Charge and spin transport over record distances in GaAs metallic n -type nanowires

We have investigated charge and spin transport in n-type metallic GaAs nanowires (≈1017cm-3 doping level) grown by hydride vapor phase epitaxy (HVPE) on Si substrates. For this doping level, charge and spin transport might appear difficult because of the expected localization of minority holes in the valence band potential fluctuations generated by statistical fluctuations of the donor concentration. In contrast with these expectations, it is found, using spatially and spectrally resolved investigation of the luminescence intensity and circular polarization under laser excitation, that (i) establishment of a charge thermodynamic equilibrium between the photoelectrons and the Fermi sea occurs over a distance from the excitation spot of 2μm. At this distance, the spin polarization is still observed, implying that photoelectrons have preserved their spin orientation and that the two spin reservoirs remain distinct. (ii) Charge can be transported over record distances larger than 20μm at 6 K. (iii) Spatially-resolved investigations show that a photoelectron spin polarization of 20% can be transported over a record distance of more than 20μm. This long distance transport occurs because of the presence of large internal electric fields of ambipolar origin, further enhanced by the spatial redistribution of the Fermi sea. These findings have potential applications for long distance spin transport in n-type doped nanowires.