How do Quantum Effects Influence the Capacitance and Carrier Density of Monolayer MoS${}_2$ Transistors?

Abstract

When transistor gate insulators have nanometer-scale equivalent oxide thickness (EOT), the gate capacitance ($C_{\text{G}}$) becomes smaller than the oxide capacitance ($C_{\text{ox}}$) due to the quantum capacitance and charge centroid capacitance of the channel. Here, we study the capacitance of monolayer MoS${}_{\text{2}}$ as a prototypical two-dimensional (2D) channel while considering spatial variations in the potential, charge density, and density of states. At 0.5 nm EOT, the monolayer MoS${}_{\text{2}}$ capacitance is smaller than its quantum capacitance, limiting the single-gated $C_{\text{G}}$ of an n-type channel to between 63% and 78% of $C_{\text{ox}}$ for gate overdrive voltages between 0.5 and 1 V. Despite these limitations, for dual-gated devices, the on-state $C_{\text{G}}$ of monolayer MoS${}_{\text{2}}$ is 50% greater than that of silicon at 0.5 nm EOT and more than three times that of InGaAs at 1 nm EOT, indicating that 2D semiconductors are promising for nanoscale devices at future technology nodes.