Suppressed efficiency droop and size effect in InGaN micro-LEDs via engineered carrier confinement using Al-composition stepwise quantum barriers.

With the growing demand for micro-light-emitting diodes (micro-LEDs) operating at high current densities, efficiency droop has become a major challenge for conventional GaN-based devices fabricated on c-plane sapphire substrates. Here, InGaN-based blue micro-LEDs incorporating Al-composition stepwise quantum barriers (QBs) were designed and fabricated. Simulations show that the stepwise QBs effectively enhance carrier confinement in the quantum wells by increasing the effective potential barrier height. Subsequent experimentally fabricated micro-LEDs with stepwise QBs exhibit significantly improved emission performance, with an external quantum efficiency (EQE) 1.2 times higher than that of conventional devices even at a high current density of 1000 A cm-2. Simultaneously, the improved radiative recombination also reduces size sensitivity, leading to smaller efficiency droop as the device size decreases from 60 to 30 μm. These results provide a promising strategy for high-efficiency micro-LEDs with suppressed efficiency droop and size effect under high-current operation.