  Experimental evidence of electron spin precession during travel through the
phosphorus-doped Si channel of an all-electrical device simultaneously
indicates two distinct processes: (i) short timescales (~50ps) due to purely
conduction-band transport from injector to detector, and (ii) long timescales
(~1ns) originating from delays associated with capture/re-emission in shallow
impurity traps. The origin of this phenomenon, examined via temperature,
voltage, and electron density dependence measurements, is established by means
of comparison to a numerical model and is shown to reveal the participation of
metastable excited states in the phosphorus impurity spectrum. This work
therefore demonstrates the potential to make the study of macroscopic spin
transport relevant to the quantum regime of individual spin interactions with
impurities as envisioned for quantum information applications.
