Toward high-efficiency deep-ultraviolet semiconductor laser sources

Short-wavelength light-producing ultraviolet-B laser diodes made of aluminum gallium nitride alloys (AlGaN-based UV-B) could become essential for medical treatment, photochemical processes, semiconductor manufacturing, quantum technologies, and more. Among other challenges, research has focused on limited wall-plug efficiency (WPE), widely believed to be the result of insufficient optical confinement.

Miyake et al. demonstrated that internal optical loss, rather than optical confinement, is the dominant factor limiting WPE.

“Our findings establish a new design principle: Reducing internal optical loss is more important than further increasing optical confinement for realizing highly efficient UV-B laser diodes,” said author Motoaki Iwaya.

The researchers fabricated UV-B laser diode structures on an AlGaN template with systematically varied ridge waveguides. They conducted experiments with the devices to carefully evaluate internal optical loss, threshold current, slope efficiency, and optical near-field characteristics.

The study revealed that further increasing optical confinement once it had been achieved provides only limited benefits, whereas a slight increase in internal optical loss significantly hinders laser performance.

Testing on the devices revealed a WPE of 5.5% — one of the highest efficiencies reported for electrically injected AlGaN UV-B laser diodes.

“The most exciting aspect of this work is not simply that we achieved one of the highest WPE values on record,” said Iwaya. “It’s that we have answered a long-standing scientific question and provided a practical design guideline for the next generation of UV semiconductor lasers. Instead of asking, ‘How can we confine light more strongly?’, future researchers should ask, ‘How can we minimize internal optical loss?’”

This new design principle could accelerate the development of practical deep-ultraviolet laser sources for a range of applications.

Source: “Internal-loss-limited 5.5% wall-plug efficiency in index-guided AlGaN UV-B laser diodes with polarization-doped cladding layers,” by Rintaro Miyake, Takumu Saito, Shion Kamiya, Ryota Watanabe, Yuma Miyamoto, Seiya Kato, Naoki Kitta, Rintaro Kobayashi, Tomoya Tanikawa, Kenta Kitagawa, Sho Iwayama, Hideto Miyake, Tetsuya Takeuchi, Satoshi Kamiyama, and Motoaki Iwaya, Applied Physics Letters (2026). The article can be accessed at https://doi.org/10.1063/5.0341819 .