The contributions of composition and strain to the phonon shift in alloys

Strained and relaxed Ge1−xSnx alloys grown on Si(001) substrates by molecular beam epitaxy have been studied by Raman scattering. The compositional dependence of the Ge–Ge Raman mode has been measured to be Δ ω ( x ) = − 30.3 x cm − 1 for the strained alloys while it is Δ ω ( x ) = − 83.1 x cm − 1 for the relaxed ones, which are in good agreement with theoretical predictions. The results clearly show that, with the increase of Sn concentration, the Ge–Ge phonon frequency decreases much more slowly in the strained alloys than in the relaxed ones.