Influence of Surface Treatment and Annealing Temperature on the Formation of Low-Resistance Au/Ni Ohmic Contacts to p -GaN

摘要

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 1016 cm−3 to 1018 cm−3. The sample with a hole concentration of 1 × 1018 cm−3, treated with the surface treatment HCl:H₂O = 3:1 solution and annealed at 500°C in a 90% N₂ and 10% O₂ atmosphere, yielded the lowest specific contact resistance of ~4 × 10−5 Ω cm2 and ~2 × 10−7 Ω cm2 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.