Gate‐Bias Controlled Charge Trapping as a Mechanism for NO₂ Detection with Field‐Effect Transistors

Detection of nitrogen dioxide, NO 2 , is required to monitor the air‐quality for human health and safety. Commercial sensors are typically chemiresistors, however field‐effect transistors are being investigated. Although numerous investigations have been reported, the NO 2 sensing mechanism is not clear. Here, the detection mechanism using ZnO field‐effect transistors is investigated. The current gradually decreases upon NO 2 exposure and application of a positive gate bias. The current decrease originates from the trapping of electrons, yielding a shift of the threshold voltage towards the applied gate bias. The shift is observed for extremely low NO 2 concentrations down to 10 ppb and can phenomenologically be described by a stretched‐exponential time relaxation. NO 2 detection has been demonstrated with n‐type, p‐type, and ambipolar semiconductors. In all cases, the threshold voltage shifts due to gate bias induced electron trapping. The description of the NO 2 detection with field‐effect transistors is generic for all semiconductors and can be used to improve future NO 2 sensors.