As COVID-19 continues to ravage global populations, the world is
singularly focused on finding ways to battle the novel coronavirus. That
includes the UC Santa Barbara’s Solid State Lighting & Energy Electronics
Center (SSLEEC) and member companies. Researchers there are developing
ultraviolet LEDs that have the ability to decontaminate surfaces — and
potentially air and water — that have come in contact with the SARS-CoV-2
virus.
“One major
application is in medical situations — the disinfection of personal protective
equipment, surfaces, floors, within the HVAC systems, et cetera,” said
materials doctoral researcher Christian Zollner, whose work centers on
advancing deep ultraviolet light LED technology for sanitation and purification
purposes. He added that a small market already exists for UV-C disinfection
products in medical contexts.
Indeed, much
attention of late has turned to the power of ultraviolet light to inactivate
the novel coronavirus. As a technology, ultraviolet light disinfection has been
around for a while. And while practical, large-scale efficacy against the
spread of SARS-CoV-2 has yet to be shown. UV light shows a lot of promise:
SSLEEC member company Seoul Semiconductor in early April reported a “99.9%
sterilization of coronavirus (COVID-19) in 30 seconds” with their UV LED
products. Their technology currently is being adopted for automotive use, in UV
LED lamps that sterilize the interior of unoccupied vehicles.
It’s worth
noting that not all UV wavelengths are alike. UV-A and UV-B — the types we get
a lot of here on Earth courtesy of the Sun — have important uses, but the rare
UV-C is the ultraviolet light of choice for purifying air and water and for
inactivating microbes. These can be generated only via human-made processes.
“UV-C light in
the 260 — 285 nm range most relevant for current disinfection technologies is
also harmful to human skin, so for now it is mostly used in applications where
no one is present at the time of disinfection,” Zollner said. In fact, the
World Health Organization warns against using ultraviolet disinfection lamps to
sanitize hands or other areas of the skin — even brief exposure to UV-C light
can cause burns and eye damage.
Before the
COVID-19 pandemic gained global momentum, materials scientists at SSLEEC were
already at work advancing UV-C LED technology. This area of the electromagnetic
spectrum is a relatively new frontier for solid-state lighting; UV-C light is
more commonly generated via mercury vapor lamps and, according to Zollner,
“many technological advances are needed for the UV LED to reach its potential
in terms of efficiency, cost, reliability and lifetime.”
In a letter published in the journal ACS Photonics, the researchers
reported a more elegant method for fabricating high-quality deep-ultraviolet
(UV-C) LEDs that involves depositing a film of the semiconductor alloy aluminum
gallium nitride (AlGaN) on a substrate of silicon carbide (SiC) — a departure
from the more widely used sapphire substrate.
According to
Zollner, using silicon carbide as a substrate allows for more efficient and
cost-effective growth of high-quality UV-C semiconductor material than using
sapphire. This, he explained, is due to how closely the materials’ atomic
structures match up.
“As a general
rule of thumb, the more structurally similar (in terms of atomic crystal
structure) the substrate and the film are to each other, the easier it is to
achieve high material quality,” he said. The better the quality, the better the
LED’s efficiency and performance. Sapphire is dissimilar structurally, and
producing material without flaws and misalignments often requires complicated
additional steps. Silicon carbide is not a perfect match, Zollner said, but it
enables a high quality without the need for costly, additional methods.
In addition,
silicon carbide is far less expensive than the “ideal” aluminum nitride
substrate, making it more mass production-friendly, according to Zollner.
Portable,
fast-acting water disinfection was among the primary applications the
researchers had in mind as they were developing their UV-C LED technology; the
diodes’ durability, reliability and small form factor would be a game changer
in less developed areas of the world where clean water is not available.
The emergence of
the COVID-19 pandemic has added another dimension. As the world races to find
vaccines, therapies and cures for the disease, disinfection, decontamination
and isolation are the few weapons we have to defend ourselves, and the
solutions will need to be deployed worldwide. In addition to UV-C for water
sanitation purposes, UV-C light could be integrated into systems that turn on
when no one is present, Zollner said.
“This would
provide a low-cost, chemical-free and convenient way to sanitize public, retail,
personal and medical spaces,” he said.
For the moment,
however, it’s a game of patience, as Zollner and colleagues wait out the
pandemic. Research at UC Santa Barbara has slowed to a trickle to minimize
person-to-person contact.
“Our next steps,
once research activities resume at UCSB, is to continue our work on improving
our AlGaN/SiC platform to hopefully produce the world’s most efficient UV-C
light emitters,” he said.
Journal article: https://pubs.acs.org/doi/10.1021/acsphotonics.9b00600
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