Date of Award

5-2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical and Computer Engineering

Committee Chair

Yong P. Chen

Committee Member 1

Zhihong Chen

Committee Member 2

Peide (Peter) Ye

Committee Member 3

Leonid P. Rokhinson

Committee Member 4

Muhammad A. Alam

Abstract

Over the past few years there has been a growing interest in layered two dimensional (2D) materials such as graphene, transition metal dichalcogenides (TMDs), and three dimensional topological insulators (TIs). In this thesis, we experimentally study electrical, thermoelectric, and phase coherent transport in these 2D materials and work on three main projects. First, we investigate the low frequency (f) flicker (also called 1/f) noise of single-layer graphene devices on h-BN along with those on SiO2/Si. We observe that the devices fabricated on h-BN have on average one order of magnitude lower noise amplitude compared with devices fabricated on SiO2/Si despite having comparable mobility at room temperature, a result that can be associated with the lower densities of impurities and trap sites in h-BN. Our study demonstrates that the use of h-BN as a substrate or dielectric can be a simple and efficient noise reduction technique valuable for electronic applications of graphene and other 2D materials. Secondly, we present a systematic study of the thickness-dependent electrical and thermoelectric properties of single-and few-layer MoS2. We observe that the electrical conductivity (σ) increases as we reduce the thickness of MoS2 and peaks at about two layers, with six times larger conductivity than the bulk. We also show that the thermoelectric power factor (PF) increases with decreasing thickness then drops abruptly from double-layer to single-layer MoS2, a feature, which according to our theoretical modeling, is due to a change in the energy dependence of the electron mean-free-path.

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