Bi2Te3, (Bi1−xSbx )2Te3 and layered Bi2Te3/(Bi1−xSbx)2Te3 superlattices fabricated by nanoalloying. Our approach is
based on the sequential sputtering of nanoscale layers of
the elements and subsequent annealing in order to induce
a solid state reaction. While conventionally Bi2(SexTe1−x )3 compounds are used as n-type V2VI3 material system, the deposition
of Se proves to be problematic especially for sputtering
deposition and is therefore replaced by (Bi1−xSbx )2Te3. A
superlattice consisting of 25 nm Bi2Te3/25 nm (Bi0:9Sb0:1)2Te3 – ML (periodicity of 50 nm) was synthesized and annealed
at temperatures of 150, 200, 225, and 250°C. The layers are
slightly rough and polycrystalline, and the grain sizes increase
with increasing annealing temperature. The XRD analysis
shows a pronounced (00l) texture of the sputtered layers.
SIMS depth profiles reveal that the chemical separation into
layers is present, yet smeared out to some degree after annealing
High Seebeck coefficients of up to ~−190 μV/K were
achieved. A high maximum power factor of 22 μW/cmK2 can be attained after annealing at 250 °C for 12 h. The superlattice
system Bi2Te3 / (Bi1−xSbx )2Te3 can compete with
Bi2Te3 / Bi2(SexTe1−x )3 in terms of electrical properties while
representing a good practical alternative for the sputter deposition
due to the substitution of problematic Se with Sb.
Cross-plane thermal conductivities are in the range of 0.55 to
0.6 W/mK. The thermal conductivity is generally reduced due
to the nanocrystallinity of the material, however, there seems
to be no measurable reduction of the thermal conductivity by
the superlattice-type 2D nanostructuring.