High-field effects in quantum-confined systems

The presence of high electric field, both in the gate-as well as in channel-direction, degrades the mobility, resulting in breakdown of familiar Ohm's law. Using the asymmetrical distribution function, we show that the velocity saturation arises due to re alignment of electrons in and opposite to the applied electric field Velocity is then limited by the thermal velocity for nondegenerate carriers and Fermi velocity for degenerate carriers, independent of the scattering-limited mobility. This ultimate velocity is further reduced by the carrier quantum remission process. Gate degradation of the mobility in the channel is shown as arising from the quantum-confinement effect, in direct contrast to the perceived gate-heating of electrons. The impact of these limitations on the performance of FETs is presented. High ohmic mobility does not necessarily lead to high saturation velocity.