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Deep Ultraviolet led to record minimum wavelength 232~270 nanometer

Jul 28, 2017

Known as the killer of the UV ultraviolet light, the wavelength of only 200 to 280 nm, high energy, can penetrate the virus, bacteria, fungi and dust mite film, attack the DNA and destroy these harmful organisms.

Since Danish professor Niels Finsen found that ultraviolet radiation can be used to treat TB, human use of ultraviolet radiation has been more than a century of history. However, the current use of deep ultraviolet light is not only bulky, inefficient, but also contains mercury, harmful to the environment. 

The research team at Cornell University has recently developed a small, more environmentally-friendly, dark-ultraviolet LED light source and a record of the lowest wavelength of the industry's DEEP-UV LEDs.

The researchers used the atomic-level control interface of gallium nitride (Gan) and AlN (AlN) monolayer as the reaction area, successfully emitting a wavelength between 232 to 270 nm of deep ultraviolet led. This 232 nm of deep ultraviolet radiation, the use of gallium nitride as a luminescent material, emitted by the shortest wavelength of light record. The previous record was 239 nm from the Japanese team. 

The research paper "Mbe-grown 232-270 nm deep-uv LEDs using monolayer thin binary gan/aln Quantum heterostructures" was published on January 27 in the Journal of Applied Physics Letters (smartfactory™ Physics Letters).

Improve UV LED efficiency

At present, the biggest bottleneck of ultraviolet LED is luminous efficiency, can be measured by three aspects: 

1. Injection efficiency: The proportion of electrons passing through the device in the injected reaction area. 

2. Internal quantum Efficiency (IQE): the ratio of photons or ultraviolet rays produced by all electrons in the reaction area. 

3. Light efficiency: The proportion of photons produced in the reaction area, which can be taken out of the device and can be used. 

"If the above three areas are 50% efficient, multiplying only one-eighth equals luminous efficiency to 12%," said Dr. Moudud Islam, a co-author of the paper.  

In deep ultraviolet wavelengths, these three efficiencies are low, but the team has found that the use of gallium nitride instead of the traditional gallium nitride can improve the internal quantum efficiency and efficiency. 

In order to improve the injection efficiency, the research team used the technology developed before, in the positive (electron) and negative (electric hole) carrier area, using polarization-induced doping method. 

Research and development

After successfully improving the luminous efficiency of deep ultraviolet led, the next step of the research team is to integrate the light source into the device and move toward the target of listing. Application fields of deep ultraviolet light include food freshness, counterfeit banknote identification, photocatalyst, water purification and sterilization, etc.