EN
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
at 200°C.
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.