ULTRAFAST PHENOMENA IN II-VI SEMICONDUCTORS

We review studies on the coherent and incoherent exciton dynamics in Z nSe-based quantum wells. First, the exciton-exciton scattering paramet er is determined from femtosecond four-wave mixing as a function of ba ckground exciton density generated by a prepulse. A linear increase in the excitonic homogeneous linewidth is found as a function of the bac kground exciton density with significant different scattering paramete rs for the cases of interaction with coherent or incoherent excitons. Second, the thermalization dynamics of spectrally narrow hot-exciton d istributions is investigated by time-resolved phonon sideband spectros copy. Thermalization assisted by acoustic phonons occurs on a 100 ps t imescale, which is in good agreement with model calculations in time d ependent perturbation theory. PACS numbers: 78.47.+p, 42.50.Md, 71.35. -y.