When 12:00 PM - 1:00 PM May 24, 2023
Where 1014 HH Dow
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PhD defense: "Development and Application of First-Principles Methods for Phonon-Assisted Quantum Processes"

Kyle Bushick
Kioupakis group

Zoom info: https://umich.zoom.us/j/95145019042
Meeting ID: 951 4501 9042
Passcode: 225509



Semiconductors are an extremely diverse class of materials critical to enabling a variety of functional energy applications, from electricity generation and power conversion to efficient lighting and computing. As society continues to grapple with the pressures of climate change and the need to increase energy efficiency and reduce greenhouse gas emissions, advances in our understanding of fundamental material behavior at the atomic level will accelerate the discovery and engineering of modern and next-generation materials and devices.


The need for microscopic study coincides with the increased availability of significant computing power and the maturation of the first-principles electronic structure code ecosystem. These codes, which implement density functional theory, density functional perturbation theory, many-body perturbation theory, and physically informed (Wannier) interpolation techniques are run on supercomputers and allow us to study a diverse array of both materials and the quantum processes governing a material's properties at the atomic level.


While the electronic structure of a material typically dictates its functionality, the interactions between electrons and lattice vibrations, or phonons, also play a role in several important material properties, such as indirect optical absorption or carrier mobility. In this work, I develop and apply first-principles methods and codes to study both direct and phonon-assisted quantum processes in three semiconductor systems: direct and phonon-assisted optical absorption in boron arsenide, phonon-limited carrier mobility in boron arsenide and rutile germanium dioxide, and direct and phonon-assisted Auger-Meitner recombination in silicon.


I first apply existing methods to study the electronic structure and resulting direct and phonon-assisted optical absorption in the novel semiconductor boron arsenide. I demonstrate the predictive capabilities of these methods in collaboration with experimental measurement. I also extend my investigation to quantifying the effects of bi-axial tensile strain on carrier mobility. I then demonstrate how these computational methods can be used to accelerate application selection and device design for novel materials, highlighting potential heterostructure pairs for boron arsenide-based optoelectronics.


In a similar vein, I apply these methods to calculate the phonon-limited carrier mobility in the novel ultrawide-band gap material, rutile germanium dioxide. Through these efforts, I motivate the continued development of this material for next-generation power electronics applications given its comparatively high carrier mobilities, which contribute to a highly competitive Baliga figure of merit.


Finally, I expand on current computational capabilities by developing a generalized code to calculate both direct and phonon-assisted Auger-Meitner recombination in semiconductors. This code leverages existing open-source density functional and density functional perturbation theory capabilities. I apply these methods to study Auger-Meitner recombination in silicon, addressing a long-standing question about the role of phonons in this efficiency limiting process. Based on my initial work, I then extend this study to demonstrate the potential of strain engineering to tune the rate of this intrinsic recombination process in silicon devices.


My research demonstrates the breadth and applicability of first-principles methods to studying phonon-assisted quantum processes in semiconductors, providing insights into the microscopic mechanisms that govern macroscopic material performance. The capabilities I discuss, both long standing and newly developed, are particularly beneficial to investigate material systems where experimental measurement is challenging or quality samples are rare or do not yet exist. Ultimately, I use this diverse computational toolkit to accelerate the materials design process and inform our understanding of material behavior at the atomic level.