Strong in-plane anisotropy in the electronic properties of doped transition metal dichalcogenides exhibited in W1−xNbxS2

We study the electronic properties of monolayer transition metal dichalcogenide materials subjected to aliovalent doping, using Nb-doped WS2 as an exemplar. Scanning transmission electron microscopy imaging of the as-grown samples reveals an anisotropic Nb dopant distribution, prompting an investigation of anisotropy in electronic properties. Through electronic structure calculations on supercells representative of observed structures, we confirm that local Nb-atom distributions are consistent with energetic considerations, although kinetic processes occurring during sample growth must be invoked to explain the overall symmetry-breaking. We perform effective bandstructure and conductivity calculations on realistic models of the material that demonstrate that a high level of anisotropy can be expected in electronic properties including conductivity. In-plane anisotropy of the conductivity is predicted to be as high as 5:1, which is higher than previously observed in any TMDC system in the [Mo,W][S,Se]2 class