Ag/Ni/Ag Multilayer Reflector for GaN-Based Vertical Light-Emitting Diode

Abstract

We investigate the effect of Ni insertion on the electrical and thermal properties of Ag-based reflectors for GaN-based light emitting diodes (LEDs). It is shown that after annealing at 500 °C, the surface of Ag only sample becomes significantly roughened due to agglomeration, whereas the surface of Ni-inserted Ag sample get roughened with elongated Ag hillocks on an ∼100-nm-thick Ag film. The Ni-inserted Ag contacts show higher reflectance (at 460 nm) than the Ag only sample after annealing at 500 °C. The 500-°C-annealed Ni-inserted Ag samples exhibit lower specific contact resistance than the annealed Ag only contacts. LEDs fabricated with the 500-°C-annealed Ni-inserted Ag contact give lower forward-bias voltage and series resistance as compared to those of LEDs with the 500-°C-annealed Ag only contact. The LEDs with the 500-°C-annealed Ni-inserted Ag contact exhibit 18% higher light output power (at 20 mA) than the LEDs with the Ag only contacts annealed at 500 °C. Based on the X-ray photoelectron spectroscopy and scanning electron microscopy results, the temperature dependence of the electrical characteristics of the Ni-inserted Ag contacts is described and discussed.