Low resistance and thermally stable Pt/Ru ohmic contacts to p-type GaN

High-quality Pt (20 nm)/Ru (50 nm) Ohmic contacts to surface-treated p-GaN with lowest resistance and thermal stability are reported. The electrical properties and interfacial reactions of the contacts to GaN were investigated using current-voltage, Auger electron spectroscopy, and glancing angle X-ray diffraction measurements. It is shown that the as-deposited contact produces a specific contact resistance of 7.8(+/-2.2) x 10(-4) Omega cm(2), while the contact annealed at 600 degrees C for 2 min yields a resistance of 2.2(+/-2.0) x 10(-6) Omega cm(2). The latter is believed to be the lowest value reported so far for Ohmic contacts to p-GaN. It is further shown that the contacts exhibit excellent thermal stability during annealing at 600 degrees C.