First-principle theory of field-effect doping in transition-metal dichalcogenides: structural properties, electronic structure, Hall coefficient, and electrical conductivity

Thomas Brumme, Matteo Calandra, Francesco Mauri

Published 2015-01-28Version 1

We investigate how field-effect doping affects the structural properties, the electronic structure, the Hall coefficient, and the electrical conductivity of few-layers transition-metal dichalcogenides (TMDs) by using DFT. We consider mono-, bi-, and trilayers of MoS2, MoSe2, MoTe2, WS2, and WSe2 and provide a full database of electronic structures and Hall coefficients for hole and electron doping. We find that the electronic structure cannot be described by a rigid band shift and that it is important to relax the structure under the asymmetric electric field. For multilayer TMDs, in the range of doping relevant for ionic-liquid based FETs, we demonstrate that the electronic structure is very different from the monolayer case and that it is incompatible with both the rigid doping and the uniform-background doping approach. Furthermore, for hole doping the width of the conducting channel decreases from three to one layer as the induced charge increases. On the contrary, for small electron doping the width varies between one and three layers in different TMDs. Increasing the number of electrons leads however also to a reduced width of one layer. Interestingly, the number of occupied bands at each given k point is almost uncorrelated with the thickness of the doping-charge distribution. Finally, we calculate within the constant-relaxation-time approximation the electrical conductivity and the inverse Hall coefficient. We demonstrate that in some cases the charge determined by Hall-effect measurements can deviate from the real charge by up to 50%. The error is even larger for hole-doped MoTe2, where the Hall charge has even the wrong polarity at low temperature. We thus provide the mapping between the doping charge and the Hall coefficient. In the appendix we provide more than 250 band structures for all doping levels of the TMDs considered within this work.