Subpicosecond ultrafast investigation of germanium nanoparticles

The ultrafast relaxation dynamics of photoexcited carriers in Ge nanocrysta ls is here investigated using a pump-and-probe technique. Three different e xcitation energies (1.59, 3.18, 4.77 eV) are used, and the spectral interva l between 1.7 and 2.8 eV is probed. The electron dynamics has been studied and the scattering times have been evaluated, together with their dependenc e on the pump energy. The transient signal has been interpreted in terms of two main contributions: (i) conduction band filling and (ii) band gap reno rmalization. A model based on the bulk band structure allows to explain the overall response.