COHERENT PLASMONS IN N-DOPED GAAS

Femtosecond laser excitation of bulk n-doped GaAs leads to coherent pl asmon excitations that emit intense submillimeter wave radiation. We i nvestigated the underlying plasmon dynamics in time-resolved experimen ts on the emitted THz radiation. The results show that THz pulses are emitted due to the coherent oscillation of the extrinsic electron plas ma in the hulk. The plasmon excitations are started by single-sided sc reening of the surface depletion field after photoexcitation. Temperat ure-dependent measurements indicate that the plasmon damping is due to phonon scattering.