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) was analyzed. The n-GaN epitaxial layers were grown on c-plane sapphire substrates using a metalorganic chemical vapor deposition (MOCVD) system. It was found 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 results show that the large number of interface states, related to nitrogen-vacancy defects led to the pinning of the Fermi level at 0.5 eV below the conduction-band edge and left the GaN surface very heavily n type.