Progress and Outlook of 10% Efficient AlGaN-Based (290-310 nm) Band UVB LEDs

Eco-friendly and low-cost aluminum gallium nitride (AlGaN) for the epitaxial growth of ultraviolet-B (UVB) light-emitting diodes (LEDs) on c-Sapphire has the possibility of high external-quantum efficiency (EQE). In this review paper a special growth techniques for 50% relaxed and 4 mu m thick AlGaN buffer layer underneath the multi-quantum wells (MQWs) are challenged to achieve a maximum internal-quantum efficiency of 50-57% in 310-290 nm band UVB LEDs. The influence of a thin "Valley" layer in p-type multi-quantum barrier electron-blocking layer on 2D hole generation and injection via intraband tunneling was attempted. Finally, the influence of soft polarized Mg-doped p-type Al-graded AlGaN hole injection layer assisted by excimer laser annealing for better hole injection toward the MQWs was investigated and quite high hole concentration of 2 x 1016 cm-3 and resistivity of 24 omega-cm at room temperature was achieved. Consequently, the EQE of transparent 310 and 304 nm UVB LEDs, respectively, reached to a confirmed world record values of approximate to 5% and approximate to 10% with light powers of 29 and 40 mW on wafer. This EQE value can surpass 21% if flip-chip, nanoPSS, photonic crystal, and lens with highly reflective p-electrodes are incorporated in LED. Herein, our 10% Efficient semiconducting Ga-polar aluminum gallium nitride (AlGaN)-based ultraviolet-B (UVB) light-emitting diodes (LEDs) grown on c-Sapphire at 304 nm emission were reviewed. Finally, it became possible by our special growth techniques of making 50% relaxed n-type AlGaN electron injection layer (EIL) and introducing soft polarized effect in Al-graded p-type AlGaN hole injection layer (HIL) as well as using reflective p-electrodes.image (c) 2024 WILEY-VCH GmbH