We investigate the contact characteristics of bi-layer thin films, Ti（20nm）/Al（200nm） on Si-doped n-type A10.6 Ga0.4 N films grown on sapphire substrate. The surface treatment was aqua regia boiling before metallization and annealing after metallization at different conditions in N2 ambient. High resolution X-ray diffractometery analysis was carried out on the contacts and the surface interfaces of these conditions were compared. A specific contact resistivity pc was determined using the circular transmission line method via current-voltage measurements. A pc of 3.42 × 10^-4 Ω·cm^2 was achieved when annealed at 670℃ for 90s. Then, this ideal ohmic contact was used in back-illuminated solar-blind AlGaN p- i-n detectors and the detectors＇ performances, such as spectral responsivity, dark-current,and breakdown voltage were optimized.
