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.
The efficiency of a conventional light emitting diode (LED) is limited by coupling of light into guided modes in the structure. Several methods to increase the extraction efficiency of nitride based LEDs are studied from the perspective of the patterned structures in LEDs. The patterned structures are made in the interface between a semiconductor and a sapphire substrate and on the surface of a semiconductor or an indium tin oxide electrode. All of these approaches show an increased light output compared to that of reference samples, which means these kinds of scattering sources are inevitable to make a highly efficient light emitter in nitride-based semiconductor system.