Numerical Study on the Light Extraction Efficiency of a Size-Dependent GaN-Based Micro-LEDs

Micro-LEDs have shown great potential in display applications due to their advantages such as low power consumption, high efficiency, long lifetime and so on. However, the quantum efficiency is significantly influenced by the small total reflection angle between GaN and air, as well as the considerable light emission from the sidewall. In this paper, a systematic theoretical study on the light extraction of GaN-based flip-chip Micro-LEDs of varying dimensions and the designs of the surface dielectric films were investigated. The results demonstrate that as the chip size decreases, the light extraction efficiency (LEE) of chips gradually increases, while the surface emission ratio (S) decreases and the top surface light extraction efficiency (LSE) always maintains a relatively stable value. The far-field light intensity distribution of the chip indicates smaller chips suffer from more severe sidewall emission. Consequently, the surface dielectric films structure designs were introduced, which can achieve a transmittance of more than 99.5% within certain angles, and enhance the LSE of a 5µm chip by 22.5%. Our study provides theoretical support for optimizing the design of Micro-LED devices and reveals the potential of improving the light extraction performance of ultra-small Micro-LEDs.