Improved light extraction efficiency in III-nitride photonic crystal light-emitting diodes

We observed a significant enhancement in light output from GaN-based light-emitting diodes (LEDs) in which two-dimensional photonic crystal (PC) patterns were integrated. We approached two types PC-LEDs. One is top loaded PC LEDs. The PC patterns were generated on the top p-GaN layer. The other is bottom loaded PC LEDs. In this LEDs, PC patterns were integrated on the sapphire substrate. Two-dimensional square-lattice air-hole array patterns, whose period was varied between 300 and 700nm, were generated by laser holography. Unlike the commonly utilized electron-beam lithographic technique, the holographic method can make patterns over a large area with high throughput. The resultant PC-LED devices with a pattern period of ∼500nm had more than double the output power. The experimental observations are qualitatively consistent with three-dimensional finite-difference-time-domain simulation results.