Ultrafast relaxation of highly excited hot electrons in Si: Roles of theL−Xintervalley scattering

Abstract

Two-photon photoemission (2PPE) spectroscopy is used to reveal dynamic relaxation of highly excited electrons generated by 3 eV photons in Si. Monochromatic 2PPE at probe-photon energies ranging from 3.2 to 3.5 eV reveals a coherent 2PPE peak from the valence band maximum, and a transiently populated photoemission peak near L 1 in the conduction band. Time-resolved 2PPE measurements show that electrons injected into the L valley undergo L-to-X intervalley scattering with a time constant of 180 fs at 293 K. A deformation potential constant of 1.2 eVÅ −1 is obtained for the scattering. The highly excited electrons are relaxed down around the conduction band minimum to form a quasi-equilibrated hot electron distribution; the highest density is accumulated at 660 fs after excitation. The hot electron distribution is equilibrated with the lattice within 2 ps after excitation. These results are compared to relaxation processes of electrons injected directly into the X valley by photons with energies below 2.2 eV.

Intrinsic coherent acoustic phonons in the indirect band gap semiconductors Si and GaP

“…In indirect gap semiconductors, however, the situation is more complicated because most of the photoexcited electrons undergo intervalley scattering and populate different satellite valleys at different times. For Si, previous studies [55,56] revealed that the electrons excited at the L valley are scattered into the X valley, as illustrated in Fig. 2b, with a time constant of 0.2−0.5 ps.…”

Common source of light emission and nonlocal molecular manipulation on the Si(111)−7 × 7 surface

“…The STL threshold found here of +2 V therefore suggests that if the same electron dynamics occur, then the light emission for injections above +2 V would be from the bottom of the U 3 state. We therefore propose that after the injected electron has undergone diffusion for 200 fs [36], it decays out of the state and may emit a photon, or manipulate a molecule. Therefore there are at least 3 decay channels: one leading to manipulation, one leading to light emission, and one that is inactive.…”

“…We take τ D =200 fs [36] and so convert the β values of figure 4 to the total probability of manipulation per injected electron N as displayed in figure 5(c). This form of analysis should be identical to the original 'scanning' manipulation work and indeed we find our results here match qualitatively and quantitatively with that earlier work [32,39].…”

Impact ionization dynamics in silicon by MV/cm THz fields

“…symmetry point (the smallest direct band gap), so interband transitions (process 1) result in electrons in the Lvalley. Then electrons undergo L-X intervalley scattering (process 2) with a time constant of 180 fs [28]. The electron distribution is thermally equilibrated with the lattice via phonon scattering within less than 2 ps [28][29][30].…”