Ultrafast hot-carrier relaxation in silicon monitored by phase-resolved transient absorption spectroscopy

The relaxation dynamics of hot carriers in silicon (100) is studied via a holistic approach based on phase-resolved transient absorption spectroscopy with few-cycle optical pulses. After excitation by a sub-5-fs light pulse, strong electron-electron coupling leads to an ultrafast single electron momentum relaxation time of 10 fs. The thermalization of the hot carriers is visible in the temporal evolution of the effective mass and the collision time as extracted from the Drude model. The optical effective mass decreases from 0.3me to about 0.125me with a time constants of 58 fs, while the collision time increases from 3 fs for the shortest timescales with a saturation at approximately 18 fs with a time constant of 150 fs. The observation shows that both Drude parameters exhibit different dependences on the carrier temperature. The presented information on the electron mass dynamics as well as the momentum-, and electron-phonon scattering times with unprecedented time resolution is important for all hot-carrier optoelectronic devices.