High performance of potassium n-doped carbon nanotube field-effect transistors

We describe a robust technique for the fabrication of high performance vertically scaled n-doped field-effect transistors from large band gap carbon nanotubes. These devices have a tunable threshold voltage in the technologically relevant range (−1.3 V⩽Vth⩽0.5 V) and can carry up to 5–6 μA of current in the on-state. We achieve such performance by exposure to potassium (K) vapor and device annealing in high vacuum. The treatment has a twofold effect to: (i) controllably shift Vth toward negative gate biases via bulk doping of the nanotube (up to about 0.6e−/nm), and (ii) increase the on-current by 1–2 orders of magnitude. This current enhancement is achieved by lowering external device resistance due to more intimate contact between K metal and doped nanotube channel in addition to potential reduction of the Schottky barrier height at the contact.