Ballistic transport based on atomic-level modeling: electron and phonon

Abstract

Shrink of modern electronic devices has attracted great attention to nanoengineered materials such as nanowires, and superlattices since their remarkable features were reported in the electronic and thermal points of view, respectively. Despite of the higher interests, inaccurate models have been still applied for nanosystems. Typically, parabolic effective mass model does not take into account strong quantization effects in nanostructures. Fourier law, the most popular in thermofluid field, also has a difficulty to describe heat transfer in those systems, particularly across heterojunctions. For their limitations, necessity for more rigorous theories has been come to the fore and such theories are mostly based on atomic-level modeling and strict carrier transport physics. In this thesis, ballistic transport properties of electron and phonon in nanoengineered materials are investigated by using atomistic-level description and quantum transport theory. This thesis is divided into two parts. The former part of this thesis is written in terms of electronic devices. Bandstructures of ultra-thin-body (UTB) and nanowire (NW) are achieved by empirical $sp^{3}d^{5}s^{*}$-SO tight-binding method one of the well-known atomistic models for energy band theory. Through the results of 20 orbitals tight-binding calculations, effective mass Hamiltonians are calibrated and quantization effects are compensated. Quantum transport properties of UTB MOSFETs with Schottky-Barrier (SB) at two contacts are described by using non-equilibrium Green`s function (NEGF) formalism in ballistic transport regime. Specifically, I-V characteristics of UTB SB-MOSFETs are obtained by self-consistent calculations of NEGF equation and Poisson equation. Furthermore, channel material engineering is attempted to explore the best III-V material for switching devices. III-V materials such as GaAs suffer from insufficient density of states in nanosystems, which is the main culprit of III-V device deg...