Low-resistance and high-reflectance Ni∕Ag∕Ru∕Ni∕Au ohmic contact on p-type GaN

We report a metallization scheme of low-resistance, high-reflectance, and thermally-stable ohmic contact on p-type GaN. The specific contact resistivity as low as 5.2×10−5Ωcm2 and the high reflectance of 91% were simultaneously obtained from Ni(50Å)∕Ag(1200Å)∕Ru(500Å)∕Ni(200Å)∕Au(500Å) contact annealed at 500°C in O2 ambient. The oxidation annealing promoted the outdiffusion of Ga atoms to dissolve in the Ag layer, leaving Ga vacancies below the contact. The Ru layer could act as a diffusion barrier for intermixing of the reflective Ag with upper layers of Ni and Au. Thus, suppression of the intermixing results in the high reflectance and good thermal stability of the contact.