Over 50% carrier injection efficiency in AlGaN-based UV-B laser diodes enabled by combining Al-content-drop design and low-temperature epitaxy

We demonstrate a significant improvement in carrier injection efficiency (ηi) in AlGaN-based UV-B laser diodes (LDs) through a combined approach of the Al-content-drop design and low-temperature epitaxy, both introduced to preserve the electron-blocking barrier and suppress Al–Ga interdiffusion at heterointerfaces. Four devices fabricated with different quantum well AlN molar fractions (0.23–0.35) showed lasing at 297–319 nm with ηi ranging from 42% to 52%, representing a more than threefold improvement over previously reported polarization-doped UV LDs. A peak optical power of 570 mW and a wall-plug efficiency of 2.9% were achieved under pulsed operation (50 ns, 0.01% duty). These results experimentally verify that maintaining a large conduction-band offset and abrupt interfaces, rather than wavelength-dependent factors, overwhelmingly governs ηi improvement in polarization-doped UV-B LDs. Our findings establish a practical design and growth guideline for highly efficient current-injection UV-B LDs.