Optical Phonon Probes of the Lateral Scale of Interface Roughness - A Theoretical Investigation

We study the effect of the different lateral scale of interface roughness on the optical photon spectrum of thin Si/Ge (001) superlattices. We find that the first Si-like confined optical mode does localize either in the thinnest or in the thicker part of the Si well already for relatively small lateral sizes of the interface terraces, contrary to the corresponding behaviour in GaAs/AlAs structures. We show that this gives rise to distinct changes in the Raman lineshape, which should be useful to discriminate between short-range intermixing and long-range interface corrugation in Si/Ge superlattices. We finallyy discuss the optimal conditions to allow experimental observations of this effect.