InGaN micro-LED technology: Recent progress in planar and nanowire architectures, fabrication challenges, and emerging surface passivation approaches

Micro light-emitting diodes (micro-LEDs) exhibit superior performance compared with organic LEDs and liquid-crystal displays in terms of brightness, color accuracy, pixel density, and endurance. Consequently, they play a pivotal role in enabling a diverse range of emerging applications, including virtual and augmented reality, ultra-high-resolution mobile displays, wearable electronics, biomedical sensors, and ultra-fast optical interconnects. The foremost challenge in achieving high-efficiency micro-LEDs is the significant reduction in device efficiency as the lateral dimensions shrink below a few micrometers, known as the efficiency cliff. This phenomenon poses a substantial hurdle to the widespread adoption of micro-LEDs. The primary factor contributing to decreased efficiency is the presence of plasma-induced defects generated during the etching process of conventional quantum well LEDs, which results in large nonradiative surface recombination and current leakage. Moreover, nitrogen-related donor compensation of defects in the p-GaN region, caused by plasma damage, can further increase device resistance. In this study, we present an overview of the fundamental obstacles in micro-LED fabrication and recent remedies, including surface passivation, dry etching methods, localized surface plasmon resonance, and alternative fabrication techniques. We also review recent progress in bottom–up nanostructure-based submicrometer LEDs, emphasizing their unique advantages, latest advancements, and significant future potential. This review advances understanding of sidewall effects in micro-LEDs and clarifies recent fabrication strategies for realizing highly efficient InGaN micro-LEDs.