The world’s first room temperature continuous-wave UV-B laser diode on a sapphire substrate

Ultraviolet-B (UV-B) semiconductor lasers are highly sought for medical, biotechnology, and precision manufacturing applications; however, previous UV-B laser diodes were limited to pulsed operation or required cryogenic cooling, making continuous room-temperature operation unattainable. Researchers in Japan report the world’s first continuous-wave UV-B semiconductor laser diode operating at room temperature on a low-cost sapphire substrate. This breakthrough advances compact, energy-efficient UV light sources, potentially replacing bulky gas-based lasers in healthcare, industrial, and scientific research applications worldwide.

Ultraviolet light is a powerful tool in science, medicine, and industry. In particular, ultraviolet-B (UV-B) radiation, which lies between visible light and shorter-wavelength ultraviolet radiation, is widely used in medical phototherapy for skin diseases, sterilization, DNA analysis, and high-precision manufacturing. Despite its importance, practical UV-B laser sources remain scarce. Most existing systems rely on gas lasers or complex optical setups that are large, costly, and difficult to integrate into compact, scalable devices.

Semiconductor laser diodes offer an attractive alternative. They are compact, energy-efficient, and well-suited for mass production. However, extending semiconductor laser technology into the UV-B range has proven extremely challenging. High aluminum-content nitride semiconductors, which are required to generate UV-B light, suffer from crystal defects, poor optical confinement, and severe heat dissipation issues. As a result, previous UV-B laser diodes were limited to pulsed operation or required cryogenic cooling to operate stably.

Professor Motoaki Iwaya from the Department of Materials Science and Engineering, Meijo University, Japan, and his team have overcome these long-standing challenges. The study was conducted in collaboration with Professor Tetsuya Takeuchi and Professor Satoshi Kamiyama from Meijo University, and Professor Hideto Miyake from the Graduate School of Electrical and Electronic Engineering at Mie University, Japan, as well as researchers from Ushio Inc. (Corporate R&D Division), Japan, and The Japan Steel Works, Ltd., Japan. The findings of the study were published in the journal Applied Physics Letters on Jan. 12, 2026.

The researchers developed a novel aluminum gallium nitride (AlGaN) laser diode structure grown on a sapphire substrate, which is inexpensive and widely used in commercial semiconductor manufacturing. The use of sapphire is particularly significant because it enables low-cost and large-scale fabrication, bringing UV-B laser diodes closer to practical and widespread deployment. To address the mismatch between the crystal structures of AlGaN and sapphire, the team employed a relaxed AlGaN template that significantly reduced defects while preserving optical quality. This approach improves device yield and reliability, which are critical for scalable manufacturing and real-world applications. They also designed a refractive-index-guided ridge waveguide to efficiently confine light and incorporated high-reflectivity dielectric mirrors to enhance laser feedback.

“These design innovations allowed us to achieve both strong optical confinement and effective thermal management,” says Dr. Iwaya. “Continuous-wave operation at room temperature has been a long-standing goal for UV-B semiconductor lasers, and this result demonstrates that it is now achievable.”

Using this approach, the team demonstrated continuous-wave lasing at a wavelength of 318 nm at 20 °C. The laser diode showed a threshold current of 64 mA, corresponding to a threshold current density of 4.3 kA cm⁻², and exhibited stable output under continuous electrical injection. Junction-down mounting further improved heat dissipation, enabling sustained operation without performance degradation.

The implications of this advance extend well beyond the laboratory. In particular, compact UV-B laser diodes could significantly improve medical phototherapy devices used to treat skin disorders and vascular conditions, making them smaller, safer, and more energy-efficient, and easier to deploy in clinical settings. Following medical applications, biotechnology and manufacturing stand to benefit substantially. In biotechnology, such lasers could enhance DNA sequencing, fluorescence analysis, and biosensing technologies. In manufacturing, they could enable next-generation, high-precision exposure systems and microfabrication tools for semiconductors and advanced materials processing.

“Our motivation comes from a long-term vision that began with the invention of the blue LED,” Dr. Iwaya explains. “We want to expand the capabilities of nitride semiconductors into the ultraviolet region and develop light technologies that directly contribute to human health and scientific advancement.”

Looking ahead, the ability to fabricate UV-B laser diodes on low-cost, mass-producible sapphire substrates could accelerate their adoption across multiple industries. Over the next 5 to 10 years, this technology may replace traditional ultraviolet gas lasers with compact, solid-state alternatives that are more reliable and easier to deploy. Such a shift could make advanced ultraviolet tools accessible to hospitals, laboratories, and manufacturing facilities worldwide.

Overall, this work represents a major milestone in ultraviolet optoelectronics, bringing UV-B semiconductor lasers closer to widespread practical use and opening new possibilities for healthcare-focused medical applications, biotechnology, and precision manufacturing.

About Meijo University

Meijo University traces its origin back to the establishment of the Nagoya Science and Technology Course in 1926, giving it a proud history of more than 90 years. As one of the largest universities in the Chubu region, Meijo University is a comprehensive learning institution that supports a wide range of academic fields from the humanities to physical sciences. With a network of more than 200,000 graduates and alumni, it strives to contribute not only to local industries but also to international communities in various fields. Meijo University is also known as the birthplace of the carbon nanotube. To foster the human resources of the next generation, the university continues to tackle ongoing challenges by further enhancing its campus and creating new faculties.

Website: https://www.meijo-u.ac.jp/english/

About Professor Motoaki Iwaya from Meijo University, Japan

Dr. Motoaki Iwaya is currently a Professor in the Department of Materials Science and Engineering at Meijo University, Japan. His research focuses on ultraviolet (UV) optoelectronic devices based on nitride semiconductors. His research interests include UV semiconductor lasers, UV emitters, laser diodes, light-emitting diodes, photosensors, and solar cells. He has played an important role in advancing ultraviolet semiconductor technologies toward practical applications. He has published more than 456 peer-reviewed scientific papers and continues to lead research aimed at expanding the capabilities of nitride semiconductor technologies for medical, industrial, and scientific applications.

Funding information

This study was partially supported by the NEDO Feasibility Study Program in Japan.