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°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, α-Ce₂O₃, and an interfacial layer of β-Ga₂O₃. The formation of α-Ce₂O₃ is due to the phase transformation of CeO₂, whereas the β-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°C shows the lowest semiconductor-oxide interface-trap density, effective oxide charge, and the highest dielectric breakdown field.