Ultrafst electron dynamics in Ge quantum dots

摘要

An analysis of the ultrafast response of Ge quantum dots, with average radii of 4 nm and 16 nm, is reported here. Pump and probe experiments allowed investigation of the wavelength region between 450 and 750 nm, characterized by the absorption peaks due to the E_1 and E_1+ DELTA _1 interband transitions. Two different time regimeshave been dientified: a first one ( tai <=1ps) associated with pump-induced conduction band filling in the GAMMA -L direction in the Brillouin zone; a second one ( tau up to 100 ps) associated with band gap renormalization caused by the carrier interaction in the conduction band. Quantum confinement effects show up in terms of size dependent blueshift of the E_1+ DELTA _1 spectral feature.