Spin relaxation of conduction electrons by inelastic scattering with neutral donors*

At low temperatures in n-doped semiconductors, a significant fraction of shallow donor sites are occupied by electrons, neutralizing the impurity core charge in equilibrium. Inelastic scattering by externally-injected conduction electrons accelerated by electric fields can excite transitions within the manifold of these localized states. Promotion into highly spin-mixed excited states results in spin relaxation that couples strongly to the conduction electrons by exchange interaction. Through experiments with silicon spin transport devices and complementary theory, we reveal the consequences of this previously unknown depolarization mechanism both below and above the impact ionization threshold and into the ``deep inelastic'' regime.