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., m_e/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.