Effect of Postdeposition Annealing in Oxygen Ambient on Gallium-Nitride-Based MOS Capacitors With Cerium Oxide Gate

This paper presents the effects of postdeposition annealing temperatures (400, 600, 800, and 1000 degrees C) in oxygen ambient on the metal-organic decomposed CeO2 films spin coated on an n-type GaN substrate. The compositions, structures, and morphologies of these samples are revealed by X-ray diffraction (XRD), field-emission scanning electron microscopy, and an atomic force microscope. XRD analysis discloses the presence of CeO2 films, alpha-Ce2O3, and an interfacial layer of beta-Ga2O3. The formation of alpha-Ce2O3 is due to the phase transformation of CeO2, whereas the beta-Ga2O3 interfacial layer is formed due to the inward diffusion of the released oxygen from CeO2 reacting with decomposed GaN. These characterization results are then correlated with the metal-oxide-semiconductor characteristics of the CeO2 gate annealed at different temperatures. It has been demonstrated that oxide annealed at 1000 degrees C shows the lowest semiconductor-oxide interface-trap density, effective oxide charge, and the highest dielectric breakdown field.