Low resistance and transparent Ni–La solid solution/Au ohmic contacts to p-type GaN

We report on the formation of reliable Ni–La solid solution (8 nm)/Au (8 nm) ohmic contacts to p-type GaN (Na=5×1017 cm−3). The as-deposited contact reveals nonlinear current–voltage (I–V) characteristics. However, the contacts show considerably improved I–V behavior when annealed at temperatures of 350–550 °C for 1 min in air ambient. For example, the specific contact resistance as low as 7.2×10−5 Ω cm2 is obtained from the samples annealed at 550 °C, whose transmittance is measured to be 82.5% at a wavelength of 470 nm. Based on Auger electron spectroscopy and x-ray photoemission spectroscopy results, possible ohmic formation mechanisms for the annealed contacts are described and discussed.