Investigating Charge Transport in Semiconducting Single-Walled Carbon Nanotube Networks by Charge Modulation Microscopy

Solution-processed networks of semiconducting single-walled carbon nanotubes (SWCNTs) hold promise as active layers for large-scale digital circuits, thermoelectric devices, and healthcare applications. Yet, the combined effects of local network properties and (n,m) species composition need to be addressed to improve the performance and reproducibility of state-of-the-art devices. Charge modulation microscopy (CMM) is used to investigate charge transport in field-effect transistors (FETs) based on monochiral (6,5) SWCNT networks and multichiral networks containing five semiconducting SWCNT species with different band gaps. By mapping the charge-modulated signal within the FET channel with sub-micrometer resolution, the spatial distribution of free carriers and its evolution during the switching of the FET are revealed. The CMM maps provide direct evidence that holes and electrons are transported preferentially through the same percolation paths. A moderate positive correlation between the SWCNT density in the monochiral (6,5) network and the charge density in subthreshold regime is demonstrated. In multichiral networks, the charge transport paths are on average less fragmented when involving low band gap species. CMM emerges as a valuable technique to estimate the size of preferential percolation domains associated with the average distance traversed by charge carriers on SWCNTs of the same chirality before tunneling onto other species.