Dec 20, 2011 |
Terahertz pulse increases electron density 1,000-fold
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(Nanowerk News) Researchers at Kyoto University have announced a breakthrough with broad implications for semiconductor-based devices. The findings, announced in the December 20 issue of the journal Nature Communications ("Extraordinary carrier multiplication gated by a picosecond electric field pulse"), may lead to the development of ultra-high-speed transistors and high-efficiency photovoltaic cells.
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Working with standard semiconductor material (gallium arsenide, GaAs), the team observed that exposing the sample to a terahertz (1,000 gigahertz) range electric field pulse caused an avalanche of electron-hole pairs (excitons) to burst forth. This single-cycle pulse, lasting merely a picosecond (10^-12 s), resulted in a 1,000-fold increase in exciton density compared with the initial state of the sample.
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A picosecond terahertz pulse causes an avalanche of excitons to burst forth from semiconductor GaAs. (Image: Courtesy Tanaka Lab, Kyoto University iCeMS)
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"The terahertz pulse exposes the sample to an intense 1 MV/cm^2 electric field," explains Hideki Hirori, team leader and Assistant Professor at Kyoto University's Institute for Integrated Cell-Material Sciences (iCeMS). "The resulting exciton avalanche can be confirmed by a bright, near-infrared luminescence, demonstrating a three-order of magnitude increase in the number of carriers."
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Research in Kyoto using terahertz waves is led by Professor Koichiro Tanaka, whose lab at the iCeMS pursues numerous applications including the development of new biological imaging technologies.
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"Since terahertz waves are sensitive to water, our goal is to create a microscope that will allow us to look inside living cells in real time," says Prof. Tanaka. "These just-released results using semiconductors are an entirely different field of science, but they demonstrate the rich potential that lies in the study of terahertz waves."
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