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Terahertz pulse increases electron density in GaAs by a thousand

These findings may lead to the development of ultra-high-speed transistors and high-efficiency photovoltaic cells using gallium arsenide

Researchers at Kyoto University have made a breakthrough with broad implications for semiconductor-based devices. 

A picosecond terahertz pulse causes an avalanche of excitons to burst forth from GaAs  (Credit:Courtesy Tanaka Lab, Kyoto University iCeMS)

Working with 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.

"The terahertz pulse exposes the sample to an intense 1 MV/cm2 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."

Research in Kyoto using terahertz waves is led by Koichiro Tanaka, whose lab at the iCeMS pursues numerous applications including the development of new biological imaging technologies.

"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 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."

This work was supported by Grant-in-Aid for Young Scientists (B) (Grant No. 21760038) of the Japan Society for the Promotion of Science, and also Grant-in-Aid for Scientific Research on Innovative Area "Optical science of dynamically correlated electrons (DYCE)" (Grant No. 20104007) and Grant-in-Aid for Creative Scientific Research (Grant No. 18GS0208) of the Ministry of Education, Culture, Sports, Science and Technology, Japan.

This research is further detailed in the paper "Extraordinary carrier multiplication gated by a picosecond electric field pulse" by H. Hirori et al in the online December 20, 2011 issue of Nature Communications.
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