p-Channel, n-Channel and ambipolar field-effect transistors based on functionalized carbon nanotube networks

We report on the transport properties of carbon nanotube network field-effect transistors (CNNFETs) produced from size-selected and functionalized single-walled carbon nanotubes (SWNTs). The SWNTs were functionalized by grafting octadecylamine chains to the tube ends and spin casting onto prefabricated bottom gated silicon field-effect transistor substrates. Acid-oxidative cutting and centrifuge fractionation were employed to select the mean diameter and length of the SWNT bundles deposited within the active area of the CNNFETs. By comparing CNNFETs with different SWNT bundle thickness, we demonstrated that thicker-bundle samples exhibited low on/off ratio but comparatively higher field-effect mobility than small-bundle samples, which yielded devices with higher on/off ratio but lower field-effect mobility. Electronic transfer characteristics of the CNNFETs were dominated by the channel rather than contact resistance. These results demonstrate a potential new route for fabricating pp- and nn-type CNNFET devices.