  Ultrathin layers of semiconducting molybdenum disulfide (MoS2) offer
significant prospects in future electronic and optoelectronic applications.
Although an increasing number of experiments bring light into the electronic
transport properties of these crystals, their thermoelectric properties are
much less known. In particular, thermoelectricity in chemical vapor deposition
grown MoS2, which is more practical for wafer-scale applications, still remains
unexplored. Here, for the first time, we investigate these properties in grown
single layer MoS2. Micro-fabricated heaters and thermometers are used to
measure both electrical conductivity and thermopower. Large values of up to ~30
mV/K at room temperature are observed, which are much larger than those
observed in other two dimensional crystals and bulk MoS2. The thermopower is
strongly dependent on temperature and applied gate voltage with a large
enhancement at the vicinity of the conduction band edge. We also show that the
Seebeck coefficient follows S~T^1/3 suggesting a two-dimensional variable range
hopping mechanism in the system, which is consistent with electrical transport
measurements. Our results help to understand the physics behind the electrical
and thermal transports in MoS2 and the high thermopower value is of interest to
future thermoelectronic research and application.
