Etching p-GaN to manage current spreading to reduce surface recombination in AlGaN micro-LEDs

Due to the high perimeter-to-area ratio of AlGaN-based deep ultraviolet (DUV) micro-light-emitting diodes (micro-LEDs), the current can easily spread to the mesa sidewall with etching damage, leading to more carriers participating in surface non-radiative recombination, thereby reducing the internal quantum efficiency (IQE). The double-mesa DUV LED was proposed to mitigate surface non-radiative recombination. This approach can mitigate the horizontal spreading of the current, thereby reducing the concentration of electrons and holes reaching the sidewall of the active region. Consequently, the surface non-radiative recombination at the sidewall was significantly reduced. By numerically simulating three different double-mesa structures, it was found that micro-LED with a double-mesa spacing of 3 µm and an etching depth of p-type layer thickness had a higher peak IQE, which was improved by 35.7% compared with the conventional structure. The experimental results showed that the LEDs with a double-mesa structure exhibited lower leakage current and higher EL intensity compared with the conventional structure, which was in good agreement with the simulation results. More importantly, the fabrication process of the double-mesa structure is simple and repeatable, which is an effective means to further improve the IQE of micro-LEDs in the future.