We have studied the influence of surface treatment and annealing temperature on the specific contact resistance of Au/Ni ohmic contacts to p-GaN with hole concentrations in the range of 10 16 cm -3 to 10 18 cm -3. The sample with a hole concentration of 1 × 10 18 cm -3, treated with the surface treatment HCl:H 2O = 3:1 solution and annealed at 500°C in a 90% N 2 and 10% O 2 atmosphere, yielded the lowest specific contact resistance of ~4 × 10 -5 cm 2 and ~2 × 10 -7 cm 2 at room temperature and at 150°C, respectively. To investigate the roles of interdiffusion between layer interfaces and the formation of NiO and nickel gallides, we examined the metallization stacks before and after annealing using high-resolution x-ray diffraction. We conclude that the nickel-gallide formation and the deterioration of the NiO layer are together responsible for the large deviation in contact resistances observed for samples annealed at various temperatures.
- Ohmic contact
- Specific contact resistance