Mitigating Polarization Field and Enhancing Carrier Overlap in Relaxed AlGaN Quantum Wells for >12% Efficient UVB LEDs

Achieving high external quantum efficiency (EQE) in AlGaN-based ultraviolet-B (UVB) light-emitting diodes (LEDs) remains a persistent challenge due to strong polarization-induced electric fields and poor electron–hole wave function overlap in strained quantum wells. Here, we report a decisive enhancement in carrier dynamics and optical efficiency by precisely engineering the QW thickness in a 40% relaxed AlGaN-based UVB LED grown on sapphire. Structural analyses confirm that controlled strain relaxation in the AlGaN quantum well effectively suppresses polarization fields, while compositional grading and optimized quantum-well thickness significantly improve carrier confinement and overlap. Systematic optimization of QW width mitigates the quantum-confined Stark effect, reducing the internal electric field from −0.97 to −0.32 MV cm –1, thereby strengthening the electron–hole wave function overlap via a 7 nm thick QW and enhancing radiative recombination. A moderately Mg-doped p-type multiquantum-barrier electron-blocking layer and a partially relaxed n-type AlGaN electron injection layer further improve carrier confinement and injection efficiency. These combined effects yield an internal quantum efficiency of 80% and a predicted high external quantum efficiency exceeding 12%, nearly doubling that of conventional devices. This study establishes QW thickness modulation and polarization field management as practical and scalable strategies to overcome intrinsic polarization effects, enabling high-efficiency, mercury-free UVB emitters for next-generation disinfection, water purification, and smart-agriculture applications.