| The characteristics of clean n- and p-type GaN (0001) surfaces and the interface between this surface and SiO2, Si3N4 , and HfO2 have been investigated. Both n- and p-type Ga-face GaN (0001) surfaces have been cleaned via an 860°C anneal in an ammonia atmosphere, and carbon and oxygen contaminants were reduced to below the detection limits. Layers of SiO2, Si3N4, or HfO 2 were carefully deposited to limit the reaction between the plasma and the GaN surface. After stepwise deposition, the electronic states were measured with x-ray photoelectron spectroscopy (XPS) and ultraviolet photoemission spectroscopy (UPS). A valence band offset (VBO) of 2.0 ± 0.2 eV with a conduction band offset (CBO) of 3.6 ± 0.2 eV was determined for the GaN/SiO2 interface. The large band offsets suggest SiO2 is an excellent candidate for passivation of GaN. For the GaN/Si3N 4 interface, type II band alignment was observed with a VBO of 0.5 ± 0.2 eV with a CBO of 2.4 ± 0.2 eV. While Si3N4 should passivate n-type GaN surfaces, it may not be appropriate for p-type GaN surfaces. A VBO of 0.4 ± 0.2 eV with a CBO of 2.0 ± 0.2 eV was determined for the GaN/HfO2 interface. An instability was observed in the HfO2 film, with energy bands shifting ∼0.5 eV during a 650°C densification anneal. The electron affinity measurements via UPS were 3.0, 1.1, 1.8, and 2.9 ± 0.1 eV for GaN, SiO2, Si3N4, and HfO2 surfaces, respectively. Electron affinity measurements, along with band alignment data, allow a deviation from the electron affinity model due to a change of the interface dipole to be observed. Interface dipoles of 1.7, 1.1 and 1.9 ± 0.2 eV were observed for the GaN/SiO2, GaN/Si3N4, and GaN/HfO 2 interfaces, respectively. The existence of Ga-O bonding at the heterojunction significantly increases the interface dipole, which raises the dielectric bands in relation to the GaN. |
