September 10, 2013…Ohio State University Researchers have developed a nanowire-based gadolinium nitride-doped UV LED on silicon. According to the researchers, the patent-pending LED creates a more precise wavelength of UV light than commercially available UV LEDs. The researchers say that it operates at much lower voltages and is more compact than other experimental methods for creating precise wavelength UV light. Possible applications for the UV LED could include: chemical detection, disinfection, and UV curing. The development is detailed in an article inApplied Physics Letters.
The engineers used semiconductor nanowires on a silicon substrate which were doped with the compound gadolinium nitride. The compound was made with rare earth metal gadolinium. Study co-author Roberto Myers, associate professor of materials science and engineering at Ohio State, says that passing electricity through the nanowires excites the rare earth metal. Doctoral students Thomas Kent and Santino Carnevale utilized a patent-pending technology for making nanowire LEDs that they had helped develop to start creating gadolinium-containing LEDs in the lab.
The team didn’t set out to make a UV LED. “As far as we know, nobody had ever driven electrons through gadolinium inside an LED before,” Myers said. “We just wanted to see what would happen.”
On a silicon wafer, they tailored the wires’ composition to tune the polarization of the wires and the wavelength, or color, of the light emitted by the LED. Gadolinium was chosen not to make a good UV LED, but to carry out a simple experiment probing the basic properties of a new material they were studying, called gadolinium nitride. During the course of that original experiment, Kent noticed that sharp emission lines characteristic of the element gadolinium could be controlled with electric current.
Gadolinium fluoresces most strongly at a very precise wavelength in the UV part of the spectrum, outside of the range of human vision. The engineers found that the gadolinium-doped wires glowed brightly at several specific UV frequencies. While the only other reported device, which can electrically control gadolinium light emission requires more than 250 volts, the Ohio State team demonstrated that in a nanowire LED structure, the same effect can occur at around just 10 volts.
“The other device needs high voltage because it pushes electrons through a vacuum and accelerates them, just like a cathode ray tube in an old-style TV.” Myers said.
The very specific wavelengths might make it useful for research spectroscopy applications that require a reference wavelength, and because it requires only 10 volts, it might be useful in portable devices. The researchers say that the same technology could conceivably be used to make UV laser diodes.
The team is now working to maximize the efficiency of the UV LED, and the university’s Technology Commercialization and Knowledge Transfer Office will license the design—as well as the method for making specially doped nanowires—to industry. The research was funded by the National Science Foundation (NSF) and Ohio State’s Center for Emergent Materials.