  We have investigated charge and spin transport in n-type metallic GaAs
nanowires (~ 10^17 cm^-3 doping level), grown by hydride vapor phase epitaxy
(HVPE) on Si substrates. This was done by exciting the nanowire by
tightly-focussed circularly-polarized light and by monitoring the intensity and
circular polarization spectrum as a function of distance from the excitation
spot. The spin-polarized photoelectrons give rise to a well-defined feature in
the nearbandgap spectrum, distinct from the main line due to recombination of
the spin-unpolarized electrons of the Fermi sea with the same minority
photoholes. At a distance of 2 (micro)m, only the main line remains, implying
that photoelectrons have reached a charge thermodynamic equilibrium with the
Fermi sea. However, although no line is present in the intensity spectrum at
the corresponding energy, the circular polarization is still observed at the
same energy in the spectrum, implying that photoelectrons have preserved their
spin orientation and that the two spin reservoirs remain distinct.
Investigations as a function of distance to the excitation spot show that,
depending on excitation power, a photoelectron spin polarization of 20% can be
transported over a record distance of more than 20 (micro)m. This finding has
potential applications for long distance spin transport in n-type doped
nanowires.
