COLUMBUS, Ohio, Sept. 10, 2013 — An ultraviolet LED created from semiconductor nanowires doped with the rare-earth element gadolinium could lead to more portable and low-cost commercial uses of the technology.
"As far as we know, nobody had ever driven electrons through gadolinium inside an LED before," said Roberto Myers, associate professor of materials science and engineering at The Ohio State University, where the LED was developed. "We just wanted to see what would happen."
There are commercially available UV LEDs now, and such uses for the light are growing, but the new LED creates a more precise wavelength of UV light and runs at much lower voltages than those currently on the market. It also is more compact than other experimental methods for creating precise-wavelength UV light.
Gadolinium was chosen, not to make a good UV LED, but to carry out a simple experiment probing the basic properties of gallium nitride, a new material the researchers were studying. During the course of that experiment, doctoral student Thomas Kent noticed that sharp emission lines characteristic of the element gadolinium could be controlled with electric current.
Materials that glow in the UV are harder to excite, but Myers' team found that the gadolinium-doped wires glowed brightly at several specific UV frequencies.
The only other reported device that can electrically control gadolinium light emission requires more than 250 V to operate, while the Ohio State's nanowire LED structure requires only about 10 V. The structure of Ohio State's LED, with the gadolinium placed in the center where the electrons are losing energy, is what makes the difference, the researchers say.
Because the LED emits at specific wavelengths, it could be useful for research spectroscopy applications that require a reference wavelength, and because it requires only 10 V, it could enable portable devices. It also could lend itself to applications for chemical detection, disinfection and UV curing. With significant further development, it might someday be able to provide a source for UV lasers for eye surgery and computer chip manufacture, they report.
The same technology could conceivably be used to make UV laser diodes. Currently, high-power gas lasers produce a laser at UV wavelengths with applications from advanced electronics manufacturing to eye surgery. These excimer lasers contain toxic gases and run on high voltages, so solid-state lasers are being explored as a lower-power, nontoxic alternative.
The LEDs are grown on standard silicon wafers, so the method is inexpensive and easily scaled for industry use.
“Using a cheap substrate is good; it balances the cost of manufacturing the nanowires,” Kent said. The wires' composition is tailored to tune the polarization of the wires and the wavelength of emitted light.
The team is now working to maximize the patent-pending UV LED's efficiency, 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, reported in Applied Physics Letters,
was sponsored by the National Science Foundation and Ohio State’s Center for Emergent Materials.
For more information, visit: www.osu.edu