TIME-RESOLVED PHOTOCURRENT RESPONSE OF METAL-SEMICONDUCTOR-METAL PHOTODETECTORS TO DOUBLE-PULSE EXCITATION

The photocurrent response of a GaAs metal-semiconductor-metal (MSM) ph otodetector was measured after excitation with two femtosecond pulses having a variable delay Delta t of 0 ps less than or equal to Delta t less than or equal to 100 ps. At low excitation densities the influenc e of the first pulse on the pulse shape of the second is negligible fo r Delta t greater than or equal to 20 ps. This corresponds to a resolv able pulse train of 50 GHz repetition rate for the detectors used in o ur experiments. The influence of space charge effects at higher excita tion density and/or lower bias could be shown.