Access Type

Open Access Dissertation

Date of Award

January 2016

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Physics and Astronomy

First Advisor

Zhixian Zhou

Abstract

The ultra-thin body of monolayer (and few-layer) two dimensional (2D) semiconducting materials such as transitional metal dichalconiges (TMDs), black phosphorous (BP) has demonstrated tremendous beneficial physical, transport, and optical properties for a wide range of applications. Because of their ultrathin bodies, the properties of 2D materials are highly sensitive to environmental effects. Particularly, the performance of 2D semiconductor electronic devices is strongly dependent on the substrate/dielectric properties, extrinsic impurities and absorbates. In this work, we systematically studied the transport properties of mechanically exfoliated few layer TMD field-effect transistors (FETs) consistently fabricated on various substrates including SiO2,Parylene –C, Al2O3, SiO2 modified by octadecyltrimethoxysilane (OTMS) self-assembled monolayer (SAMs), and hexagonal boron nitride (h-BN). We performed variable temperature transport measurements to understand the effects of various scattering mechanisms such as remote surface phonon scattering, coulomb scattering, surface roughness scattering on the mobility of these devices. To reveal the intrinsic channel properties, we also investigated TMD devices encapsulated by h-BN. To further optimize the dielectric interface and electrostatic control of the TMD channels, we developed a novel thermal-oxidation method to turn few-layer 2D metals into ultrathin and atomically flat high –κ dielectrics. In order to optimize the performance of TMD electronic devices, it is also critical to fabricate low resistance ohmic contacts required for effectively injecting charge carriers into the TMD channel. Along this direction, we developed a new contact strategy to minimize the contact resistance for a variety of TMDs by van der Waals assembly of doped TMDs as contacts and undoped TMDs as channel materials. The developed unique method for low-resistance ohmic contacts achieved using the 2D/2D contact strategy and novel technique for high-k dielectric integration is expected to open the path to explore the rich quantum physics in TMDs 2DEGs and 2DHGs.

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