Phonon focusing in superlattices

Abstract

Phonon focusing in periodic superlattices is studied in terms of the plane-wave expansion method rather than the conventional transfer matrix method. At the frequencies where the intramode and intermode Bragg reflections of phonons occur the group velocity of phonons along the growth direction vanishes, giving rise to the disappearance and/or appearance of phonon caustics. This can be explicitly shown by plotting theoretical phonon images in the planes both normal and perpendicular to the growth direction. Numerical examples are given for (001)GaAs/AlAs superlattices.