Negative differential transconductance in deterministically transferred CVD-Grown monolayer WSe2/MoS2 heterostructures

Electrostatic control of the band alignment in two-dimensional van der Waals (vdW) heterostructures is a fundamental requirement for realizing low-power tunnelling electronics, multi-valued logic and next-generation functional devices. Yet, its experimental demonstration in scalable chemical vapour deposition (CVD)-grown heterostructures remains largely unexplored. Here, we demonstrate a simple heterostructure field-effect transistor based on deterministically transferred CVD-grown monolayers of WSe2 and MoS2. These materials are stacked using a contact-first, transfer-later fabrication strategy that enables localized electrostatic modulation of the heterointerface. The fabricated device exhibits two distinct drain-current minima in its transfer characteristics, with the first minimum occurring at a fixed back-gate voltage, while the second minimum shifts with drain voltage. Analysis around the first current minimum reveals a pronounced negative differential transconductance (NDT), with a peak-to-valley current ratio (PVCR) of 16 at room temperature, providing a clear electrical signature of band-to-band tunnelling (BTBT). The observed transport behaviour originates from strong electrostatic doping induced by the back gate, which drives the WSe2/MoS2 heterointerface from a staggered (type-II) to a broken (type-III) bandgap alignment, enabling interlayer BTBT under large negative gate bias. As the gate voltage is increased, the loss of the broken-gap alignment terminates the tunnelling process, producing a gate-voltage-pinned current minimum and the associated NDT response. These findings establish that CVD-grown vdW heterostructures can achieve controllable electrostatic band engineering and room-temperature tunnelling phenomena using a simple single-back-gate architecture, providing an experimentally practical pathway towards future low-power tunnelling transistors, multi-valued logic circuits, and electrically reconfigurable two-dimensional electronic devices.