Simulations of Nanowire Transistors: Atomistic vs. Effective Mass Models

TL;DR

This paper compares atomistic and effective mass models for simulating electron transport in nanowire transistors, revealing that the effective mass approximation often fails for small diameters due to quantum effects.

Contribution

It provides a detailed comparison between atomistic tight-binding and effective mass models, highlighting the limitations of the latter in nanowire transistor simulations.

Findings

Effective mass varies significantly under strong quantization.

Valley degeneracies are lifted due to valley splitting.

Effective mass approximation agrees with atomistic models only in certain cases.

Abstract

The ballistic performance of electron transport in nanowire transistors is examined using a 10 orbital sp3d5s* atomistic tight-binding model for the description of the electronic structure, and the top-of-the-barrier semiclassical ballistic model for calculation of the transport properties of the transistors. The dispersion is self consistently computed with a 2D Poisson solution for the electrostatic potential in the cross section of the wire. The effective mass of the nanowire changes significantly from the bulk value under strong quantization, and effects such as valley splitting strongly lift the degeneracies of the valleys. These effects are pronounced even further under filling of the lattice with charge. The effective mass approximation is in good agreement with the tight binding model in terms of current-voltage characteristics only in certain cases. In general, for small diameter wires, the effective mass approximation fails.