Light Extraction in InGaN-based Light-emitting Diodes Integratedwith UV-curable Optical Adhesive Microlens Arrays of High RefractiveIndex and Packaged with Molding Epoxy

Abstract

We fabricated InGaN-based 460-nm light-emitting diodes (LEDs) integrated with microlens arrays made of UV-curable optical adhesive to achieve enhanced light output [Son et al., J. Korean Phys. Soc. 51, 377 (2007)]. This enhanced output due to the integrated microlens obtained from a chiplevel LED may not be present in commercial LEDs after packaging because the refractive index of the molding epoxy used in the packaging process is similar to that of the UV-curable optical adhesive. In this paper, we describe the integration of microlens arrays with InGaN LEDs by using an UV-curable optical adhesive with a relatively high refractive index and the packaging of those LEDs in molding epoxy with a normal refractive index. We observed a greater light output in the packaged LEDs with the microlenses than in the conventional packaged LEDs, thereby confirming that the enhancement effect of the integrated microlens was preserved in the final LED structure after packaging. We performed raytracing simulations on our LED structures to confirm that the numerical results support the experimental findings.