Band modulation and in situ doping control of carbon-nanotube field-effect transistors by work-function engineering

An inability to precisely control doping has hindered the development of electrically reliable and predictable low-dimensional devices. Here, we demonstrated a modulation of electronic bands of one-dimensional carbon nanotubes (CNTs) over a wide range by using metal electrodes having almost the same work function as the CNT in a dual-gate mode. Gate-response curves obtained from Ti versus In metal-contacted devices showed opposite behaviors in shape and magnitude in an ambipolar state, which was shown to be due to the difference between the pinned positions of their Fermi levels in the band gap of the CNT with different work functions of the metals. By varying the gate-bias voltages of the dual gates, we successfully demonstrated that the electronic band profile of the CNT can be modulated precisely and over a wide range to higher and lower energy levels, resulting in the ability to have it form p-metal, p-type semiconductor, ambipolar, n-type semiconductor, and n-metallic electronic states.