Raman and FTIR investigations of CdS based strained layer superlattices

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