Scientists demonstrate continuous wave lasing of a deep-ultraviolet laser diode at room temperature – ScienceDaily

A research group led by 2014 Nobel Laureate Hiroshi Amano at the Institute of Materials and Systems for Sustainability (IMaSS) at Nagoya University in central Japan, in collaboration with Asahi Kasei Corporation, has successfully performed the world’s first room-temperature continuous wave lasering of a depth – ultraviolet laser diode (wavelengths up to the UV-C range). These results, published in Applied physics lettersrepresent a step towards the widespread adoption of a technology that has the potential for a wide range of applications, including sterilization and medicine.

Since their introduction in the 1960s and after decades of research and development, successful commercialization of laser diodes (LDs) has finally been achieved for a range of applications with wavelengths ranging from infrared to blue-violet. Examples of this technology are optical communication devices with infrared LDs and blue-ray discs with blue-violet LDs. However, despite the efforts of research groups around the world, no one has been able to develop deep-ultraviolet LDs. A major breakthrough came only after 2007 with the advent of technology to fabricate aluminum nitride (AlN) substrates, an ideal material for growing aluminum gallium nitride (AlGaN) films for UV light-emitting devices.

From 2017, Professor Amano’s research group started developing a deep-ultraviolet LD in collaboration with Asahi Kasei, the company that provided 2-inch AlN substrates. Initially, sufficient current injection into the device was too difficult, preventing further development of UV-C laser diodes. But in 2019, the research group successfully solved this problem with a polarization-induced doping technique. For the first time, they produced a short-wavelength UV-visible (UV-C) LD that works with short current pulses. However, the input power required for these current pulses was 5.2 W. This was too high for CW lasing because the power would cause the diode to heat up quickly and stop lasing.

But now researchers at Nagoya University and Asahi Kasei have redesigned the structure of the device itself, reducing the drive power required to operate the laser to just 1.1 W at room temperature. It has been found that previous devices require high operating power due to the inability of effective current paths due to crystal defects occurring at the laser stripe. But in this study, the researchers found that the strong crystal strain creates these defects. By cleverly cutting the sidewalls of the laser stripe, they suppressed the defects, achieved efficient current flow to the active area of ​​the laser diode, and reduced the operating power.

Nagoya University’s collaborative platform called the Center for Integrated Research of Future Electronics, Transformative Electronics Facilities (C-TEFs) enabled the development of the new UV laser technology. Through C-TEFs, researchers from partners like Asahi Kasei share access to state-of-the-art facilities on the Nagoya University campus, providing them with the people and tools needed to build reproducible high-quality devices. Zhang Ziyi, a representative of the research team, was in his second year with Asahi Kasei when he helped found the project. “I wanted to do something new,” he said in an interview. “Back then, everyone thought the deep ultraviolet laser diode was an impossibility, but Professor Amano told me, ‘We’ve made it to the blue laser, now it’s time for ultraviolet’.”

This research is a milestone in the practical application and development of semiconductor lasers in all wavelength ranges. In the future, UV-C LDs could be used in healthcare, virus detection, particle measurement, gas analysis, and high-resolution laser processing. “Its application in sterilization technology could be groundbreaking,” Zhang said. “Unlike current LED sterilization methods, which are time-inefficient, lasers can disinfect large areas in a short time and over long distances.” This technology could particularly benefit surgeons and nurses who need sterilized operating rooms and tap water.

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Materials provided by Nagoya University. Note: Content can be edited for style and length.

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