Fabrication of GaN-based resonant cavity LEDs

This article describes a fabrication process for GaN based resonant cavity (RC) LEDs. The devices emit through the transparent sapphire substrate. An AlGaN/GaN DBR forms the bottom mirror, while a PdAg-based p-contact metallisation serves as top mirror. The PdAg mirrors have been characterized optically by reflectometry, and electrically by circular TLM measurements. A specific contact resistivity of 1.0 × 10^-2 Ωcm² has been measured, without any annealing of the contacts. For the GaN to PdAg interface a reflectivity of 60% has been measured for a wavelength of 510 nm. At 20 mA bias the RC-LEDs show a forward voltage of 3.5 V and an optical output of 330 μW through the back of the wafer.