We investigated field screening mechanisms in large-aperture GaAs photoconductors, using an ultrafast pump–probe terahertz technique. After photoexcitation the bias field decreases to an intensity-dependent value as a result of near-field screening of the bias field. For longer delays the field exhibits an intensity-dependent decrease that results from a space-charge field caused by transport-induced charge separation. These measurements support recent theoretical results that the dominant saturation mechanism that limits terahertz output from large-aperture photoconductors is near-field screening of the bias field because the space-charge field develops on a much longer time scale than that of the terahertz pulse.
© 1997 Optical Society of America
A. J. Taylor, G. Rodriguez, and D. Some, "Ultrafast field dynamics in large-aperture photoconductors," Opt. Lett. 22, 715-717 (1997)