Effects of composition, strain, and atomic disorder on optical phonon frequencies in Si1−xGex

Abstract

Optical phonon shift coefficients are studied over the entire composition range of Si1−xGex, 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−xGex 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.

Structural and vibrational properties of SnxGe1-x: Modeling and experiments

“…It is known that the Raman frequency shift in semiconductor solid solutions is affected by the composition and strain, which are not always independent [28,29].…”

Micro and nanofabrication of SiGe/Ge bridges and membranes by wet-anisotropic etching

“…4, where the two spectra are plotted, displaying an intense Ge peak and the small Ge-Ge and Si-Ge bands of the SiGe alloy. [27][28][29] Due to the low silicon content of the alloy, the Si-Si band of the SiGe is too low to be detected. The SiGe bands prove that the top layer is preserved in both cases.…”

Hydrostatic strain enhancement in laterally confined SiGe nanostripes

“…Several authors 40,41 reported that for x Ge larger than 50%, the Si-Ge peak shifts to lower frequency values as the strain changes from compressive (negative) to tensile (positive). Thus the red shift of the Si-Ge peak, measured while moving from the edge to the center of the nano-stripe (see Fig.…”