Improvement in extraction efficiency of GaN-based light-emitting diodes with textured surface layer by natural lithography

In this study, p-side-up GaN-based light-emitting diodes (LEDs) with textured indium-tin oxide (ITO) or silicon dioxide (SiO₂) surface layers were investigated by natural lithography using polystyrene spheres (PSs) as an etching mask. It was found that the ITO top layer provides better roughness than SiO₂. Under the optimum surface treatment parameter, the roughnesses of textured ITO and SiO₂ surface layers are 140 nm and 15 nm, respectively. The diameter of PSs in the textured ITO surface is still maintained at about 250-300 nm. Correspondingly, the size of PSs in the SiO₂ surface is reduced to about 100 nm. The output powers of LEDs with textured ITO and SiO₂ surfaces and conventional LEDs are 10.9, 9.5, and 8.5 mW at 20 mA, respectively. LEDs fabricated using the textured ITO surface produced an output power that exceeded that of planar-surface LEDs by about 28% at 20mA dc current. (c)2005 The Japan Society of Applied Physics.