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https://hdl.handle.net/2142/23923
Description
Title
Dispersive phonon imaging in III-V semiconductors
Author(s)
Hebboul, Saad Eddine
Issue Date
1988
Doctoral Committee Chair(s)
Wolfe, J.P.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
dispersive phonon imaging
III-V Semiconductors
low-temperature transport properties
high-frequency acoustic phonons
GaAs
InSb
InP
InAs
Language
en
Abstract
"Low-temperature transport properties of high-frequency acoustic phonons
are investigated in GaAs, InSb, InP and InAs using the phonon-imaging technique.
In this method, a focused laser beam provides a movable heat source on one side
of a cooled crystal (~ 2 K). A single small phonon detector on the opposite face
records the transmitted heat flux as a function of propagation direction. Ballistic
phonons channel along directions in the crystal which are completely determined by
the detailed shape of constant-energy surfaces in wavevector space. The resulting
focusing patterns are characterized by sharp phonon caustics which are clearly identified
from the continuous background due to scattered phonons. In the dispersive
regime, where phonon wavelength is comparable to atomic spacing, the angular positions
of these caustic lines are very sensitive to phonon frequency, thus providing a
novel test for lattice dynamics theories. Experiments are performed with superconducting
tunnel junctions and Al bolometers to probe both the high-frequency and
low-frequency regimes, respectively. We find that large-k ballistic phonons give rise
to distinct focusing patterns in all four types of crystals, with thicknesses varying
between 0.4 and 0.8 mm. Due to isotope scattering in the bulk, tunnel-junction
experiments yield well-defined caustic patterns with a dominant frequency given by
the detector gap 2.6.. In InSb, where zone boundary frequencies are small ( VT A ""'
1.2 THz), the frequency dependence of the dispersive phonon focusing patterns are
Ill
measured using PbTl (0.43, 0.59 THz) and PbBi (0.69, 0.73, 0.78, 0.82 THz) tunnel
junction detectors. The results are interpreted with Monte Carlo calculations
based on rigid, dipole, shell, and bond-charge models. Although each model yields
satisfactory fits to the previously measured dispersion curves, the predicted patterns
show remarkable differences in the caustic structures. This result underscores
the utility of phonon imaging in providing new information about the elastic forces
between atoms in crystals."
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