Femtosecond carrier dynamics in an asymmetrically excited GaAs photoconductive switch

We present a detailed analysis of the field screening and carrier dynamics which exist in the high-field region of an asymmetrically excited coplanar transmission line. Through time-resolved reflectivity measurements, it is found that the ballistic acceleration of carriers, and subsequent field screening, dominate the ultrashort electrical pulse generation. In addition, the formation of an instantaneous macroscopic polarization and the creation of coherently coupled plasmon–phonon modes are found to effect the electric field screening response. The results are in agreement with the field screening picture of edge-illuminated photoconduction and suggest that pulses as short as 110 fs can be generated.