  Dislocations, one-dimensional lattice imperfections, are common to
technologically important materials such as III-V semiconductors, and adversely
affect heat dissipation in e.g., nitride-based high-power electronic devices.
For decades, conventional models based on nonlinear elasticity theory have
predicted this thermal resistance is only appreciable when heat flux is
perpendicular to the dislocations. However, this dislocation-induced
anisotropic thermal transport has yet to be seen experimentally. In this study,
we measure strong thermal transport anisotropy governed by highly oriented
threading dislocation arrays along the cross-plane direction in micron-thick,
single-crystal indium nitride (InN) films. We find that the cross-plane thermal
conductivity is more than tenfold higher than the in-plane thermal conductivity
at 80 K when the dislocation density is on the order of ~3x10^10 cm^-2. This
large anisotropy is not predicted by the conventional models. With enhanced
understanding of dislocation-phonon interactions, our results open new regimes
for tailoring anisotropic thermal transport with line defects, and will
facilitate novel methods for directed heat dissipation in thermal management of
diverse device applications.
