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

Current-voltage (I-V) characteristics of Al, Mg, and Au Schottky contacts t o atomically clean n-GaN(0001)-1 x 1 surfaces prepared in an ultrahigh vacu um were investigated. The Al/n-GaN contact is rectifying at room temperatur e and becomes Ohmic after annealing at 500 degreesC. Coupled with previous photoemission spectroscopy data, this result demonstrates that the origin o f the Ohmicity is the reaction-induced doping of the interface. For nonanne aled interfaces, the Schottky barrier heights determined from I-V character istics are in qualitative agreement with the results obtained by photoemiss ion 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 res ults suggest that the reaction-induced defects and thermionic field emissio n play an important role in the electrical behavior of these interfaces. (C ) 2001 American Institute of Physics.