Design, fabrication, and effect of polymeric passivation layers to suppress sidewall recombination in high efficiency GaN µLEDs

GaN-based micro light-emitting diodes (µLEDs) are promising for next-generation display and solid-state lighting applications, including micro-displays, optical communication, and sensing. Performance is limited by non-radiative recombination (NRR) from both bulk and surface defect states. This work introduces the critical diameter (𝑑crit), a proposed parameter to distinguish these effects, evaluate performance limits, and guide design improvements for a specific fabrication platform. 𝑑crit defines the µLED size at which surface and bulk recombination contribute equally to the total NRR. Using this framework, 6 µm InGaN µLEDs with treated sidewalls and polymeric passivation were fabricated, achieving a mean peak wall-plug efficiency of 20.3% at 2.5 A/cm2 and an optical power density of 1.4 W/cm2. The devices exhibited a surface recombination velocity below 10 cm/s—among the lowest reported—and a 𝑑crit < 0.1 µm. By suppressing surface losses, this approach enables the exploration and utilization of size-depend