SiO2/GaN interfaces with low defect densities and high breakdown electric fields formed by plasma-enhanced atomic layer deposition

Abstract

We present SiO2/GaN interfaces with a low interface state density and a high breakdown electric field. The SiO2 films were deposited by plasma-enhanced atomic layer deposition (ALD) using bis(diethylamino)silane and O2 plasma at 300 °C on n-type GaN (0001) homoepitaxial layers. An interface state density of less than 1011 cm−2 eV−1 at 0.3 eV below the conduction band edge was confirmed by the conductance method. The value is much lower than those of previously reported ALD-SiO2/GaN interfaces (1012–1013 cm−2 eV−1). A low fixed charge density at the SiO2/GaN interface of 3.7 1011 cm−2 and a high dielectric breakdown field of ~10 MV cm–1 were obtained. Moreover, the interface state density and current−voltage characteristics were further improved by post-deposition annealing at 400 °C in N2 ambient. Scanning transmission electron microscopy with energy-dispersive X-ray analysis revealed the existence of a GaO x interlayer between SiO2 and GaN. The unintentionally formed interlayer could be one of the reasons for the improvement of interface properties at ALD-SiO2/GaN.