And they can be integrated with some materials readily. In recent years, the researches and developments of ZnO films have attracted great attention and interest in researchers and industry.ZnCuO films and ZnAgO films were grown by a RF reactive magnetron sputtering method. X-Ray Diffraction (XRD), Electron Probe Micro-Analyzer (EPMA), Transmission Electron Microscope (TEM), transmission spectrum, photoluminescence (PL) and Raman analysis are used to test the microstructure, content and the optical properties of the ZnO-based materials. This work is focus on the optical properties of doped ZnO-based materials, as follow:1. All the ZnCuO films are highly (001) textured without any precipitated phase, and Cu dopants hardly change the c parameter of ZnO. In the transmittance spectra, there is obvious abnormal absorbability in near ultraviolet and visible area. Being consist with the calculation, the band gap of ZnCuO films decrease with the increasing Cu concentration. Significant reduction of the PL efficiency caused by Cu dopants is seen in PL spectra, but the PL peak doesn't move. We believe that the absorbability and the emission in near ultraviolet and visible area can be related to the impurity levels caused by Cu dopants. The impurity levels are found in the first-pricinple calculations, in which Cu-3d states are located in the forbidden band.2. A viable method to fabricate ZnO films embedded with metallic Ag nano-particles (NPs) is supplied. The films are found to have a large enhancement in the intensity of ultraviolet PL emission, which is assigned to be from the strong interaction between the localized surface plasmons in the Ag NPs and the near band edge emission of ZnO.3. It is demonstrated that the interference fringes are observable in the films that are even enough. Photonic interference is shown to be responsible for the different peaks observed in the emission spectra of ZnO films, which are often assigned to the electron transition of various defects. Due to the photonic interference, the intensity, peak position, and peak shape of ultraviolet emission are also found to be of periodic variation with the increase of film thickness.