Efficiency improvement of GaN-based LEDs with ITO texturing window layers using natural lithography

In conventional GaN light-emitting diodes (LEDs), a significant gap exists between the internal and external efficiencies owing to the narrow escape cone for light in high refractive index semiconductors. In this paper, p-side-up GaN/sapphire LEDs with surface-textured indium-tin-oxide (ITO) window layers were investigated using natural lithography with polystyrene spheres as the etching mask. Under optimum etching conditions, the surface roughness of the ITO film can reach 140 nm, while the polystyrene sphere on the textured ITO surface is maintained at about 250-300 nm in diameter. The LEDs fabricated using the surface-textured ITO provided an output power that exceeded that of the planar-surface LED by about 30% and 40% at 20 and 400 mA current injection, respectively. After calculating, the extraction quantum efficiency of ITO/GaN LEDs with and without textured surface is 22.6% and 17.4%, respectively. There is about 5.3% improvement in the extraction quantum efficiency.