9:30 AM - 9:45 AM
▼ [17a-A303-1] The importance of sidewall conditions on the performance of micro-LEDs
Keywords:micro-LEDs, Sidewall conditions, EQE
In this study, we shed light on the sidewall conditions of micro-light-emitting diodes (μLEDs) change both internal quantum efficiency (IQE) and light extraction efficiency (LEE), which are the production of external quantum efficiency (EQE). To reveal the effect of sidewall condition, an equilateral triangle μLEDs with m-planar sidewalls on the scales of 100 μm2 and 400 μm2 were intentionally designed. ITO was used as a p electrode and mesa size were identically etched using ICP-RIE. After ICP-RIE, we eliminated the sidewall damage using tetramethylammonium hydroxide (TMAH) that etches non-polar III-nitride surface as shown in Fig. 1. Subsequently, n electrode (CrAu) was deposited. To form the p electrode, the samples were covered by SiO2 layer using plasma enhanced chemical vapor deposition. Then, via hole was formed by an RIE. Finally, AlNiAu p electrode was deposited. The Al layer served as a reflection layer to lead the light moves to downward. Fig. 2 shows the size and TMAH dependent relative EQE. For 400 μm2 μLEDs, It was shown that for 400 μm2 μLEDs, TMAH effectively enhanced EQE by around 10% in low current operation, whereas for 100 μm2 μLEDs, EQE was slightly reduced by around 3%. Although TMAH could remove the sidewall damage induced by ICP-RIE, the sidewall morphology simultaneously changed, resulting in decreasing LEE. Interestingly, at a high current regime (Inset of Fig. 2), EQE of 400 μm2 μLEDs decreased after TMAH. This different behavior at the low and high current regime indicates that TMAH affects both IQE and LEE. For detail, we will discuss through photoluminescence, X-ray photoemission spectroscopy, and transmission electron microscopy.