  For applications in energy harvesting, environmentally friendly cooling, and
as power sources in remote or portable applications, it is desired to enhance
the efficiency of thermoelectric materials. One strategy consists of reducing
the thermal conductivity while increasing or retaining the thermoelectric power
factor. An approach to achieve this is doping to enhance the Seebeck
coefficient and electrical conductivity, while simultaneously introducing
defects in the materials to increase phonon scattering. Here, we use Mg ion
implantation to induce defects in epitaxial ScN (111) films. The films were
implanted with Mg+ ions with different concentration profiles along the
thickness of the film, incorporating 0.35 to 2.2 at.% of Mg in ScN.
Implantation at high temperature (600 C), with few defects due to the
temperature, does not substantially affect the thermal conductivity compared to
a reference ScN. Samples implanted at room temperature, in contrast, exhibited
a reduction of the thermal conductivity by a factor of three. The sample doped
with 2.2 at.% Mg also showed an increased power factor after implantation. This
study thus shows the effect of ion-induced defects on thermal conductivity of
ScN films. High-temperature implantation allows the defects to be annealed out
during implantation, while the defects are retained for room-temperature
implanted samples, allowing for a drastic reduction in thermal conductivity.
