Efficiency improvement and droop behavior in nanospherical-lens lithographically patterned bottom and top photonic crystal InGaN/GaN light-emitting diodes.

Large-scale SiO2 nanodisk arrays fabricated by nanospherical-lens lithography are embedded in the n-GaN and p-GaN layer of an InGaN/GaN light-emitting diode (LED) to produce photonic crystal (PC) structures for efficiency improvement. Following the obvious reduction of view angle, the light output power of bottom, top, and double PC LEDs is enhanced by 74.5%, 60.1%, and 88.2% compared to that of a conventional LED at 350 mA current, respectively. Despite the enhanced external quantum efficiency due to improved crystalline quality and light extraction, these PC LEDs exhibit lower peak efficiency current density and more serious efficiency droop than conventional LEDs. Combined with the rate equation, the droop mechanisms of PC LEDs have also been investigated experimentally and by simulation.