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Abstract
We show that certain three-dimensional (3D) superlattice nanostructure based on Bi2Te3 topological insulator thin films has better thermoelectric performance than two-dimensional (2D) thin films. The 3D superlattice shows a predicted peak value of ZT of approximately 6 for gapped surface states at room temperature and retains a high figure of merit ZT of approximately 2.5 for gapless surface states. In contrast, 2D thin films with gapless surface states show no advantage over bulk Bi2Te3. The enhancement of the thermoelectric performance originates from a combination of the reduction of lattice thermal conductivity by phonon-interface scattering, the high mobility of the topologically protected surface states, the enhancement of Seebeck coefficient, and the reduction of electron thermal conductivity by energy filtering. Our study shows that the nanostructure design of topological insulators provides a possible new way of ZT enhancement.
Highlights
The search of good thermoelectrics with high figure of merit [1,2] ZT 1⁄4S2σT κe þ κl ð1Þ is usually baffled by the competition of the Seebeck coefficient S, the electrical conductivity σ, the electron thermal conductivity κe and the lattice thermal conductivity κl
The consideration of nanostructures of thin films is motivated by the fact that a single layer of thin film is not of much practical use for thermoelectric applications, and stacks of thin films have much lower lattice thermal conductivity compared with the bulk [21]
ZT values depend on the geometric parameters a, b, c and d since both the lattice thermal conductivity and the electronic transport coefficients depend on these parameters
Summary
High ZT values of Bi2Te3 thin films depend crucially on the opening of a subgap at the surface, which disappears quickly with the increasing of the film thickness, China. Despite the high mobility [18] of the surface electrons, the gapless surface states would lead to poor thermoelectric performance due to low Seebeck coefficient and high electron thermal conductivity. By creating suitable nanostructures, extra energy-dependent electron scattering mechanisms can be introduced, which could increase the Seebeck coefficient [19,20] and reduce the electron thermal conductivity. The consideration of nanostructures of thin films is motivated by the fact that a single layer of thin film is not of much practical use for thermoelectric applications, and stacks of thin films have much lower lattice thermal conductivity compared with the bulk [21]
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