Title: Hot Phonon and Carrier Relaxation in Si(100) Determined by Transient Extreme Ultraviolet Spectroscopy,
Abstract: The thermalization of hot carriers and phonons gives direct insight into the
scattering processes that mediate electrical and thermal transport. Obtaining
the scattering rates for both hot carriers and phonons currently requires
multiple measurements with incommensurate timescales. Here, transient
extreme-ultraviolet (XUV) spectroscopy on the silicon 2p core level at 100 eV
is used to measure hot carrier and phonon thermalization in Si(100) from tens
of femtoseconds to 200 ps following photoexcitation of the indirect transition
to the {\Delta} valley at 800 nm. The ground state XUV spectrum is first
theoretically predicted using a combination of a single plasmon pole model and
the Bethe-Salpeter equation (BSE) with density functional theory (DFT). The
excited state spectrum is predicted by incorporating the electronic effects of
photo-induced state-filling, broadening, and band-gap renormalization into the
ground state XUV spectrum. A time-dependent lattice deformation and expansion
is also required to describe the excited state spectrum. The kinetics of these
structural components match the kinetics of phonons excited from the
electron-phonon and phonon-phonon scattering processes following
photoexcitation. Separating the contributions of electronic and structural
effects on the transient XUV spectra allows the carrier population, the
population of phonons involved in inter- and intra-valley electron-phonon
scattering, and the population of phonons involved in phonon-phonon scattering
to be quantified as a function of delay time.