Mitigating sidewall damage effects in GaN-based multi-quantum-well micro-LEDs prepared by top-down fabrication

Abstract This review examines sidewall damage effects in GaN-based micro-and nano-Light Emitting Diodes (μLEDs/nLEDs) fabricated via topdown Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE). We analyze the structural and electronic properties of etched surfaces, damage mitigation strategies through process optimization and post-etch treatments, and evaluate models explaining performance degradation as device dimensions decrease. Blue InGaN/GaN μLEDs exhibit severe efficiency degradation below ~20 μm diameter (the «efficiency cliff»), while green and red devices show greater resilience. We attribute this behavior to differences in surface recombination velocity, carrier diffusion length, and localization effects. Surface treatments including TMAH etching, (NH4)2S passivation, hydrogen plasma treatment, and atomic layer deposited dielectrics significantly mitigate damage. Deep-level transient spectroscopy reveals nitrogen interstitial (Ni) acceptors near EC-1 eV and gallium vacancy (VGa) complexes near EV+0.8 eV as dominant recombination centers. The damaged region extends 0.5-1 μm from sidewalls-significantly beyond the structurally damaged zone (~40-100 nm). Emerging approaches including neutral beam etching and localized surface plasmon coupling show promise for achieving high efficiency in sub-5 μm devices required for advanced display applications.