The Ultimate Drift Velocity in Two Dimensional Quantum Limit

Abstract

In a conventional MOSFET, carriers are confined in a direction normal to the channel, and free to move in two dimensions. It is, however, now with nanotubes possible to make structures that confine carriers in two dimensions, so that they are free to move only in one direction. The nanowires and nanotubes are being considered as best candidates for high-speed applications because of the high mobility due to the suppression of the ionized impurity scattering especially at low temperatures. It is shown that the high mobility does not always lead to higher carrier velocity. Using the distribution function that takes into account the asymmetrical distribution of drifting electrons in an electric field is presented .This distribution function transforms the random motion of electrons into a streamlined one that gives the ultimate saturation velocity that is a function of temperature in nondegenerate regime and a function of carrier concentration in the degenerate regime The ultimate drift velocity is found to be appropriate thermal velocity for a given dimensionality for nondegenerately doped samples. However, the ultimate drift velocity is the appropriate average of the Fermi velocity for degenerately doped samples.