Optically induced voltage pulses by resonant excitation of a passive GaAs photoconductive switch

We have investigated the all-optical generation of ultrashort voltage pulses that are launched by resonant excitation of a passive GaAs photoconductive switch with no electric bias field applied. Due to a specially designed geometry, we can distinguish between electrical transients generated in the Schottky field region of the metal/GaAs contact and shift currents resulting from nonlinear optical effects in the GaAs material. The shift current contribution is smaller than the Schottky field contribution but possesses a higher bandwidth with frequency components exceeding 1 THz. For small bias fields, the contribution of all-optically-generated currents to the overall voltage signal may be significant and needs to be accounted for when modeling photoconductive switches.