Dissertation
Theory of optical and electrical probes of spin defect dynamics in wide-gap semiconductors
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2026
Abstract
Spin defects, spinful atomic-sized impurities with quantized energy levels, have garnered much interest in recent years due to their long coherence times and susceptibilities to magnetic fields, electric fields, strain fields, temperature and pressure fluctuations; making them an attractive choice as quantum sensors. Spin defects in silicon carbide are especially attractive, since their coherent spin dynamics can be read out optically and electrically. In this dissertation, simulations of optical and electrical techniques for control and readout of spin defects in wide bandgap semiconductors using Lindblad master equations are presented, and specifically applied to silicon vacancy spin centers in silicon carbide.
In the first section, we present a quantitative theory for simulating optically detected magnetic resonance (ODMR) measurements of optically-active spin centers using steady-state Lindblad equations. We compare the theoretical simulations to an experimental ODMR spectrum associated with the negatively-charged silicon vacancy V2 center in 6H-SiC, showing that spin Hamiltonian parameters and coherence times may be extracted, with values consistent with recent literature. Furthermore, we simulate the ODMR spectra of a V2 center in isotopically-purified 6H-SiC, and predict an order-of-magnitude narrowing of some, but not all spectral lines compared with natural abundance samples.
In the second section, we further investigate the ODMR spectrum of silicon vacancies at low magnetic field and in isotopically-purified 4H-SiC. These simulations revealed novel multi-photon and multi-quantum transitions and anti-crossings. We provided a full description of these emergent features, derived effective Hamiltonianians through a Floquet-Schrieffer-Wolff transformation, and identified leading-order AC Stark shifts. We also investigated the interplay between inhomogeneous noise, microwave power, and double-quantum-enhanced sensing; and predicted the necessary experimental conditions for double-quantum transitions to provide a sensing advantage. This work highlights the necessity of isotopic purity for utilizing both multiphoton and double-quantum spin transitions for enhanced sensing.
In the final section, we presented a quantitative theory for simulating electrically detected magnetic resonance (EDMR) measurements of silicon vacancy-related spin pairs in silicon carbide. In our theory, we consider both V1a and V2a deep level silicon vacancies near the (0/-) charge state transition level in proximity to a previously-measured nitrogen-related complex, which we treat as either a shallow donor or acceptor and show the implications of both models. We first compared the theoretical simulations to a recent room temperature measurement attributed to V1a silicon vacancies and extracted spin coherence times and electrical transport rates. We also simulated the effect of lower temperatures and predicted that while resolving the hyperfine structure of the silicon vacancy may be possible at room temperature, the shallow level hyperfine structure may only be resolvable at lower temperatures. Finally, we predicted the EDMR spectrum of V2a silicon vacancy-related spin pairs and showed that the experimental observation of two-photon transitions would be evidence of the shallow level acceptor model.
Details
- Title: Subtitle
- Theory of optical and electrical probes of spin defect dynamics in wide-gap semiconductors
- Creators
- David A. Fehr
- Contributors
- Michael E. Flatte (Advisor)Denis R. Candido (Committee Member)Patrick M. Lenahan (Committee Member)Craig E. Pryor (Committee Member)Ravi Uppu (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Physics
- Date degree season
- Spring 2026
- Publisher
- University of Iowa
- Number of pages
- xiii, 169 pages
- Copyright
- Copyright 2026 David A. Fehr
- Language
- English
- Date submitted
- 04/28/2026
- Description illustrations
- color illustrations
- Description bibliographic
- Includes bibliographical references (page 153-169).
- Public Abstract (ETD)
The invention of transistors has enabled incredible miniaturization of computers: from room-sized machines to smart phones. However, progress has slowed in recent years as devices have approached the size of tens of atoms. At devices sizes about 10,000× thinner than a hair, particles follow the counter-intuitive rules of quantum mechanics, causing our technology to start failing. Thus, the atomic scale puts a hard limit on the size and performance of modern technology. What if, instead of avoiding quantum effects, our technology harnessed it?
Spin defects, atom-sized imperfections found in materials like silicon carbide, act as tiny traps for electrons that can be manipulated using lasers and microwaves. Although spin defects have been examined for energy-efficient sensors, memory storage, and resistors over the past two decades; their performance still lags behind current technologies. In this dissertation, we propose modern methods for simulating open quantum systems to enhance the sensitivity of these defects to magnetic fields.
We first developed a theory for simulating the response of silicon vacancies - spin defects in SiC consisting of a missing silicon atom - to lasers and magnetic fields. By monitoring the amount of light emitted by the silicon vacancies at special values of magnetic field, the mysterious quantum behaviors can be revealed. In fact, our simulations show that the coherence time - the quantum lifetime of spin defects - can be determined without complicated pulses.
In another theory, we simulated the response of current flowing through electrical devices containing silicon vacancies to microwaves and magnetic fields. By monitoring the changes in current at these same special values of magnetic field, quantum behaviors can be revealed electrically. This work shows the potential of silicon vacancies as energy-efficient magnetic field sensors that can be readily integrated into modern electronics.
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9985177373802771
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