Low Resistance Ni-Mg Solid Solution/Pt Ohmic Contacts to p-Type GaN

We investigate Ni-Mg solid solution (4 nm)/Pt (6 nm) metallization schemes for use in forming high-quality ohmic contacts to p-GaN:Mg (5 × 10 ¹⁷ cm^-3). The as-deposited Ni-Mg solid solution/Pt contact reveals nonlinear current-voltage characteristics. Annealing the contacts at 450 and 550°C for 1 min in air ambient, however, improves electrical behaviors significantly. For example, specific contact resistance as low as 6.7 × 10^-5 Ω cm² is obtained, when the contacts are annealed at 450°C. Based on the I-V measurement, Auger electron spectroscopy, and X-ray photoemission spectroscopy results, possible ohmic formation mechanisms for the Ni-Mg solid solution/Pt contacts are discussed.