Carrier dynamics in silicon nanowires studied via femtosecond transient optical spectroscopy from 1.1 to 3.5 eV

TL;DR

This study uses femtosecond transient spectroscopy across a broad energy range to comprehensively analyze carrier dynamics in silicon nanowires, revealing detailed electron and hole behaviors near the direct band gap.

Contribution

It provides the first complete spectral analysis of carrier dynamics in silicon nanowires from below to above the band gap, including band gap renormalization and phonon-assisted processes.

Findings

Disentangled electron and hole dynamics near the direct band gap.

Observed band gap renormalization effects at different pump energies.

Highlighted the role of phonon-assisted processes below 3.3 eV.

Abstract

We present femtosecond transient transmission (or absorbance) measurements in silicon nanowires in the energy range 1.1-3.5 eV, from below the indirect band-gap to above the direct band-gap. Our pump-probe measurements allow us to give a complete picture of the carrier dynamics in silicon. In this way we perform an experimental study with a spectral completeness that lacks in the whole literature on carrier dynamics in silicon. A particular emphasis is given to the dynamics of the transient absorbance at the energies relative to the direct band gap at 3.3 eV. Indeed, the use of pump energies below and above 3.3 eV allowed us to disentangle the dynamics of electrons and holes in their respective bands. The band gap renormalization of the direct band gap is also investigated for different pump energies. A critical discussion is given on the results below 3.3 eV where phonon-assisted processes are required in the optical transitions.