Impact of sidewall conditions on internal quantum efficiency and light extraction efficiency of micro-LEDs

Abstract The sidewall condition is a key factor determining the performance of micro-light emitting diodes (μLEDs). In this study, we prepared equilateral triangular III-nitride blue μLEDs with exclusively m-plane sidewall surfaces to confirm the impact of sidewall conditions. It was found that inductively coupled plasma-reactive ion etching (ICP-RIE) caused surface damages to the sidewall and resulted in rough surface morphology. As confirmed by time-resolved photoluminescence (TRPL) and X-ray photoemission spectroscopy (XPS), tetramethylammonium hydroxide (TMAH) eliminated the etching damage and flattened the sidewall surface. After ICP-RIE, 100 µm 2 -micro-LEDs (µLEDs) yielded higher external quantum efficiency (EQE) than 400 µm 2 -µLEDs. However, after TMAH treatment, the peak EQE of 400 µm 2 -µLEDs increased by around 10% in the low current regime, whereas that of 100 µm 2 -µLEDs slightly decreased by around 3%. The EQE of the 100 µm 2 -µLED decreased after TMAH treatment although the internal quantum efficiency (IQE) increased. Further, the IQE of the 100 µm 2 -µLEDs before and after TMAH treatment was insignificant at temperatures below 150 K, above which it became considerable. Based on PL, XPS, scanning transmission electron microscopy, and scanning electron microscopy results, mechanisms for the size dependence of the EQE of µLEDs are explained in terms of non-radiative recombination rate and light extraction.