Microstructure characterization and sidewall treatment of GaN/InGaN micro-light-emitting diodes

Microdisplays based on an array of micro-sized GaN-based light emitting diodes (μLEDs) are very promising for high brightness applications. As the size of Micro-LED decreases, the sidewall damage caused by plasma etching becomes an important factor in reducing the luminescence efficiency. Here, the photoluminescence, scanning electron microscope (SEM) and high‑resolution transmission electron microscopy (HR‑TEM) were combined to reveal physical defects on the sidewall surface, such as plasma-induced lattice disorder, the enrichment of impurity atoms such as oxygen, and the destruction of the exposed part of the quantum well during etching. The structure of the 20 um mesa after inductively coupled plasma (ICP) dry etching was characterized optically, and the luminescence intensity begins to decrease gradually at 5 um from the sidewall, which was caused by the surface non-radiative recombination. Finally, through the combination of tetramethylammonium hydroxide (TMAH) treatment and SiO2 passivation, the sidewall passivation process is optimized, and the luminous efficiency of Micro-LED edge is effectively improved 4.5 times. These results have reference significance for reducing sidewall defects to improve Micro-LEDs luminescence efficiency in the future.