SANTA BARBARA, April 15 (WNM / UC Santa Barbara) – The world of research is focused on finding ways to combat the corona virus. This also includes the Solid State Lighting & Energy Electronics Center (SSLEEC) at UC Santa Barbara. There, researchers and partner companies are developing ultraviolet LEDs that can decontaminate surfaces – and possibly air and water – that have come into contact with the Covid 19 virus (https://www.news.ucsb.edu/2020/019860/ power-light).
“A main application is in medical situations – the disinfection of personal protective equipment, surfaces, floors within the HVAC systems, etc.”, said Christian Zollner, whose research focus is on the further development of LED technology for deep ultraviolet light for hygiene and cleaning. He added that there is already a small market for UV-C disinfectants in the medical field.
Disinfection with ultraviolet light has been a technology for some time. While the practical effectiveness on a large scale against the spread of SARS-CoV-2 has not yet been proven, UV light is promising: SSLEEC member company Seoul Semiconductor reported in early April that it had “99.9% sterilized the coronavirus (COVID – 19) in 30 seconds ”with their UV LED products. Their technology is currently used in automobiles in UV LED lamps that sterilize the interior of unoccupied vehicles.
Not all UV wavelengths are the same. UV-A and UV-B – the types that we receive frequently on Earth thanks to the sun – have important uses, but the rare UV-C is the ultraviolet light of choice for cleaning air and water and inactivating microbes. These can only be generated via artificial processes.
“UV-C light in the 260 to 285 nm range, which is most relevant for current disinfection technologies, is also harmful to human skin. Therefore, it is currently mainly used in applications where no one is present at the time of disinfection, ”said Zollner.
In fact, the World Health Organization warns against using UV disinfection lamps to disinfect hands or other skin areas – even a short exposure to UV-C light can cause burns and eye damage. Before the COVID-19 pandemic gained momentum worldwide, SSLEEC material scientists were already working on the further development of UV-C LED technology.
UV-C light is generated more often by mercury vapor lamps. According to Zollner, “a lot of technological advances are required for the UV LED to develop its potential in terms of efficiency, cost, reliability and service life”.
In a letter published in the journal ACS Photonics, the researchers reported on a more elegant method for producing high-quality UV-C LEDs, in which a film made of the semiconductor alloy aluminum gallium nitride (AlGaN) is sedimented on a substrate of silicon carbide (SiC) – a departure from most common sapphire substrate.
According to Zollner, the use of silicon carbide as a substrate enables high-quality UV-C semiconductor material to grow more efficiently and cost-effectively than the use of sapphire. This is due to how closely the atomic structures of the materials match.
“As a rule of thumb, the more structurally (in terms of atomic crystal structure) the substrate and the film resemble each other, the easier it is to achieve high quality materials,” he said. The better the quality, the better the efficiency and performance of the LED. Sapphire is structurally dissimilar, and manufacturing material without defects and misalignments often requires complicated additional steps. Silicon carbide doesn’t fit perfectly, Zollner said, but it enables high quality without the need for costly additional methods. In addition, silicon carbide is far cheaper than the “ideal” aluminum nitride substrate, which makes it easier to mass-produce, according to Zollner.
Portable, fast-acting water disinfection was one of the main applications the researchers had in mind when developing their UV-C LED technology. The durability, reliability and small form factor of the diodes would play a crucial role in less developed areas of the world where clean water is not available.
The advent of the COVID-19 pandemic has added another dimension. While the world is looking for vaccines, therapies, and cures for the disease, disinfection, decontamination, and isolation are the few weapons we have to defend and the solutions need to be used worldwide.
In addition to UV-C for water treatment purposes, UV-C light could be integrated into systems that turn on when no one is present, Zollner said. “This would be an inexpensive, chemical-free, and convenient way to clean public, retail, personal, and medical spaces,” he said.
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