GaN-based flip-chip LEDs with highly reflective ITO/DBR p-type and via hole-based n-type contacts for enhanced current spreading and light extraction

We demonstrate GaN-based double-layer electrode flip-chip light-emitting diodes (DLE-FCLED) with highly reflective indium-tin oxide (ITO)/distributed bragg reflector (DBR) p-type contact and via hole-based n-type contacts. Transparent thin ITO in combination with TiO2/SiO2 DBR is used for reflective p-type ohmic contact, resulting in a significant reduction in absorption of light by opaque metal electrodes. The finely distributed via hole-based n-type contacts are formed on the n-GaN layer by etching via holes through p-GaN and multiple quantum well (MQW) active layer, leading to reduced lateral current spreading length, and hence alleviated current crowding effect. The forward voltage of the DLE-FCLED is 0.31V lower than that of the top-emitting LED at 90mA. The light output power of DLE-FCLED is 15.7% and 80.8% higher than that of top-emitting LED at 90mA and 300mA, respectively. Compared to top- emitting LED, the external quantum efficiency (EQE) of DLE-FCLED is enhanced by 15.4% and 132% at 90mA and 300mA, respectively. The maximum light output power of the DLE-FCLED obtained at 195.6A/cm2 is 1.33 times larger than that of the top-emitting LED obtained at 93A/cm2. •Highly reflective ohmic contact to p-GaN is made by using ITO/DBR.•Via hole-based n-type contacts is made by forming blind vias etched to the n-GaN layer.•Current access to the n-GaN is provided by filling vias with metallic column electrodes.•P-type contact hole circles around n-type contact vias for enhancing current spreading.