Effect of strain on electronic and thermoelectric properties of few layers to bulk MoS$_{2}$

TL;DR

This study uses first principles calculations to show how different strains can tune the electronic and thermoelectric properties of MoS₂, inducing a reversible semiconductor-metal transition and optimizing thermoelectric performance.

Contribution

It reveals how normal compressive, biaxial compressive, and biaxial tensile strains affect the band gap and transport properties of MoS₂, providing insights for straintronics applications.

Findings

Reversible semiconductor-metal transition under all strain types.

Optimal thermoelectric performance in 2L and 3L MoS₂ under specific strains.

Large thermopower comparable to top thermoelectric materials.

Abstract

The sensitive dependence of electronic and thermoelectric properties of MoS$_2$ on the applied strain opens up a variety of applications in the emerging area of straintronics. Using first principles based density functional theory calculations, we show that the band gap of few layers of MoS$_2$ can be tuned by applying i) normal compressive (NC), ii) biaxial compressive (BC), and iii) biaxial tensile (BT) strain. A reversible semiconductor to metal transition (S-M transition) is observed under all three types of strain. In the case of NC strain, the threshold strain at which S-M transition occurs increases with increasing number of layers and becomes maximum for the bulk. On the other hand, the threshold strain for S-M transition in both BC and BT strain decreases with the increase in number of layers. The difference in the mechanisms for the S-M transition is explained for different types of applied strain. Furthermore, the effect of strain type and number of layers on the transport properties are also studied using Botzmann transport theory. We optimize the transport properties as a function of number of layers and applied strain. 3L- and 2L-MoS$_2$ emerge as the most efficient thermoelectric material under NC and BT strain, respectively. The calculated thermopower is large and comparable to some of the best thermoelectric materials. A comparison between the feasibility of these three types of strain is also discussed.