Theory of optical spin orientation in silicon

TL;DR

This paper provides a theoretical analysis of optical spin orientation in silicon, detailing the mechanisms, selection rules, and temperature effects on carrier and spin injection using advanced models.

Contribution

It introduces a comprehensive theoretical framework for understanding indirect optical spin injection in silicon, including valley anisotropy and temperature dependence.

Findings

Maximum spin polarization reaches 25% at low temperature

Injection rates are strongly valley-dependent

Temperature reduces spin polarization from 25% to 15%

Abstract

We theoretically investigate the indirect optical injection of carriers and spins in bulk silicon, using an empirical pseudopotential description of electron states and an adiabatic bond charge model for phonon states. We identify the selection rules, the contribution to the carrier and spin injection in each conduction band valley from each phonon branch and each valence band, and the temperature dependence of these processes. The transition from the heavy hole band to the lowest conduction band dominates the injection due to the large joint density of states. For incident light propagating along the $[00\bar{1}]$ direction, the injection rates and the degree of spin polarization of injected electrons show strong valley anisotropy. The maximum degree of spin polarization is at the injection edge with values 25% at low temperature and 15% at high temperature.