Femtosecond charge transport in polar semiconductors

The transient current response of bulk GaAs and InP is investigated at ultr ahigh electric fields. On ultrashort time scales, the electronic system is far from equilibrium and overshoot velocities as high as 8 x 10(7) cm/s are observed. Our studies also lead to a detailed understanding of the ionic r esponse of polar semiconductors. For the first time, carrier motion is dete rmined with a resolution of 20 fs at fields up to 130 kV/cm. The dependence of the ultrafast dynamics on material and electric field provides new insi ghts into the microscopic mechanisms governing nonequilibrium transport.