Date of Award
Doctor of Philosophy (PhD)
Physics and Astronomy
Ramesh G. Mani
The 2D confinement of electrons modifies the physical properties of the electronic system, and this has significant implications for electrons' interactions and kinetic behavior. A 2D electron system (2DES) exposed to a magnetic field at low temperatures provides an excellent platform for mesmerizing physical phenomena such as weak localization and weak anti-localization, giant negative/positive magnetoresistance, Shubnikov-de Haas oscillations (SdHOs), and quantum Hall effects. The photoexcitation of a 2DES has also introduced new phenomena such as radiation-induced magnetoresistance oscillations and zero resistance states. Exploring and understanding novel physical phenomena in 2DES would benefit future advanced semiconductor technology.
This dissertation is based on magnetotransport studies of the 2DES in GaAs/AlGaAs and graphene, and investigation of chemical vapor deposition (CVD) techniques for graphene growth. The effect of microwave (MW) radiation on electron temperature was studied by investigating the photo-excited transport at zero magnetic field and in the SdHOs regime where the cyclotron frequency ωc and the MW angular frequency ω satisfy 2.3 < ωc/ω ≤ 5.2. The results show small discernible electron heating under modest MW radiation, in agreement with theoretical predictions. Additionally, the activation energy at the odd integer filling factors in GaAs/ AlGaAs 2DES was examined using a novel technique of microwave induced heating instead of conventional temperature dependent measurements. We also performed magnetotransport measurements on epitaxial graphene samples, which show large longitudinal resistance values, and examined the Hall resistance values that shift away from the quantized values with increments of temperature. This dissertation also discusses the research efforts on growth and techniques of low pressure CVD graphene. A dual treatment technique was utilized to lower the nucleation density of single crystal graphene grown on copper. Additionally, we discuss an impurity-assisted growth mechanism which governs the growth of single-crystal graphene via isotropic diffusion, producing two-fold, four-fold, and six-fold symmetries in the resulting flakes. We also examine electrical transport measurements across a graphene p-n junction formed in a single gated field effect transistor made from CVD graphene.
Nanayakkara, Tharanga, "Magnetotransport Studies of GaAs/AlGaAs Heterostructures, Epitaxial Graphene, and CVD Graphene, and Growth of CVD Graphene." Dissertation, Georgia State University, 2022.
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