Date of Award

2017

Document Type

Open Access Dissertation

Department

Physics and Astronomy

Sub-Department

College of Arts and Sciences

First Advisor

Timir Datta

Abstract

Geometric influence on electrical and magneto transport properties has been investigated in three types of systems: (i) Graphene, a single layer of carbon atoms; (ii) Two-dimensional electron gas (2DEG) in AlInN/GaN heterostructure; and (iii) 3D carbon nanostructures, a special type of three-dimensional materials with spherical voids. Due to unique structures and energy dispersion relations, these three systems demonstrate distinct physical properties.

AlInN is the newest and amongst the widest band gap semiconductors. The 2DEG in AlInN/GaN heterostucture displays long transport lifetime along with conventional behaviors, including Shubnikov-de Haas (SdH) oscillation and weak localization. From SdH oscillation, the effective mass of electron is obtained as 0.2327me. We report the first observation of weak localization in this heterostructure. Electron-electron scattering is the principal phase breaking mechanism in this system.

In contrast, graphene has an unconventional linear energy dispersion relation near the Dirac points. We determine the effective mass of electron is 0.087me in CVD graphene, much smaller than that in 2DEG. In addition, due to pseudo spin and nonzero Berry phase, weak localization in graphene is more complex. Furthermore, the introduction of an antidot lattice has great influence on transport in graphene. We demonstrate that the carrier density and effective mass can be controlled by such manipulation. By tuning antidot size, a band gap ~ 10 meV is obtained. Geometric control of the band gap is likely to promote electronic applications of graphene.

As observed in graphene and the 2DEG, the magneto response is typically sensitive to the orientation between the applied magnetic field and input current. However, we demonstrate that orientation independent response and linear magnetoresistance can be achieved in three-dimensional carbon nanostructures with spherical voids. With the increasing void size, the linear magnetoresistance is enhanced and a metal to insulator transition is observed. The combination of orientation insensitivity and linear magnetoresistance is very useful for magnetic field detectors, particularly at high magnetic fields.

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