Charge Density Depinning in Defective MoTe₂ Transistor by Oxygen Intercalation

Molybdenum ditelluride is prone to various defects. Among them, tellurium vacancies lead to the significant reduction of band gap as revealed by density functional theory (DFT) calculations. They are responsible for inducing spatial band structure variation and localized charge puddles in MoTe₂. As a result, undesirable charge density pinning is anticipated in the channel-dominated MoTe₂ field-effect transistors (FETs) even with much improved ohmic contacts, resulting in poor device characteristics, for example, conductivity minimum point (CMP) pinning and weak gate tunability. DFT simulations suggest occupying tellurium vacancies with oxygen can effectively restore MoTe₂ to its intrinsic properties and therefore remove charge density pinning. Experimentally, this can be realized by oxygen intercalation during low-pressure annealing without bringing in additional defects to MoTe₂. The CMP is unpinned in the FETs made of annealed MoTe₂, which can be tuned by changing the contact metals with varied work functions. Moreover, much improved device characteristics, for example, a high hole current density exceeding 20 μAμm⁻¹, a record high hole mobility of 77 cm² V⁻¹ s⁻¹, are obtained.