Water-assisted mobile charge induced screening and origin of hysteresis in carbon nanotube field-effect transistors

Carbon nanotube field-effect transistors (CNT FETs) have many possible applications in future nanoelectronics due to their excellent properties. However, one of the major challenges regarding their performance is the noticeable gate hysteresis which is often displayed in their transfer characteristics. The hysteresis phenomenon is often attributed to water-mediated charge transfer between the CNT and the dielectric layer or the CNT and the water layer itself. In this study, we implement the usage of current versus time measurements in addition to the traditional transfer characteristics to accurately extract the time constants of the hysteresis of suspended and on-surface CNT FETs. Following a thorough study, we provide experimental evidence that the hysteresis phenomenon of suspended CNT FETs, as well as of on-surface CNT FETs which operate at low gate voltage regimes (vertical bar V-g vertical bar < 3 V), is based on gate-induced, water-assisted redistribution of mobile charge on the SiO2 surface, and is not related to charge injection from the CNT itself. Our model is confirmed by an electronic-force-microscopy-based measurement technique which enables us to quantify the temporal surface charge distribution while measuring CNT currents.