Gas Sensing by Ambipolar Carbon Nanotube Based Transistors

The nitrogen dioxide (NO2) gas response and recovery properties of ambipolar carbon nanotube (CNT) field-effect transistors were measured to investigate the effect of CNT amount on gas response. For the device with a small amount of CNTs, responses from the CNT bulk and CNT/electrode contacts were observed. For devices with a large amount of CNTs, in which a network-like structure of CNTs was observed near the electrodes, increased current in both electron and hole conduction regions was observed compared with that for the device with a small amount of CNTs. The increased current in the electron conduction region rapidly decreased during recovery. This response is consistent with that of CNT/CNT X-type contacts, which have high resistance before NO2 adsorption. Equivalent circuits of CNT channels with CNT/CNT contacts were developed. Evaluation of time constants revealed that CNT/electrode contacts and CNT/CNT X-type contacts exhibited high NO2 adsorption and desorption rates, respectively.