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Nanowire LEDs

Infrared light-emitting nanowires could lead to optical communications on microchips.
August 1, 2007

Researchers at IBM Research in Yorktown Heights, NY, have demonstrated a new way to convert electricity into light in nanowire-based light-emitting devices (LEDs). The nanowire LEDs could eventually be used for telecommunications and for faster communications between devices on microchips. The approach could also pave the way for a new type of bright, efficient display.

Microscopic LED: A thin indium-nitride nanowire spans two electrodes. When a current is applied, it emits infrared light.

The researchers built an LED resembling a transistor that consists of an indium-nitride nanowire stretched between two electrodes on top of a silicon substrate. The nanowire is about 100 nanometers wide and spans a distance of less than 10 micrometers. When the researchers apply a current to the nanowire, it emits light. While nanowires that emit light have been made before, the new devices rely on different physical mechanisms that are simpler; as a result, the nanowire LED could be more efficient and have improved performance. What’s more, the device succeeds in emitting infrared light, which has been particularly difficult for nanowires to do, says Phaedon Avouris, one of the IBM researchers.

Typically, light in LEDs is produced by injecting both electrons and their positive counterparts, holes, into an active material, where they combine and emit light. With the new devices, the researchers only have to inject electrons; these cause electrons and holes to form locally, inside the nanowires. The mechanism could be more efficient because a single electron can be used to generate more than one electron-hole pair. What’s more, the researchers have demonstrated that the nanowires can produce more intense light emission than other LEDs.

The nanowires’ small size and compatibility with silicon make them attractive for integration on chips, says Eugene Fitzgerald, a professor of materials science and engineering at MIT. The nanowires also emit infrared light, which makes them ideal for fiber-optic telecommunications and for optical communications between devices on microchips that could help dramatically speed up computers.

The nanowire LEDs extend the range of colors that can be emitted from nitride-based materials, Fitzgerald says. Nitride materials are the basis of the blue lasers in high-definition DVD players, he says, and they have also been useful for emitting green light. If the nanowires can be tuned to emit red light, as seems likely, then red, green, and blue LEDs could all be created with variations of the same material, making it practical to manufacture them all on the same substrate. Eventually, it may be possible to arrange such LEDs into the pixels of full-color displays that are brighter, more efficient, and better looking than today’s flat-panel LCD displays, Fitzgerald says.

Not only did the wires emit infrared light, but they also showed a peculiar ability to emit more intense light as temperatures rose; ordinarily, at high temperatures light emission dims or stops. This could lead to LEDs that can withstand high temperatures, a property that could be useful for certain military applications, Avouris says.

The novel physical mechanisms underlying the indium-nitride nanowires’ ability to emit light might have wider implications for nanowire research. If the mechanism used here works in other materials, it could expand the number of materials that might be used to create LEDs, Fitzgerald says. That could make LEDs cheaper and give researchers far greater versatility in creating devices with improved performance.

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