The Ultimate Drift Velocity in Two Dimensional Quantum Limit Mohammad Taghi Ahmadi, Ismail Saad, Razali Ismail, Vijay K. Arora Faculty of Electrical Engineering University Technology of Malaysia 81310 Johor Skudai Email:ahmadiph@gmail.com 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 nondegenrate 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 nondegenrately doped samples. However, the ultimate drift velocity is the appropriate average of the Fermi velocity for degenerately doped samples. I. Introduction The research for high-speed devices for future electronic is continuing. The speed is calculated with which the carrier (electron or holes) can propagate through the length of the device. In nanoscale devices it became clear that the saturation velocity plays an important role. The higher mobility brings an electron closer to saturation as a high electric field is encountered, but saturation velocity remaining the same. The reduction in conducting channel length of the device results in reduced transit-time-delay and hence enhanced operational frequency. There isn’t any agreement on the interdependence of saturation velocity on low-field mobility that is scattering-limited [1]. In any solid state device, it is very clear that the band structure parameters, doping profiles (degenerate or nondegenrate), and ambient temperatures play a variety of roles in limiting optoelectronic properties. The outcome that higher mobility leads to higher saturation is not supported by experimental observations [2]. Therefore we focused on the process controlling the ultimate saturation. In the following, the fundamental processes that limit drift velocity are delineated. The ultimate drift velocity due to the high- field streaming are based on the asymmetrical distribution function that converts randomness in zero- field to streamlined one in a very high electric field. The limitation drift velocity is found to be appropriate thermal velocity for a non- degenerately doped sample of silicon, increasing with the temperature, but independent of carrier concentration. However, the limitation drift velocity is the Fermi velocity for degenerately doped silicon, increasing with carrier concentration but independent of the temperature. II. Theory In one dimensional semiconductor, only one Cartesian directions are much larger than the de Broglie wavelength. Therefore energy spectrum is analog-type in y, z direction as given by Fig.1. ,........ 3 , 2 , 1 , ) ( 2 2 2 2 * 2 = ∈ + ∈ + + = n m m n k m E E oye oze x e co = (2-1) Here 2 * ) ( 2 2 ) ( 2 z h e h oze L m = π = ∈ and 2 * ) ( 2 2 ) ( 2 y h e h oye L m = π = ∈ and e (h) for electron (hole). In the other hand energy spectrum is digital type in x direction. Second Asia International Conference on Modelling & Simulation 978-0-7695-3136-6/08 $25.00 © 2008 IEEE DOI 10.1109/AMS.2008.53 980 Authorized licensed use limited to: UNIVERSITY TEKNOLOGI MALAYSIA. Downloaded on January 6, 2009 at 20:25 from IEEE Xplore. Restrictions apply.