  Aluminum scandium nitride alloy (Al1-xScxN) is regarded as a promising
material for high-performance acoustic devices used in wireless communication
systems. Phonon scattering and heat conduction processes govern the energy
dissipation in acoustic resonators, ultimately determining their performance
quality. This work reports, for the first time, on phonon scattering processes
and thermal conductivity in Al1-xScxN alloys with the Sc content (x) up to
0.26. The thermal conductivity measured presents a descending trend with
increasing x. Temperature-dependent measurements show an increase in thermal
conductivity as the temperature increases at temperatures below 200K, followed
by a plateau at higher temperatures (T> 200K). Application of a virtual crystal
phonon conduction model allows us to elucidate the effects of boundary and
alloy scattering on the observed thermal conductivity behaviors. We further
demonstrate that the alloy scattering is caused mainly by strain-field
difference, and less by the atomic mass difference between ScN and AlN, which
is in contrast to the well-studied Al1-xGaxN and SixGe1-x alloy systems where
atomic mass difference dominates the alloy scattering. This work studies and
provides the quantitative knowledge for phonon scattering and the thermal
conductivity in Al1-xScxN, paving the way for future investigation of materials
and design of acoustic devices.
