Ultrafast carrier dynamics in germanium nanoparticles

It is shown that the ultrafast carrier dynamics in Ge nanoparticles involving 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 the absorption around 490 nm and a slower one (up to a few hundred picoseconds) governed by band gap renormalization. There is also a clear correspondence between the spectral response in both regimes and a bulk-like band structure for sizes below the exciton Bohr radius. Quantum confinement is manifested through the measurable blueshift of E-1+Delta(1) spectral structure in the ultrafast optical response. (C) 1999 American Institute of Physics. [S0003-6951(99)03028-4].