Takumu Saito, Rintaro Miyake, Shundai Maruyama, Y. Sasaki, Shogo Karino, Ryota Watanabe, Y. Miyamoto, Tomoya Tanikawa, Rintaro Kobayashi, Sho Iwayama, Hideto Miyake, Koichi Naniwae, Satoshi Kamiyama, Tetsuya Takeuchi, Motoaki Iwaya
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.