Schottky barrier height and nitrogen–vacancy-related defects in Ti alloyed Ohmic contacts to n-GaN

The relationship between the Schottky barrier height and nitrogen–vacancy-related defects in Ti alloyed Ohmic contacts to n-type GaN (n-GaN) has been investigated using x-ray photoelectron spectroscopy measurements. It is shown that the alloyed Ohmic behavior of the contacts can be attributed to the presence of a large number of nitrogen–vacancy-related defects and not to the formation of lower barriers at the annealed Ti/n-GaN interface. The large number of interface states, related to the nitrogen–vacancy defects has led to the pinning of the Fermi level at 0.5 eV below the conduction-band edge, and has left the GaN surface very heavily n type, thereby forming a tunneling junction.