Time-resolved photoresponse of a gallium-doped germanium photoconductor using a variable pulse-width terahertz source

Picosecond to nanosecond-wide terahertz pulses are used to study the fast photoresponse of a gallium-doped germanium (Ge:Ga) photoconductor operating at 4.2 K. A recombination time of about 2 ns is observed in the time-resolved photoresponse. Laser-activated semiconductor reflection switches are used to “slice” the variable-width terahertz pulses from the quasicontinuous-wave output of a free-electron laser.