Enhanced light-extraction from hierarchical surfaces consisting of p-GaN microdomes and SiO₂ nanorods for GaN-based light-emitting diodes

We report an efficient light-extraction scheme employing the hierarchical structure, p-GaN microdomes/SiO₂ nanorods (NRs), on GaN light-emitting diodes (LEDs). Compared with the flat LED, the LEDs with hierarchical surfaces exhibits a light-output improvement of 36.8%. The considerable enhancement in light-extraction efficiency is attributed to the multiple tilted surfaces of microdomes and the graded refractive indexes provided by the SiO₂ NRs, reducing total internal reflection and Fresnel reflection. The enhanced optical performances are supported by the finite-difference time-domain analysis. Advances in light extraction scheme employing hierarchical structures demonstrated here pave the way to solid-state lighting technology.