Fig. 3: Analysis of device characteristics.
a,b, Transfer characteristics change of CNFET upon NO2 exposure (a) and NH3 exposure (b). c,d, Transfer characteristics change of CNFET upon NO2 exposure (c) and NH3 (d). The modulation of transfer characteristics upon gas exposure is enhanced compared with unfunctionalized CNFETs. The dashed grey line in each plot is provided to compare the modulations in each corresponding case at VG = −0.5 V. e,f, Threshold voltage change (e) and subthreshold swing (SS) change (f) of both CNFET and NiHHTP-CNFET upon NO2 and NH3 exposure. g, Illustration of Schottky barrier modulation in NiHHTP-CNFETs upon gas exposure near the source contact in the on-state (upper) and the off-state (lower). The y axis represents the relative potential, defined as the energy difference between the valence band edge (Ev) and the metal work function (Φm). The grey, orange and blue lines represent NiHHTP-CNFETs exposed to dry air, NO2 and NH3, respectively. In the on-state, upon NO2 exposure, the reduction in the Schottky barrier for holes enhances the tunnelling current, whereas NH3 exposure increases the Schottky barrier, decreasing the tunnelling current. In the off-state, modulation of the Schottky barrier affects thermionic emission, resulting in either an increase or decrease in leakage current and, consequently, a corresponding change in the subthreshold swing. h, Response of both NiHHTP-CNFET and CNFET to NO2 and NH3 gases with respect to the applied gate voltage.
