Low resistance Ni-Zn solid solution/Pd ohmic contacts to p-type GaN

We have investigated Ni-Zn alloy(5 nm)/Pd(5 nm) metallization schemes for use in forming high-quality ohmic contacts to p-GaN (5 × 10¹⁷ cm^-3). The as-deposited Ni-Zn alloy/Pd contact exhibits nonlinear current-voltage (I-V) characteristics. However, annealing the contacts at 530°C for 1 min in either air or N₂ ambient improves I-V behaviour drastically. It is shown that the contacts produce specific contact resistance of 6.95 × 10^-5 and 4.8 × 10^-5 Ω cm² when annealed in N₂ and air ambient, respectively. It is further shown that multi-quantum-well light-emitting diodes fabricated with the annealed Ni-Zn alloy/Pd contact layers give a forward-bias voltage of 3.17 and 3.28 V at an injection current of 20 mA when annealed in air and N₂ ambient, respectively.