Doping effect on the physical properties of zinc oxide thin films

Gallium, aluminum, fluorine, and indium doped ZnO (ZnO:Ga, ZnO:Al, ZnO:F, and ZnO:In) thin films have been deposited by the chemical spray technique on soda lime glass substrates. The effect of different dopant elements on the electrical, optical, structural, and morphological properties has been investigated. The X-ray diffraction (XRD) patterns reveal that all deposited films are polycrystalline with a hexagonal wurtzite-type structure with a (002) preferential orientation for ZnO:Al, and ZnO:F, and (101) for ZnO:In, and ZnO:Ga films. The lowest electrical resistivity, around 1.5×10^-3Ωcm, was presented in indium-doped ZnO films. SEM micrographs show a surface morphology dependent on the dopant element. The ZnO:Ga, ZnO:F, and ZnO:In films show a rough surface, whereas the surface corresponding to ZnO:Al film shows a smoother surface texture. All deposited films show an average optical transmittance in the UV-vis spectra oscillating between 75-80 %. Green light emission from F-doped ZnO was observed when excited by 325 nm He-Cd laser, which means that these films are good candidate for green light-emitting devices.