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Growth and applications of epitaxial transition metal nitride thin film heterostructures

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Abstract

Continued improvements in the efficiency and speed of computation and telecommunication requires leveraging the properties of novel materials and materials interfaces. Superconductivity, a phenomenon that until now has not seen widespread application in microelectronic devices, appears poised for extensive implementation in technologies such as single flux quantum (SFQ) digital logic and Josephson junction-based quantum computing. The development of these technologies requires addressing outstanding materials challenges, such as realizing new materials and devices to enable improvements such as increased circuit density for SFQ circuits and low microwave noise Josephson junctions for enhanced coherence time superconducting qubits. Furthermore, while the existing nitride semiconductor materials have enabled new applications in optoelectronics, power electronics, and RF electronics, the ability to integrate these materials in epitaxial structures containing metallic and superconducting thin film materials creates new dimensions in the design space of semiconductor devices, allowing for the creation of novel devices. With these goals in mind, we have pursued the integration of metallic and superconducting transition metal nitrides, such as NbN and TiN, with III-N semiconductors (AlN, GaN, InN). Firstly, we have studied the growth and properties of NbN and TiN films grown by molecular beam epitaxy. We demonstrate that exceptionally high quality epitaxial thin films of NbN can be grown, and that tuning of the growth variables, such as elemental fluxes and substrate temperature, can control the structural phase and superconducting properties of the resultant NbN films. We demonstrate, for the first-time, phase pure beta-Nb2N thin films of the hexagonal crystal structure, and examine their superconducting and structural properties. Additionally, to better understand the electronic properties of both NbN and NbN/III-N interfaces, we examine the electronic interface between GaN and NbN using both Schottky barrier diodes and SX-ARPES, presenting the k-resolved imaging of the electronic states at this technologically interesting materials interface. To enable the realization of hybrid metal-semiconductor nitride devices, a detailed study of the growth of AlN and GaN on NbN is performed. We demonstrate that lattice misfit, surface energy mismatch, and chemical compatibility all present challenges to the realization of these heterostructures. Through the development of new growth strategies, we overcome these issues and demonstrate the growth of high crystal quality epitaxial AlN thin films grown on NbN. Finally, we utilize these films and heterostructures to fabricate several devices. We demonstrate the utilization of ultra-thin epitaxial NbN to fabricate superconducting nanowire single photon detectors (SNSPD). Utilizing the piezoelectric properties of AlN and the metallic properties of NbN, we fabricate epitaxial bulk acoustic wave (BAW) resonators. Finally, using NbN films as superconducting electrodes and an AlN film as a wide band gap semiconductor, we examine the properties of MBE grown NbN/AlN/NbN Josephson junctions.

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255 pages

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2022-08

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Keywords

Epitaxy; nitride; Superconductivity; Thin film

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Committee Chair

Jena, Debdeep

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Committee Member

Xing, H. Grace
Muller, David Anthony

Degree Discipline

Materials Science and Engineering

Degree Name

Ph. D., Materials Science and Engineering

Degree Level

Doctor of Philosophy

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Government Document

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Attribution-NonCommercial-ShareAlike 4.0 International

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dissertation or thesis

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