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

Wafer-scale SiO2photonic crystal(PhC)patterns(SiO2air-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 SiO2PhC 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.