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Petr Markov


Submitted to the Faculty of the

Graduate School of Vanderbilt University

in partial ful�llment of the requirements

for the degree of



Electrical Engineering

May, 2015

Nashville, TN


Professor Sharon M. Weiss

Professor Richard F. Haglund, Jr.

Professor Jason Valentine

Professor Kirill Bolotin

Professor Yaqiong Xu

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Copyright' 2015 by Petr Markov
All Rights Reserved

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wavelength, as illustrated in Fig. 3.2(d). This configuration allows for the insertion loss to

be decreased dramatically and the modulation depth increased to 7 dB. In this work, the

modulator switching time was commensurate with the full-width-at-half-maximum of the

exciting laser pulse (∼25 ns).

The two aforementioned experiments laid the ground work for future investigation of

Si-VO2 hybrid electro-optic modulators, but the devices in these experiments were not

electro-optic modulators. In both experiments, it was not an electrical signal triggering an

optical change, but rather a change in temperature either by thermal or optical heating. The

next step in VO2 modulator research was to integrate an electrical signal for triggering the

phase transition in VO2. In order to activate the phase transition based on an applied bias,

Joushaghani et. al. used an integrated heater made of silver that also served as a plasmonic

waveguide [15]. The device achieved high modulation depth (7 dB), but relatively slow

modulation speed: 40 kHz. Since the voltage and resulting current are completely localized

within the silver layer, electrical switching of VO2, as considered by the VO2 community,

was not accomplished. Electrical switching of VO2 is described in detail in the next section.

3.1.2 VO2 Electrical Switching

Experiments investigating the underlying mechanism of the electrically induced semiconductor-

metal transition (SMT) in VO2 date back to 2000 when Stefanovich et. al. [57] reported

that electric field or electron injection could induce the SMT in VO2. They argued that

their modeling showed that the leakage current was insufficient to raise the temperature of

the device above the critical temperature Tc [90]. In the ensuing years, several groups have

studied the electrically induced SMT in VO2 and argued that the primary switching mech-


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Figure 3.2: The SEM images of (a) a lithographically defined 2 µm-wide polycrystalline
VO2 tab across a Si waveguide from ref. [14], (b) a Si ring resonator modulator with VO2
patch in false color (red) from ref. [9], and (c) a hybrid SPP-VO2 switch with an integrated
heater from ref. [15]. (d) Optical resonance spectrum for on and off states for hybrid
Si-VO2 ring resonator from ref. [9].


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