Impact of oxygen adsorption on a population of mass produced carbon nanotube field effect transistors

A large population of carbon nanotube field effect transistors (CNT-FETs), including a variety of channel morphologies with single and multiple tubes, was electrically characterized in atmospheric, ultra-high vacuum (UHV) and oxygen-rich environments. Devices were systematically classified according to the number and nature of the bridging CNTs based on a rigorous device characterization methodology. A statistical analysis of the interaction of oxygen with such a complex population of devices reveals shifts in carrier type, contact resistance and threshold voltages indicative of both charge trapping and transport barrier modulation at the tube–electrode interface. Devices with a single semiconducting tube could be changed from p-type (hole conduction) at atmosphere to n-type (electron conduction) through vacuum-annealing. Furthermore, the average resistance of these CNT-FETs after annealing was observed to decrease from 2.16 MΩ under UHV to 1.0 MΩ in the presence of pure oxygen while threshold voltages shifted from −5.5 V to −2.2 V. Overall responses to ambient conditions is dependent on the device morphology as well as the use of thermal annealing.