Thermoelectric transport contribution from topological surface states vs 2D-electron gas in 10 nm Bi₂Se₃

Topological surface states (TSSs) coexist with a rapidly formed two-dimensional electron gas (2DEG) at the surface of Bi2Se3. While this complex band structure has been widely studied for its interactions between the two states in terms of electrical conductivity and carrier density, the resulting thermopower has not been investigated as thoroughly. Here, we report measurements of the temperature dependent Seebeck coefficient (S) and electrical conductivity (σ) on an undoped 10 nm thin Bi2Se3 film over the temperature range of 100-300 K to find an overall metal-like behavior. The measured S is consistent with the theory when assuming that both the TSS and the 2DEG contribute to thermoelectric transport. Our analysis further shows that the coefficient corresponds to a Fermi level situated well above the conduction band minima of the 2DEG, resulting in comparable contributions from the TSS and the 2DEG. The thermoelectric power factor (S2σ) at 300 K increases by 10%-30% over the bulk. This work provides insights into understanding and enhancing thermoelectric phenomena in topological insulators.