Computational Modeling of Atomistic Dynamics in Semiconductors and Molecular Sensors

Abstract

Density functional theory (DFT) is a landmark development in theoretical condensed matter physics that continues to be a powerful tool for exploring the behavior and properties of matter at the atomic scale. My work has centered on using DFT to gain several insights into problems and areas of active interest in device physics and materials design. I have identified a novel mass diffusion mechanism contributing to device failure in GaN/AlGaN HEMTs in which charged vacancies are induced to migrate at room temperature by an external electric field. These results provide insight into how to make these devices more robust and to manage similar phenomena in other oxides. I have identified and characterized a reaction pathway by which Fe-porphyrin catalyzes two-step self-cleaning exothermic reactions between DNT and atmospheric oxygen at room temperature. The reactions can potentially be used in molecular sensor applications designed to detect the heat released by these reactions into a substrate. I have also investigated the dynamics of hydrogen in VO2 and established that the experimentally observed stabilization of the metallic phase at room temperature is due to lattice distortion, that hydrogen preferentially diffuses along oxygen channels in the monoclinic [100] direction, and that dissociation and association of molecular hydrogen at a monoclinic (100) VO2 surface has a 1.6 eV barrier, too high for room-temperature activation. This information shows that extracting hydrogen from VO2 requires elevated temperatures and that the surface orientation can be optimized to allow fast hydrogen diffusion into the bulk by exposing oxygen channels to the surface.