Thermally stable and reflective RhZn/Ag ohmic contacts to p-type GaN for near-UV flip-chip light-emitting diodes

We investigated Rh-Zn solid solution (3 nm)/Ag(200 nm) schemes in order to produce thermally stable and low-resistance p-type Ohmic reflectors for high-performance flip-chip light-emitting diodes (LEDs). The Rh-Zn solid solution/Ag contacts show a specific contact resistance of 1.2 × 10^-4 Ωcm² and a reflectance of about 78% at a wavelength of 395 nm when annealed at 500 °C for 1 min in air. Scanning electron microscopy results show that unlike Ag only contacts, the Rh-Zn solid solution/Ag contacts experience insignificant morphological degradation even after annealing at 500 °C for 1 min. Near-UV InGaN/GaN LEDs (1200 × 600 μm² in chip size) fabricated with the annealed Rh-Zn solid solution/Ag reflectors give a forward-bias voltage of 3.43 V at an injection current of 80 mA, which is lower than that (3.65 V) of LEDs with Ag only reflectors. LEDs with the annealed RhZn solid solution/Ag reflectors exhibit 43% higher light output power (at 80 mA) than the LEDs with annealed Ag contacts. X-ray photoemission spectroscopy examinations were performed to investigate possible Ohmic formation behaviors.