Study of Far-Field Electroluminescence Emission to Enhance Micro-LED Performance

Abstract

This study investigates the angular dependence of far-field electroluminescence (EL) emission in InGaN/GaN LEDs and micro-LEDs to enhance their performance for micro-display and visible optical communication applications. We developed a measurement setup to analyze far-field EL emission across various wavelengths and compared the results with 1D optical simulations. This approach allowed us to observe the well-known dependence of emission directivity and light extraction efficiency (LEE) on the structural parameters of flip-chip LEDs, particularly the thicknesses of p-GaN and n-GaN layers, and to quantify the impact of total thickness variation resulting from wafer thinning processes. Using larger LEDs, the test vehicle offers a valuable tool for designing micro-LEDs with the desired directivity and for process monitoring. We also observed that the angular dependence of far-field emission varies with the applied bias and demonstrated how this could affect wafer-level micro-LED characterizations. Finally, we showed that the far-field EL emission of micro-LEDs progressively deviates from the description by a 1D optical cavity alone, suggesting an increasing influence of the limited size and necessitating 3D-FDTD simulations to accurately model both vertical cavity and sidewall effects. However, for sizes down to 5 μm, the directivity predicted by a 1D model seems roughly preserved.