Investigation of hysteresis and polarization mechanism in top-gated aligned carbon nanotube FETs

The transfer characteristics and hysteresis of top-gated aligned carbon nanotube field-effect transistors are systematically investigated using a series of fast gate pulse schemes. The devices exhibit clockwise hysteresis accompanied by polarization-modulated charge transport. Controlled-environment experiments reveal that the clockwise hysteresis window is modulated by vacuum pumping, humidity variation, and nitrogen purging and can be restored upon returning to the original ambient conditions. As the fast gate sweep duration decreases, the hysteresis evolves from clockwise to counterclockwise, a signature of charge trapping effects. The underlying mechanism is ascribed to the coexistence of water molecular polarization and charge trapping within the device. By tuning the amplitude and duration of gate voltage pulses, we identify voltage- and time-dependent regimes dominated by either polarization or charge-trapping processes. These findings are further validated by current transient analysis upon the application and removal of tailored poling or trapping gate pulses.