Continuous-wave UV-B laser diode is a first
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 have reported the world’s first continuous-wave UV-B semiconductor laser diode operating at room temperature on a low-cost sapphire substrate. This breakthrough, published in the journal Applied Physics Letters on Jan. 12, 2026, advances compact, energy-efficient UV light sources, potentially replacing bulky gas-based lasers in healthcare, industrial, and scientific research applications worldwide.
Ultraviolet light is used in medical phototherapy for skin diseases, sterilisation, 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. However, extending semiconductor laser technology into the UV-B range has proven 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.
Motoaki Iwaya from the Department of Materials Science and Engineering, Meijo University, Japan, and his team have overcome these long-standing challenges.
The researchers developed a novel AlGaN laser diode structure grown on a sapphire substrate. The use of sapphire is 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 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,” 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.”
The study was conducted in collaboration with Tetsuya Takeuchi and Satoshi Kamiyama from Meijo University, and Hideto Miyake from the Graduate School of Electrical and Electronic Engineering at Mie University, Japan, as well as researchers from Japan's firms Ushio Inc and The Japan Steel Works.
