Fabrication of high-efficiency LED using moth-eye structure

Abstract

To realize high-efficiency light-emitting diodes (LEDs), it is essential to increase light extraction efficiency. The moth-eye structure, consisting of periodic cones with a submicron-scale pitch on a surface/interface, is known to enhance the light extraction efficiency of light-emitting diodes. Previously, nitride-based flip-chip blue LEDs with the moth-eye structure on the backside of the substrate were demonstrated to exhibit high light extraction efficiency. In this report, face-up blue LEDs with a double moth-eye structure are described. One moth-eye structure was formed on the sapphire substrate and the other structure was formed on the ITO contact, where the pitch of the cones in both structures was 500 nm. The patterning of cones with such a small pitch was carried out by a low-energy electron-beam lithography technique. The output powers of mounted LEDs without resin encapsulation were measured using an integrated sphere. For reference, face-up LEDs without a moth-eye structure and with a single moth-eye structure on an ITO contact were also examined. The single moth-eye and double moth-eye LEDs have 1.2 and 1.4 times higher output power than the non-moth-eye LED, receptively.