The contributions of composition and strain to the phonon shift in Ge1−xSnx 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 Δω(x)=−30.3xcm−1 for the strained alloys while it is Δω(x)=−83.1xcm−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.

Research highlights
► Raman scattering in both strained and relaxed Ge1−xSnx alloys.
► Experimental and theoretical study of the linear frequency-shift coefficient.
► Experimental results are in good agreement with theoretical predictions.
► The contributions of composition and strain have been clarified.