Doctoral Dissertations
Date of Award
12-2025
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Major
Physics
Major Professor
Joon S Lee
Committee Members
Hanno H. Weitering, Ruixing Zhang, Gong Gu
Abstract
Hybrid quantum devices, which integrate superconductors with semiconductor or topological materials, represent versatile platforms for quantum computing, quantum sensing, and fundamental studies of novel quantum phenomena. A critical requirement for realizing such technologies is the development of scalable and reliable growth and fabrication techniques capable of producing nanostructures with precise control over geometry, positioning, and interface quality. Selective area growth (SAG), a catalyst-free epitaxial technique, addresses this requirement by enabling deterministic synthesis of semiconductor nanowires directly onto lithographically patterned substrates, facilitating seamless integration into device architectures. However, SAG-grown nanowires frequently suffer from interfacial defects arising from lattice mismatch with the substrate, leading to reduced electronic performance. Ad ditionally, hybrid nanowire devices fabricated through post-growth processing often experience interface contamination and structural degradation, limiting quantum coherence and device reproducibility. Moreover, SAG has remained restricted to a limited range of material systems, constraining broader applicability. This thesis addresses these critical challenges through multiple innovative strate gies. We first systematically explore and establish optimal selectivity windows for SAG of various III–V semiconductor nanowires, including InAs, GaAs, and InGaAs, achieving controlled growth and uniform morphology. To mitigate interfacial defects, we introduce lattice-matched InGaAs buffer and capping layers, significantly enhancing the electrical performance of SAG-grown InAs nanowires, as evidenced by improved electron mobility and extended quantum coherence lengths. To circumvent issues associated with post-growth fabrication, we develop a pre-fabricated shadow bridge platform for the in-situ realization of hybrid quantum devices, successfully demonstrating gate-tunable superconductivity in Al–InAs Josephson junction device without post growth fabrication. Furthermore, we extended the SAG approach to the facet-selective growth of in plane bismuth (Bi) nanowires. This achievement considerably broadens the material scope of SAG and paves the way toward investigating higher-order topological states. Collectively, this work positions selective area growth, in combination with the shadow-bridge platform, as a robust, versatile, and scalable technique. By addressing fundamental challenges associated with hybrid quantum devices, this approach provides new pathways toward the realization of advanced quantum technologies and the exploration of novel topological states.
Recommended Citation
Adhikari, Pradip, "Advances in Selective Area Growth and in-situ Shadowing for Hybrid and Topological Nanowire Devices. " PhD diss., University of Tennessee, 2025.
https://trace.tennessee.edu/utk_graddiss/13576