Converging omni-directional reflector boosted wall-plug efficiency and light output power of sub-250 nm deep-ultraviolet LEDs

Extremely low light extraction efficiency (LEE) remains a major bottleneck limiting the wall-plug efficiency (WPE) of AlGaN-based deep-ultraviolet (DUV) light-emitting diodes (LEDs). This challenge is particularly pronounced for devices with wavelengths below 250 nm, where strong transverse magnetic (TM) mode emission drives a large fraction of photons to propagate laterally and thus, impedes the light extraction. Here, we demonstrate, to our knowledge, a novel device architecture that combines a distributed array of emitting units with a converging omnidirectional reflector (ODR) to realize efficient LEE in sub-250 nm flip-chip DUV LEDs. This architecture features an ultrathin p-GaN contact layer and an ITO current-spreading layer, which allow the intentionally designed resonant reflective cavity on the p-side to be fully utilized for enhanced axial light output. Simultaneously, a sidewall reflective coating applied on the miniaturized emitting units further facilitates the forward convergence of laterally propagating photons. These combined measures finally achieve comprehensive photon management and result in high LEE for the device. Through optimization of the distributed emitting-unit dimensions, the device attains a WPE of up to 1.67% and a peak light output power of 83.2 mW. Benefiting from the improved LEE, the realized WPE represents a record value within this wavelength range, underscoring the strong application potential of both the proposed chip architecture and the implemented photon-management strategy.