Spin relaxation via exchange with donor impurity-bound electrons

TL;DR

This paper uncovers a new spin relaxation mechanism in low-temperature silicon, where exchange interactions with impurity-bound electrons cause depolarization of conduction electron spins, supported by experiments and theory.

Contribution

It introduces a novel spin relaxation process involving exchange with impurity-bound electrons, expanding understanding of spin dynamics in semiconductors.

Findings

Identified a new spin depolarization mechanism at low temperatures.

Demonstrated the mechanism's effects below and above impact ionization threshold.

Supported findings with silicon spin transport experiments and theoretical analysis.

Abstract

At low temperatures, electrons in semiconductors are bound to shallow donor impurity ions, neutralizing their charge in equilibrium. Inelastic scattering of other externally-injected conduction electrons accelerated by electric fields can excite transitions within the manifold of these localized states. Promotion of the bound electron into highly spin-orbit-mixed excited states drives a strong spin relaxation of the conduction electrons via exchange interactions, reminiscent of the Bir-Aronov-Pikus process where exchange occurs with valence band hole states. Through low-temperature experiments with silicon spin transport devices and complementary theory, we reveal the consequences of this previously unknown spin depolarization mechanism both below and above the impact ionization threshold.