Abstract:
The ultrathin two-dimensional semiconductor of MoS2 demonstrates prominent field-effect performances for down-sizing transistors. Electron transport and thermoelectric properties have only been investigated in few-layer MoS2 at low temperatures. The interrelation between electrical and thermoelectric properties has not been studied yet. Here, thermoelectric field-effect transistor devices are fabricated using MoS2 flakes with thicknesses ranging from 1 to 39 layers. Electrical and thermoelectric properties are measured at temperatures ranging from 80 to 600 K and analyzed by Mott’s hopping transport, thermal activation, and phonon scattering theories. The carrier concentration dependences are investigated using hopping transport and enhanced phonon scattering theories. With fittings to theoretical models, we experimentally obtained the universal constant and the electron’s effective mass. Seebeck coefficients, conductivities, and power factors are sketched as a function of the MoS2 flake thickness, pointing to higher Seebeck coefficients and power factors at thicknesses less than 20 layers, exhibiting the best candidate for thermopower applications among all two-dimensional semiconductors. Additionally, we probe the extrinsic effect of memory steps due to trapped charges releasing at temperatures above 450 K in the modulation of electrical and thermoelectric properties, playing an important role in applying to high-temperature thermometers.