  Nowadays, making thermoelectric materials more efficient in energy conversion
is still a challenge. In this work, to reduce the thermal conductivity and thus
improve the overall thermoelectric performances, point and extended defects
were generated in epitaxial 111-ScN thin films by implantation using argon
ions. The films were investigated by structural, optical, electrical, and
thermoelectric characterization methods. The results demonstrated that argon
implantation leads to the formation of stable defects (up to 750 K operating
temperature) were identified as interstitial type defect clusters and so-called
argon-vacancy complexes. The insertion of those specific defects induces
acceptor-type deep levels in the bandgap yielding to a reduce of the free
carrier mobility. With a reduce electrical conductivity, the irradiated sample
exhibited higher Seebeck coefficient maintaining the power factor of the film.
The thermal conductivity is strongly reduced from 12 to 3 W.m-1.K-1 at 300 K,
showing the effect of defects in increasing phonon scattering. Subsequent high
temperature annealing, at 1573 K, leads to the progressive evolution of
defects: the initial clusters of interstitial evolved to the benefit of smaller
clusters and the formation of bubble. Thus, the number of free carriers, the
resistivity and the Seebeck coefficient are almost restored but the mobility of
the carriers remains low and a 30% drop in thermal conductivity is still
effective (8.5 W.m-1.K-1). This study shows that the control defect engineering
with defects introduced by irradiation using noble gases in a thermoelectric
coating can be an attractive method to enhance the figure of merit of
thermoelectric materials.

Materials Science