SnTe
is an attractive candidate for applications as a p-type thermoelectric
semiconductor. The pristine SnTe compound exhibits poor thermoelectric
performance at high temperatures because of its high hole concentration,
small band gap, and large energy difference between the light and
heavy bands (ΔE(L – Σ)). To overcome
these problems, we investigate band structure changes upon the addition
of trivalent dopants based on the tight-binding (TB) model and density
functional theory (DFT) calculations. We find that tuning the relative
on-site energies of the cation and anion s and p orbitals is a potential
route for engineering band convergence. Codoping with Ge in addition
to trivalent substitutions further enhances thermoelectric performance.
We find that a low concentration of the isovalent Ge as well as As,
which also acts as a donor (Sn0.952Ge0.016As0.016Te), induces band convergence (ΔE(L – Σ) = 0.12 eV) and enlarges the band gap (0.20 eV).
This band convergence results in a remarkable increase of the peak
power factor, while the increased band gap energy suppresses detrimental
bipolar effects. We find that the theoretical and experimental results
are in good agreement here, and the high power factor (high weighted
mobility) can be attributed to the increased band convergence. Our
work can efficiently screen the promising trivalent substitutions
in SnTe-based materials codoped with Ge and find promising candidates
for improved thermoelectric performance.
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