Laser Diode Scientists develop semiconductor laser that emits 'world's shortest lasing wavelength'

Researchers at Nagoya University in Japan, in cooperation with Asahi Kasei Corporation, have designed a laser diode that emits the shortest-wavelength ultraviolet light ever. The semiconductor laser constitutes a variety of applications in treating skin conditions such as psoriasis, or gas and DNA analysis.

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Scientists at Nagoya University in Japan, in partnership with Asahi Kasei Corporations, have managed to design a laser diode that emits the shortest-wavelength ultraviolet light to-date. The research is published in Applied Physics Express.

"Our laser diode emits the world's shortest lasing wavelength, at 271.8 nanometers (nm), under pulsed [electric] current injection at room temperature," says Professor Chiaki Sasaoka of Nagoya University's Center for Integrated Research of Future Electronics.

Obstacles for pushing semiconductors lasers into the deep UV

The new ultraviolet short-wavelength (UV-C) semiconductor laser uses a 2-inch uses an aluminum nitride (AlN) substrate manufactured by Crystal IS, Inc., an Asahi Kasei Group company.

In the past ten years, the world has seen considerable advances in light-emitting diodes (LEDs) for the deep UV. New developments have been mainly possible thanks to so-called group III-nitride materials—particularly aluminum gallium nitride (AlGaN). Emissions from this type of material can be tuned to create LEDs covering virtually the entire UV spectral range.

Extending progress in LEDs to push semiconductors lasers into the deep UV has, however, proven a tougher proposition. One reason why lasing under current injection in the ultraviolet range has been considered challenging is the extremely high resistance of the material. When an active layer of AlGaN crystals are grown on conventional substrates such as silicon carbide or sapphire, it can lead to the formation of internal dislocations and cracks, degrading the quantum efficiency of the active layer.

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A tough threshold to cross

Previous short-wavelength semiconductor lasers have only been able to achieve emissions down to 336 nm, according to Chiaki Sasaoka of Nagoya University, one of the new study's senior authors. The Nagoya University semiconductor laser can achieve emissions down to 271.8 nm.

Key factors in their successful development have been:

• Employing a specially designed p-side layer to realize sufficient light confinement and reduced device resistance simultaneously.

• Suppressing light scattering loss by using AlN substrate with few defects.

• Combining Asahi Kasei's leading thin-film crystal growth technology with the outstanding process technology and evaluation technology of Nagoya University's CIRFE Transformative Electronics Facilities (C-TEFs). This research result thus holds the key to high-output UV-C solid-state light sources that have long been sought.

Moving toward real-world application

In the report in Applied Physics Express, the authors point out that the graded valence-band profile enabled by DPD led to a "remarkably low operating voltage" of 13.8 V for the diode at that current.

The new semiconductor laser could be used for treating skin conditions such as psoriasis, or gas and DNA analysis. The researchers are now working with Asahi Kasei Corporation to get to continuous deep-UV emission from the device at room temperature, to set the diode up for real-world applications.

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