Measurements of the band offset of SiO ₂ on clean GaN

The band alignment of SiO ₂ and GaN is important for passivation of high voltage devices and for gate insulator applications. In this study XPS and UPS techniques are employed to determine the electronic states as SiO ₂ is deposited onto a clean GaN surface. The substrate was epitaxially grown n-type GaN on 6H-SiC (0001) substrates with an AlN (0001) buffer layer. The GaN surface was atomically cleaned via a 860°C anneal in an NH ₃ atmosphere. For the clean GaN surface, upward band bending of ∼0.3 ± 0.1 eV was measured, and the electron affinity was measured to be ∼2.9 eV. Layers of Si were deposited on the GaN surface via Molecular Beam Epitaxy (MBE), and the Si was oxidized by a remote O ₂ plasma. The oxidation of the Si occurred without oxidizing the GaN. Densification of the created SiO ₂ film was achieved by annealing the substrate at 650°C. Surface analysis techniques were performed after each process, and yielded a valence band offset of ∼2.0 eV, and a conduction band offset of ∼3.6 eV for the GaN-SiO ₂ interface.