An ultra-sensitive and recyclable FET-type toxic gas sensor based on WTe2 monolayers

Abstract

Field-effect-transistor (FET)-type gas sensors have attracted a surge of research interest due to their low power dissipation and exceptional sensitivity. However, theoretical explorations into their sensing capability and underlying mechanism remain scarce. Herein, taking the pure and defective WTe₂ monolayers as the sensing platforms, we systematically investigate the sensing characteristics and working principles of FET-type gas sensors in response to various hazardous gases, including SO₂, CO, NO, NH₃, and NO₂, using first-principles calculations and statistical thermodynamic modeling. Our findings reveal that the pure WTe₂-based FET-type gas sensor, operating at zero gate voltage, shows remarkably high sensitivity and reusability for NO₂ detection, achieving 96% sensitivity at a low concentration of 20 ppb. Our research demonstrates that the introduction of Te-vacancies serves as a highly efficient strategy for enhancing the sensitivity of the gas sensor towards all tested toxic gases, while ensuring its reusability. Applying a gate voltage to the pure WTe₂-based FET-type gas sensor further improves its sensitivity to NO₂, surpassing 90% within the whole bias range, and reaching 97% under the gate voltage of 3 V. This improvement is attributed to the upward shift of the conduction bands under a positive gate voltage with respect to the chemical potential of the source, which increases the electron barrier and decreases the conductance. Our research offers a promising approach for achieving ultra-sensitive and recyclable detection of toxic gases at ppb-level concentration.