Quantitative Evaluation of Carrier Dynamics in Blue Micro-LEDs: The Impact of Size and Current Density on Recombination and Injection Efficiency

In this work, we fabricated blue micro-LEDs of five different sizes to investigate the size-dependent carrier dynamics. To make the results more precise, micro-LEDs with integrated sensors were used to measure the real-time junction temperature and exclude the interference of temperature on the carrier dynamics. Utilizing the ABC model and the surface recombination model, we successfully calculated the surface recombination rates for devices of five sizes as well as the coefficients for bulk-SRH recombination, radiation recombination, and Auger recombination. We employed the calculated surface recombination rates to extrapolate the peak internal quantum efficiency (IQE) and the corresponding current densities across a range of device sizes. The calculation results show that as the device size decreases from 500 to 8 μm, peak IQE drops from 86.7 to 63.9%. This approach establishes a valuable method for assessing the recombination coefficients of micro-LEDs of different sizes and predicting their efficiency performance under various currents. This capability provides substantial guidance for optimizing micro-LEDs tailored to specific application scenarios. We also calculated the electron injection efficiency (ηEIE) under varying current densities from the experimental and fitted values. It can be found that under high current density, the ηEIE decays more severely as the device size decreases. We propose that this is because there are relatively more defects in the sidewalls of the electronic blocking layer and quantum barriers for smaller micro-LED, resulting in relatively more defected-aided electron leakage and a decrease in ηEIE.