22 December 2011

Terahertz pulse increases electron density in GaAs 1000-fold

Researchers at Kyoto University have reported what they claim is a breakthrough with broad implications for semiconductor-based devices (‘Extraordinary carrier multiplication gated by a picosecond electric field pulse’ by H. Hirori et al, published online in the 20 December issue of Nature Communications; DOI: 10.1038/ncomms1598). The findings could lead to the development of ultra-high-speed transistors and high-efficiency photovoltaic cells, it is reckoned.

Working with standard gallium arsenide, the team observed that exposing the sample to a terahertz (1000GHz)-range electric field pulse caused an avalanche of electron-hole pairs (excitons) to burst forth. This single-cycle pulse, lasting just a picosecond (10-12s), resulted in a 1000-fold increase in exciton density compared with the initial state of the sample.

Picture: A picosecond terahertz pulse causes an avalanche of excitons to burst forth from GaAs. (Graphic courtesy Tanaka Lab, Kyoto University iCeMS.)

“The terahertz pulse exposes the sample to an intense 1MV/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,” he adds.

Research at 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. “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,” he adds.

The 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 by 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 Japan’s Ministry of Education, Culture, Sports, Science and Technology.

Tags: GaAs GaAs high-speed transistors GaAs PV solar cells

Visit: www.nature.com/ncomms/journal/v2/n12/full/ncomms1598.html

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