Changes in the work function of the contact metal, and the atomic composition in the vicinity of metal/GaN interfaces, were studied in in situ annealed Ti on n-type GaN by using synchrotron radiation photo-emission spectroscopy. The Ti layer transformed to TiN, and its work function increased, as the annealing temperature was increased. Meanwhile, the atomic Ga/N composition ratio below the TiN contact increased; thus indicating the creation of N vacancies. This constituted evidence that N vacancies produced below the contact, and acting as donors for electrons, played a main role in forming an ohmic contact.

Mechanism for Ohmic Contact Formation of Ti on n-Type GaN Investigated using Synchrotron Radiation Photoemission Spectroscopy. J.K.Kim, H.W.Jang, J.L.Lee: Journal of Applied Physics, 2002, 91[11], 9214-7