The temperature dependence of the specific resistance ρc in annealed TiAlNiAu contacts on n-type GaN was monitored, obtaining information on the current transport mechanisms. After annealing at 600°C, the contacts exhibited a rectifying behavior and became Ohmic only after high temperature processes (>700°C), with ρc in the low 105Ωcm2 range. The results demonstrated that the current transport is ruled by two different mechanisms: thermoionic field emission occurs in the contacts annealed at 600°C, whereas field emission dominates after higher temperature annealing. The significant physical parameters related to the current transport, i.e., the Schottky barrier height and the carrier concentration under the contact, could be determined. In particular, a reduction of the Schottky barrier from 1.21eV after annealing at 600°Cto0.81eV at 800°C was determined, accompanied by a strong increase of the carrier concentration, i.e., from 2×1018cm3 in the as-prepared sample to 4.6×1019cm3 in the annealed contacts. The electrical properties were correlated to the microstructure of the interfacial region, providing a scenario to explain the transition from Schottky to Ohmic behavior in annealed TiAlNiAu contacts.

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