Bipolar conduction and drain-induced barrier thinning in carbon nanotube FETs

The drain current-voltage (I-V) characteristics of Schottky-barrier carbon nanotube field-effect transistors (FETs) are computed via a self-consistent solution to the two-dimensional potential profile, the electron and hole charges in the nanotube, and the electron and hole currents. These out-of-equilibrium results are obtained by allowing splitting of both the electron and hole quasi-Fermi levels to occur at the source and drain contacts to the tube, respectively. The interesting phenomena of bipolar conduction in a FET, and of drain-induced barrier thinning (DIBT) are observed. These phenomena are shown to add a breakdown-like feature to the drain I-V characteristic. It is also shown that a more traditional, saturating-type characteristic can be obtained by workfunction engineering of the source and drain contacts.