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200933 https://hdl.handle.net/2286/R.2.N.200933 http://rightsstatements.org/vocab/InC/1.0/ All Rights Reserved 2025 106 pages Doctoral Dissertation Academic theses en Herath Mudiyanselage, Dinusha Indunil Bandara Mawathagama Fu, Houqiang Kalarickal, Nidhin Kurian Esqueda, Ivan Sanchez Goodnick, Stephen M. Arizona State University Partial requirement for: Ph.D., Arizona State University, 2025 Field of study: Electrical Engineering Recently, Aluminum Nitride (AlN - 6.2 eV) and Gallium Oxide (β-Ga2O3 - 4.9 eV) have garnered significant attention as two promising ultra-wide bandgap (UWBG) semiconductors for power electronic applications. Their popularity mainly stems from high bandgaps and high breakdown fields. Additionally, high-quality epilayers can be grown using molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD). Both AlN and Ga2O3 have high Baliga's Figure of Merit compared to Si, with values of ~40,000 for AlN and ~3,000 for Ga2O3, making them ideal candidates for efficient, high-power, high-voltage electronic devices.Chapter 1 introduces UWBG materials for power electronics, highlighting key properties of AlN and β-Ga2O3. It includes a brief review of electronic devices demonstrated with both materials and an overview of theoretical aspects of electric power conversion. Chapter 2 delves into the development of AlN Schottky barrier diodes (SBDs) on AlN bulk substrates. This chapter details the first demonstration of 3 kV AlN-on-AlN SBDs, improvements in Ohmic contacts to AlN epilayers, studies on low ideality factors SBDs and high-temperature performance of Ohmic contacts and SBDs. Chapter 3 focuses on AlN-based heterostructure diodes. BN can serve as excellent UWBG material to passivate AlN-based devices. As an initial demonstration, BN epilayers grown on AlN via microwave plasma chemical vapor deposition (MPCVD) were used to demonstrate metal-insulator-semiconductor (MIS) diodes. The electronic properties of the MIS diode were also investigated. One of the significant challenges in UWBG semiconductors is the lack of viable p-type doping due to the high activation energy of acceptors. This chapter also discusses using p-type NiOx as a viable solution for creating p-n diodes with UWBG semiconductors, specifically in developing NiOx/AlN p-n diodes with reduced leakage current compared to AlN SBDs. Chapter 4 focuses on Ga2O3-based devices. The first half of this chapter investigates β-(AlxGa1−x)2O3/Ga2O3 heterostructure vertical SBDs, elucidating the mechanisms behind their forward and reverse currents. The second half examines the anisotropic properties of NiOx/β-Ga2O3 heterojunction diodes by analyzing their electrical properties in different crystal orientations. Chapter 5 outlines the future directions of this research, while the final chapter provides a conclusion and an outlook. Electrical Engineering Aluminum nitride Gallium oxide Power Electronics Ultra-wide Bandgap Semiconductors Ultra-wide Bandgap Semiconductors Aluminum Nitride and Gallium Oxide for Next-generation Efficient Power Electronics