Group blazes path to efficient, eco-friendly deep-ultraviolet LED

March 2, 2017 by Tom Fleischman
Members of the Xing Research Group—Debdeep Jena, Moudud Islam, Huili (Grace) Xing, Vladimir Protasenko, Kevin Lee and Shyam Bharadwaj—are pictured in front of one of the molecular beam epitaxy systems used in their latest work. Credit: Cornell University

The darkest form of ultraviolet light, known as UV-C, is unique because of its reputation as a killer – of harmful organisms.

With wavelengths of between 200 and 280 nanometers, this particular form of UV light penetrates the membranes of viruses, bacteria, mold and dust mites, attacking their DNA and killing them. Sanitization with UV-C light has been around for more than 100 years, following Niels Finsen's discovery of UV light as an antidote to tuberculosis, which won the Faroese-Danish physician the 1903 Nobel Prize for Medicine.

Currently, most deep-UV lamps are mercury-based. They pose a threat to the environment, and are bulky and inefficient. A Cornell research group led by Huili (Grace) Xing and Debdeep Jena, along with collaborators from the University of Notre Dame, has reported progress in creating a smaller, more earth-friendly alternative.

Using atomically controlled thin monolayers of (GaN) and aluminum nitride (AlN) as active regions, the group has shown the ability to produce deep-UV emission with a light-emitting diode (LED) between 232 and 270 nanometer wavelengths. Their 232- nanometer emission represents the shortest recorded wavelength using GaN as the light-emitting material. The previous record was 239 nanometers, by a group in Japan.

"MBE-grown 232-270 nm deep-UV LEDs using monolayer thin binary GaN/AlN quantum heterostructures" was published online Jan. 27 in Applied Physics Letters.

Postdoctoral researcher SM (Moudud) Islam, the lead author, said: "UV-C light is very attractive because it can destroy the DNA of species that cause infectious diseases, which cause contamination of water and air."

One of the major challenges with ultraviolet LEDs is , which is measured in three areas: injection efficiency – the proportion of electrons passing through the device that are injected into the ; internal quantum efficiency (IQE) – the proportion of all electrons in the active region that produce photons or UV light; and light extraction efficiency – the proportion of photons generated in the active region that can be extracted from the device and are actually useful.

"If you have 50 percent efficiency in all three components … multiply all of these and you get one-eighth," Islam said. "You're already down to 12 percent efficiency."

In the deep-UV range, all three efficiency factors suffer, but this group found that by using gallium nitride instead of conventional aluminum gallium nitride, both IQE and extraction efficiency are enhanced.

Injection efficiency is improved through the use of a polarization-induced doping scheme for both the negative (electron) and positive (hole) carrier regions, a technique the group explored in previous work.

Now that the group has proven its concept of enhanced deep-UV LED efficiency, its next task is packaging it in a device that could one day go on the market. Deep-UV LEDs are used in food preservation and counterfeit currency detection, among other things.

Further study will include packaging both the new technology and existing technologies in otherwise similar devices, for the purpose of comparison.

"In terms of quantifying the efficiency, we do want to package it within the next few months and test it as if it was a product, and try to benchmark it against a product with one of the available technologies," Jena said.

Explore further: Relocating LEDs from silicon to copper enhances efficiency

More information: S. M. Islam et al. MBE-grown 232–270 nm deep-UV LEDs using monolayer thin binary GaN/AlN quantum heterostructures, Applied Physics Letters (2017). DOI: 10.1063/1.4975068

Related Stories

Self-assembling particles brighten future of LED lighting

January 16, 2017

Just when lighting aficionados were in a dark place, LEDs came to the rescue. Over the past decade, LED technologies—short for light-emitting diode—have swept the lighting industry by offering features such as durability, ...

Trace metal recombination centers kill LED efficiency

November 3, 2016

Using cutting-edge first-principles calculations, researchers at the University of California, Santa Barbara (UCSB) have demonstrated the mechanism by which transition metal impurities - iron in particular - can act as nonradiative ...

Recommended for you

Clothing fabric keeps you cool in the heat

November 16, 2017

(Phys.org)—Researchers have designed a thermal regulation textile that has a 55% greater cooling effect than cotton, which translates to cooler skin temperatures when wearing clothes made of the new fabric. The material ...

Semiconductors with an aligned interface

November 13, 2017

The electronic characteristics of an interface between two wide bandgap semiconductors are determined by researchers at KAUST: an insight that will help improve the efficiency of light-emitting and high-power electronic devices.

Zipping DNA

November 13, 2017

ETH researchers have developed a method that allows large amounts of genetic information to be compressed and then decompressed again in cells. This could aid in the development of new therapies.

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

rrrander
not rated yet Mar 13, 2017
UV is a half-measure. Gamma rays used to irradiate milk can make it last for six months. Gamma irradiation of polyethylene makes it far more resistant to heat. Gamma irradiation of foodstuffs would eliminate the spoilage seen in places that don't have efficient refrigeration facilities and help alleviate food shortages.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.