Non-Asymptotic Quantum Scattering Theory for Low-Dimensional Materials Public
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Over the past few decades, solid-state devices have steered the field of nanoelectronics. The advancement in semiconductor technology has led to the development of classical integrated circuits, which follows the trend defined by Moore’s law. However, in order to achieve the next generation of computing circuits, one requires to go beyond the limits of Moore’s law. This has led to a revolution in the development of new quantum materials, and harnessing their physical properties. This new class of quantum materials constitutes low-dimensional systems such as semiconductor heterostructures and atomically thin two-dimensional (2D) materials. Tunability of the physical properties offered by these structures, makes them ideal candidates to host high performance nanoelectronic circuits and quantum information platforms. In this thesis, we develop a scalable first-principles informed quantum transport theory to investigate the carrier transport properties of low-dimensional materials, and reveal their novel electronic and thermoelectric properties. While first-principles calculations effectively determine the atomistic potentials associated with defects and impurities, they are ineffective for direct modeling of carrier transport properties at length scales relevant for device applications. Traditionally, scattering properties are obtained by applying the asymptotic boundary conditions. However, these boundary conditions do not account for the decaying evanescent mode contributions, that are crucial while determining the transport properties of low-dimensional systems. Here, we develop a novel non-asymptotic quantum scattering theory to obtain the transport properties in proximity to the scattering centers, for confined as well as open domain in one-, two- and three-dimensional systems. We then bridge this scattering theory and the k.p perturbation theory, with inputs from ab-initio electronic structure calculations, to construct a versatile multiscale formalism. The continuum nature of the formalism enables us to model realistic meso- and nano-scale devices. The given formalism is applied to study electron scattering in quantum waveguides. Several interesting phenomena are revealed through our analysis. The Fano resonance profile for the transmission spectrum of both propagating and evanescent modes is observed. An enhancement of power factor far beyond the earlier proposed limits is obtained by embedding attractive impurities within the waveguide. A current rectification device is simulated, which is expected to find applications in quantum transport. We further apply this formalism to reveal the novel electronic and thermoelectric properties of monolayer lateral transition-metal dichalcogenide (TMDC) heterostructures. We show that material inclusions in such heterostructures leads to enhancement of electron mobility by an order of magnitude larger than pristine TMDCs. The band alignment between the materials also enhances the thermoelectric figure-of-mertit (ZT) and power factor far beyond the pristine TMDCs. Our study opens new avenues for constructing ultra-efficient in-plane thermoelectric devices using lateral TMDC heterostructures.
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