Junctionless Electric-Double-Layer MoS₂ Field-Effect Transistor with a Sub-5 nm Thick Electrostatically Highly Doped Channel

Junctionless transistors are suitable for sub-3 nm applications because of their extremely simple structure and high electrical performance, which compensate for short-channel effects. Two-dimensional semiconductor transition-metal dichalcogenide materials, such as MoS₂, may also resolve technical and fundamental issues for Si-based technology. Here, we present the first junctionless electric-double-layer field-effect transistor with an electrostatically highly doped 5 nm thick MoS₂ channel. A double-gated MoS₂ transistor with an ionic-liquid top gate and a conventional bottom gate demonstrated good transfer characteristics with a 10⁴ on-off current ratio, a 70 mV dec^-1 subthreshold swing at a 0 V bottom-gate bias, and drain-current versus top-gate-voltage characteristics were shifted left significantly with increasing bottom-gate bias due to an electrostatically increased overall charge carrier concentration in the MoS₂ channel. When a bottom-gate bias of 80 V was applied, a shoulder and two clear peak features were identified in the transconductance and its derivative, respectively; this outcome is typical of Si-based junctionless transistors. Furthermore, the decrease in electron mobility induced by a transverse electric field was reduced with increasing bottom-gate bias. Numerical simulations and analytical models were used to support these findings, which clarify the operation of junctionless MoS₂ transistors with an electrostatically highly doped channel.