  From electrodeless time-resolved microwave conductivity measurements, the
efficiency of charge carrier generation, their mobility, and decay kinetics on
photo-excitation were studied in arrays of Si nanowires grown by the
vapor-liquid-solid mechanism. A large enhancement in the magnitude of the
photoconductance and charge carrier lifetime are found depending on the
incorporation of impurities during the growth. They are explained by the
internal electric field that builds up, due to a higher doped sidewalls, as
revealed by detailed analysis of the nanowire morphology and chemical
composition.
