Formation of low resistance and transparent ohmic contacts to p-type GaN using Ni–Mg solid solution

We report on the formation of Ni–Mg solid solution/Au ohmic contacts on p-GaN (5×1017 cm−3). The as-deposited Ni–Mg solid solution (8 nm)/Au (8 nm) contact shows near-linear I–V characteristics. However, oxidizing the contacts at 450 and 550 °C for 1 min in air results in a dramatic improvement in their I–V behaviors, producing specific contact resistance of ∼10−6 Ω cm2, which is much better than the conventional oxidized Ni/Au contacts. The light transmittance of the Ni–Mg solid solution/Au contacts annealed at 550 °C is measured to be better than 79% at a wavelength of 460 nm. Based on the I–V measurements, Auger electron spectroscopy, and x-ray photoemission spectroscopy results, possible ohmic formation mechanisms are described.