Ultrafast
Electrical Measurements of Isolated Silicon
Nanowires and Nanocrystals
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Abstract
We
simultaneously determined the charge carrier mobility and picosecond
to nanosecond carrier dynamics of isolated silicon nanowires (Si NWs)
and nanocrystals (Si NCs) using time-resolved terahertz spectroscopy.
We then compared these results to data measured on bulk c-Si as a
function of excitation fluence. We find >1 ns carrier lifetimes
in
Si NWs that are dominated by surface recombination with surface recombination
velocities (SRV) between ∼1100–1700 cm s<sup>–1</sup> depending on process conditions. The Si NCs have markedly different
decay dynamics. Initially, free-carriers are produced, but relax within
∼1.5 ps to form bound excitons. Subsequently, the excitons
decay with lifetimes >7 ns, similar to free carriers produced in
bulk
Si. The isolated Si NWs exhibit bulk-like mobilities that decrease
with increasing excitation density, while the hot-carrier mobilities
in the Si NCs are lower than bulk mobilities and could only be measured
within the initial 1.5 ps decay. We discuss the implications of our
measurements on the utilization of Si NWs and NCs in macroscopic optoelectronic
applications