Ambipolar Surface State Thermoelectric Power of Topological Insulator Bi2Se3

TL;DR

This study investigates the thermoelectric properties of Bi2Se3 thin films in the topological insulator regime, revealing ambipolar behavior, surface state contributions, and potential for thermoelectric device optimization.

Contribution

It provides the first detailed gate-tuned thermoelectric measurements of Bi2Se3 surface states, highlighting the role of surface and bulk states in thermoelectric performance.

Findings

Thermoelectric power sign changes across charge neutrality point.

Power factor is enhanced near electron-hole puddle density.

Surface state thermoelectric behavior aligns with Mott relation at low doping.

Abstract

We measure gate-tuned thermoelectric power of mechanically exfoliated Bi2Se3 thin films in the topological insulator regime. The sign of the thermoelectric power changes across the charge neutrality point as the majority carrier type switches from electron to hole, consistent with the ambipolar electric field effect observed in conductivity and Hall effect measurements. Near charge neutrality point and at low temperatures, the gate dependent thermoelectric power follows the semiclassical Mott relation using the expected surface state density of states, but is larger than expected at high electron doping, possibly reflecting a large density of states in the bulk gap. The thermoelectric power factor shows significant enhancement near the electron-hole puddle carrier density ~ 0.5 x 1012 cm-2 per surface at all temperatures. Together with the expected reduction of lattice thermal conductivity in low dimensional structures, the results demonstrate that nanostructuring and Fermi level tuning of three dimensional topological insulators can be promising routes to realize efficient thermoelectric devices.