Ultrafast carrier relaxation in Si studied by time-resolved two-photon photoemission spectroscopy: intravalley scattering and energy relaxation of hot electrons.

The dynamical relaxations of photogenerated hot carriers in the X valley of Si have been studied using time-resolved two-photon photoemission spectroscopy. Intravalley scattering is completed within 100 fs to form a quasiequilibrated electron distribution near the conduction-band minimum, while maintaining about half the excess energy given to hot electrons. The energy relaxation follows the scattering with a 240-fs time constant that is independent of the excess energy.