Low-resistance ohmic contacts to N-type GaN using Ti/Al/Re/Au multilayer scheme

A Ti/Al/Re/Au multilayer scheme has been developed for obtaining very low ohmic contact to moderately doped n-type GaN (4.07 x 10(18) cm(-3)). It is shown that the I-V characteristics of the as-deposited contacts improved upon annealing temperatures in the range of 550-750degreesC. Specific contact resistance as low as 1.3 x 10(-6) Omegacm(2) is obtained from the Ti (150Angstrom)/Al (600Angstrom)/Re (200Angstrom)/Au (500Angstrom) contact annealed at 750degreesC for 1 min in a N-2 ambient. It is also shown that annealing results in a large reduction (by similar to150 meV) in the Schottky barrier heights of contact, compared to the as-deposited one. Based on the XPS and AES results, possible explanations for the annealing temperature dependence of the specific contact resistance of the Ti/Al/Re/Au contacts are described and discussed.