X-Ray Photoelectron Spectroscopy Characterization of Aluminum Nitride Surface Oxides: Thermal and Hydrothermal Evolution

Oxidized surfaces of aluminum nitride (AlN) epilayers grown on sapphire substrates and of AlN bulk crystals grown by physical vapor transport were studied by x-ray photoelectron spectroscopy (XPS). Analysis of the oxygen core level spectra showed approximately equal contributions from oxygen in two bonding states, which were identified by the binding energies and relative separation of the fitted peaks as OH− and O2−. The oxide on air-exposed AlN surfaces was identified as aluminum oxide hydroxide. Systematic annealing experiments were conducted in vacuum to study the thermal evolution of hydroxide layers, and a dehydration mechanism resulting in the formation of Al2O3 at high temperature was identified.