AUGER-PROCESS-INDUCED CHARGE SEPARATION IN SEMICONDUCTOR NANOCRYSTALS

Femtosecond nonlinear transmission techniques are applied to study mec hanisms for optical nonlinearities and ultrafast carrier dynamics in C dS nanocrystals (NC's). The obtained data indicate the change in a dom inant hole relaxation channel at high pump levels where nonlinear reco mbination effects start to play a significant role. This is manifested as a distinct difference in nonlinear-optical responses measured at l ow and high pump intensities in quasiequilibrium at long times after e xcitation. The analysis of the wavelength and time dependence of the n onlinear transmission over a wide pump-intensity range shows clearly t hat this difference is due to an Auger-process-assisted trapping of ho les at surface/interface-related states. This trapping leads to effici ent charge separation and the generation of a dc electric field that m odifies the nonlinear optical response in NC's at high pump intensitie s.