Epitaxial Growth of BaTiO$_{3}$/SrTiO$_{3}$ and BaO/SrTiO$_{3}$ Superlattices for Phonon Confinement*

We discuss the design and material parameters of BaTiO$_{3}$/SrTiO$_{3}$ and BaO/SrTiO$_{3}$ heterostructures relevant for novel phonon devices, including mirrors, filters, and cavities for coherent phonon generation and control. The advantages of using these ferroelectric superlattices include that they have an enormous stop band compared to the GaAs/AlAs superlattices previously reported for this application and that there can be greatly amplified light-sound interaction in these ferroelectric materials. We have grown BaTiO$_{3}$/SrTiO$_{3}$ and BaO/SrTiO$_{3}$ superlattices on TiO$_{2}$-terminated SrTiO$_{3}$ substrates by reactive MBE. Structural characterization by XRD and TEM revealed that the samples studied are of high quality with nearly atomically abrupt interfaces. We have observed folded acoustic phonons at the expected frequencies using UV Raman spectroscopy.