Enhanced thermoelectric power in two-dimensional transition metal dichalcogenide monolayers

The carrier-density-dependent conductance and thermoelectric properties of large-area $\mathrm{Mo}{\mathrm{S}}_{2}$ and $\mathrm{WS}{\mathrm{e}}_{2}$ monolayers are simultaneously investigated using the electrolyte gating method. The sign of the thermoelectric power changes across the transistor off-state in the ambipolar $\mathrm{WS}{\mathrm{e}}_{2}$ transistor as the majority carrier density switches from electron to hole. The thermopower and thermoelectric power factor of monolayer samples are one order of magnitude larger than that of bulk materials, and their carrier-density dependences exhibit a quantitative agreement with the semiclassical Mott relation based on the two-dimensional energy band structure, concluding the thermoelectric properties are enhanced by the low-dimensional effect.