INTERPRETATION OF PHOTOCURRENT CORRELATION-MEASUREMENTS USED FOR ULTRAFAST PHOTOCONDUCTIVE SWITCH CHARACTERIZATION

Photocurrent correlation measurements used for the characterization of ultrafast photoconductive switches based on GaAs and silicon-on-sapph ire are demonstrated, The correlation signal arises from the interplay of the photoexcited carriers, the dynamics of the bias field and a su bsequent recharging of the switch. By using both photocurrent measurem ents and terahertz spectroscopy we verify the importance of space-char ge effects on the carrier dynamics. Photocurrent nonlinearities and co herent effects are discussed as they appear in the correlation signals . An analysis based on a simple model allows an estimate of the carrie r lifetimes associated with the photoconductive switching process. We illustrate how pulse propagation can be studied sequentially using thi s technique and how a minor modification of the experimental setup ena bles the study of screening from long-lived carriers. We emphasize in what ways the different techniques of measuring ultrashort electrical pulses are sensitive to different aspects of the pulse forming mechani sms. (C) 1996 American Institute of Physics.