New angles of phonon refraction

Abstract The true phonon analog of optical focusing is the redirection of flux at an interface, where continuity of interface strains requires the conservation of the wave vector component parallel to the interface on either side. Such refraction is observable only at extremely clean defect-free interfaces. We have conducted phonon imaging studies of a variety of wafer-bonded samples in which the bonded materials have a large lattice mismatch at the interface (e.g., [0 1 1] GaAs bonded to [0 0 1] GaAs). The materials on either side of the bond are of the same crystalline type but are acoustically distinct because of the deliberate misorientation of the sample faces. Phonon imaging reveals a combination of refraction and diffuse scattering at these interfaces. Comparison of the experimental images to computer simulations confirms the dominance of refraction without energy down-conversion at high quality interfaces and provides interesting evidence of inelastic phonon–defect interactions.