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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. (C) 2002 Elsevier Science B.V. All rights
reserved.