Low Resistance and High Reflectance Pt/Rh Contacts to p-Type GaN for GaN-Based Flip Chip Light-Emitting Diodes

We report on a Pt(8 nm)/Rh(200 nm) metallization scheme for use in low resistance and high reflectance ohmic contacts to p-GaN for use in flip chip light-emitting diodes (FCLED) applications. The thermal annealing of a Pt/Rh contact at 500DGC led to linear current-voltage characteristics with a specific contact resistance of 9.0 X 10-5 Omega cm2 while the as-deposited Pt/Rh contact showed nonohmic characteristics. It was also shown that the 500DGC annealed contact produces a high reflectance of 62% at a wavelength of 460 nm. Auger electron spectroscopy depth profiles and glancing-angle X-ray diffraction results indicated that the low contact resistance of the annealed sample can be attributed to the formation of Ga-Pt and Ga-Rh intermetallic phases. Furthermore, the electrical performance of an FCLED with the Pt/Rh reflector scheme was superior to that of a FCLED with a Ni/Au/Ag reflector scheme.