The time evolution of high-field carrier transport in bulk GaAs is studied with intense femtosecond THz pulses. While ballistic transport of electrons occurs in an $n$-type sample, a transition from ballistic to driftlike motion is observed in an electron-hole plasma. This onset of friction is due to the holes, which are heated by THz absorption. Theoretical calculations, which reproduce the data quantitatively, show that both electron-hole scattering and local-field effects in the electron-hole plasma are essential for the time-dependent friction.

• Received 1 July 2011

DOI:https://doi.org/10.1103/PhysRevLett.107.256602