Ultrafast carrier dynamics in germanium nanoparticles

It is shown that the ultrafast carrier dynamics in Ge nanoparticles involvi ng the electronic density of states well above the gap can be separated in two regimes: a faster one (similar to 1 ps) characterized by bleaching of t he absorption around 490 nm and a slower one (up to a few hundred picosecon ds) governed by band gap renormalization. There is also a clear corresponde nce between the spectral response in both regimes and a bulk-like band stru cture for sizes below the exciton Bohr radius. Quantum confinement is manif ested through the measurable blueshift of E-1+Delta(1) spectral structure i n the ultrafast optical response. (C) 1999 American Institute of Physics. [ S0003-6951(99)03028-4].