Raman scattering characterization of strain in Ge-Si core-shell nanowires

Strain relaxation in Ge-Si core-shell nanowires is studied by means of Raman spectroscopy. A recently developed model of strain in these structures is extended to allow for partial strain relaxation and used to calculate the core and shell Raman spectra of the nanowires. We find that all Ge-Si core-shell nanowires studied here, with core diameters of 11nm or higher, have partially relaxed strains. This agrees with some theoretical predictions of critical thicknesses in these structures. Our Raman data also show strong evidence for Ge-Si intermixing at the core-shell interface.