Droop and light extraction of InGaN-based red micro-light-emitting diodes

In this letter, we investigate the impact of periphery, width, length and area on the external quantum efficiency (EQE) of stripe-type InGaN-based red micro-light-emitting diodes (mu LEDs). A longer periphery resulted in a higher light extraction efficiency ( eta e ) via the sidewall regardless of the area of the mu LEDs. However, as the injection current increased a somewhat larger efficiency droop was observed at the longer periphery due to current crowding. Additionally, larger mu LEDs experienced more self-heating than smaller ones, resulting in a red shift of wavelengths and a larger efficiency droop. When the current density exceeded 100 A cm-2, the EQE ratio of smaller-area mu LEDs to larger-area ones increased significantly due to the difference in efficiency droop. Besides, a short light propagation length and a long emission width yielded a higher eta e . Hence, the periphery, width, length and area of the mu LEDs determine EQE, which provides insight into the pixel design of mu LED displays.