Formation, integration, and control of semiconductor spin-defects in electronic and photonic devices

Abstract

Can we identify new techniques to better create, control, and understand quantum systems? This is the central question of my thesis, which I explore by focusing on a particular class of quantum system--semiconductor-hosted spin-defects, namely the silicon monovacancy in silicon carbide, and the G center and T center in silicon. In this thesis, I investigate laser-mediated local defect formation in nanophotonics (create - Ch. 3), electrical manipulation of telecom defects in a silicon lateral PIN-diode (control - Ch. 4), and defect-enabled mapping of carrier phase transitions revealing negative differential resistance in silicon (understand - Ch. 5). Together, these results underpin the wealth of insight to be probed at the intersection of semiconductor physics and quantum science, as decades-old solid-state theories can be rediscovered in emergent quantum networking candidates. Detailed: In the recent decade, the ideas of quantum information science (QIS) have begun to become realized through the rapid development of technology which directly rely upon the principles of quantum mechanics such as superposition and entanglement. Computing, sensing, and communications are the three principal modalities which quantum technology is re-imagining, enabling enhanced capabilities unrivaled by their classical counterparts such as information theoretic security and efficient simulation of quantum phenomena. Fundamentally, a quantum technology platform is constituted by an isolated quantum two-level system (qubit) in which information can be controllably stored, manipulated, and accessed. However, each candidate offers vastly different advantages and challenges toward experimental implementation. The great promise of these technologies has motivated an intense study of quantum engineering to realize platforms ideally suited to their respective QIS task. While atoms, ions, superconducting Josephson-junctions, and photons are all compelling candidate qubits, a class of quantum systems known as solid-state spin-defects (color centers) are particularly exciting due to their natural environmental coupling (quantum sensing) and inherent spin-photon interface with facile deployment in nanofabricated devices which enhance their performance (quantum communications and networking). Spin-defects are imperfections in an otherwise perfect crystal lattice, whereby an electronic structure is localized in the bandgap via the removal or addition of atoms in the crystal, leaving behind some isolated electron system. While imperfections exist in every crystal, their utility toward quantum technology varies drastically--reliant on features such as their possession of: microwave-controllable spin, optically-active charge state, robust spin-photon interface, and host material quality. Considering all of these traits, the current leading solid-state spin defect qubits are the Silicon Vacancy (SiV) and Nitrogen Vacancy (NV) in diamond. However more recently, there has been great interest in evaluating emergent spin defects which may exist in other crystal hosts and offer inherent unique benefits not possessed by these leading diamond candidates. For instance, quantum-grade diamond is highly-specialized and hard to fabricate, the NV and SiV visible-photon emission exhibits tremendous loss in conventional telecom fiber, and the SiV spin requires milliKelvin temperatures to utilize. In contrast, silicon (Si) and silicon carbide (SiC) are ubiquitous commercial semiconductors with nearly a century of development in growth, material purity, and nanofabrication techniques--therefore, quantum technology stands to benefit greatly by leveraging the wealth of research and development of semicondcutor hosts. Furthermore, a class of carbon-related color centers in Si have been recently re-discovered which emit photons in the low propagation loss (0.3dB/km) telecommuncations O-Band (1260-1360nm) of the optical fiber which circles the globe for classical internet, and which possess an optically-addressable spin. The immense practical advantages of material host and emission frequency for these semiconductor spin-defects renders them exciting candidates for scalable quantum networking, however their nascency requires significant investigation to compete with existing leading systems in diamond. In this thesis, I present work on the investigation and device engineering of semiconductor-hosted spin-defects, focusing on the silicon monovacancy (VSi) in silicon carbide (SiC) and the G and T centers in silicon. I first introduce the relevant background information to support this thesis in Chapter 1, from QIS theory to the varied platforms which enable it. In Chapter 2 I introduce solid-state spin defects, analyze the leading host materials and defect qubit trade-offs, then describe the intersection of defect integration with quanutum photonics, electronics, acoustics, and nanofabrication techniques. At the conclusion of this section I detail the thin-film SiC platform our group has developed for device nanofabrication of SiC defects. In Chapter 3 I develop a laser-based approach for controllably forming silicon vacancy defects (VSi) within these fabricated nanophotonic crystal cavities in SiC. Chapters 4 and 5 then focus on electrical integration, characterization, and control of silicon color centers in lateral PIN-diodes. Using these principles, chapter 4 presents stark tuning and optical charge state control of a G center ensemble, and chapter 5 reports direct optical observation of carrier phase transitions characteristic of negative differential resistance through the coupling of electrical nonlinearities to a T center ensemble. Finally Chapter 6 describes the outlook for semiconductor spin-defects, detailing the remaining challenges faced by VSi, G centers, and T centers, and discussing exciting new opportunities with color centers such as Vanadium.