Comparison of light extraction efficiency between InGaN and AlGaInP red micro-LED structures using numerical simulations

For red micro-light-emitting diode (micro-LED) structures, InGaN or AlGaInP is typically used as the active material, and these materials exhibit markedly different size-dependent external quantum efficiency (EQE) behaviors. While previous analyses of InGaN and AlGaInP micro-LEDs have mainly focused on internal quantum efficiency, the influence of light extraction efficiency (LEE) on size-dependent EQE has been relatively unexplored. In this study, we numerically investigated the LEE characteristics of InGaN and AlGaInP micro-LED structures using finite-difference time-domain simulations. We compared the LEE characteristics of InGaN and AlGaInP micro-LEDs by systematically varying structural parameters, such as the distance from the quantum well to the Ag reflector, the side length, and the height of the micro-LED structures. In planar geometry, the LEE of InGaN LEDs can be up to twice that of AlGaInP LEDs due to their large refractive index contrast. However, in micro-LED structures, the LEE ratio of InGaN to AlGaInP was found to decrease significantly as the side length decreased, especially in the epoxy-encapsulated structure. For a side length of 2 μm with epoxy encapsulation, the total-emission LEE of InGaN micro-LEDs was only about 20% higher than that of AlGaInP micro-LEDs. The substantial size-dependent LEE variations between InGaN and AlGaInP micro-LEDs highlight the importance of considering LEE differences when comparing the EQE characteristics of red micro-LEDs based on these materials.