Ohio university researchers develop UV LED12 Sep 2013
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Researchers at Ohio State University used the rare earth element gadolinium and semiconductor nanowires to create a novel ultraviolet LED. The technology could be used in the future for chemical detection, eye surgery UV lasers, computer chip manufacturing and various other portable and low-cost applications.
The patent-pending LED creates a more precise wavelength of UV light than today's commercially available UV LEDs, and runs at much lower voltages and is more compact than other experimental methods for creating precise wavelength UV light.
In the journal Applied Physics Letters, Ohio State engineers describe how they created LEDs out of semiconductor nanowires which were doped with the rare earth element gadolinium. The unique design enabled the engineers to excite the rare earth metal by passing electricity through the nanowires, said study co-author Roberto Myers, associate professor of materials science and engineering at Ohio State.
When doctoral students Thomas Kent and Santino Carnevale started creating gadolinium-containing LEDs in the lab, they utilised another patent-pending technology they had helped develop—one for creating nanowire LEDs. On a silicon wafer, they tailor the wires' composition to tune the polarisation of the wires and the wavelength, or colour, 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.
Different elements fluoresce at different wavelengths when they are excited, and gadolinium fluoresces most strongly at a very precise wavelength in the UV, outside of the range of human vision. The engineers found that the gadolinium-doped wires glowed brightly at several specific UV frequencies.
The Ohio State team showed that in a nanowire LED structure, the same effect can occur, but at far lower operating voltages: around 10V. High voltage devices are difficult to miniaturize, making the nanowire LEDs attractive for portable applications.
Because the LED emits light at specific wavelengths, it could be useful for research spectroscopy applications that require a reference wavelength, and because it requires only 10V, it might be useful in portable devices.
The same technology could conceivably be used to make UV laser diodes. Currently high-powered gas lasers are used to produce a laser at UV wavelengths with applications from advanced electronics manufacturing to eye surgery. The so-called excimer lasers contain toxic gases and run on high voltages, so solid-state lasers are being explored as a lower power—and non-toxic—alternative.
As to cost, Kent pointed out that the team grows its LEDs on a standard silicon wafer, which is inexpensive and easily scaled up to use in industry.
"Using a cheap substrate is good; it balances the cost of manufacturing the nanowires," he said.
The team is now working to maximise the efficiency of the UV LED, and the university's Technology Commercialisation and Knowledge Transfer Office will license the design, as well as the method for making specially doped nanowires.
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