Theory of Optical Orientation in n-Type Semiconductors

TL;DR

This paper develops a theoretical model for spin relaxation in n-GaAs semiconductors, explaining various experimental observations of spin decoherence processes and relaxation times under different conditions.

Contribution

It introduces a set of rate equations for localized and itinerant spins, providing a comprehensive explanation of temperature, doping, and field effects on spin relaxation.

Findings

The model explains temperature and doping dependence of spin relaxation times.

It accounts for both localized and conduction band spin interactions.

The theory aligns with experimental data from time-resolved magnetization measurements.

Abstract

Time resolved measurements of magnetization in n-GaAs have revealed a rich array of spin decoherence processes, and have shown that fairly long lifetimes (\sim 100 ns) can be achieved under certain circumstances. In time-resolved Faraday rotation and time-resolved Kerr rotation the evolution of the magnetization can be followed as a function of temperature, applied field, doping level and excitation level. We present a theory for the spin relaxation in n-GaAs based on a set of rate equations for two interacting thermalized subsystems of spins: localized states on donor sites and itinerant states in the conduction band. The conduction band spins relax by scattering from defects or phonons through the D'yakonov-Perel' mechanism, while the localized spins relax by interacting with phonons (when in an applied field) or through the Dzyaloshinskii-Moriya interaction. In this model, numerous features of the data, including puzzling temperature and doping dependences of the relaxation time, find an explanation.