A barrier-free bipolar diode (BFBD) and an ambipolar field-effect transistor (FET) are fabricated based on a doping-free carbon nanotube (CNT) CMOS inverter. The basic CNT device unit consists of two Pd and two Sc electrodes deposited side-by-side on a single CNT, and can be used as an n-FET, p-FET, CMOS inverter, and high-performance ambipolar FET and BFBD in which both electrons and holes contribute effectively to the forward current.