1 research outputs found
Probing ultrafast carrier dynamics and nonlinear absorption and refraction in core-shell silicon nanowires
We investigate the relaxation dynamics of photogenerated carriers in silicon
nanowires consisting of a crystalline core and a surrounding amorphous shell,
using femtosecond time-resolved differential reflectivity and transmission
spectroscopy at photon energies of 3.15 eV and 1.57 eV. The complex behavior of
the differential transmission and reflectivity transients is the mixed
contributions from the crystalline core and the amorphous silicon on the
nanowire surface and the substrate where competing effects of state filling and
photoinduced absorption govern the carrier dynamics. Faster relaxation rates
are observed on increasing the photo-generated carrier density. Independent
experimental results on crystalline silicon-on-sapphire help us in separating
the contributions from the carrier dynamics in crystalline core and the
amorphous regions in the nanowire samples. Further, single beam z-scan
nonlinear transmission experiments at 1.57 eV in both open and close aperture
configurations yield two-photon absorption coefficient \ (~3 cm/GW) and
nonlinear refraction coefficient \ (-2.5x10^-4 cm2/GW).Comment: 6 pages, 6 figure