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.