DISPERSIVE PHONON IMAGING OF INAS

The phonon-focusing patterns of ballistic phonons in InAs are measured in the frequency range 0.1 to 1 THz, in an effort to test the global validity of lattice dynamics models for this semiconductor. Phonon cau stic patterns depend sensitively on the shapes of constant frequency s urfaces. Several tunnel-junction detectors with sensitivity onsets in this frequency range are used to measure dispersive shifts in the phon on caustics. The measured caustic positions are compared to those pred icted by rigid-ion and bond-charge models. Similar to the case of InSb studied by Hebboul and Wolfe, a 6-parameter bond-charge model (BCM) - with force constants determined by neutron, X-ray, and Raman scatteri ng - reproduces the phonon-imaging data both qualitatively and quantit atively. Comparisons of the focusing patterns with an 11-parameter rig id-ion model (RIM) do not show good agreement. New structures are pred icted in the phonon-focusing patterns at frequencies above about 1.2 T Hz - presently outside our experimental range - which are highly sensi tive to the theoretical modeling.