UNDERSTANDING NITRIDE MATERIALS FOR THERMAL AND DIELECTRIC FUNCTIONALITY IN POWER ELECTRONICS AND SUPERCONDUCTING CIRCUITS
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This dissertation presents two studies which develop strategies that leverage the thermal transport properties of nitrides to reduce thermally mediated degradation of device performance in power electronics and superconducting circuits. (1) Ultra-wide bandgap (UWBG) semiconductors host the large critical electric fields necessary to support a leap in the power density of next-generation power and radio-frequency electronics. However, effective thermal management of the heat flux incited by high-voltage operation remains a limiting challenge. The current understanding of thermal transport in UWBG semiconductors neglects the departure from equilibrium driven by electric field (E), which becomes more severe at higher power density. We develop a new computational method to obtain non-equilibrium ab initio thermal transport properties under E within the density-functional theory - non-equilibrium green’s function (DFT-NEGF) framework. The predicted cross-plane thermal conductivity of wurtzite Aluminum Nitride (AlN) is modified by a cross-plane electric field (Ez), where the change in cross-plane thermal conductivity depends on the direction of Ez with respect to the polarity of the AlN thin film. The findings provide critical insights to understand thermal transport in devices under operating conditions and design effective thermal management for high-power electronics. (2) The search for low-loss dielectrics compatible with superconducting circuits is of importance to the functionality of quantum computers and sensors. We investigate the compatibility of hexagonal boron nitride (hBN) thin films with superconducting circuits, towards a novel strategy that applies the thermal transport properties of 2D materials for mitigation of phonon-mediated quasiparticle poisoning. The research encompasses the growth of epitaxial hBN thin films using molecular beam epitaxy, fabrication of superconducting resonators incorporating hBN at the superconductor-substrate interface, and radio-frequency measurements which probe responses to power, temperature, and temporal fluctuations known to arise from two-level systems. We conclude the inclusion of hBN thin films in the materials stack introduces minimal additional dielectric loss.