Presence of nanosize Au dots on the formation of ohmic contact for the Ni-Au base film to p -GaN

The role of nanosize Au dots in the contact characteristic of AuNiNiO stacked films to p -type GaN is studied. The nanosize Au dots were fabricated by heating a 1-nm-thick Au film at 150 °C in nitrogen ambient for 6 min. The NiO(2 nm), Ni(2 nm), and Au(2 nm) films were deposited sequentially on p -GaN, without or with the preformed Au dots. Without the nanosize Au dots, the AuNiNiOp-GaN structure shows nonlinear current-voltage (I-V) curves, even after annealing at 400 °C. On the contrary, the AuNiNiOdot-Aup-GaN structure exhibits linear I-V curves of ohmic behavior after annealing at 400 °C in oxygen ambient. The nanosize Au dots indirect contact with p -GaN imitate the microstructure of Au islands in the annealed Au-Ni system and they create a microstructure of the Au-NiO-GaN triple-phase junction. The mechanism for the formation of contact via annealing and the presence of triple-phase junction are discussed.