Vertical and In-Plane Current Devices Using NbS2/n-MoS2 van der Waals Schottky Junction and Graphene Contact

A van der Waals (vdW) Schottky junction between two-dimensional (2D) transition metal dichalcogenides (TMDs) is introduced here for both vertical and in-plane current devices: Schottky diodes and metal semiconductor field-effect transistors (MESFETs). The Schottky barrier between conducting NbS2 and semiconducting n-MoS2 appeared to be as large as ∼0.5 eV due to their work-function difference. While the Schottky diode shows an ideality factor of 1.8–4.0 with an on-to-off current ratio of 103−105, Schottky-effect MESFET displays little gate hysteresis and an ideal subthreshold swing of 60–80 mV/dec due to low-density traps at the vdW interface. All MESFETs operate with a low threshold gate voltage of −0.5 ∼ −1 V, exhibiting easy saturation. It was also found that the device mobility is significantly dependent on the condition of source/drain (S/D) contact for n-channel MoS2. The highest room temperature mobility in MESFET reaches to approximately more than 800 cm2/V s with graphene S/D contact. The NbS2/n-MoS2 MESFET with graphene was successfully integrated into an organic piezoelectric touch sensor circuit with green OLED indicator, exploiting its predictable small threshold voltage, while NbS2/n-MoS2 Schottky diodes with graphene were applied to extract doping concentrations in MoS2 channel.