Significant enhancement in thermoelectric power with Iso-electronic doping in c-axis oriented MoTe2 nano bulk sheets

The search for techniques to enhance thermoelectric power as well as figure of merit is indispensable in the development of thermoelectric materials. In this work, iso-electronic substitution of Tellurium with 9% Sulfur in MoTe2 nano-bulk sheets showed an 88% room temperature enhancement in thermopower combined with a 13% increase in power factor with a negative temperature coefficient of resistivity below 80 K. To correlate the results, a two-band model was successfully applied to temperature variation of both thermopower and resistivity. The results ascribe the thermopower enhancement to the formation of a narrow sulfur impurity band, which causes, a considerable percentage of the holes to pop-up to the valence band maximum and get localized around the S2-cores, resulting in a sharp depletion in hole density available for transport. The application of the two-carrier model to the field dependent magneto resistance, supports the above proposed reduction in hole density. Our results shed light on doping induced thermopower tuning, leading to more efficient thermo-electrics.