Light extraction enhancement of light-emitting diodes by nanopillar hierarchical structures

Patterning of p-GaN and/or indium-tin-oxide (ITO) surfaces is investigated to improve light extraction efficiency for GaN-based light-emitting diodes (LEDs). A nanopillar-patterned p-GaN layer, a nanopillar-patterned ITO contact layer, and dual nanopillar-patterned p-GaN and ITO layers are fabricated. When compared with conventional LEDs, LEDs with the nanopillar-patterned p-GaN, nanopillar-patterned ITO, and dual nanopillar-patterned p-GaN and ITO layers showed light output enhancement by 50%, 90%, and 120%, respectively. The light extraction enhancement mechanism of these nanopillar-patterned nanostructures is investigated via the 3D finite-difference time-domain method. The results show that the LED with the dual nanopillar-patterned p-GaN and ITO layers offers the best light extraction efficiency, which could stimulate further efforts to increase the escape light cone effectively and overcome total internal reflection. This methodology for synchronous nanopatterning of two light-emitting interfaces is believed to provide a major light extraction enhancement.