Control of valley degeneracy in MoS2 by layer thickness and electric field and its effect on thermoelectric properties

Abstract

We have investigated the valley degeneracy of MoS2 multilayers and its effect on thermoelectric power factors. By modulating the layer thickness and external electric field strength, the hole valleys in the highest energy valence band at Gamma and K points and the electron valleys in the lowest energy conduction band at K and Sigma(min) points are shifted differently. The hole valley degeneracy is observed in MoS2 monolayer, while that of electron valley is in MoS2 bilayer and monolayer under the external electric field. By tuning the valley degeneracy, the Seebeck coefficient and electrical conductivity can be separately controlled, and the maximum power factor can be obtained in n-type (p-type) MoS2 monolayer with (without) the external electric field. We suggest that the transition metal dichalcogenides are good examples to investigate the role of valley degeneracy in the thermoelectric and optical properties with the control of interlayer interaction and external electric field strength.