Stress-induced efficiency degradation mechanism of InGaN-based red micro-LEDs depending on their size

This study systematically investigates the influence of forward current-induced stress on the optoelectronic performance of InGaN/GaN-based red micro light-emitting diodes with pixel sizes of 20 × 20 and 40 × 40 μm2. A constant forward current density of 3 A/cm2 was applied for 420 min. After aging, the 20-μm device exhibits a pronounced reduction in external quantum efficiency (EQE) by 43.2%, whereas the 40-μm device showed only a 16.5% decrease. Micro-photoluminescence mapping reveals that point defect formation near the mesa sidewalls is more prominent in the smaller device. Moreover, the degradation of peak emission intensity was more severe near the sidewall than in the center region after aging, which is more significant in the 20-μm device. This degradation is attributed to carrier tunneling through defect states generated during prolonged operation. Consequently, the pronounced EQE degradation observed in smaller devices is primarily ascribed to defect-assisted carrier tunneling. Additionally, this study elucidates the origin of the shorter peak emission wavelength observed near the mesa sidewall compared to that at the center region, which arises from strain relaxation.