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LED action heats up

P-type zinc oxide nanowires.
P-type zinc oxide nanowires.

As energy-efficient light sources from the macro to nano scale, LEDs (light emitting diodes) are red hot. A Jacobs School research group led by electrical and computer engineering professor Deli Wang is pushing hard to make an LED that has thus far eluded researchers: LEDs made from zinc oxide (ZnO) nanowires. These LEDs could compete with today's widely used gallium nitride LEDs as well as serve as high efficiency nanoscale light sources for optical data storage, imaging, and biological and chemical sensing. To build an LED, you need holes from positively charged semiconductors and electrons from negative semiconductors. When an electron meets a hole, the electron falls into a lower energy level and releases a photon of light. In the January 2007 issue of Nano Letters, Wang and colleagues at UCSD and Peking University documented a critical step forward towards the goal of ZnO nanowire LEDs: synthesis of "p-type" ZnO nanowires—which, by definition, are endowed with free or positively charged carriers or holes. The race is now on to engineer nanoscale applications from combinations of p-type and n-type (negatively charged carriers or electrons rich) nanowires. In related work to be published in Nano Letters, members of the Deli Wang and Yu-Hwa Lo research groups at the Jacobs School have demonstrated ZnO nanowire UV photodetectors with ultrahigh sensitivity and high internal gain.