Enhancement of the Light-Extraction Efficiency of GaN-Based Light Emitting Diodes Using Graded-Refractive-Index Layer by SiO2 Nanosphere Lithography

Abstract

A benzocyclobutene (BCB)-based graded-refractive-index (GRIN) layer was deposited on gallium nitride (GaN)-based blue light-emitting diodes (LEDs) to enhance the light-extraction efficiency. The GRIN layer, which was composed of both a BCB thin film and a porous structure, was fabricated by nanospheres lithography using SiO2 nanospheres. The refractive index of the porous BCB layer was intentionally controlled to reduce the total internal reflection of GaN-based LEDs. The refractive indexes of the BCB layer and porous BCB layer were 1.58 and 1.2, respectively. Consequently, the photoluminescence intensity was enhanced 1.6 times after employing the GRIN BCB layer on the GaN layer, and the electroluminescence intensity at a 10 mA injection current was increased by 22% after employing the GRIN BCB layer on an indium tin oxide layer.