Phonon-Wind-Driven Electron-Hole Plasma in Si

The spatial expansion of electron-hole plasma created by nanosecond pulsed-laser excitation of Si is examined by time-resolved luminescence imaging. On a several-nanosecond time scale, the plasma created by 0.5-{μ}J excitation expands from the excitation point at subsonic velocities, contrary to a fast-diffusing plasma model recently proposed to explain spectroscopic anomalies. For 50-{μ}J excitation, time-resolved images show a shell of plasma expanding at near-sonic velocities, indicating phonon-wind-driven transport with highly non-linear damping.