Simultaneous enhancement in electrical conductivity and Seebeck coefficient by single- to double-valley transition in a Dirac-like band

Abstract

SnTe possesses a single- to double-valley transition in the conduction band minimum when a compressive strain is applied. Through a tight-binding analysis, it is shown that the variation of the band structure is attributed to the strain-induced delocalization of both the Sn-5s orbitals and Te-5p orbitals with different angular momenta. This effect can largely increase the electron density of states near the band edge and thus keep the Fermi level of the compressed SnTe closer to it, where the electrons have lower scattering rates. The strain-induced double valleys lead to simultaneous increases in the electrical conductivity and the Seebeck coefficient and thereby nearly four times the enhancement of the power factor at the doping concentration of 5×1019cm–3. This work suggests a feasible concept that can be employed to promote the power factor of a Dirac semiconductor via manipulating the valley degeneracy in the conduction band minimum.