Enhanced light extraction efficiency via double-mesa structure for 273 nm and 244 nm AlGaN-based deep ultraviolet light-emitting diodes

• A double-mesa-structured AlGaN-based DUV LED is proposed, with a second inclined sidewall by etching n-AlGaN and AlN layers. • The double mesa design introduces extra reflection paths, enhancing the extraction of photons in the n-AlGaN and AlN layers. • For 273 nm AlGaN-based DUV LEDs, the double-mesa structure improves EQE and WPE by 12.69 % and 11.79 %, respectively. • For 244 nm AlGaN-based DUV LEDs, the double-mesa structure improves EQE and WPE by 17.68 % and 12.80 %, respectively. This study proposes a double mesa sidewall reflector structure to optimize the light extraction efficiency (LEE) of AlGaN-based deep ultraviolet (DUV) light-emitting diodes (LEDs). Traditional sidewall reflector designs rely on a single mesa etched down to the n-AlGaN layer. However, a considerable portion of emission from the active region fails to be efficiently reflected, leaving photons remain trapped within the n-AlGaN and AlN layers beneath the mesa. To address this issue, we further etch the n-AlGaN and AlN layers between and outside the interdigitated mesas, creating a second mesa with inclined sidewalls. The sidewall reflection from this second mesa effectively extracts the previously confined light, thereby enhancing the device performance. Here, double mesa AlGaN-based DUV LEDs are fabricated and characterized at two distinct wavelengths of 273 nm and 244 nm. For the 273 nm LED with dominant transverse electric (TE) −polarized emission, enhancements in external quantum efficiency (EQE) and wall-plug efficiency (WPE) of approximately 12.69 % and 11.79 % are achieved, respectively. Meanwhile, the 244 nm LED with dominant transverse magnetic (TM) −polarized emission exhibits even greater EQE and WPE improvements of 17.68 % and 12.80 %, respectively. The proposed double mesa sidewall architecture offers a practical and effective way for optimizing sidewall reflectors — particularly when implemented with interdigitated electrodes — and provides valuable insight into enhancing the LEE of AlGaN-based DUV LEDs.