Air Stable Doping and Intrinsic Mobility Enhancement in Monolayer Molybdenum Disulfide by Amorphous Titanium Suboxide Encapsulation

To reduce Schottky-barrier-induced contact and access resistance, and the impact of charged impurity and phonon scattering on mobility in devices based on 2D transition metal dichalcogenides (TMDs), considerable effort has been put into exploring various doping techniques and dielectric engineering using high-κ oxides, respectively. The goal of this work is to demonstrate a high-κ dielectric that serves as an effective n-type charge transfer dopant on monolayer (ML) molybdenum disulfide (MoS₂). Utilizing amorphous titanium suboxide (ATO) as the "high-κ dopant", we achieved a contact resistance of ∼180 Ω·μm that is the lowest reported value for ML MoS₂. An ON current as high as 240 μA/μm and field effect mobility as high as 83 cm²/V-s were realized using this doping technique. Moreover, intrinsic mobility as high as 102 cm²/V-s at 300 K and 501 cm²/V-s at 77 K were achieved after ATO encapsulation that are among the highest mobility values reported on ML MoS₂. We also analyzed the doping effect of ATO films on ML MoS₂, a phenomenon that is absent when stoichiometric TiO₂ is used, using ab initio density functional theory (DFT) calculations that shows excellent agreement with our experimental findings. On the basis of the interfacial-oxygen-vacancy mediated doping as seen in the case of high-κ ATO-ML MoS₂, we propose a mechanism for the mobility enhancement effect observed in TMD-based devices after encapsulation in a high-κ dielectric environment.