Effects of oxygen thermal annealing treatment on formation of ohmic contacts to n-GaN

A contact scheme to undoped and n-type GaN was identified that does not require a post deposition anneal. As-deposited Ti/Al/Ti/Au usually forms a Schottky contact. However, we find that by means of an oxygen rapid thermal annealing prior to metal deposition, the contact will develop an ohmic behavior with a specific contact resistance of 3.8 10-5 Omega cm2. In X-ray photoelectron spectroscopy, we find that the Ga 3 d electron binding energy increases with this pre-treatment, indicating a shift of the Fermi level closer to the conduction band. This sequence reversion of high temperature processing steps allows important gain in device fabrication flexibility.