Quantitative Analysis and Characterization of Sidewall Defects in InGaN-Based Blue Micro-LEDs

Inorganic micro-light-emitting diodes (mu LEDs) have emerged as promising candidates to fulfill the demand for high-performance display technologies like immersive virtual or augmented displays. However, reducing mu LED size for increasing pixel density results in poor external quantum efficiency (EQE), caused by the pronounced impact of defects-mediated Shockley-Read-Hall (SRH) nonradiative recombination at the etched sidewalls. Distinguishing the SRH coefficient, denoted as A coefficient, and the associated energy trap levels specific to the defects on the etched sidewalls from those in the bulk can be very advantageous to identify the origin of the defects responsible for the size-dependent EQE degradation. This, in turn, facilitates the development of appropriate strategies for high performance mu LED-based displays. In this study, the effect of etched sidewall on the EQE of blue mu LEDs is distinguished from that of bulk by investigating size- and temperature-dependent EQE values versus current density. The energy trap levels of both bulk and sidewall defects, as well as the minority carrier lifetime (tau 0) associated with each defect, were estimated through temperature-dependent characterization of the A coefficient in mu LEDs. The tau 0 values associated with sidewall defects are approximately 12 times shorter than those for bulk defects, indicating that the SRH recombination process predominantly occurs at the sidewall rather than bulk in mu LEDs. This quantitative analysis elucidates the significance of sidewall defect mitigation strategies in advancing high-resolution mu LED display technologies.