The Global View

Sub-atomic ‘avalanche’ could pave way for super solar cells

Researchers at Kyoto University have discovered a way to unleash an “avalanche” of excitons — electron-hole pairs — 1,000 times as dense as normal from semiconductor material.

The finding could help lead to the development of extra-efficient solar cells and ultra-high-speed transistors, they say.

Scientists at the university’s Institute for Integrated Cell-Material Sciences blasted a standard semiconductor material of gallium arsenide with a large but ultra-quick electric field pulse. A single-cycle, one-terahertz (1,000 gigahertz)-range pulse lasting just one picosecond (10-12, or 0.000000000001, second) led to a 1,000-fold increase in exciton density.

Excitons are electrically neutral quasiparticles created when photons — light particles — are absorbed by a semiconductor. They’re able to transport energy without transporting a net electric charge.

The results “demonstrate the rich potential that lies in the study of terahertz waves,” said Koichiro Tanaka, whose lab pursues numerous applications including the development of new biological imaging technologies.