Aluminum, magnesium, and gold contacts to contamination free n-GaN surfaces

Current-voltage (I-V) characteristics of Al, Mg, and Au Schottky contacts to atomically clean n-GaN(0001)-1 × 1 surfaces prepared in an ultrahigh vacuum were investigated. The Al/n-GaN contact is rectifying at room temperature and becomes Ohmic after annealing at 500°C. Coupled with previous photoemission spectroscopy data, this result demonstrates that the origin of the Ohmicity is the reaction-induced doping of the interface. For nonannealed interfaces, the Schottky barrier heights determined from I-V characteristics are in qualitative agreement with the results obtained by photoemission spectroscopy. We find that the ideality factor of the barrier is close to unity for the unreactive interface i.e. Au/GaN, but significantly higher for the reactive interfaces, i.e., Al/GaN and Mg/GaN. Our experimental results suggest that the reaction-induced defects and thermionic field emission play an important role in the electrical behavior of these interfaces.