Deep ultraviolet LED light output power exceeding 90mW can replace sterilizing mercury lamp

The deep UV LED device structure developed this time (above) and the two light extraction structures formed on the surface of the AlN substrate. By changing from a single photonic crystal structure (lower left) to a mixed structure (lower right) after adding a structure with a smaller wavelength, the light extraction efficiency is greatly increased from about 140% to 196%.

The National Institute of Information Communications and Research (NICT) announced that the newly developed 265-nm deep ultraviolet LED has achieved continuous light output of up to 90mW/cm2, which is sufficient for practical applications. Deep UV LEDs can replace existing mercury lamps for sterilization, and can also implement portable sterilization systems, and even create new markets for medical diagnostics and medical analysis.

Electromagnetic waves near the wavelength of 265 nm are called deep ultraviolet rays and can effectively destroy the DNA and RNA of organisms. Therefore, they can effectively kill bacteria and viruses. LEDs emitting light at this wavelength are called deep ultraviolet LEDs. If the deep-UV LED reaches the practical level, it can replace the existing sterilization mercury lamp, and its size is much smaller than the mercury lamp, and can create new markets, so the industry has been advancing related development, but the main issues facing The output power is not high.

3 times light extraction efficiency

This time, NICT replaced the original sapphire substrate with an aluminum nitride (AlN) substrate and developed a deep ultraviolet LED. The AlN substrate is characterized by a significant reduction in crystal defects compared to sapphire substrates.

However, the AlN substrate has a problem that the refractive index is large and the light extraction efficiency is very low. The NICT forms a pattern of a two-dimensional photonic crystal structure having a substantially same size and wavelength on the surface of an AlN substrate as a light extraction surface, and a combination of nanostructures having a smaller size than the wavelength. The light extraction efficiency reached 196% (approximately 3 times the original) when this surface treatment was not performed.

The external quantum efficiency is 6.3% (at a current of 200mA). According to NICT, this is the highest value in the world at wavelengths below 270nm. (Reporter: Nozawa Tetsuo)