Drain-Induced Threshold-Voltage Shift Greater than 90 V/V in Molecule-Decorated MoS₂ Field-Effect Transistors Operated in Air

Deposition of a molecular overlayer can effectively control the electrical properties of ultrathin layered materials. Interfacial charge transfer from the overlayers has been widely used to statically control the threshold and turn-on voltages of field-effect transistors (FETs). Herein, we report dynamic control of the threshold (turn-on) voltage of FETs deposited with a layer of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), a well-known electron-accepting molecule. The turn-on voltage of FETs based on molybdenum disulfide flakes exfoliated onto a 285 nm-thick SiO 2 gate dielectric can shift by as much as 74 V when the drain voltage increases from 0.2 to 1 V, which is 3 orders of magnitude higher than the well-known drain-induced barrier lowering. This dynamic shift is accompanied by a rectification behavior in the current–voltage characteristics and requires water molecules to be present in the environment. These facts indicate that water-induced Schottky-barrier modulation is the cause of this shift. The shift is quite weak in the case of TCNQ deposition, suggesting the role of dipoles at the fluorine substituents. Our findings suggest a new mechanism for the instability in FETs composed of layered two-dimensional semiconductors operated in air, which in turn can be exploited to impart dynamic tunability to FETs.