ITHACA, N.Y. — Using atomically controlled thin monolayers of gallium nitride (GaN) and aluminum nitride (AIN) as active regions, a research group has shown the ability to produce deep-UV emission with an LED between 232- and 270-nm wavelengths. Currently, most deep-UV lamps are mercury-based and are bulky and inefficient. A deep-UV LED would provide a smaller, more eco-friendly alternative to a mercury lamp.
Researchers at Cornell University, along with collaborators from the University of Notre Dame, achieved electrically injected deep UV emission using monolayer thin GaN/AlN quantum structures as active regions; and tuned the emission wavelength by controlling the thickness of ultrathin GaN layers using plasma assisted molecular beam epitaxy. In experiments the team achieved single peaked emission spectra with narrow full width at half maximum for three different LEDs operating at 232, 246 and 270 nm. The team believes that
232 nm (5.34 eV) is the shortest electroluminescence emission wavelength reported so far using GaN as
the light emitting material.
Members of the Jena-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.
One of the challenges with UV LEDs is efficiency, which is measured in terms of the proportion of electrons passing through the device that are injected into the active region; the proportion of electrons in the active region that produce photons; and the proportion of photons generated in the active region that can be extracted for practical use. In the deep-UV range, efficiency can be impaired in all three areas.
“If you have 50 percent efficiency in all three components . . . multiply all of these and you get one-eighth,” said researcher Moudud Islam. “You're already down to 12 percent efficiency.”
By using GaN instead of conventional aluminum gallium nitride (AlGaN), the researchers were able to increase the proportion of electrons that produced photons, as well as the proportion of electrons that could be extracted for actual use. They increased the proportion of electrons injected into the active region by using a polarization-induced doping scheme for both the negative (electron) and positive (hole) carrier regions.
The research team’s next task will be to package their technique for enhancing deep-UV LED efficiency in a device that could one day be available for purchase. Further study will include packaging both the researchers’ technology and existing technologies in 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,” researcher Debdeep Jena said.
Deep-UV LEDs are used to destroy harmful organisms including viruses, bacteria, mold and dust mites, as well as in food preservation and counterfeit currency detection.
The research was published in Applied Physics Letters (doi: 10.1063/1.4975068).