The electrical properties and the magnitude of the indirect gap in the semiconducting transition metal dichalcogenide layer crystals

Room-temperature electrical resistivity and Hall effect measurements as a function of pressure are reported on p-type MoS2 and on n-type MoS2, MoSe2 and MoTe2. In each case, the resistivity decreases under pressure, due to an increase in the carrier concentration. The Hall mobility is relatively pressure-independent. The data are consistent with the predominance of extrinsic conduction in these semiconductors until well above room temperature. The impurity activation energy and its pressure dependence are given, together with estimates of the intrinsic indirect bandgap obtained from high temperature conductivity measurements, photoemission studies and band structure calculations.