Air Stable p‑Doping of WSe2 by Covalent Functionalization

Covalent functionalization of transition metal dichalcogenides (TMDCs) is investigated for air-stable chemical doping. Specifically, p-doping of WSe2 via NOx chemisorption at 150 °C is explored, with the hole concentration tuned by reaction time. Synchrotron based soft X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS) depict the formation of various WSe2–xyOxNy species both on the surface and interface between layers upon chemisorption reaction. Ab initio simulations corroborate our spectroscopy results in identifying the energetically favorable complexes, and predicting WSe2:NO at the Se vacancy sites as the predominant dopant species. A maximum hole concentration of ∼1019 cm–3 is obtained from XPS and electrical measurements, which is found to be independent of WSe2 thickness. This degenerate doping level facilitates 5 orders of magnitude reduction in contact resistance between Pd, a common p-type contact metal, and WSe2. More generally, the work presents a platform for manipulating the electrical properties and band structure of TMDCs using covalent functionalization.