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 (5x10(17) 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 degreesC for 1 min in air results in a dramatic improvement in their I-V behaviors, producing specific contact resistance of similar to10(-6) Omega cm(2), 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 degreesC 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. (C) 2003 American Institute of Physics.