Numerical Study on the Light Extraction Efficiency and Angular Energy Distribution of Micro-LEDs

Micro light emitting diodes (Micro-LEDs) possess advantages of high optical efficiency, high resolution and long lifetime, leading to a very broad application prospect in the future. This study uses Monte Carlo ray tracing method to study the variation of the luminescence characteristics of light emitting diode (LED) chips including horizontal electrode chip, flip chip, and vertical electrode chip while the size of LED chip decreases from conventional high-power LED size to micrometer size LED. As the size of LED chip gets smaller, the luminescence characteristics will be significantly affected. The changes of the chip’s luminescence characteristics are simulated as a function of dam’s angle or reflectivity. Through simulations, it is found that when the size decreases from 1000 to 20 $\mu$m, the light extraction efficiency (LEE) of the three structures has reached more than 200% of the conventional LED chips, while the side emission ratio (SER) has increased by more than 50%. The simulation also reveals that for Micro-LED with flip electrode structure, adding the dam brings the following changes: the LEE increases as the rise of reflectivity of the dam. The half-peak width of the angular energy distribution curve decreases firstly and then increases with the increase of the dam’s angle. The dam’s angle of 30° can not only optimize the angular energy distribution curve, but also have a higher LEE. The results of this numerical study have an important significance for optical design and future application of Micro-LEDs.