Nonequilibrium ac quantum transport in nanoscale transistors

This paper presents the small-signal (ac) nonequilibrium Green function (NEGF) simulation approach. By utilizing the solution of the steady-state (dc) NEGF solutions, the ac responses of the electrostatic potential and the electron density can be calculated. For the self-consistent solution considering the long range Coulomb interaction, the Poisson equation is coupled with the NEGF equations for both ac and dc cases. Especially, for the ac case, the NEGF and Poisson equations are fully coupled and solved in a single system matrix. In order to take into account the mode interaction fully, the real-space approach is presented. For the application of the ac quantum transport, a silicon based highly scaled nanosheet metal–oxide–semiconductor field-effect transistor is simulated under the ballistic transport approximation at room temperature. The simulation results at a low frequency are verified against the quasi-static results. We present the ac intrinsic performance of the device at the terahertz range. At the high-frequency range, the plasma instability from the ungated silicon region is investigated.