On November 24, a group of foreign research teams announced that they had successfully demonstrated the continuous wave laser of the world's first deep ultraviolet laser diode (wavelength to the UV-C region) at room temperature. This achievement represents a step forward for the wide application of this technology in the future, including sterilization and a series of medical scenarios.

On the same day, two related research papers were published in the Journal of Applied Physics Letters. The research project was jointly carried out by the research team under the Institute of Sustainable Materials and Systems (IMaSS) of Nagoya University led by Hiroshi Amano, the 2014 Nobel Prize winner, and Asahi Kasei Corporation of Japan.

Since its introduction in the 1960s, after decades of research and development, laser diodes (LDs) have finally been commercialized and applied to many wavelengths from infrared to blue violet. Examples of this technology include optical communication equipment with infrared laser diodes and blue optical discs using blue violet diodes. However, with the efforts of researchers all over the world, no one has been able to develop deep ultraviolet diodes. Until 2007, the aluminum nitride (AlN) substrate technology has become a key breakthrough. It is an ideal material for growing aluminum gallium nitride (AlGaN) films for ultraviolet light emitting devices. Since then, scientists have gained more impetus to promote the development of deep UV diodes.

Since 2017, Professor Hiroshi Amano's research team has cooperated with Asahi Kasei Co., Ltd., which provides 2-inch AlN substrate, to develop deep ultraviolet diodes. At first, they found that it was too difficult to inject enough current into the equipment, and the team's pace of developing UV-C laser diodes was once blocked. However, in 2019, the research team successfully solved this problem using polarization induced doping technology. For the first time, they produced a short wave ultraviolet visible (UV-C) diode, which works with a short pulse current. However, the input power required for these current pulses is 5.2W - this is too high for CW lasers, causing the diode to rise rapidly and stop emitting light.

Recently, however, researchers from Nagoya University and Asahi Kasei Co., Ltd. have modified the structure of the device itself, reducing the driving power required for the laser to work at room temperature of only 1.1W. Early devices were found to require a high level of operating power because they could not form an effective current path, which was due to the crystal defects of laser stripes.

However, in this latest study, researchers found that these defects were caused by strong crystal strain. By skillfully clipping the side wall of the laser stripe, they suppress the defects, achieve effective current flow to the active area of the laser diode, and reduce the working power.

The production university research cooperation platform of Nagoya University - Future Electronic Comprehensive Research Center (C-TEFs) has made this new development of ultraviolet laser technology possible. With the support of C-TEFs, researchers from Japan's Asahi Kasei Co., Ltd. and other partners can share the most advanced facilities on the campus of Nagoya University, and provide them with the personnel and tools needed to manufacture reproducible high-quality equipment.

This research is a milestone for the practical application and development of semiconductor lasers in all wavelength ranges, especially for surgeons and nurses who need to disinfect operating rooms. In the future, UV-C lasers can be used in medical care, virus detection, particle measurement, gas analysis and high-definition laser processing. Zhang Ziyi, the representative of the research group, was in the second grade of Asahi Kasei Co., Ltd. when he participated in the creation of the project. He said that "its application in sterilization technology may be a breakthrough. Unlike the current inefficient LED sterilization method, laser can disinfect large areas in a short time and a long distance."

Source: OFweek Laser Network

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