Properties of the phase transition in a ZnO film on silicon substrate

Abstract

ZnO films were spin-coated on silicon substrates by using the sol-gel method and were characterized as a function of the sintering temperature (600 ∼ 1000 °C). The phase transition from the ZnO phase to the Zn₂SiO₄ phase was investigated by using X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), and cathodoluminescence (CL). The XRD pattern of the ZnO film sintered at 600 °C showed a typical polycrystalline hexagonal wurtzite structure. However, at a sintering temperature of 1000 °C, only the 21.72° and the 32.64° peaks were found, which could be attributed to the (300) and the (013) planes of Zn₂SiO₄, respectively. In FE-SEM, the grain size of the ZnO film sintered at 900 °C increases abruptly, and the samples sintered at 1000 °C showed dense, grains with enlarged grains. In EDX, as the sintering temperatures were increased, the relative amounts of silicon atom were decreased, and the relative amounts of oxygen were increased. In CL, the UV emission (375 ∼ 379 nm) was well measured in the ZnO films sintered at 600 ∼ 800 °C. However, the intensity of the UV emission at 379 nm in the ZnO film decreased abruptly when the film was sintered at 900 °C, and the very intensive peaks were measured at 284 nm and 589 nm. At a sintering temperature of 1000 °C, the UV emission at about 375 nm in the ZnO film disappeared. From this study, we could confirm that a phase transition toward the Zn₂SiO₄ phase had completely occurred at a sintering temperature at 1000 °C.