MICROSTRUCTURE, ELECTRICAL-PROPERTIES, AND THERMAL-STABILITY OF AU-BASED OHMIC CONTACTS TO P-GAN

The work described in this paper is part of a systematic study of ohmi c contact strategies for GaN-based semiconductors. Gold contacts exhib ited ohmic behavior on p-GaN when annealed at high temperature. The sp ecific contact resistivity (rho(c)) calculated from TLM measurements o n Au/p-GaN contacts was 53 Ohm . cm(2) after annealing at 800 degrees C. Multilayer Au/Mg/Au/p-GaN contacts exhibited linear, ohmic current- voltage (I-V) behavior in the as-deposited condition with rho(c) = 214 Ohm . cm(2). The specic contact resistivity of the multilayer contact increased significantly after rapid thermal annealing (RTA) through 7 25 degrees C. Cross-sectional microstructural characterization of the Au/p-GaN contact system via high-resolution electron microscopy (HREM) revealed that interfacial secondary phase formation occurred during h igh-temperature treatments, which coincided with the improvement of co ntact performance. In the as-deposited multilayer Au/Mg/Au/p-GaN conta ct, the initial 32 nm Au layer was found to be continuous. However, Mg metal was found in direct contact with the GaN in many places in the sample after annealing at 725 degrees C for 15 s. The resultant increa se in contact resistance is believed to be due to the barrier effect i ncreased by the presence of the low work function Mg metal.