Characterization of picosecond GaAs metal-semiconductor-metal photodetectors.

Interdigitated GaAs metal-semiconductor-metal Schottky photodiodes have been studied experimentally and theoretically. The time evolution of the response current has been measured by means of photoconductive and electrooptic sampling with a time resolution of 0.8 and 0.3 ps, respectively. The response current to a 70 fs laser pulse reaches maximum within 2-5 ps, then shows a fast decay of about 10 ps followed by a slower one. Self-consistent, two-dimensional Monte Carlo particle simulation predicts that the former is due to electrons, the latter to holes. With a sufficiently strong electric field the two species of carriers get separated. With increased light intensity a screened plasma forms that vanishes only through recombination which takes of the order of nanoseconds.