Preparation and X-ray photoelectron spectroscopy studies of ZnGa2O4 thin films

ZnGa2O4 thin films coated on quartz substrate were prepared by sol-gel spinning method. The preparation condition has great effect on the film structure. When the concentration ratio of polyvinylpyrrolidone and cations in the precursor solution was small (similar to 0.50), the films showed larger particle size and porous structure, and more oxygen vacancy defects. Moreover, the self stimulated luminescence of the films at 400 nm was weak. On the contrary, when the ratio was more than 0.83, the films with better quality were obtained and the emission at 400 nm was stronger. The existence of surface contamination was confirmed by depth profiling analysis of the film using X-ray photoelectron spectroscopy. The results indicated that the films contained zinc, gallium, oxygen, and a significant amount of carbon on the surface. As sputtering proceeded, the carbon content gradually decreased and the contents of composition elements increased. The O/Zn ratio is close to 4.0 and Ga/Zn ratio is close to 2.0 after the disappearance of the contamination layer, which indicates that the as-obtained ZnGa2O4 films are stoichiometric. At the film interface, a new Zn 2p XPS peak emerged, and we think that zinc interacted with the quartz substrate to form a new phase.