Low-resistance and thermally stable ohmic contact on p-type GaN using Pd/Ni metallization

We report a low-resistance thermally stable ohmic contact on p-type GaN using a promising contact scheme of Pd/Ni. Specific contact resistance as low as 5.7×10−5 Ω cm2 was obtained from the Pd (30 Å)/Ni (70 Å) contact annealed at 500 °C under an oxidizing ambient. NiO that formed at the surface prevented Pd atoms from outdiffusing, promoting the formation of Pd gallides, Ga2Pd5 and Ga5Pd. This reaction produces Ga vacancies below the contact, leading to enhancement of the thermal stability as well as reduction of the contact resistivity.