Analytical Models for the Insight Into the Use of Alternative Channel Materials in Ballistic nano-MOSFETs

This paper presents new analytical derivations for the ballistic current of n-MOSFETs as a function of the transport direction, of the properties of the channel material, and of the technological parameters. The main purpose of the analytical expressions is to provide an insight into the optimization of the transistors with alternative channel materials. Our results simply explain why, for a given two-dimensional (2-D) density of states, an elliptic 2-D minimum can provide a current larger than a circular minimum if the best transport direction is selected. Furthermore, we analytically show that the use of channel materials with very small transport masses implies a tradeoff between the electron velocity and the gate drive capacitance, because of the finite capacitance of the inversion layer. This latter effect should be seriously considered in the context of the aggressive scaling of the equivalent oxide thickness enforced by the introduction of high-K dielectrics and multigate MOSFETs