Optical phonon shift coefficients are studied over the entire composition range of Si1-x Gex, taking into account the effects of composition, atomistic disorder and strain. Ab initio calculations complement various experimental observations found in the literature by revealing that strain effects on the optical phonons-both hydrostatic and biaxial-vary nonlinearly with composition. Additionally, the pure mode frequencies of the highest optical phonon modes in unstrained Si1-x Gex are found to shift linearly with composition, while the mixed-mode frequency shifts quadratically with composition around x=0.5. While atomic randomness affects the composition dependence of the optical phonons, the strain-shift coefficients are approximately insensitive to the local atomic configuration. Short range atomic ordering increases the linear and nonlinear effects.
ASJC Scopus subject areas
- Physics and Astronomy(all)