As noted in Tech-On!, The National Institute of Information and Communications Technology (NICT; Tokyo, Japan) announced that it has achieved continuous light emission with an output of 90 mW/cm2 from a deep-ultraviolet (DUV) LED emitting at a wavelength of 265 nm.
The new LED is expected to be used in a portable sterilizer and virucidal system, and could also help create a new market for small medical diagnosis/analysis devices.
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Light at DUV wavelengths breaks down the DNA and RNA of living organisms, making the light effective at sterilizing and detoxifying germs and viruses. If deep UV LEDs are commercialized, they can be used to replace existing 254-nm-emitting bactericidal mercury lamps, which are quite bulky, costly, and, due to the fact that they are gas-filled glass, not rugged.
Tripled light-extraction efficiency
NICT developed the high-output DUV LED by using an aluminum nitride (AlN) substrate rather than the more-usual sapphire substrate, which NICT has used in the past. Compared with sapphire substrates, AlN substrates lead to a drastic reduction in the number of crystal defects.
However, existing AlN substrates have high refractive index and very low light-extraction efficiencies (the DUV light is extracted through the substrate in a back-side illumination configuration). On the back-side light-extraction surface of the AlN substrate, NICT formed a pattern combining two-dimensional photonic crystals (with a size equivalent to the wavelength) and nanostructures (with a size smaller than the wavelength). The result was an improvement of the light extraction efficiency by 196% in comparison with a an AlN substrate with an unpatterned surface.
The external quantum efficiency of the new LED is 6.3% at a current of 200 mA, which NICT claims is the world's highest for an LED having a wavelength of 270 nm or lower.
Source: http://techon.nikkeibp.co.jp/english/NEWS_EN/20150403/412622/
John Wallace | Senior Technical Editor (1998-2022)
John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.