Elimination of total internal reflection in GaInN light-emitting diodes by graded-refractive-index micropillars

A method for enhancing the light-extraction efficiency of GaInN light-emitting diodes (LEDs) by complete elimination of total internal reflection is reported. Analytical calculations show that GaInN LEDs with multilayer graded-refractive-index pillars, in which the thickness and refractive index of each layer are optimized, have no total internal reflection. This results in a remarkable improvement in light-extraction efficiency. GaInN LEDs with five-layer graded-refractive-index pillars, fabricated by cosputtering $TiO2$ and $SiO2$⁠, show a light-output power enhanced by 73% and a strong side emission, consistent with analytical calculations and ray-tracing simulations.