First-principles calculations of mobilities in ultrathin double-gate MOSFETs

For several decades, electron and hole mobilities have been adequately modeled using a semiclassical approximation of the Boltzamnn equation, using either an effective-mass expression or the bulk energy bands of Si to describe the carriers’ kinetic energy. The Si-SiO2 interface is modeled by an infinite potential wall. Scattering mechanisms are described using phenomenological models. In recent years, with the advent of new materials and device structures (strained Si, alternate dielectrics, double-gate MOSFETs), the existing methods lack the necessary predictive power. Here we give an overview of a recently developed method to calculate mobilities from ‘first principles’ using atomic-scale models of the interface and employing state-of-the-art density functional theory to construct scattering potentials and to compute mobilities without any adjustable parameters. Several examples are used to illustrate the method.