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 Δ 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 with density functional theory. 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.

Layer-resolved ultrafast extreme ultraviolet measurement of hole transport in a Ni-TiO 2 -Si photoanode

“…Changes in the L2,3 edge are therefore representative of the underlying carrier and lattice dynamics, and not simply due to changes in the core-hole perturbation, as shown by the L2,3 edge absorption of different Si oxidation states in Supplementary Figure 4A. After photoexcitation, the differential absorption features above 101 eV are known to correspond to structural changes 31 Figure 2A), an increased absorption is measured below 99 eV (holes) and above 101 eV (structural). A decreased absorption is measured around 100 eV (electrons).…”

“…The photoexcited data are then fit at each time point as equilibrium changes to the ground state. For the Si, the electron and hole signatures are fit based on previous analysis ( Figure 3A) 22,31 . For the Ni and Ti, the edge shifts are fit since no distinct spectral signature exists for the photoexcited electrons and holes ( Figure 3B).…”

Differentiating Photoexcited Carrier and Phonon Dynamics in the Δ, L, and Γ Valleys of Si(100) with Transient Extreme Ultraviolet Spectroscopy

“…Recent reports suggest that the core-hole in covalent semiconductors with delocalized valence electrons, like Ge and Si, is negligible enough that the electron and hole energies can be measured as a function of time over a broad XUV energy range [31][32][33][34] . It remains less clear to what degree transient XUV spectra can be used to distinguish the occupation of non-degenerate valleys in semiconductor band structures.…”

Transient extreme ultraviolet measurement of element-specific charge transfer dynamics in multiple-material junctions

“…Further, with appropriate analysis of the core-hole perturbation, the spectral signatures of photoexcited electron and holes can be energetically separated in the transient XUV spectrum [12][13][14] . The averaged lattice dynamics due to excited phonon modes can also be measured 15,16 .…”

“…The simultaneous observation of carriers and vibrational dynamics was first achieved in the gas phase 11 . The additional many-body effects present in a solid required further theoretical development to interpret the XUV spectral changes 15 . The evolution of measuring transition metal oxides, to covalently bonded semiconductors, to metals is described.…”