  Thermal transport in bulk ternary III-V arsenide (III-As) semiconductor
alloys was investigated using equilibrium molecular dynamics with optimized
Albe-Tersoff empirical interatomic potentials. Existing potentials for binary
AlAs, GaAs, and InAs were optimized to obtain accurate phonon dispersions and
temperature-dependent thermal conductivity. Calculations of thermal transport
in ternary III-Vs commonly employ the virtual-crystal approximation (VCA),
where the structure is assumed to be a random alloy and all group-III atoms
(cations) are treated as if they have an effective weighted-average mass. Here,
we showed that is critical to treat atomic masses explicitly, and that the
thermal conductivity obtained with explicit atomic masses differs considerably
from the value obtained with the average VCA cation mass. The larger the
difference between the cation masses, the poorer the VCA prediction for thermal
conductivity. The random-alloy assumption in the VCA is also challenged,
because X-ray diffraction and transmission electron microscopy show order in
InGaAs, InAlAs, and GaAlAs epi-layers. We calculated thermal conductivity for
three common types of order [CuPt-B, CuAu-I, and triple-period-A (TPA)] and
showed that the experimental results for In$_{0.53}$Ga$_{0.47}$As and
In$_{0.52}$Al$_{0.48}$As, which are lattice matched to the InP substrate, can
be reproduced in molecular dynamics simulation with 2% and 8% of random
disorder, respectively. Based on our results, thermal transport in ternary
III-As alloys appears to be governed by the competition between mass-difference
scattering, which is much more pronounced than the VCA suggests, and the
long-range order that these alloys support.
