Spin-orbit and strain effect on power factor in monolayer MoS2

• Spin-orbit coupling (SOC) has remarkable effect on power factor.
• SOC can not only reduce power factor, but also enhance one.
• Strain can induce significantly enhanced power factor.
• Enhanced power factor can be explained by strain-induced accidental degeneracies.

Biaxial strain dependence of electronic structures and thermoelectric properties of monolayer MoS2MoS2, including compressive and tensile strain, are investigated by using local-density approximation (LDA) plus spin-orbit coupling (SOC). Both LDA and LDA + SOC results show that MoS2MoS2 is a direct gap semiconductor with optimized lattice constants. It is found that SOC has important effect on power factor. In n-type doping, the power factor with SOC is larger than that without SOC. However, in p-type doping, the power factor using LDA + SOC becomes very small compared to one using LDA. Both compressive and tensile strain can induce direct-indirect gap transition, which produce remarkable influence on power factor. Calculated results show that strain can induce significantly enhanced power factor in n-type doping by compressive strain and in p-type doping by tensile strain at the critical strain of direct-indirect gap transition. These can be explained by strain-induced accidental degeneracies, which leads to improved Seebeck coefficient. Calculated results show that n-type doping can provide better power factor than p-type doping. These results make us believe that thermoelectric properties of monolayer MoS2MoS2 can be improved in n-type doping by compressive strain.

In wide temperature range, strain can induce significantly enhanced power factor in n-type doping by compressive strain at the critical strain of direct-indirect gap transition.Figure optionsDownload as PowerPoint slide