Photoemission investigation of the electronic properties of gallium-face gallium nitride (0001)-dielectric interfaces.

摘要

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.