GaN-Based LEDs with High Emission Directionality Using Photonic Crystal Structures for Sidewall Reflection and Light Extraction

Abstract

GaN-based light emitting diodes with photonic crystal at the light emitting mesa and nano-hole at the periphery of the mesa using the same photonic crystal pattern are designed and fabricated. Optical properties such as luminescence-current characteristics, radiation profiles and angular spectra of the three kinds of devices (planar, photonic crystal on mesa surface, photonic crystal on mesa surface and sidewall nano-hole arrays) are considered. We demonstrate that the output power enhancement is primarily due to the photonic crystal but the effect on radiation profile is nearly omnidirectional. On the other hand, the sidewall nano-hole array contributes to the optical intensity at the surface normal direction by redirect the lateral emission of the device. By proper design of the photonic crystal pattern, high directionality and high extraction LEDs can be achieved.