Ballistic carrier transport in a quasi-two-dimensional nanoscale field effect transistor (FET)

Abstract

The saturation velocity is found to be ballistic regardless of the device dimensions. This saturation velocity is limited by the intrinsic velocity appropriate to the 2D band structure of a MOSFET. The ballistic intrinsic velocity arises from the fact that randomly oriented velocity vectors in zero electric field are streamlined and become unidirectional. In the degenerate realm, the saturation velocity is shown to be the Fermi velocity that is independent of temperature but strongly dependent on carrier concentration. In the non-degenerate realm, the intrinsic velocity is the thermal velocity that depends only on the ambient temperature. The drain carrier velocity is revealed to be smaller than the saturation velocity due to the presence of a finite electric field at the drain. An excellent agreement of the models developed and applied to 80 nm MOSFET validates the physics behind ballistic carrier transport. The results presented will have profound influence in interpreting the data for a variety of low-dimensional nanoscale FET.