All-Electrical High-Sensitivity, Low-Power Dual-Mode Gas Sensing and Recovery with a WSe₂/MoS₂ pn Heterodiode

Two-dimensional MoS₂ gas sensors have conventionally relied on a change in field-effect-transistor (FET) channel resistance or in the Schottky contact/pn homojunction barrier. We demonstrate an enhancement in sensitivity (6×) and dynamic response along with a reduction in detection limit (8×) and power (10⁴×) in a gate-tunable type-II WSe₂(p)/MoS₂(n) heterodiode gas sensor over an MoS₂ FET on the same flake. Measurements for varying NO₂ concentration, gate bias, and MoS₂ flake thickness, reinforced with first-principles calculations, indicate dual-mode operation due to (i) a series resistance-based exponential change in the high-bias thermionic current (high sensitivity), and (ii) a heterointerface carrier concentration-based linear change in near-zero-bias interlayer recombination current (low power) resulting in sub-100 μW/cm² power consumption. Fast and gate-bias tunable recovery enables an all-electrical, room-temperature dynamic operation. Coupled with the sensing of trinitrotoluene (TNT) molecules down to 80 ppb, this study highlights the potential of the WSe₂/MoS₂ pn heterojunction as a simple, low-overhead, and versatile chemical-sensing platform.