Source: Eurekalert.

Findings point to advances in transistor and solar cell development

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, may lead to the development of ultra-high-speed transistors and high-efficiency photovoltaic cells.

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.

¡°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.¡±

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.

¡°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.¡±

The article, ¡°Extraordinary carrier multiplication gated by a picosecond electric field pulse¡± by H. Hirori, K. Shinokita, M. Shirai, S. Tani, Y. Kadoya, and K. Tanaka was published online in the December 20, 2011 issue of Nature Communications.