Formation, Spectroscopy, and Optical Control of Donor Spin Defects in ZnO

Abstract

This thesis investigates shallow donor spin defects in ZnO as optically addressable qubits, with emphasis on their controlled formation, spectroscopic identification, and spin properties. ZnO is an attractive host for donor qubits because it combines weak spin-orbit coupling, strong zero-phonon optical transitions, and optical access to coupled electron--nuclear spin degrees of freedom through donor-bound excitons and hyperfine interactions. The work addresses three related goals: establishing the properties of implanted donor qubits in ZnO, identifying and characterizing a ``deep'' shallow donor complex with enhanced hyperfine coupling, and exploring materials routes toward more scalable donor-qubit platforms. First, indium donors in ZnO are studied as a donor-qubit system formed by controlled ion implantation and annealing. Optical spectroscopy confirms the formation of donor-bound excitons associated with implanted indium. Time-resolved and two-laser measurements are used to characterize their spin relaxation, coherence, and hyperfine structure. These results establish implanted indium donors as a reproducible platform for studying donor-spin qubits in ZnO. Second, this thesis demonstrates the controlled formation and identification of the Sn-Li donor complex associated with the I$_{10}$ line in ZnO. Ion implantation and annealing are used to form the defect, and optical spectroscopy reveals its donor-bound-exciton structure. Two-laser coherent population trapping measurements resolve the electron--$^{119}$Sn hyperfine interaction, showing that this donor exhibits substantially stronger hyperfine coupling than previously studied shallow donors in ZnO. Together with first-principles calculations, these measurements support the assignment of I$_{10}$ to the Sn-Li complex and establish it as a coupled electron-nuclear spin register of particular interest for donor-based quantum memories. Finally, this thesis explores directions toward scalable donor-qubit platforms by examining ZnO nanostructures and post-growth processing. Bulk-like nanorods and colloidal ZnO nanostructures are investigated as possible hosts for isolated donor defects, and annealing studies are used to improve optical quality and to assess the effects of morphology and surface environment on donor-related emission. These studies identify both opportunities and materials challenges in extending donor qubits in ZnO beyond bulk substrates. Taken together, the results of this thesis advance ZnO as a host for donor-based spin qubits by demonstrating controlled donor formation through ion implantation, establishing optical and spin signatures of implanted donor systems, and identifying a Sn-Li donor with enhanced hyperfine interaction. More broadly, this work contributes to the development of semiconductor spin-photon interfaces and coupled electron-nuclear qubit registers in engineered solid-state defect systems.