ZrB2-based Ohmic contacts to p-GaN

The annealing temperature dependence of contact resistance and layer stability of ZrB2/Ti/Au and Ni/Au/ZrB2/Ti/Au Ohmic contacts on p-GaN is reported. The as-deposited contacts are rectifying and transition to Ohmic behavior for annealing at ≥750 °C, a significant improvement in thermal stability compared to the conventional Ni/Au Ohmic contact on p-GaN, which is stable only to <600 °C. A minimum specific contact resistance of ∼2 × 10−3 Ω cm−2 was obtained for the ZrB2/Ti/Au after annealing at 800 °C while for Ni/Au/ZrB2/Ti/Au the minimum value was 10−4 Ω cm−2 at 900 °C. Auger Electron Spectroscopy profiling showed significant Ti, Ni and Zr out diffusion at 750 °C in the Ni/Au/ZrB2/Ti/Au while the Ti and Zr intermix at 900 °C in the ZrB2/Ti/Au. These boride-based contacts show promise for contacts to p-GaN in high temperature applications.