Strong light extraction enhancement using TiO2 nanoparticles-based microcone arrays embossed on III-Nitride light emitting diodes

Colloidal TiO2 nanoparticles were used for embossing of composite microcone arrays on III-Nitride vertical-thin-film blue light emitting diodes (LEDs) as well as on silicon, glass, gallium arsenide, and gallium nitride surfaces. Ray tracing simulations were performed to optimize the design of microcones for light extraction and to explain the experimental results. An optical power enhancement of ∼2.08 was measured on III-Nitride blue LEDs embossed with a hexagonal array of TiO2 microcones of ∼1.35 μm in height and ∼2.6 μm in base width, without epoxy encapsulation. A voltage increase in ∼70 mV at an operating current density of ∼35 A/cm2 was measured for the embossed LEDs. The TiO2 microcone arrays were embossed on functioning LEDs, using low pressures (∼100 g/cm2) and temperatures ≤100 °C.