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All Subjects: quantum physics
Creators: Saraniti, Marco

Conductance fluctuations in GaAs nanowires and graphene nanoribbons

Description

In mesoscopic physics, conductance fluctuations are a quantum interference phenomenon that comes from the phase interference of electron wave functions scattered by the impurity disorder. During the past few decades, conductance fluctuations have been studied in various materials including metals, semiconductors and graphene. Since the patterns of conductance fluctuations is related to the distributions and configurations of the impurity scatterers, each sample has its unique pattern of fluctuations, which is considered as a sample fingerprint. Thus, research on conductance fluctuations attracts attention worldwide for its importance in both fundamental physics and potential technical applications. Since early experimental measurements of conductance fluctuations showed that the amplitudes of the fluctuations are on order of a universal value (e2/h), theorists proposed the hypothesis of ergodicity, e.g. the amplitudes of the conductance fluctuations by varying impurity configurations is the same as that from varying the Fermi energy or varying the magnetic field. They also proposed the principle of universality; e.g., that the observed fluctuations would appear the same in all materials. Recently, transport experiments in graphene reveal a deviation of fluctuation amplitudes from those expected from ergodicity.

Thus, in my thesis work, I have carried out numerical research on the conductance fluctuations in GaAs nanowires and graphene nanoribbons in order to examine whether or not the theoretical principles of universality and ergodicity hold. Finite difference methods are employed to study the conductance fluctuations in GaAs nanowires, but an atomic basis tight-binding model is used in calculations of graphene nanoribbons. Both short-range disorder and long-range disorder are considered in the simulations of graphene. A stabilized recursive scattering matrix technique is used to calculate the conductance. In particular, the dependence of the observed fluctuations on the amplitude of the disorder has been investigated. Finally, the root-mean-square values of the amplitude of conductance fluctuations are calculated as a basis with which to draw the appropriate conclusions. The results for Fermi energy sweeps and magnetic field sweeps are compared and effects of magnetic fields on the conductance fluctuations of Fermi energy sweeps are discussed for both GaAs nanowires and graphene nanoribbons.

ContributorsLiu, Bobo (Author) / Ferry, David K. (Thesis advisor) / Akis, Richard (Committee member) / Saraniti, Marco (Committee member) / Goryll, Michael (Committee member) / Arizona State University (Publisher)

Created2015

Full band Monte Carlo simulation of nanowires and nanowire field effect transistors

Description

In this work, transport in nanowire materials and nanowire field effect transistors is studied using a full band Monte Carlo simulator within the tight binding basis. Chapter 1 is dedicated to the importance of nanowires and nanoscale devices in present day electronics and the necessity to use a computationally efficient tool to simulate transport in these devices. Chapter 2 discusses the calculation of the full band structure of nanowires based on an atomistic tight binding approach, particularly noting the use of the exact same tight binding parameters for bulk band structures as well as the nanowire band structures. Chapter 3 contains the scattering rate formula for deformation potential, polar optical phonon, ionized impurity and impact ionization scattering in nanowires using Fermi’s golden rule and the tight binding basis to describe the wave functions. A method to calculate the dielectric screening in 1D systems within the tight binding basis is also described. Importantly, the scattering rates of nanowires tends to the bulk scattering rates at high energies, enabling the use of the same parameter set that were fitted to bulk experimental data to be used in the simulation of nanowire transport. A robust and efficient method to model interband tunneling is discussed in chapter 4 and its importance in nanowire transport is highlighted. In chapter 5, energy relaxation of excited electrons is studied for free standing nanowires and cladded nanowires. Finally, in chapter 6, a full band Monte Carlo particle based solver is created which treats confinement in a full quantum way and the current voltage characteristics as well as the subthreshold swing and percentage of ballistic transport is analyzed for an In0.7Ga0.3As junctionless nanowire field effect transistor.

ContributorsHathwar, Raghuraj (Author) / Goodnick, Stephen M (Committee member) / Saraniti, Marco (Committee member) / Vasileska, Dragica (Committee member) / Ferry, David K. (Committee member) / Arizona State University (Publisher)

Created2016

The History and Importance of the Double-Slit Experiment: From Classical to Quantum Physics

Description

This paper analyzes the history and impact of the double-slit experiment on the world of physics. The experiment was initially created by Thomas Young in the early nineteenth century to prove that light behaved as a wave, and the experiment’s findings ended up being foundational to the classical wave theory of light. Decades later, the experiment was replicated once more with electrons instead of light and shockingly demonstrated that electrons possessed a dual nature of behavior in that they acted in some instances as particles and in others as waves. Despite numerous modifications and replications, the dual behavior of electrons has never been definitively explained. Numerous interpretations of quantum mechanics all offer their own explanations of the double-slit experiment’s results. Notably, the Copenhagen Interpretation states that an observer measuring a quantum system, such as the double-slit experiment, causes the electrons to behave classically (i.e. as a particle.) The Many Worlds Interpretation offers that multiple branching worlds come into existence to represent the physical occurrence of all probable outcomes of the double-slit experiment. In these and other interpretations, explanations of the double-slit experiment are key to proving their respective dogmas. The double-slit experiment has historically been very important to the worlds of both classical and quantum physics and is still being modified and replicated to this day. It is clear that it will continue to remain relevant even in the future of physics.

ContributorsRodriguez, Zachary M (Author) / Foy, Joseph (Thesis director) / Hines, Taylor (Committee member) / Department of Information Systems (Contributor) / Barrett, The Honors College (Contributor)

Created2021-05