Light Extraction Efficiency of GaN-based LEDs with Non-periodic and Periodic Sub-wavelength Structures

Antireflective non-periodic and periodic sub-wavelength structures (SWSs) are fabricated on indium tin oxide (ITO) layers deposited on p-GaN layers of GaN-based green light-emitting diodes (LEDs). The light output powers of the LEDs using non-periodic and periodic SWSs are increased by 18% and 39% at a 20-mA input current, respectively, compared to LEDs with flat ITO layers. Periodic ITO SWSs show a larger enhancement of output power because they have more effective profiles of the graded refractive index. The output power of periodic SWS LEDs is improved in all angular directions, indicating that the improved output power is attributed to lower total internal reflection and lower Fresnel reflection.