The N-polar face of the GaN high electron mobility transistor (HEMT) is capable of forming a low-resistivity ohmic contact. However, few reports to date describe the process of fabricating N-polar GaN HEMTs. In the present study, we investigated the dependence of the contact electrode metal resistance on the annealing temperature. A circular transmission line model was used to measure the contact resistance. Low resistances of 10 −5 -10 −6 Ω cm 2 in the as-deposited state were observed. Contact characteristics following the annealing treatment deteriorated at low temperatures and improved again at high temperatures. This tendency is possibly related to the thin oxide layer at the interface between Ti and GaN. Using Ti/Al/Ti/Au electrodes of 20/100/10/50 nm, we observed a contact resistivity of 2.9 × 10 −6 Ω cm 2 after annealing at 775 °C.

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