Electronic Theses and Dissertations Archive

Date

2026

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Physics

Committee Chair

Xiao Shen

Committee Member

Firouzeh Sabri

Committee Member

Shawn Pollard

Committee Member

Yongmei Wang

Abstract

Ferroelectric hafnium oxide (HfO2) has emerged as a promising material for next-generation non-volatile memory and computing technologies because of its compatibility with complementary metal-oxide-semiconductor (CMOS) processing, scalability, and robust ferroelectricity. However, the atomistic mechanisms governing ferroelectric phase stabilization, defect interactions, and polarization switching remain incompletely understood, limiting the rational design of high-performance HfO2-based devices. This dissertation employs first-principles density functional theory calculations to establish atomistic design principles for engineering ferroelectricity in HfO2 through strain, dopant incorporation, oxygen-vacancy engineering, and multivalent defect chemistry. The effects of strain orientation, yttrium (Y) doping, and oxygen vacancies on ferroelectric phase stability were first investigated. The results demonstrate that biaxial compressive strain stabilizes the ferroelectric orthorhombic phase, with the (111) orientation exhibiting greater effectiveness than the (001) orientation owing to its higher atomic packing density and favorable crystallographic response to strain. Cooperative interactions between yttrium dopants and oxygen vacancies further reduce the transition stress required for phase transformation, while increased flexibility around the tri-coordinated oxygen environment promotes stabilization of the ferroelectric phase. The influence of vanadium (V) doping on ferroelectric stability, energetic phase competition, defect electronic structure, and polarization switching was subsequently investigated. The calculations reveal the coexistence of +3 and +4 oxidation states of V arising from oxygen-vacancy-mediated charge compensation. Vanadium doping favors the ferroelectric Pca21 phase over the competing antipolar Pbca phase, with the V3+ configuration producing the largest energetic separation between the two phases. This configuration plays a dual role by enhancing ferroelectric phase stability and transforming mid-gap oxygen vacancy-induced trap states into deeper defect-complex states, thereby increasing the trap-assisted tunneling barrier and indicating improved leakage characteristics. In contrast, the V4+ configuration, which occurs in the absence of an oxygen vacancy, substantially lowers the polarization-switching barrier. These complementary effects originate from preferred dopant proximity and charge-state-dependent changes in local coordination, bond lengths, and ionic size. Overall, this dissertation provides atomistic insight into the mechanisms governing ferroelectric phase stabilization, defect chemistry, and polarization switching in HfO2. The results establish strain engineering, dopant-vacancy interactions, and multivalent dopant chemistry as complementary strategies for tailoring the structural, electronic, and switching properties of hafnia-based ferroelectrics. More broadly, this work demonstrates that multivalency within a single dopant species provides a viable route for overcoming key trade-offs in ferroelectric HfO2, offering practical design principles for the development of high-performance materials for future non-volatile memory, logic, and neuromorphic computing technologies.

Comments

Data is provided by the student.

Library Comment

Dissertation or thesis originally submitted to ProQuest/Clarivate.

Notes

Open Access

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