Time-dependent quantum transport and nonquasistatic effects in carbon nanotube transistors

Nonquasistatic effects in ac characteristics of carbon nanotube field-effect transistors are examined by solving a full time-dependent, open-boundary Schrodinger equation. The nonquasistatic characteristics, such as the finite channel charging time, and the dependence of small signal transconductance and gate capacitance on the frequency, are explored. The validity of the widely used quasistatic approximation is examined. The results show that the quasistatic approximation overestimates the transconductance and gate capacitance at high frequencies, but gives a more accurate value for the intrinsic cutoff frequency over a wide range of bias conditions. (c) 2006 American Institute of Physics.