Increased Light Extraction From Vertical GaN Light-Emitting Diodes With Ordered, Cone-Shaped Deep-Pillar Nanostructures

In this paper, improved light extraction using cone-shaped deep-pillar nanostructures is demonstrated on the Honeycomb-type vertical GaN light-emitting diodes (VLEDs). In order to produce ordered, cone-shaped deep-pillar patterns on the surface of an n-type GaN, double-layered polystyrene (PS) nanospheres of 500-nm size were coated onto the n-GaN layer by a simple spin-coating. Then, immediately after the O-2 plasma ashing for double-layered PS beads, the Ni metal was deposited and lifted off to form a hard mask for deep pillar etching. Then, the three VLEDs - the reference VLED with no patterns and the two VLEDs with ordered, cone-shaped pillar patterns of 1.0 and 1.5 mu m depth on the n-type GaN surface - were prepared for comparison. As a result, the output power for the proposed VLEDs with 1.0- and 1.5-mu m-deep cone-shaped patterns has been increased by 200% and 214%, respectively, at 350 mA as compared to the reference VLED. There was a slight sacrifice of operational voltage and leakage current. The improved optical properties are attributed to the multiple scattering of light from the sidewall of the cone-shaped patterns and the increased surface dimension.