High-resolution visualization of sidewall defects in gallium nitride micro light-emitting diode via multi-physical field luminescence imaging microscopy

Localization and characterization of defects are particularly critical for optimizing the performance of a gallium nitride (GaN) micro light-emitting diode (Micro LED). In this work, we develop a multi-physical field microscopic imaging system, which is capable of achieving high spatiotemporal resolution characterization in an individual GaN Micro LED. By integrating fluorescence imaging, fluorescence lifetime imaging microscopy, hyperspectral imaging, and time-correlated single-photon counting, our system enables real-time tracking of the evolution of defects under coupled optical, electrical, and thermal fields. Equipped with this system, we systematically analyze the spatial distribution and depth of defects introduced by inductively coupled plasma (ICP) etching. Two distinct regions are observed: a narrow fluorescence lifetime decrease zone (∼2 μm) near the chip edges and a broader fluorescence intensity decrease zone (∼5 μm). To explain this, we propose a physical model that describes the interplay between defect-induced non-radiative recombination and carrier diffusion. Furthermore, we demonstrate that wet etching effectively mitigates these ICP-induced damages, leading to enhanced brightness across a wide range of Micro LED sizes. Notably, this passivation process enables a 3 μm size blue Micro LED chip to achieve a peak external quantum efficiency of 27.6% with a current density of 33.7 A/cm2. These findings provide insights into the localized impact of plasma etching and highlight the potential of wet etching for enhanced performance in Micro LED.