Vacuum Transistors Based on III-Nitrides Field Emitter Arrays with Self-Aligned Gate

Abstract

Vacuum electronics are promising future high-frequency and harsh-environment devices thanks to their scattering-free and radiation-robust vacuum channels. Field-emission vacuum transistors based on silicon and metals have been demonstrated over past 30 years, however the power consumption and long-term device stability are still issues. To further improve the field emission device performance and stability, III-Nitride semiconductors are attracting significant attention recently thanks to their engineerable electron affinities and high bonding energies. Ideally, the degenerately-doped n-type semiconductors with low electron affinities can have low work functions, leading to small electron Fowler-Nordheim tunneling barriers and thus low operating voltage and reduced power consumption. Moreover, materials with large bonding energies are expected to be more robust towards ion-bombardment-induced degradation. In spite of the great potential of III-Nitride vacuum transistors, there are still very limited transistor-level demonstrations with performance comparable to Si and metal-based field emitters.

This thesis aims to identify the key challenges of III-Nitride vacuum transistors and demonstrate new approaches to tackle these issues. First, GaN field emission diodes are studied to understand the basic device operation and the long-term stability of GaN emitter tips. Second, self-aligned-gate structures are developed on GaN field emitter arrays to demonstrate vacuum transistors with reduced operating voltages. The device performance is further improved by sharpening the field emission tips and optimizing device geometries. Third, N-polar GaN and AlGaN self-alignedgate field emitter arrays are also fabricated and their material properties for field emission applications are investigated. Finally, a new technology to demonstrate fully-integrated III-Nitride vacuum transistors is discussed. This thesis work serves as a foundation for future high-frequency (above-100 GHz) and high-power III-Nitride vacuum electronics.