Thickness and strain effects on the thermoelectric transport in nanostructured Bi₂Se₃

The structural stability, electronic structure, and thermal transport properties of one to six quintuple layers (QLs) of Bi₂Se₃ are investigated by van der Waals density functional theory and semi-classical Boltzmann theory. The bandgap amounts to 0.41 eV for a single QL and reduces to 0.23 eV when the number of QLs increases to six. A single QL has a significantly higher thermoelectric figure of merit (0.27) than the bulk material (0.10), which can be further enhanced to 0.30 by introducing 2.5% compressive strain. Positive phonon frequencies under strain indicate that the structural stability is maintained.