Raman and FTIR Investigations of CdS Based Strained Layer Superlattices

Abstract

The lattice dynamical properties of cubic CdS/ZnS(e) and hexagonal CdSe/CdS superlattices are investigated by means of Raman and FTIR spectroscopy. Due to the good lateral and in-depth homogeneity of the layer thicknesses folded longitudinal acoustic phonons are observed for all three superlattice systems. The determined frequencies agree quite well with calculations based on the Rytov model. For the optical phonons strain-induced energy shifts become important. Besides, we observe higher order confined longitudinal optical phonons in CdS/ZnSe superlattices. Our experimental results are compared with calculations based on a linear-chain model showing that in this AB/CD type superlattice real interface modes can be observed.