Correlation of contact resistance with metal diffusion for oxidized Au/Ni/p-GaN contacts studied using Rutherford backscattering spectroscopy

Abstract

The temperature- and time-dependent diffusion behaviours of oxidized Au/Ni/p-GaN ohmic contacts were studied with Rutherford backscattering spectroscopy/channelling (RBS/C). It was found that, after annealing at 450 °C, the Au diffused into the electrodes and contacted to the p-GaN and the O diffused into the electrodes to form NiO. Both of these processes are believed to be responsible for the sharp decrease in the specific contact resistance (ρc) at 450 °C. At 500 °C, the O diffused deeper into the interface. As a result, the ρc reached the lowest value at this temperature. The influence of the annealing time was also investigated. It was found that, at 500 °C, 1 min annealing caused obvious in-diffusion of Au and O and out-diffusion of Ni. The Au has even diffused into the p-GaN/metal interface. These diffusion behaviours are believed to cause the sharp decrease of ρc. Annealing for 5 min at 500 °C caused Au and Ni to in-diffuse and out-diffuse further, respectively. A longer annealing time, e.g. 10 min, only caused further in-diffusion of O. As for Au and Ni, no further in-diffusion and out-diffusion has been found for the samples annealed for 10 min at 500 °C. Therefore, the further decrease of ρc (5 × 10−4 Ω cm2) after 10 min annealing is attributed to the formation of more NiO at the interface. However, when the annealing temperature reached 600 °C, the ρc increases greatly. The reason for the increase of the ρc is also discussed.