Role of surface microstructure and shape on light extraction efficiency enhancement of GaN micro-LEDs: A numerical simulation study

•Trapezoidal chip, surface grating and coarsening can all increase the light extraction of micro-LEDs.•At 12 degree, the micro-LED light extraction efficiency can be as high as 64.5%.•The extraction efficiency is 72% and 56% for optimized surface grating and coarsening, respectively. One of the bottlenecks for today’s micro-light-emitting-diodes (micro-LEDs) is the low light extraction efficiency. How to effectively boost this efficiency is especially important for micro-LEDs because their surface-to-volume ratio is much larger than normal LEDs. The trapezoidal chip structure, surface grating, and surface coarsening are simulated in this paper, with the aim to obtain their contributions to enhance the light extraction efficiency. Through the simulation, we have found that all of the three methods can increase the light extraction, but with different extents. When the trapezoidal angle of the mesa is 12°, the extraction efficiency reaches its maximum (by this method) of 64.5%. If the surface grating on n-GaN (the light output surface) has a period of 300 nm, a height of 147 nm and width of 243 nm, the light extraction efficiency can be as high as 72%, which is much higher than that of the micro-LED without any grating. For the random roughening of n-GaN, a maximum value of 56% can be obtained if the roughness extent is optimized. Our results are of reference value for scientists and engineers working in micro-LEDs and can serve as guidelines for GaN based high efficiency micro-LED design for future displays.