Ultrafast carrier dynamics in nanocrystalline silicon

We present studies of the ultrafast dynamics of photoexcited carriers in thin-film nanocrystalline silicon materials in which the degree of crystallinity has been systematically varied by controlling the deposition conditions. Femtosecond pump-probe measurements reveal a multicomponent response that can be understood in terms of the separate phases of the heterogeneous material. We observe a 240-fs exponential relaxation process associated with intraband carrier relaxation in the silicon crystallites, a response characteristic of bimolecular recombination in the amorphous silicon matrix, and a long-lived component assigned to grain-boundary states.