Figure 3: Energy band diagrams, carrier distributions and measured capacitance-voltage profile of the MoS₂ TFT device.

(a–c) Energy band diagrams of the MoS₂/Al₂O₃/p⁺Si device under various bias conditions. The band offsets and physical parameters relevant for the calculation are described in the Supplementary methods. The self-consistent Schrödinger-Poisson calculation shows that at large positive gate bias, a 2D electron gas is formed at the MoS₂/Al₂O₃ interface. (d) The 2D electron gas that forms the conductive channel is shown in an enlarged scale. Most conduction occurs by electrons accumulated in a few layers at the MoS₂/Al₂O₃ interface. With increasing bias, the centroid of the electron distribution shifts closer to the interface. This indicates that the 'quantum' capacitance in the semiconductor increases with positive gate bias. (e) Measured capacitance-voltage curves of the MoS₂/Al₂O₃/back-gate capacitors (circles). The solid lines show the calculated capacitance for three different doping densities (red: 10¹⁸, blue: 10¹⁷ and green: 10¹⁶ cm⁻³), not including parasitic pad capacitances. The slope indicates a doping density close to 10¹⁶ cm⁻³.