Ultrafast high-field transport in semiconductors

Non-equilibrium transport in GaAs and InP is investigated at electric fields up to 130 kV/cm and with a time resolution of 20 fs. The experiment is based upon ultrabroadband detection of the THz transient emitted by accelerating carriers photo-excitated with 12 fs laser pulses. The strong dependence of the ultrafast dynamics on material and electric field provides new insights into the microscopic mechanisms governing ultrafast electronic conduction. Overshoot velocities as high as 6 x 10(7) and 8 x 10(7) cm/s are obtained in GaAs and InP, respectively. Depending on the experimental conditions, the drift distances during the non-thermal regime can exceed 100 nm even at room temperature. In addition, the measurements lead to a detailed understanding of the interplay between free carrier displacement and dielectric response of the polar semiconductors. (C) 1999 Elsevier Science B.V. All rights reserved.