Ultrafast carrier and plasmon-phonon dynamics in ion-irradiated n-GaAs

Ultrafast dynamics of plasmon-phonon coupled modes and photoexcited carriers in He ion irradiated n-GaAs has been investigated with a femtosecond pump-probe technique. The frequencies of the coupled modes shift as the ion dose increases, and after 1.9x10(13) He+/cm(2) irradiation the coherent oscillation of the coupled modes disappear. The relaxation time of the photoexcited carriers decreases with increasing ion dose, which is explained quantitatively by trapping of carriers via the deep levels related to single vacancies. The dose dependence of the dephasing time of the coupled modes and the relaxation time of the photoexcited carriers reveal that the trapping of the majority carriers dominates the disappearance as well as the frequency shift of the coupled mode oscillation. (C) 2003 American Institute of Physics.