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Title:Carrier manipulation in graphene/ferroelectric hybrid structures
Author(s):Baeumer, Christoph
Advisor(s):Shim, Moonsub; Martin, Lane W.
Department / Program:Materials Science & Engineerng
Discipline:Materials Science & Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Chemical Vapor Deposition of Graphene
Raman Spectroscopy
Photocurrent Response
Lithium niobate (LiNbO3)
Polarization Reversal
Graphene Transistor
Domain Structure
Abstract:The combination of two novel classes of functional materials with exciting prospects for future nanoelectronic applications, i.e. carbon nanoelectronics and complex oxide thin film electronics, is expected to lead to a range of new phenomena being accessible for observation, scientific characterization and understanding, as well as for utilization in future electronic devices. This thesis reports significant advancement in the integration of two prominent representatives of these material classes - graphene and ferroelectric oxides. First, the major road blocks complicating previous attempts to integrate graphene with ferroelectric oxides are identified. The hybrid devices fabricated so far suffered from extrinsic hysteresis effects from adsorbed molecules screening any coupling between the graphene charge carriers and the ferroelectric polarization. The experimental methods utilized to overcome these challenges are introduced for device fabrication and characterization. The resulting graphene/PbZr0.2Ti0.8O3 hybrid structures presented here exhibit bidirectional interdependency between the graphene doping level and the ferroelectric polarization. Using graphene-based electrodes, the polarization of the PbZr0.2Ti0.8O3 can be switched reliably and fast with low voltages, which in turn can change the doping level in graphene channels. One of the most striking consequences of ferroelectriccpolarization switching dominating electron transport in graphene is the complete reversalcof the hysteresis direction in transistor devices. This reversible and permanent switching behavior can now be used in non-volatile ferroelectric graphene transistors. To overcome the low on/off ratio of these devices, a utilization of complex domain structures underlying a graphene transistor channel is explored for novel carrier manipulation. Through the detailed characterization with Raman spectroscopy and scanning photocurrent measurements, the creation of potential steps in graphene at domain walls of the underlying ferroelectric is demonstrated. Carrier density modulations of approximately 5x 10^12 cm^-2 now provide a platform that offers graphene devices exhibiting potential steps which can be tuned from p+-p to p-n to n-n+ junctions through the application of a single gate for the entire channel area. This is particularly useful for the implementation and utilization of the exciting two-dimensional phenomena in graphene.
Issue Date:2013-05-24
Rights Information:Copyright 2013 by Christoph Baeumer. All rights reserved.
Date Available in IDEALS:2013-05-24
Date Deposited:2013-05

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