INTERPLAY OF ATOMICITY, POLARIZATION, AND QUANTIZATION ON PERFORMANCE AND RELIABILITY IN GaN FINFETS
Date of Award
8-1-2026
Degree Name
Doctor of Philosophy
Department
Electrical and Computer Engineering
First Advisor
Shaikh, Ahmed
Abstract
GaN based nanoscale high-electron-mobility transistors (HEMTs) are the next generation of transistor technology that features the unique combination of higher power, wider bandwidth, low noise, higher efficiency, and temperature/radiation hardness than conventional AlGaAs and Si based technologies. However, enhancement mode operation for nanoscale channel region is the most recent needed area of research. As well as reliability of these devices remains a major concern. The main objective of this proposed research is to numerically investigate the role of atomistic inhomogeneity and quantization in low-dimensionality lateral tri-gated AlGaN/GaN FinFET devices. It is shown that 3-D configured AlGaN/GaN FinFETs with narrow enough fins (e.g. fin width < 10 nm) and appropriate Schottky gating of the side contacts can offer normally-off operation. Also, atomicity leads to pronounced dependence of the threshold voltage on the barrier layer thickness. This demands the use of atomistic (non-symmetry preserving) models in the calculation of polarization fields and induced interfacial charges in device simulation.The overall simulation makes use of the in-house QuADS 3-D simulator that bridges the gap between continuum and ab initio modeling paradigms and enable the quantum-corrected atomistic numerical modeling of non-equilibrium charge and phonon transport phenomena in realistically-sized devices. QuADS 3-D is primarily being built upon extended versions of three modules: (i) Open source LAMMPS molecular dynamics code for geometry construction and modeling structural relaxation; (ii) Open source NEMO 3-D tool for the calculation of electronic and phonon spectra. NEMO 3-D enables the computation of electronic structure using a variety of tight-binding models (s, sp3s*, sp3d5s*) that are optimized with a genetic algorithm tool. Whereas, for the calculation of atomistic (non-linear) strain relaxation, NEMO 3-D currently employs the atomistic valence-force field (VFF) with strain-dependent Keating potentials; and (iii) A quantum-corrected 3-D Monte Carlo transport kernel. Given the nanoscale dimensionality of the devices under study and the possible use in harsh environments, our work included the following: i) device variability that can originate from inhomogeneous distributions of the charged entities in the barrier/channel region, ii) thermal effects, that is, internal self-heating (via coupling the appropriate heat transport equations), and iii) the effects of contact degradation (via the coupling the LAMMPS molecular dynamics simulator). Experimental data, as available in literature, were also used to benchmark our models, as and when needed.
Access
This dissertation is Open Access and may be downloaded by anyone.