Effect of thermal annealing on Ni/Au contact to p-GaN

We deposited Ni (13 nm) / Au (30 nm) layers on p-GaN by using the dc sputtering method in order to produce low-resistivity Ohmic contacts. The Ni (13 nm) / Au (30 nm) contact layers were annealed in air for 15 min at various temperatures. The electrical and the structural properties of the Ni/Au contact to p-GaN were investigated. The current-voltage measurement showed that the resistance of the as-deposited sample was very high. However, the sample annealed at 600 °C showed Ohmic-like behavior with a specific contact resistance of 1.9 × 10^-3 Ωcm². Further increasing the temperature caused the Ohmic-like behavior to be degraded. Transmission electron microscopy and Auger electron spectroscopy were used to characterize the interfacial structure between the Ni/Au electrode and the p-GaN layers. The Ni layer was in contact with the p-GaN before annealing. However, after annealing, the Au layer had diffused from the top layer to the interface. The Au layer on the p-GaN surface resulting from the indiffusion of Au atoms during annealing may contribute to effective Ohmic contact formation.