  We have used a polarized microluminescence technique to investigate
photocarrier charge and spin transport in n-type depleted GaAs nanowires ($
\approx 10^{17}$ cm$^{-3}$ doping level). At 6K, a long-distance tail appears
in the luminescence spatial profile, indicative of charge and spin transport,
only limited by the length of the NW. This tail is independent on excitation
power and temperature. Using a self-consistent calculation based on the
drift-diffusion and Poisson equations as well as on photocarrier statistics
(Van Roosbroeck model), it is found that this tail is due to photocarrier drift
in an internal electric field nearly two orders of magnitude larger than
electric fields predicted by the usual ambipolar model. This large electric
field appears because of two effects. Firstly, for transport in the spatial
fluctuations of the conduction band minimum and valence band maximum, the
electron mobility is activated by the internal electric field. This implies, in
a counter intuitive way, that the spatial fluctuations favor long distance
transport. Secondly, the range of carrier transport is further increased
because of the finite NW length, an effect which plays a key role in
one-dimensional systems.
