Charge and spin transport over record distances in GaAs metallic n-type nanowires : I photocarrier transport in a dense Fermi sea

TL;DR

This study demonstrates record-long charge and spin transport distances in n-type GaAs nanowires, revealing that spin polarization can be maintained over 20 micrometers despite charge reaching equilibrium.

Contribution

It provides the first evidence of long-distance spin transport in metallic GaAs nanowires, with spin polarization preserved over record distances of more than 20 micrometers.

Findings

Spin polarization of 20% transported over 20 micrometers.

Charge reaches thermodynamic equilibrium within 2 micrometers.

Spin reservoirs remain distinct despite charge equilibrium.

Abstract

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.