Spatially resolved ultrafast transport current in GaAs photoswitches

Abstract

We apply a pump- and probe-scheme to coplanar stripline circuits to investigate the photocurrent response of GaAs photoswitches in time and space. We find a displacement current pulse, as reported earlier. We interpret a time-delayed second pulse as a transport current. In a time-of-flight analysis we determine the velocity of the photogenerated charge carriers in the transport current. It exceeds the Fermi and the single-particle quantum velocities. This suggests that the excitation of an electron-hole plasma and not single charge-carriers dominates the ultrafast transport current in GaAs photoswitches.