Scientists measure speedy electrons in silicon

The entire semiconductor industry, not to mention Silicon Valley, is built on the propensity of electrons in silicon to get kicked out of their atomic shells and become free. These mobile electrons are routed and switched though transistors, carrying the digital information that characterizes our age. In semiconductors like silicon, electrons attached to atoms in the crystal lattice can be mobilized into the conduction band by light or voltage. Berkeley scientists have taken snapshots of this very brief band-gap jump and timed it at 450 attoseconds. Stephen Leone image. An international team of physicists and chemists based at the University of California, Berkeley, has for the first time taken snapshots of this ephemeral event using attosecond pulses of soft X-ray light lasting only a few billionths of a billionth of a second. While earlier femtosecond lasers were unable to resolve the jump from the valence shell of the silicon atom across the band-gap into the conduction electron region, the new experiments now show that this transition takes less than 450 attoseconds.