Plasmonic Strategy for Highly Efficient Micro-LEDs with Nanometer-Scale Sidewall Spacing

The performance of InGaN/GaN microlight-emitting diodes (μLED) deteriorates rapidly as chip dimensions shrink to the few-micrometer regime, primarily due to fabrication-induced sidewall damage that introduces severe nonradiative recombination losses. Localized surface plasmon (LSP) coupling has emerged as a promising strategy to mitigate these losses. Here, we present a sidewall-integrated plasmonic μLED architecture in which the multiquantum wells (MQW)-nanoparticle distance is precisely controlled by scaling the dielectric spacer thickness down to the nanometer regime. By employing an ultrathin 5 nm Al2O3 spacer, strong near-field LSP coupling is achieved at the mesa sidewalls. As a result, 10 μm μLEDs exhibit a 24% enhancement in photoluminescence intensity and a 44% improvement in external quantum efficiency compared to the reference. Systematic analysis across a wide range of chip dimensions reveals that the contribution of sidewall-based LSP coupling becomes increasingly dominant as the perimeter-to-area (P/A) ratio increases, thereby compensating for surface-related losses. These findings establish precise spatial engineering as a definitive strategy for maximizing the potential of plasmonic enhancements in next-generation high-efficiency μLEDs.