Influence of the short-range structural properties on the elastic constants of Si/Ge superlattices

The elastic constant tensor of Si-m/Ge-n superlattices with different modul ation wavelengths has been determined by Brillouin light scattering spectro scopy. The C-11 elastic constant obtained for Si-n/Ge-n (where bilayers are built up by an equal number of Si and Ge monolayers) and Si-n/Ge-4n superl attices are 13% above the predictions of the continuum elasticity theory, u sing the C-ij Values of bulk Si and Ge. On the other hand, the elastic cons tant tensor of Si-4n/Ge-n and Si-3n/Ge-n superlattices matches perfectly th e predictions. A structural analysis by extended x-ray absorption fine stru cture spectroscopy of the interfaces has been carried out and the unexpecte d different elastic behaviour can be explained by the observed strains at t he superlattice interfaces.