Over the past few
decades, telluride-based chalcogenide
multilayers,
such as PbSeTe/PbTe, Bi2Te3/Sb2Te3, and Bi2Te3/Bi2Se3, were shown to be promising high-performance thermoelectric films.
However, the stability of performance in operating environments, in
particular, influenced by intermixing of the sublayers, has been studied
rarely. In the present work, the nanostructure, thermal stability,
and thermoelectric power factor of Sb2Te3/Ge1+xTe multilayers prepared by pulsed laser
deposition are investigated by transmission electron microscopy and
Seebeck coefficient/electrical conductivity measurements performed
during thermal cycling. Highly textured Sb2Te3films show p-type semiconducting behavior with superior power factor,
while Ge1+xTe films exhibit n-type semiconducting
behavior. The elemental mappings indicate that the as-deposited multilayers
have well-defined layered structures. Upon heating to 210 °C,
these layer structures are unstable against intermixing of sublayers;
nanostructural changes occur on initial heating, even though the highest
temperature is close to the deposition temperature. Furthermore, the
diffusion is more extensive at domain boundaries leading to locally
inclined structures there. The Sb2Te3sublayers
gradually dissolve into Ge1+xTe. This
dissolution depends markedly on the relative Ge1+xTe film thickness. Rather, full dissolution occurs rapidly
at 210 °C when the Ge1+xTe sublayer
is substantially thicker than that of Sb2Te3, whereas the dissolution is very limited when the Ge1+xTe sublayer is substantially thinner. The resulting
variations of the nanostructure influence the Seebeck coefficient
and electrical conductivity and thus the power factor in a systematic
manner. Our results shed light on a previously unreported correlation
of the power factor with the nanostructural evolution of unstable
telluride multilayers.