Highly Reliable Ohmic Contacts to N-Polar n-Type GaN for High-Power Vertical Light-Emitting Diodes

We report on the formation of highly reliable Ti/Al-based Ohmic contacts to N-polar n-GaN for vertical light-emitting diodes via laser-annealing. All as-deposited samples are Ohmic with specific contact resistances of 1.1 - 4.3 × 10^-4 Ω cm². After annealing at 250°C, unlike the untreated sample, the laser-annealed samples remain Ohmic with specific contact resistances of 2.6- 3.9 × 10^-4 Ω cm². The laser-annealed samples remain electrically stable up to 60 min at 300°C. Laser-annealing causes the formation of interfacial TiN/β -AlN phases with rock salt structure. Based on X-ray photoemission spectroscopy and scanning transmission electron microscopy results, possible Ohmic mechanisms are described.