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Photo-Assisted Electrical Oscillation in Two-Terminal Device Based on Vanadium Dioxide Thin Film
Giwan Seo,Bong-Jun Kim,Hyun-Tak Kim,Yong Wook Lee IEEE 2012 Journal of Lightwave Technology Vol.30 No.16
<P>By adjusting an infrared laser power illuminated onto a vanadium dioxide (VO<SUB>2</SUB>) thin film, we have demonstrated laser-assisted control of field-induced electrical oscillation in a planar junction device based on a VO<SUB>2</SUB> thin film. Before the illumination, the VO<SUB>2</SUB>-based two-terminal device was arranged in the electrical circuit for creating the field-induced oscillation. With the increase of the illumination power, the oscillation could be initiated, and the oscillation frequency could be also continuously and fully tuned until the extinguishment of the oscillation through the variation of the light power. The tuning sensitivity and linearity of the oscillation frequency with respect to the illumination power were evaluated as ~7.732 MHz/W and ~0.9903 (an <I>R</I> -squared value of a linear fit), respectively.</P>
Bong-Jun Kim,Giwan Seo,Yong Wook Lee,Sungyoul Choi,Hyun-Tak Kim IEEE 2010 IEEE electron device letters Vol.31 No.11
<P>In order to apply a VO<SUB>2</SUB> metal-insulator transition (MIT) device to a temperature sensor with temperature and voltage, we measure the linear characteristic of the MIT voltage for a VO<SUB>2</SUB>-based device when a pulse voltage of 10 μs is applied to the device to reduce Joule heat. Moreover, the MIT oscillation frequency and the infrared-induced MIT voltage also are linear with temperature. The linear characteristic may come from the breakdown of an energy gap by excitation.</P>
Bidirectional laser triggering of planar device based on vanadium dioxide thin film.
Kim, Bong-Jun,Seo, Giwan,Lee, Yong Wook Optical Society of America 2014 Optics express Vol.22 No.8
<P>By incorporating a 1550 nm laser diode, bidirectional laser triggering was investigated in a two-terminal planar device based on vanadium dioxide (VO2) thin film grown by sol-gel method. A specific bias voltage range enabling the bidirectional laser triggering was experimentally found from the current-voltage characteristics of the VO2-based device, which was measured in a current-controlled mode. At a bias voltage selected within the range, 10 mA bidirectional triggering was implemented with a maximum amplitude switching ratio of ~68.2, and the transient responses of light-triggered currents were also analyzed.</P>
Magnetic field-dependent ordinary Hall effect and thermopower of VO2 thin films
Jeongyong Choi,Bong-Jun Kim,Giwan Seo,Hyun-Tak Kim,Sunglae Cho,Yong Wook Lee 한국물리학회 2016 Current Applied Physics Vol.16 No.3
We investigated the magnetic field-dependent Hall effect and the thermopower in VO2 thin films at various temperatures by using physical property measurement systems. From the ordinary Hall effect measured at 300e370 K, it was found that the Hall voltage decreased with increasing magnetic field, attributed to the weakening of strong electron correlation, and dominant charge carriers were changed implying the existence of mixed phases near the critical temperature of VO2. A gradual thermopower increase and its sign inversion with increasing temperature gradient were observed at 320e350 K, which seems to stem from percolation processes during the phase transition in VO2.
Kim, Hyun-Tak,Kim, Minjung,Sohn, Ahrum,Slusar, Tetiana,Seo, Giwan,Cheong, Hyeonsik,Kim, Dong-Wook IOP 2016 Journal of physics, an Institute of Physics journa Vol.28 No.8
<P>In order to elucidate a mechanism of the insulator-to-metal transition (IMT) for a Mott insulator VO<SUB>2</SUB> (3<I>d</I> <SUP>1</SUP>), we present Schottky nanojunctions and the structural phase transition (SPT) by simultaneous nanolevel measurements of photocurrent and Raman scattering in microlevel devices. The Schottky nanojunction with the monoclinic metallic phase between the monoclinic insulating phases is formed by the photoheat-induced IMT not accompanied with the SPT. The temperature dependence of the Schottky junction reveals that the Mott insulator has an electronic structure of an indirect subband between the main Hubbard <I>d</I> bands. The IMT as reverse process of the Mott transition occurs by temperature-induced excitation of bound charges in the indirect semiconductor band, most likely formed by impurities such as oxygen deficiency. The metal band (3<I>d</I> <SUP>1</SUP>) for the Mott insulator is screened (trapped) by the indirect band (impurities).</P>
Thompson, Zachary J.,Stickel, Andrew,Jeong, Young-Gyun,Han, Sanghoon,Son, Byung Hee,Paul, Michael J.,Lee, Byounghwak,Mousavian, Ali,Seo, Giwan,Kim, Hyun-Tak,Lee, Yun-Shik,Kim, Dai-Sik American Chemical Society 2015 NANO LETTERS Vol.15 No.9
<P>We demonstrate that high-field terahertz (THz) pulses trigger transient insulator-to-metal transition in a nanoantenna patterned vanadium dioxide thin film. THz transmission of vanadium dioxide instantaneously decreases in the presence of strong THz fields. The transient THz absorption indicates that strong THz fields induce electronic insulator-to-metal transition without causing a structural transformation. The transient phase transition is activated on the subcycle time scale during which the THz pulse drives the electron distribution of vanadium dioxide far from equilibrium and disturb the electron correlation. The strong THz fields lower the activation energy in the insulating phase. The THz-triggered insulator-to-metal transition gives rise to hysteresis loop narrowing, while lowering the transition temperature both for heating and cooling sequences. THz nanoantennas enhance the field-induced phase transition by intensifying the field strength and improve the detection sensitivity via antenna resonance. The experimental results demonstrate a potential that plasmonic nanostructures incorporating vanadium dioxide can be the basis for ultrafast, energy-efficient electronic and photonic devices.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2015/nalefd.2015.15.issue-9/acs.nanolett.5b01970/production/images/medium/nl-2015-01970q_0007.gif'></P>