Layer Stacking-Induced Transition to a Kane-Band Semiconductor in Sb₂Te₃

We investigate the electronic properties of phases in the Sb2Te3 system based on the alternate AA stacking that was recently experimentally identified in Sb2Te3 nanowires. The conventional ABC stacking of these materials is the basis of well-established thermoelectric materials related in part to their complex topological electronic structures. We find topological behavior in AA-stacked Sb2Te3, as in the ABC-stacked case, but the carrier pockets are distinctly different from those in the ABC-stacked case. While the electronic structure near the band edges remains three-dimensional with the AA-stacked Sb2Te3, it is less so than in the ABC case, particularly for n-type. The band structure shows a Kane band shape in the in-plane direction, with a small band gap and small effective masses. We find an unusual combination of low in-plane effective mass and relatively high optical absorption. This combination is a sought-after feature for infrared detection. AA-stacked Sb2Te3 has a quasi-direct band gap (0.14 eV) and ultrasmall hole and electron transport effect masses at low carrier concentrations (e.g., me/h(ab)* ≈ 2 × 10–2 at 1017 cm–3 and 2 × 10–3 at 1016 cm–3). The distinctly different electronic properties of AA-stacked Sb2Te3 as compared to the conventional ABC stacking yield different properties that may potentially be exploited in bulk form or in heterostructures. We additionally report results for the hypothetical AA-stacked Bi2Te3 sister compound.