Substrate-induced phonon frequency shifts of (Si)4/(Ge)4superlattices

Abstract
The substrate-induced phonon frequency shifts of strained (Si)4/(Ge)4 superlattices, grown pseudomorphically on a (001)-oriented Si1-xGex(0<or=x<or=1) substrate at the zone centre, are studied by the Keating model. It is found that the longitudinal modes decrease almost linearly with an increase in the Ge fraction factor x and the transverse modes increase linearly.