Designing Rashba systems for high thermoelectric performance based on the van der Waals heterostructure

The electronic structures of semiconductors and their related transport properties can be tuned via the Rashba effect, which improves thermoelectric performance. The Rashba effect is caused by spin–orbit coupling and breaking of inversion symmetry. Here, we engineer the Rashba effect by constructing two-dimensional (2D) van der Waals heterostructures (vdWHs) Sb/As and Bi/Sb. These break the z-inversion symmetry by removing the reflection along the z-direction, affording Rashba splitting at the top of the valence band. The resulting complex energy bands exhibit enhanced electronic density of states near the band edge and maintain the electrical conductivity. The Sb/As heterostructure has Seebeck coefficients 1.5 times larger than those of the corresponding monolayers, and the Bi/Sb system has an enhanced Seebeck coefficient at high carrier concentrations. Our work demonstrates that 2D vdWHs can be used to induce Rashba splitting with band structure changes that yield favorable thermoelectric properties. This offers a new strategy for designing novel 2D functional materials.