Design of high-voltage deep ultraviolet LED sub-mesas toward improved optoelectronic performance

Here, we systematically investigate the effect of mesa/sub-mesa sidewall engineering on single-junction (SJ) and high-voltage (HV) deep ultraviolet light-emitting diodes (DUV LEDs). The configuration of ∼46° inclined angle of the mesa/sub-mesa sidewall and Al reflector optimally promotes light extraction of SJ/HV DUV LEDs. We further observe substantial improvements in the self-heating and external quantum efficiency (EQE) droop effects of HV DUV LEDs with an increasing number of sub-mesas. Specifically, the EQE droops are 27.6% and 34.6% for HV DUV LEDs with two and four sub-mesas, respectively, at an input power of 6.4 W. These values are markedly lower than the 51.6% droop observed in the SJ DUV LEDs, which is partly attributed to the superior heat dissipation and light extraction facilitated by a high perimeter-to-area ratio of the sub-mesas. This investigation sheds light on mesa design-related efficiency droop behaviors and contributes to enhancing the optoelectronic performance of AlGaN-based DUV LEDs.