Enhanced light extraction of micro-pixelated LEDs by arc-shaped mesa sidewall

The micro-structuring of heterostructure layers is an efficient method to enhance the light extraction efficiency of light emitting diodes (LEDs). The light extraction efficiency of micro-pixelated LEDs emitting at 230 nm with arc-shaped mesa sidewalls has been studied by Monte-Carlo ray-tracing simulation and experimentally confirmed by processing LED chips with different pixel diameters. According to simulations, LEDs whose mesa sidewalls are arc-shaped and inclined by 40° show a higher light extraction efficiency than LEDs with a straight inclined mesa sidewall for both transverse-electric and -magnetic polarized light. Experimentally, an eightfold increase in the peak external quantum efficiency was observed for micro-pixelated LEDs with a pixel diameter of 1.5 μm and arc-shaped mesa sidewalls compared to reference LEDs without micro-pixels. With an arc-shaped mesa design, an external quantum efficiency of 1.8% and a wall plug efficiency of 1% were achieved for LEDs emitting at 230 nm.