  Carrier recombination dynamics in strip silicon nano-waveguides is analyzed
through time-resolved pump-and-probe experiments, revealing a complex
recombination dynamics at densities ranging from ${10^{14}}$ to
${10^{17}}\,$cm$^{{-3}}$. Our results show that the carrier lifetime varies as
recombination evolves, with faster decay rates at the initial stages (with
lifetime of ${\sim 800}\,$ps), and much slower lifetimes at later stages (up to
${\sim 300}\,$ns). We also observe experimentally the effect of trapping,
manifesting as a decay curve highly dependent on the initial carrier density.
We further demonstrate that operating at high carrier density can lead to
faster recombination rates. Finally, we present a theoretical discussion based
on trap-assisted recombination statistics applied to nano-waveguides. Our
results can impact the dynamics of several nonlinear nanophotonic devices in
which free-carriers play a critical role, and open further opportunities to
enhance the performance of all-optical silicon-based devices based on carrier
recombination engineering.
