Committee Members Information

• Ph.D. Advisor: Professor Xiaohang Li
• Committee Chair: Professor Nazek El-Atab
• External Examiner: Professor Aimin Song
• Committee Member: Professor Alfonso Caraveo

Abstract:

Ultra-wide bandgap (UWBG) semiconductors are emerging as the next frontier beyond wide bandgap materials, enabling high-power, high-frequency, deep-UV, and extreme-environment electronics. Among these candidates, β-Ga2O3 is particularly promising because it combines excellent intrinsic properties with practical advantages such as scalable, low-cost bulk growth using melt-based methods and superior dopant activation efficiency, as captured by the modified Baliga figure of merit. These attributes distinguish it from other UWBG semiconductors like AlN and diamond and have fueled sustained research activity and rapid device development.

This dissertation investigates how nanoscale devices can extend the potential of β-Ga2O3 beyond conventional implementations, enabling new functionalities. To establish the fabrication foundation, inductively coupled plasma reactive ion etching was systematically studied, revealing how etch parameters govern sidewall taper angle, surface morphology, and etch rate. These insights enable the realization of nanoscale features for β-Ga2O3 devices. On this basis, self-switching diodes (SSDs)—nanoscale nonlinear devices—were fabricated on both sapphire and β-Ga2O3 substrates. These devices demonstrated multifunctional operation by combining rectification, high current density handling, robust breakdown performance, and deep-UV photoresponse, underscoring their promise as versatile building blocks for integrated β-Ga2O3 electronic and optoelectronic circuits.

Finally, motivated by the SSDs, a novel transistor architecture—the semiconductor–free-space gate transistor (SFGT)—was introduced and experimentally demonstrated. The SFGT eliminates the solid dielectric, mitigating dielectric charge- and trap-related limitations of conventional metal-oxide-semiconductor structures while providing direct electrostatic access to the gate region. The devices exhibited competitive performance, enhanced stability following atomic layer etching, reversible threshold-voltage tunability through modulation of the free-space gate, and operation down to 2 K. These results highlight their potential for sensing and memory applications, as well as stable functionality across a wide temperature range. Together, these studies demonstrate that β-Ga2O3 nano-devices can be engineered to unlock new device functionalities