Spin-dependent optical properties in strained silicon and germanium

TL;DR

This paper develops a detailed theoretical framework to analyze how strain affects spin-polarized circularly polarized luminescence in silicon and germanium, linking symmetry considerations with numerical calculations.

Contribution

It introduces a comprehensive theory connecting strain, symmetry, and optical polarization in Si and Ge, with explicit ratios for luminescence intensities and polarization degrees.

Findings

Derived concise ratios for circular polarization intensities.

Explained polarization peaks in strained Si and Ge spectra.

Numerically modeled luminescence spectra using empirical methods.

Abstract

We present a comprehensive theory of the circularly polarized luminescence and its dependence on strain in spin-polarized Si and Ge. Symmetries of wavefunctions and interactions are used to derive concise ratios between intensities of the right and left circularly polarized luminescence for each of the dominant phonon-assisted optical transitions. These ratios are then used to explain the circular polarization degrees of the luminescence peaks in the spectra of biaxially-strained Si and Ge, and of relaxed ${\rm{Si}}_{1-x}{\rm{Ge}}_{x}$ alloys. The spectra are numerically calculated by a combination of an empirical pseudopotential method, an adiabatic bond-charge model and a rigid-ion model.