Transport of degenerate electron-hole plasmas in Si and Ge

At low crystal temperatures, pulsed-laser excitation of Si and Ge can produce a mobile electron-hole plasma with a Fermi energy much larger than k_BT. The motion of this degenerate plasma away from the excitation surface depends intimately on its interactions with high-frequency phonons. Momentum damping and phonon-wind forces are principal factors which determine the plasma motion on nanosecond and longer time scales. A variety of luminescence and heat-pulse experiments are reviewed here which characterize the transport behavior of photo-generated electron-hole plasma in these indirect-gap semiconductors.