Large-scale SiO₂ photonic crystal for high efficiency GaN LEDs by nanospherical-lens lithography

Wafer-scale SiO₂ photonic crystal (PhC) patterns (SiO₂ air-hole PhC, SiO₂-pillar PhC) on indium tin oxide (ITO) layer of GaN-based light-emitting diode (LED) are fabricated via novel nanospherical-lens lithography. Nanoscale polystyrene spheres are self-assembled into a hexagonal closed-packed monolayer array acting as convex lens for exposure using conventional lithography instrument. The light output power is enhanced by as great as 40.5% and 61% over those of as-grown LEDs, for SiO₂-hole PhC and SiO₂-pillar PhC LEDs, respectively. No degradation to LED electrical properties is found due to the fact that SiO₂ PhC structures are fabricated on ITO current spreading electrode. For SiO₂-pillar PhC LEDs, which have the largest light output power in all LEDs, no dry etching, which would introduce etching damage, was involved. Our method is demonstrated to be a simple, low cost, and high-yield technique for fabricating the PhC LEDs. Furthermore, the finite difference time domain simulation is also performed to further reveal the emission characteristics of LEDs with PhC structures.