Ohmic contacts to GaN with rapid thermal annealing

This research attempted to use metals with lower work functions, such as Ti, Al, to form ohmic contacts to n-GaN. Then we used metals with higher work functions, such as Ni, Pd, Pt, and Au to form ohmic contacts to p-GaN. The work functions of these metals indeed influence the performance of ohmic contacts, indicating that the Fermi level of GaN is unpinned. The specific contact resistance measured and calculated by TCL model, was 2.35×10^-3 Ωcm² for as-deposited Ti/Al on GaN. After RTA processes at different temperatures in the range of 400 to approximately 900 °C, the minimum ρ_c of 7.4×10^-5 Ωcm² can be obtained for RTA temperature of 600 °C. The oxidized Ni/Au contact exhibited the lowest contact resistance of 1.02×10^-2 Ωcm², among Ni/Au, Pd/Au, Pt/Au contact schemes on p-GaN. It was also observed that the I-V curves of the triple-layer contact, Pt/Ni/Au, was near-linear while the others were rectifying even after annealing.