Semiconductor-metal transition in epitaxial VO_2 thin films on TiO_2 (100) considering a phase equilibrium

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dc.contributor Gupta, Arunava
dc.contributor Butler, W. H.
dc.contributor Kung, Patrick
dc.contributor Sarker, Sanjoy Kumar
dc.contributor Hilton, David J.
dc.contributor.advisor LeClair, Patrick R. Zhong, Xing 2017-03-01T16:48:51Z 2017-03-01T16:48:51Z 2013
dc.identifier.other u0015_0000001_0001303
dc.identifier.other Zhong_alatus_0004D_11613
dc.description Electronic Thesis or Dissertation
dc.description.abstract Vanadium dioxide (VO_2), standing out from the thermochromic vanadium oxide family (VO,V_2 O_3,V_2 O_5 ,VO_2), is intensively studied for its abrupt and reversible semiconductormetal transition (SMT) that happens slightly above room temperature (T_c 340 K). Interestingly, the transition can be triggered not only by temperature change, but also by many other forms of excitations, e.g. infrared irradiation, external strain, and applied voltage. The underlying mechanism of the transition is still in debate, and a model to describe the transport properties near T_c is needed for utilizing this material. Recent studies have revealed that near the transition, there is a phase coexistence between the semiconducting monoclinic phase and the metallic rutile phase in this material. In this presentation, the growth of epitaxial VO_2 thin films on TiO_2 substrates by chemical vapor deposition and the characterizations of their structural and electrical properties will be discussed. Detailed studies on DC resistivity, current-voltage characteristics and impedance spectroscopy of deposited films at various ambient temperatures have been performed. By considering the ensemble average of the transport properties of VO_2 films near T_c as a superposition of the transport properties of the two phases, and assuming a distribution of transition temperatures across the whole film, we have derived parameterized models to fit the temperature dependence of both resistivity and impedance of VO_2 thin films in the vicinity of SMT. Voltage triggered breakdown in micron-scale two-terminal planar VO_2 devices has been tested and modeled. An avalanching-like breakdown mechanism is elicited by considering a competition between Joule heating and heat dissipation, that could explain the faster-than-expected transition observed in this kind of devices. To further study the physics of SMT, the design and implementation of a cross-spectrum analyzer for measuring VO_2 transport noise near T_c will be demonstrated. Our preliminary results reveal a significant increase in the noise power spectral density near the transition, possibly induced by the metastability of current percolation.
dc.format.extent 133 p.
dc.format.medium electronic
dc.format.mimetype application/pdf
dc.language English
dc.language.iso en_US
dc.publisher University of Alabama Libraries
dc.relation.ispartof The University of Alabama Electronic Theses and Dissertations
dc.relation.ispartof The University of Alabama Libraries Digital Collections
dc.relation.hasversion born digital
dc.rights All rights reserved by the author unless otherwise indicated.
dc.subject.other Materials Science
dc.title Semiconductor-metal transition in epitaxial VO_2 thin films on TiO_2 (100) considering a phase equilibrium
dc.type thesis
dc.type text University of Alabama. Dept. of Physics and Astronomy Materials Science The University of Alabama doctoral Ph.D.

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