LEE enhancement in AlGaN UVC LED using photonic crystal reflector fabricated on p-GaN contact layer (Conference Presentation)

Abstract

AlGaN UV-C light-emitting diodes (LEDs) are attracting a great deal of attentions for applications of sterilization, water purification, in the medical fields, and so on. The increase in wall-plug efficiency (WPE) is a recent main subject for an AlGaN UVC-LED. The main cause for reducing WPE is a significant reduction in light-extraction efficiency (LEE) owing to a heavy light absorption by p-GaN contact layer. If we introduce transparent p-AlGaN contact layer for increasing LEE, the contact resistance is increased, resulting in the significant increase of operating voltage. In order to achieve both of low contact resistance and high-reflectivity in a p-contact layer, we introduced a photonic crystal (PhC) reflector on a p-contact layer. We predicted by a simulation analysis that an LEE of UVC-LED can be increased by 2.8 times by introducing a PhC reflector on p-GaN contact layer. Previously, we fabricated a 283nm AlGaN DUV-LED with PhC reflector on a p-AlGaN transparent contact layer, and obtained an increase of external quantum efficiency (EQE) from 8 to 10 % by introducing PhC reflector. However, the contact resistance was increased. In this work, we fabricated a 273nm AlGaN UVC-LED with PhC reflector on p-GaN contact layer. The EQE was increased by about 1.7 times by introducing PhC reflector. The operating voltage was not changed even when introducing PhC and remained low value. We confirmed that it is possible to realize high WPE by introducing PhC reflector on the p-GaN contact layer of UVC-LED.