Nitrogen Dioxide Detection with Ambipolar Silicon Nanowire Transistor Sensors.

Si nanowire transistors are ideal for the sensitive detection of atmospheric species due to their enhanced sensitivity to changes in the electrostatic potential at the channel surface. In this study, we present unique ambipolar Si junctionless nanowire transistors (Si-JNTs) that incorporate both n- and p-type conduction within a single device. These transistors enable scalable detection of nitrogen dioxide (NO₂), a critical atmospheric oxidative pollutant, across a broad concentration range, from high levels (25-50 ppm) to low levels (250 ppb-2 ppm). Acting as an electron acceptor, NO₂ generates holes and functions as a pseudodopant for Si-JNTs, altering the conductance and other device parameters. Consequently, ambipolar Si-JNTs exhibit a dual response at room temperature, reacting on both p- and n-conduction channels when exposed to gaseous NO₂, thereby offering a larger parameter space compared to a unipolar device. Key characteristics of the Si-JNTs, including on-current (I_on), threshold voltage (V_th) and mobility (μ), were observed to dynamically change on both the p- and n-channels when exposed to NO₂. The p-conduction channel showed superior performance across all parameters when compared to the device's n-channel. For example, within the NO₂ concentration range of 250 ppb to 2 ppm, the p-channel achieved a responsivity of 37%, significantly surpassing the n-channel's 12.5%. Additionally, the simultaneous evolution of multiple parameters in this dual response space enhances the selectivity of Si-JNTs toward NO₂ and improves their ability to distinguish between different pollutant gases, such as NO₂, ammonia, sulfur dioxide and methane.