Enhanced thermal stability of Ag ohmic reflector for InGaN/GaN light-emitting diode using a Ru capping layer

Abstract

A Ru capping layer is employed to improve the thermal stability of Ag ohmic reflectors for high-power GaN-based light-emitting diodes (LEDs). The 20-nm-thick Ru capping layer is shown to be fairly effective in suppressing agglomeration by forming RuO2. The Ag/Ru contacts exhibit specific contact resistance of 8.1 x 10(-5) Omega cm(2) and reflectance of similar to 89% at a wavelength of 450 urn when annealed at 500 degrees C for 1 min, which are much better than that of Ag only contacts. Blue LEDs fabricated with the 500 degrees C-annealed Ag/Ru contacts give a forward voltage of 2.98 V at an injection current of 20 mA, which is lower than that (3.02 V) of LEDs with the 500 degrees C-annealed Ag only contacts. LEDs with the 500 degrees C-annealed Ag/Ru contacts show 25% higher output power (at 20 mA) than LEDs with the 500 degrees C-annealed Ag only contacts. X-ray photoemission spectroscopy examinations are performed to describe the improved electrical performance of the Ag/Ru contacts. (C) 2012 Elsevier Ltd. All rights reserved.