172 results on '"Kookrin Char"'
Search Results
2. Low Leakage in High‐k Perovskite Gate Oxide SrHfO 3
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Juhan Kim, Dowon Song, Hwanhui Yun, Jaehyeok Lee, Jae Ha Kim, Jae Hoon Kim, Bongju Kim, and Kookrin Char
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Electronic, Optical and Magnetic Materials - Published
- 2023
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Catalog
3. High-Mobility Field-Effect Transistor Using 2-Dimensional Electron Gas at the LaScO3/BaSnO3 Interface
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Hyeongmin Cho, Dowon Song, Youjung Kim, Bongju Kim, and Kookrin Char
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Materials Chemistry ,Electrochemistry ,Electronic, Optical and Magnetic Materials - Published
- 2021
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4. The role of coherent epitaxy in forming a two-dimensional electron gas at LaIn1-xGaxO3/BaSnO3 interfaces
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Kookrin Char, Youjung Kim, and Young Mo Kim
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Electron density ,Materials science ,Condensed matter physics ,Oxide ,chemistry.chemical_element ,Conductance ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Epitaxy ,01 natural sciences ,Discontinuity (linguistics) ,chemistry.chemical_compound ,chemistry ,Mechanics of Materials ,0103 physical sciences ,TA401-492 ,Polar ,General Materials Science ,Gallium ,010306 general physics ,0210 nano-technology ,Fermi gas ,Materials of engineering and construction. Mechanics of materials - Abstract
Some oxide interfaces are known to exhibit unique properties such as a 2D electron gas, controlled by epitaxial strain and coherency between the two layers. Here, we study variation in the 2D electron density in the polar LaIn1-xGaxO3/Ba0.997La0.003SnO3 interface with changing x and LaIn1-xGaxO3 layer thickness. We find that the 2D electron density decreases as the gallium alloying ratio increases and the interface conductance eventually disappears, which shows that an interface with polar discontinuity is not a sufficient condition for 2D electron gas formation. The interface conductance reaches its maximum value when the LaIn1-xGaxO3 layer thickness is approximately 20 Å, beyond which conductance decreased to a constant value. Atomistic imaging reveals that dislocations start to form as the gallium ratio increases, forming away from the interface and then moving closer with increasing gallium alloying. The dislocations eventually destroy coherency in the case of LaGaO3 and suppress the formation of a 2D electron gas. more...
- Published
- 2021
5. Deep-UV Transparent Conducting Oxide La-Doped SrSnO
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Juhan, Kim, Hwanhui, Yun, Jihoon, Seo, Jae Ha, Kim, Jae Hoon, Kim, K Andre, Mkhoyan, Bongju, Kim, and Kookrin, Char
- Abstract
Perovskite stannate SrSnO
- Published
- 2022
6. Critical role of terminating layer in formation of 2DEG state at the $LaInO_{3}$/$BaSnO_{3}$ interface
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Seonghyeon Kim, Mikk Lippmaa, Jaehyeok Lee, Hyeongmin Cho, Juhan Kim, Bongju Kim, and Kookrin Char
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Condensed Matter - Materials Science ,Mechanics of Materials ,Mechanical Engineering ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences - Abstract
Based on the interface polarization model, the two-dimensional electron gas (2DEG) at $LaInO_{3}$(LIO)/$BaSnO_{3}$(BSO) interfaces is understood to originate from a polarization discontinuity at the interface and the conduction band offset between LIO and BSO. In this scenario, the direction of polarization at the interface is determined by whether the first atomic LIO layer at the interface is LaO$^{+}$ or InO$_{2}^{-}$. We investigate the role of the terminating layer at the LIO/BSO interface in creating the 2DEG. Based on conductance measurements of our in-situ grown LIO/BSO heterostructures, we report in this work that the 2DEG only forms when the BSO surface is terminated with a SnO$_{2}$ layer. We controlled the terminating layer by additional SnO$_{2}$ deposition on the BSO surface. We show that the as-grown BSO surface has a mixed terminating layer of BaO and SnO$_{2}$ while the BSO surfaces prepared with additional SnO$_{2}$ deposition are terminated mainly with the SnO$_{2}$ layer. The terminating layer was confirmed by coaxial impact collision ion scattering spectroscopy (CAICISS). Our finding is consistent with the interface polarization model for 2DEG formation at LIO/BSO interfaces, in which the direction of the interfacial polarization in LIO is determined by the terminating layer of the BSO surface., 22 pages more...
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- 2022
7. High- k perovskite gate oxide for modulation beyond 10 14 cm −2
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Dowon Song, Myoungho Jeong, Juhan Kim, Bongju Kim, Jae Ha Kim, Jae Hoon Kim, Kiyoung Lee, Yongsung Kim, and Kookrin Char
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Multidisciplinary - Abstract
Scaling down of semiconductor devices requires high- k dielectric materials to continue lowering the operating voltage of field-effect transistors (FETs) and storing sufficient charge on a smaller area. Here, we investigate the dielectric properties of epitaxial BaHf 0.6 Ti 0.4 O 3 (BHTO), an alloy of perovskite oxide barium hafnate (BaHfO 3 ) and barium titanate (BaTiO 3 ). We found the dielectric constant, the breakdown field, and the leakage current to be 150, 5.0 megavolts per centimeter (MV cm −1 ), and 10 −4 amperes per square centimeter at 2 MV cm −1 , respectively. The results suggest that two-dimensional (2D) carrier density of more than n 2D = 10 14 per square centimeter (cm −2 ) could be modulated by the BHTO gate oxide. We demonstrate an n-type accumulation mode FET and direct suppression of more than n 2D = 10 14 cm −2 via an n-type depletion-mode FET. We attribute the large dielectric constant, high breakdown field, and low leakage current of BHTO to the nanometer scale stoichiometric modulation of hafnium and titanium. more...
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- 2022
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8. High
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Dowon, Song, Myoungho, Jeong, Juhan, Kim, Bongju, Kim, Jae Ha, Kim, Jae Hoon, Kim, Kiyoung, Lee, Yongsung, Kim, and Kookrin, Char
- Abstract
Scaling down of semiconductor devices requires high
- Published
- 2022
9. Transport Properties of the LaInO3/BaSnO3 Interface Analyzed by Poisson-Schrödinger Equation
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Youjung Kim, Seonghyeon Kim, Hyeongmin Cho, Young Mo Kim, Hiromichi Ohta, and Kookrin Char
- Subjects
General Physics and Astronomy - Published
- 2022
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10. Confinement of Electrons at the LaInO 3 /BaSnO 3 Heterointerface
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Daniel Pfützenreuter, Seonghyeon Kim, Hyeongmin Cho, Oliver Bierwagen, Martina Zupancic, Martin Albrecht, Kookrin Char, and Jutta Schwarzkopf
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Mechanics of Materials ,Mechanical Engineering - Published
- 2022
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11. Low resistance epitaxial edge contacts to buried nanometer thick conductive layers of BaSnO3
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Jaehyeok Lee, Hyeongmin Cho, Bongju Kim, Myoungho Jeong, Kiyoung Lee, and Kookrin Char
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Physics and Astronomy (miscellaneous) - Abstract
As the size of the semiconductor device decreases, the importance of the low resistance contacts to devices cannot be overstated. Here, we studied the contact resistance to buried nanometer thick δ-doped Ba1-xLaxSnO3 (BLSO) layers. We have used epitaxial 4% (x = 0.04) BLSO as a contact material, which has additional advantages of forming Ohmic contacts to BaSnO3 and providing thermal stability even at high temperatures. The contact resistance was measured by a modified transmission line method designed to eliminate the contribution from the resistance of the contact material. The upper bound for the contact resistance to a 12 nm thick δ-doped 1% BLSO conductive layer was measured to be 1.25 × 10−1or 2.87 × 10−7 Ω cm2. Our results show that it is possible to provide low resistance epitaxial edge contacts to an embedded nanometer-thick BLSO conductive layer using an ion-milling process. Our low resistance contact method can be easily extended to a two-dimensional electron gas at the oxide interfaces such as LaInO3/BaSnO3. more...
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- 2022
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12. Role of the interface in controlling the epitaxial relationship between orthorhombic LaInO3 and cubic BaSnO3
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Kookrin Char, Wahib Aggoune, Martina Zupancic, Claudia Draxl, Toni Markurt, Martin Albrecht, Youjung Kim, and Young Mo Kim
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Condensed Matter::Materials Science ,Crystallography ,Materials science ,Physics and Astronomy (miscellaneous) ,0103 physical sciences ,General Materials Science ,Orthorhombic crystal system ,02 engineering and technology ,021001 nanoscience & nanotechnology ,010306 general physics ,0210 nano-technology ,Epitaxy ,01 natural sciences - Abstract
Epitaxial perovskite oxide interfaces with different symmetry of the epitaxial layers have attracted considerable attention due to the emergence of novel behaviors and phenomena. In this paper, we show by aberration-corrected transmission electron microscopy (TEM) that orthorhombic ${\mathrm{LaInO}}_{3}$ films grow in form of three different types of domains on the cubic ${\mathrm{BaSnO}}_{3}$ pseudosubstrate. Quantitative evaluation of our TEM data shows that ${c}_{\mathrm{pc}}$-oriented and ${a}_{\mathrm{pc}}/{b}_{\mathrm{pc}}$-oriented domains are present with similar probability. While continuum elasticity theory suggests that ${c}_{\mathrm{pc}}$-oriented domains should exhibit a significantly higher strain energy density than ${a}_{\mathrm{pc}}/{b}_{\mathrm{pc}}$-oriented domains, density-functional calculations confirm that ${c}_{\mathrm{pc}}$- and ${a}_{\mathrm{pc}}$-oriented domains on ${\mathrm{BaSnO}}_{3}$ have similar energies. more...
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- 2020
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13. Remote Doping of the Two-Dimensional-Electron-Gas State at the LaInO3 / BaSnO3 Polar Interface
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Kookrin Char, Juyeon Shin, Chulkwon Park, and Young Mo Kim
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Materials science ,Scattering ,Doping ,General Physics and Astronomy ,Heterojunction ,02 engineering and technology ,State (functional analysis) ,021001 nanoscience & nanotechnology ,01 natural sciences ,Condensed Matter::Materials Science ,Crystallography ,Band bending ,Impurity ,Ionization ,0103 physical sciences ,Dislocation ,010306 general physics ,0210 nano-technology - Abstract
We investigate the transport properties of a modified interface by intentionally inserting a nanometer-scale undoped ${\mathrm{Ba}\mathrm{Sn}\mathrm{O}}_{3}$ spacer layer at the ${\mathrm{La}\mathrm{In}\mathrm{O}}_{3}$/${\mathrm{Ba}}_{1\text{\ensuremath{-}}x}{\mathrm{La}}_{x}{\mathrm{Sn}\mathrm{O}}_{3}$ interface, thereby creating remotely doped heterostructures. Both the carrier density $({n}_{s})$ and the Hall mobility $({\ensuremath{\mu}}_{H})$ continuously decrease as the thickness of the ${\mathrm{Ba}\mathrm{Sn}\mathrm{O}}_{3}$ spacer layer at the interface increases, indicating a changing electron-density profile as a function of the spacer thickness. We find the behavior is consistent with the recently proposed ``interface-polarization'' model by self-consistent one-dimensional Poisson-Schr\"odinger calculations. The decrease of ${n}_{s}$ makes it difficult to see the effect of the spacer layer on the mobility in the remotely doped structures due to the simultaneous decrease of $\ensuremath{\mu}$ caused by the ineffective screening of the remote Coulomb scattering from ionized donors in addition to the threading dislocation scattering. Hence, we control the band bending continuously via the field effect with a fixed spacer-layer thickness, leading to observation of enhanced mobility $({\ensuremath{\mu}}_{\mathrm{FE}})$ in the remotely doped 2DEG heterostructures in spite of high-density threading dislocations acting as the background charged impurities. more...
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- 2020
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14. 2×2R45∘ surface reconstruction and electronic structure of BaSnO3 film
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Changyoung Kim, Sungyun Hong, Bongju Kim, Tae Won Noh, D. C. Kim, Kookrin Char, Shoresh Soltani, Jong Keun Jung, and Byungmin Sohn
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Materials science ,Physics and Astronomy (miscellaneous) ,Band gap ,Photoemission spectroscopy ,Fermi level ,Angle-resolved photoemission spectroscopy ,02 engineering and technology ,Electronic structure ,021001 nanoscience & nanotechnology ,01 natural sciences ,Crystallography ,symbols.namesake ,Electron diffraction ,0103 physical sciences ,Valence band ,symbols ,General Materials Science ,010306 general physics ,0210 nano-technology ,Surface reconstruction - Abstract
We studied the surface and electronic structures of barium stannate (${\mathrm{BaSnO}}_{3}$) thin films by low-energy electron diffraction (LEED) and angle-resolved photoemission spectroscopy (ARPES) techniques. ${\mathrm{BaSnO}}_{3}/{\mathrm{Ba}}_{0.96}{\mathrm{La}}_{0.04}{\mathrm{SnO}}_{3}/{\mathrm{SrTiO}}_{3}$ (10 nm/100 nm/0.5 mm) samples were grown using the pulsed-laser deposition (PLD) method and were ex situ transferred from the PLD chamber to ultrahigh vacuum (UHV) chambers for annealing, LEED, and ARPES studies. UHV annealing starting from $300{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ up to $550{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$, followed by LEED and ARPES measurements, show $1\ifmmode\times\else\texttimes\fi{}1$ surfaces with nondispersive energy-momentum bands. The $1\ifmmode\times\else\texttimes\fi{}1$ surface reconstructs into a $\sqrt{2}\ifmmode\times\else\texttimes\fi{}\sqrt{2}R{45}^{\ensuremath{\circ}}$ one at an annealing temperature of $700{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ where the ARPES data show clear dispersive bands with a valence band maximum located around 3.3 eV below the Fermi level. While the $\sqrt{2}\ifmmode\times\else\texttimes\fi{}\sqrt{2}R{45}^{\ensuremath{\circ}}$ surface reconstruction is stable under further UHV annealing, it is reversed to a $1\ifmmode\times\else\texttimes\fi{}1$ surface by annealing the sample in 400 mTorr oxygen at $600{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$. Another UHV annealing at $600{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$, followed by LEED and ARPES measurements, suggests that LEED $\sqrt{2}\ifmmode\times\else\texttimes\fi{}\sqrt{2}R{45}^{\ensuremath{\circ}}$ surface reconstruction and ARPES dispersive bands are reproduced. Our results provide a better picture of the electronic structure of ${\mathrm{BaSnO}}_{3}$ surfaces and are suggestive of the role of oxygen vacancies in reversible $\sqrt{2}\ifmmode\times\else\texttimes\fi{}\sqrt{2}R{45}^{\ensuremath{\circ}}$ surface reconstruction. more...
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- 2020
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15. Interface polarization model for a 2-dimensional electron gas at the BaSnO3/LaInO3 interface
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Toni Markurt, Youjung Kim, Martin Albrecht, Juyeon Shin, Martina Zupancic, Kookrin Char, and Young Mo Kim
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Multidisciplinary ,Materials science ,Condensed matter physics ,lcsh:R ,Doping ,lcsh:Medicine ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Lattice expansion ,Polarization (waves) ,01 natural sciences ,Charge-carrier density ,Octahedron ,0103 physical sciences ,lcsh:Q ,lcsh:Science ,010306 general physics ,0210 nano-technology ,Fermi gas ,High-resolution transmission electron microscopy - Abstract
In order to explain the experimental sheet carrier density n2D at the interface of BaSnO3/LaInO3, we consider a model that is based on the presence of interface polarization in LaInO3 which extends over 2 pseudocubic unit cells from the interface and eventually disappears in the next 2 unit cells. Considering such interface polarization in calculations based on 1D Poisson-Schrödinger equations, we consistently explain the dependence of the sheet carrier density of BaSnO3/LaInO3 heterinterfaces on the thickness of the LaInO3 layer and the La doping of the BaSnO3 layer. Our model is supported by a quantitative analysis of atomic position obtained from high resolution transmission electron microscopy which evidences suppression of the octahedral tilt and a vertical lattice expansion in LaInO3 over 2–3 pseudocubic unit cells at the coherently strained interface. more...
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- 2019
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16. Interface polarization model for a 2-dimensional electron gas at the BaSnO
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Young Mo, Kim, T, Markurt, Youjung, Kim, M, Zupancic, Juyeon, Shin, M, Albrecht, and Kookrin, Char
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Electronic properties and materials ,Surfaces, interfaces and thin films ,Semiconductors ,Article - Abstract
In order to explain the experimental sheet carrier density n2D at the interface of BaSnO3/LaInO3, we consider a model that is based on the presence of interface polarization in LaInO3 which extends over 2 pseudocubic unit cells from the interface and eventually disappears in the next 2 unit cells. Considering such interface polarization in calculations based on 1D Poisson-Schrödinger equations, we consistently explain the dependence of the sheet carrier density of BaSnO3/LaInO3 heterinterfaces on the thickness of the LaInO3 layer and the La doping of the BaSnO3 layer. Our model is supported by a quantitative analysis of atomic position obtained from high resolution transmission electron microscopy which evidences suppression of the octahedral tilt and a vertical lattice expansion in LaInO3 over 2–3 pseudocubic unit cells at the coherently strained interface. more...
- Published
- 2019
17. Melt Growth and Physical Properties of Bulk LaInO 3 Single Crystals
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Steffen Ganschow, Robert Schewski, Kookrin Char, Martin Albrecht, Albert Kwasniewski, Detlef Klimm, Martina Zupancic, Andrea Dittmar, Claudia Draxl, Wahib Aggoune, Klaus Irmscher, Raimund Grueneberg, Thomas Schroeder, Sabine Bergmann, Mike Pietsch, Matthias Bickermann, Uta Juda, Zbigniew Galazka, Hyeongmin Cho, and Tobias Schulz more...
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Materials science ,Materials Chemistry ,Surfaces and Interfaces ,Electrical and Electronic Engineering ,Composite material ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Published
- 2021
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18. High mobility field effect transistor of SnOx on glass using HfOx gate oxide
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Hyeonseok Yang, Young Mo Kim, Chanjong Ju, Kookrin Char, Chulkwon Park, and Useong Kim
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010302 applied physics ,business.industry ,Annealing (metallurgy) ,General Physics and Astronomy ,02 engineering and technology ,Partial pressure ,021001 nanoscience & nanotechnology ,01 natural sciences ,Sputtering ,Gate oxide ,Thin-film transistor ,0103 physical sciences ,Optoelectronics ,General Materials Science ,Field-effect transistor ,Crystallite ,Thin film ,0210 nano-technology ,business - Abstract
We report on the electrical properties of SnO x thin films made by reactive sputtering of a Sn metal target and the performance of their field effect transistors with HfO x gate insulator on glass substrates. We investigated the electrical properties of SnO x films by controlling the oxygen partial pressure during growth. The mobility of the SnO x films on glass substrates was as high as 20.28 cm 2 V −1 s −1 after post-deposition annealing at 400 °C, while its carrier density was 4.21 × 10 18 cm −3 . Moreover, we fabricated high mobility thin film transistors using polycrystalline SnO x as the channel and the atomic-layer-deposited HfO x as the gate oxide. The field-effect mobility values were 5.01–20.15 cm 2 V −1 s −1 , the I on /I off were 10 3 ∼10 4 , and the subthreshold swing were 1.05–1.60 V dec −1 . We discuss the origins for the non-ideal performance and the future direction for improvement. more...
- Published
- 2016
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19. Fermi level pinning and band bending in δ-doped BaSnO3
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Hyeongmin Cho, Kookrin Char, and Youjung Kim
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010302 applied physics ,Surface (mathematics) ,Materials science ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Doping ,Macroscopic quantum phenomena ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Layer thickness ,Condensed Matter::Materials Science ,Band bending ,Condensed Matter::Superconductivity ,Fermi level pinning ,0103 physical sciences ,Condensed Matter::Strongly Correlated Electrons ,Boundary value problem ,0210 nano-technology ,Semiconductor heterostructures - Abstract
Various δ-doped semiconductor heterostructures have been effectively used for devices at room temperature and for quantum phenomena at low temperatures. Here, we use BaSnO3 and investigate its δ-doped system, focusing on its band bending and surface boundary conditions. We measured the two-dimensional carrier density (n2D) of the δ-doped BaSnO3 system of various thicknesses and doping levels. We also studied the effect of the BaSnO3 capping layer thickness on n2D. We show that the δ-doped BaSnO3 system can be very well described by band bending with the aid of the Poisson–Schrodinger simulation. At the same time, the capping layer thickness dependence of n2D reveals how the boundary condition on the surface of La-doped BaSnO3 evolves as a function of its capping layer thickness. more...
- Published
- 2021
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20. Thin film transistors based on ultra-wide bandgap spinel ZnGa2O4
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Seongyun Hong, Zbigniew Galazka, Yeaju Jang, Kookrin Char, Jihoon Seo, and Hyeongmin Cho
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010302 applied physics ,Materials science ,Physics and Astronomy (miscellaneous) ,business.industry ,Band gap ,Spinel ,02 engineering and technology ,engineering.material ,021001 nanoscience & nanotechnology ,Epitaxy ,01 natural sciences ,Pulsed laser deposition ,Transmission electron microscopy ,Gate oxide ,Thin-film transistor ,0103 physical sciences ,engineering ,Optoelectronics ,0210 nano-technology ,business ,Layer (electronics) - Abstract
We report on thin film transistors (TFTs) based on spinel ZnGa2O4 (ZGO) that was recently spotlighted as an ultra-wide bandgap oxide semiconductor. The ZGO layers were grown in a spinel structure by pulsed laser deposition on the cubic spinel MgAl2O4 (MAO) as well as on cubic MgO substrates while changing the Zn/Ga ratio. The compressive strained epitaxial growth of ZGO on MgAl2O4 (100) and the tensile strained epitaxial growth of ZGO on MgO (100) without any misfit or threading dislocations were confirmed by the reciprocal space map and cross-sectional transmission electron microscopy. The electrical transport properties were demonstrated through TFTs based on ZGO as the channel layer, Al2O3 as the gate oxide, and Sn-doped In2O3 as the source, drain, and gate electrodes. When the Zn/Ga ratio is slightly lower than the ideal value of 0.5 on MgO substrates, the ZGO TFT showed the highest mobility of 5.4 cm2/V s. The ION/IOFF ratio and subthreshold swing (S) value are 4.5 × 108 and 0.19 V/dec, respectively. more...
- Published
- 2020
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21. Transparent thin film transistors of polycrystalline SnO2−x and epitaxial SnO2−x
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Hahoon Lee, Kookrin Char, and Yeaju Jang
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010302 applied physics ,Materials science ,business.industry ,General Physics and Astronomy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Epitaxy ,01 natural sciences ,lcsh:QC1-999 ,Hysteresis ,Thin-film transistor ,0103 physical sciences ,Sapphire ,Optoelectronics ,Grain boundary ,Field-effect transistor ,Crystallite ,Thin film ,0210 nano-technology ,business ,lcsh:Physics - Abstract
We report on transparent thin film field effect transistors (TFTs) based on polycrystalline SnO2−x and epitaxial SnO2−x. Polycrystalline SnO2−x TFTs of the top and the bottom gate geometries exhibited high mobility values of 145.7 cm2/V s and 160.0 cm2/V s, respectively. However, our polycrystalline SnO2−x devices showed non-ideal behaviors in their output and transfer characteristics; a large hysteresis was observed along with large voltage dependence. The probable origin of these non-ideal behaviors is the barrier formation across grain boundaries of polycrystalline SnO2. To confirm this, we used SnO2−x epitaxially grown on r-plane sapphire substrates as a channel layer and compared their performance with those of polycrystalline SnO2−x based TFTs. Although the mobility of epitaxial SnO2−x TFTs was not as high as that of the polycrystalline SnO2−x TFTs, the non-ideal voltage dependence in output and transfer characteristics disappeared. We believe our direct experimental comparison clearly demonstrates the grain boundary issue in polycrystalline SnO2−x. more...
- Published
- 2020
22. Oxygen diffusion process in a Ba0.96La0.04SnO3thin film on SrTiO3(001) substrate as investigated by time-dependent Hall effect measurements
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Woong-Jhae Lee, Kookrin Char, Jin Hyeok Kim, Hoon Kim, Tai Hoon Kim, Egon Sohn, Hyung Joon Kim, and Kee Hoon Kim
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Electron mobility ,Diffusion ,Doping ,Analytical chemistry ,chemistry.chemical_element ,Surfaces and Interfaces ,Condensed Matter Physics ,Oxygen ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,chemistry ,Hall effect ,Electrical resistivity and conductivity ,Materials Chemistry ,Electrical and Electronic Engineering ,Thin film ,Perovskite (structure) - Abstract
We investigate the oxygen diffusion phenomena in a Ba0.96La0.04SnO3 (BLSO) thin film on SrTiO3(001) substrate by measurements of time-dependent Hall effect at high temperatures around 500 °C under different gas atmosphere. Under the Ar (O2) atmosphere, carrier density (n) and electrical conductivity (σ) are increased (decreased) while electron mobility (µ) is slightly reduced (enhanced). This observation supports that although both n and µ are affected by the oxygen diffusion process, the change of n is a major factor of determining σ in the BLSO film. Detailed analyses of the time-dependent n exhibit fast and slow dynamics that possibly correspond to the oxygen exchange reaction at the surface and oxygen diffusion into the BLSO grains, respectively. Fitting the time dependence of n reveals that the chemical diffusion coefficient of oxygen in the BLSO grains becomes ∼10−16 cm2 s−1. This coefficient marks the lowest value among perovskite oxides around 500 °C, directly proving excellent thermal stability of oxygen in BLSO. The present results support that the donor-doped BaSnO3 system could be useful for realizing transparent semiconductor devices at high temperatures. more...
- Published
- 2015
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23. Band gap and mobility of epitaxial perovskite BaSn1−xHfxO3 thin films
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Chulkwon Park, Jae Hoon Kim, J. D. Lim, Kookrin Char, Taewoo Ha, Jaejun Yu, Young Mo Kim, and Juyeon Shin
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Materials science ,Physics and Astronomy (miscellaneous) ,Dopant ,Band gap ,Heterojunction ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Pulsed laser deposition ,Condensed Matter::Materials Science ,Crystallography ,Lattice constant ,0103 physical sciences ,Content (measure theory) ,General Materials Science ,010306 general physics ,0210 nano-technology ,Solid solution ,Perovskite (structure) - Abstract
A wide band-gap perovskite oxide $\mathrm{BaSn}{\mathrm{O}}_{3}$ is attracting much attention due to its high electron mobility and oxygen stability. On the other hand, $\mathrm{BaHf}{\mathrm{O}}_{3}$ was recently reported to be an effective high-$k$ gate oxide. Here, we investigate the band gap and mobility of solid solutions of $\mathrm{BaS}{\mathrm{n}}_{1\ensuremath{-}x}\mathrm{H}{\mathrm{f}}_{x}{\mathrm{O}}_{3}$ ($x=0\ensuremath{-}1$) (BSHO) as a basis to build advanced perovskite oxide heterostructures. All the films were epitaxially grown on MgO substrates using pulsed laser deposition. Density functional theory calculations confirmed that Hf substitution does not create midgap states while increasing the band gap. From x-ray diffraction and optical transmittance measurements, the lattice constants and the band-gap values are significantly modified by Hf substitution. We also measured the transport properties of $n$-type La-doped BSHO films $[(\mathrm{Ba},\mathrm{La})(\mathrm{Sn},\mathrm{Hf}){\mathrm{O}}_{3}]$, investigating the feasibility of modulation doping in the $\mathrm{BaSn}{\mathrm{O}}_{3}/\mathrm{BSHO}$ heterostructures. The Hall measurement data revealed that, as the Hf content increases, the activation rate of the La dopant decreases and the scattering rate of the electrons sharply increases. These properties of BSHO films may be useful for applications in various heterostructures based on the $\mathrm{BaSn}{\mathrm{O}}_{3}$ system. more...
- Published
- 2018
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24. Structural characterization of the LaInO3/BaSnO3 interface via synchrotron scattering
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Kookrin Char, Fred Walker, Claudia Lau, Chong H. Ahn, Youjung Kim, and Stephen D. Albright
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010302 applied physics ,Electron mobility ,Materials science ,Condensed matter physics ,lcsh:Biotechnology ,Doping ,General Engineering ,Synchrotron radiation ,Heterojunction ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,lcsh:QC1-999 ,Pulsed laser deposition ,lcsh:TP248.13-248.65 ,0103 physical sciences ,X-ray crystallography ,General Materials Science ,Orthorhombic crystal system ,Thin film ,0210 nano-technology ,lcsh:Physics - Abstract
The alkaline earth stannate BaSnO3 is a semiconductor with high carrier mobility at room-temperature when doped with La3+. When a thin epitaxial layer of LaInO3 is grown on lightly doped BaSnO3, a polar discontinuity between the orthorhombic, polar LaInO3 and the cubic, nonpolar Ba0.998La0.002SnO3 leads to an electronic reconstruction, where LaInO3 remotely dopes Ba0.998La0.002SnO3, creating carriers for high mobility devices. We determine aspects of the crystalline structure of the LaInO3/BaSnO3 film that affect the polar discontinuity using synchrotron x-ray diffraction. Specifically, we examine the role of oxygen octahedral rotations and anti-parallel cation displacements in influencing the polarization of the LaInO3/BaSnO3 interface. These structural distortions are characterized by measuring half-order Bragg peaks of thin film LaInO3/BaSnO3/SrTiO3 heterostructures grown by pulsed laser deposition. We find that for films as thin as 3 unit cells, epitaxial LaInO3 has 2 distinct domains, one with the same Glazer tilt pattern as that of bulk LaInO3, a+b−b−, and a second rotated 90° in-plane from the first and having tilt pattern b−a+b−. Additionally, we observe a sudden and large increase in cation displacements along the [011] and [101] directions across the LaInO3/BaSnO3 interface due to the strength of the octahedral rotations. more...
- Published
- 2019
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25. Role of oxygen vacancies formed between top electrodes and epitaxial NiO films in bipolar resistance switching
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Jae Hyuck Jang, Ran J. Jung, Seung-Yoon Lee, Min-Saeng Kim, S. Seo, Kookrin Char, Deok-Kyu Kim, Myung Rae Cho, Hyeongmun Kim, and Yun Daniel Park
- Subjects
Materials science ,business.industry ,Non-blocking I/O ,General Physics and Astronomy ,chemistry.chemical_element ,Epitaxy ,Oxygen ,Oxygen vacancy ,Metal ,chemistry ,visual_art ,Electrode ,Electroforming ,visual_art.visual_art_medium ,Optoelectronics ,General Materials Science ,business ,Oxygen content - Abstract
We investigated bipolar resistance switching (RS) behavior of a top electrode/epitaxial NiO using Al and Pt as the top electrodes (TEs) and epitaxial NiO deposited at 500 °C (NiO-500) and 700 °C (NiO-700). We found that the contact between Al and Pt TEs and NiO-500 was a high resistance insulating contact, while the contact between the two TEs and NiO-700 was a low-resistance metallic contact. We also found that only NiO-500 with the Pt TE exhibited bipolar RS after an electroforming process. This study suggests that during the formation of the Pt/NiO-500 interface, the amount and behavior of oxygen at the interface seem to play the most important role in bipolar RS behavior. In order to improve the device performance, better control of oxygen content and its movement at the interface seems necessary. more...
- Published
- 2012
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26. Effects of tensile stress on the resonant response of Al thin-film and Al-CNT nanolaminate nanomechanical beam resonators
- Author
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Yun Jeong Yi, Kookrin Char, Young Duck Kim, Seunghun Hong, Jung Hoon Bak, Seung Ran Lee, Kwang Heo, and Yun Daniel Park
- Subjects
Materials science ,Tension (physics) ,General Physics and Astronomy ,Carbon nanotube ,law.invention ,Resonator ,Quality (physics) ,Flexural strength ,law ,General Materials Science ,Thin film ,Composite material ,Elastic modulus ,Beam (structure) - Abstract
We report on the dependence of resonant response to applied tensile stress in Al and Al-CNT (carbon nanotube) nanolaminate thin-film nanomechanical beam resonators. We optically measure the dynamic flexural response, while a chip-bending method is utilized to apply a static tension along its axis. For Al thin-film resonators, large and reversible increases in the resonant frequencies are observed along with near doubling of the resonator quality factor; while, for Al-CNT, largely unaffected with a slight decrease in resonant frequencies. Such behavior gives an insight on the role of CNT as a structural reinforcement in the Al thin-film based nanolaminate. more...
- Published
- 2011
- Full Text
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27. LaInO3/BaSnO3 polar interface on MgO substrates
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Juyeon Shin, Kookrin Char, Young Mo Kim, and Youjung Kim
- Subjects
Materials science ,lcsh:Biotechnology ,Fermi level ,Doping ,General Engineering ,Analytical chemistry ,Conductance ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Acceptor ,lcsh:QC1-999 ,Ion ,symbols.namesake ,Transmission electron microscopy ,lcsh:TP248.13-248.65 ,0103 physical sciences ,symbols ,General Materials Science ,010306 general physics ,0210 nano-technology ,Layer (electronics) ,lcsh:Physics ,Deposition (law) - Abstract
We report on a new property of the LaInO3 (LIO)/(Ba,La)SnO3 (BLSO) polar interface using MgO substrates. The growth of well-formed LIO/BLSO interface structures on non-perovskite MgO substrates was confirmed by reciprocal space mapping image and transmission electron microscopy. Subsequently, we measured electrical properties as a function of the La doping rate of the BLSO layer and found that the LIO/BLSO polar interface shows conductance enhancement after the deposition of the polar LaInO3 layer on the BLSO layer, in agreement with our earlier results on SrTiO3 (STO) substrates. However, different electrical properties of the interfaces were found on MgO from those on STO substrates; we observed conductance enhancement even at the interface with undoped BaSnO3 (BSO) on the MgO substrates. We attribute such different behavior to the difference in the Fermi levels of BSO on MgO and STO substrates, either due to the larger donor density or the smaller acceptor density in BSO on MgO. Using such a nominally undoped interface, we fabricated the field effect transistors and presented their performances with Ion/Ioff ∼ 109. more...
- Published
- 2018
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28. Identification of F impurities in F-doped ZnO by synchrotron X-ray absorption near edge structures
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Kookrin Char, Deok-Yong Cho, Sukit Limpijumnong, Sutassana Na-Phattalung, Seungran Lee, Jaejun Yu, and Chul-Hee Min
- Subjects
010302 applied physics ,Materials science ,Doping ,Analytical chemistry ,General Physics and Astronomy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,XANES ,Synchrotron ,law.invention ,Pulsed laser deposition ,law ,Impurity ,0103 physical sciences ,Atom ,0210 nano-technology ,Absorption (electromagnetic radiation) ,Wurtzite crystal structure - Abstract
Synchrotron X-ray absorption near edge structure (XANES) measurements of F K-edge in conjunction with first-principles calculations are used to identify the local structure of the fluorine (F) atom in F-doped ZnO. The ZnO film was grown by pulsed laser deposition with an Nd:YAG laser, and an oxyfluoridation method was used to introduce F ions into the ZnO films. The measured XANES spectrum of the sample was compared against the first-principles XANES calculations based on various models for local atomic structures surrounding F atoms. The observed spectral features are attributed to ZnF2 and FO defects in wurtzite bulk ZnO. more...
- Published
- 2018
- Full Text
- View/download PDF
29. Effect of F-inclusion in nm-thick MgO tunnel barrier
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Jun Hyung Kwon, Kookrin Char, Tesu Kim, and Jino Lee
- Subjects
Tunnel barrier ,chemistry ,Aluminium ,Magnesium ,Analytical chemistry ,General Physics and Astronomy ,chemistry.chemical_element ,General Materials Science ,Nanotechnology ,Oxidation process ,Inclusion (mineral) ,Layer (electronics) ,Quantum tunnelling - Abstract
We investigated the electrical characteristics of MgO tunnel barriers while we add F during oxidation process of nm-thick Mg layer. Specifically we measured d I /d V and d 2 I /d V 2 data of MgO tunnel barriers as we add F. When comparing the data of magnesium oxyfluoride tunnel barriers to those of aluminum oxyfluoride data, we have found that effect of F-inclusion in MgO is different from that in AlO x ; F-inclusion in MgO barrier makes the barrier more symmetric while F-inclusion in AlO x barrier makes the barrier more asymmetric. However, the d 2 I /d V 2 data of MgO did not change much even after F-inclusion, suggesting a very small amount of F-doping can make significant change in oxidation process of nm-thick Mg layer. We believe this result from the fact the oxidation process of nm-thick Mg layer is reaction-limited while the oxidation process of Al layer is diffusion-limited. more...
- Published
- 2009
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30. High-frequency micromechanical resonators from aluminium–carbon nanotube nanolaminates
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Miyoung Kim, Seung Sae Hong, Jae Hyuck Jang, Yun Daniel Park, Seunghun Hong, Seung Ran Lee, Kookrin Char, Jung Hoon Bak, Young Duck Kim, and Byung Yang Lee
- Subjects
Fabrication ,Nanocomposite ,Materials science ,Nanotubes, Carbon ,Mechanical Engineering ,Oxide ,chemistry.chemical_element ,Nanotechnology ,General Chemistry ,Carbon nanotube ,Condensed Matter Physics ,Smart material ,law.invention ,Resonator ,chemistry.chemical_compound ,chemistry ,Flexural strength ,Mechanics of Materials ,Aluminium ,law ,General Materials Science ,Composite material ,Aluminum - Abstract
Composites with added carbon nanotubes are known for their improved mechanical strength. Laminates of thin films of aluminium and carbon nanotubes are now used for the fabrication of micromechanical resonators with significantly enhanced mechanical properties. At micro- and nanoscales, materials with high Young’s moduli and low densities are of great interest for high-frequency micromechanical resonator devices1,2,3,4,5,6,7,8. Incorporating carbon nanotubes (CNTs), with their unmatched properties, has added functionality to many man-made composites9,10,11. We report on the fabrication of ≤100-nm-thick laminates by sputter-deposition of aluminium onto a two-dimensional single-walled CNT network12,13. These nanolaminates—composed of Al, its native oxide Al2O3 and CNTs—are fashioned, in a scalable manner, into suspended doubly clamped micromechanical beams. Dynamic flexural measurements show marked increases in resonant frequencies for nanolaminates with Al–CNT laminae. Such increases, further supported by quasi-static flexural measurements, are partly attributable to enhancements in elastic properties arising from the addition of CNTs. As a consequence, these nanolaminate micromechanical resonators show significant suppression of mechanical nonlinearity and enhanced strength, both of which are advantageous for practical applications and analogous to biological nanocomposites, similarly composed of high-aspect-ratio, mechanically superior mineral platelets in a soft protein matrix14. more...
- Published
- 2008
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31. Observation of biological samples using a scanning microwave microscope
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Jewook Park, Ts Kim Tong Suk Kim, Kookrin Char, Ahram Kim, and S. Hyun
- Subjects
Microscope ,Chemistry ,Analytical chemistry ,Water ,Dielectric ,Microscopy, Scanning Probe ,Sodium Chloride ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,law.invention ,Resonator ,Scanning probe microscopy ,law ,Yucca ,Dissipation factor ,Ionic conductivity ,Microwaves ,Instrumentation ,Microwave ,High-κ dielectric - Abstract
We present the application of a scanning microwave microscope technique to biological samples. Since dielectric properties of most biological samples originate mainly from the water they contain, we were able to obtain microscope images of biological samples by our scanning microwave microscope technique. As a model system, we have measured the electrical properties of water in the microwave region. The high dielectric constant and the large loss tangent of water were verified. Furthermore, we have measured the properties of water with differing amounts of sodium chloride concentration ranging from de-ionized water to the saturated solution. We have observed a significant change in the resonant frequency and Q value of the resonator as a function of sodium chloride concentration. The concentration dependence of the signals shows that our scanning microwave microscope technique can be useful for investigating the local electric behavior of biological samples with a simple model of ionic conduction. more...
- Published
- 2005
- Full Text
- View/download PDF
32. Electrical characteristics and interface structure of magnetic tunnel junctions with hafnium oxyfluoride barrier
- Author
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Kookrin Char, Y. Y. Yu, and D. S. Kim
- Subjects
Materials science ,Magnetoresistance ,Inorganic chemistry ,Analytical chemistry ,General Physics and Astronomy ,chemistry.chemical_element ,Electron spectroscopy ,Hafnium ,Tunnel effect ,Tunnel magnetoresistance ,chemistry ,X-ray photoelectron spectroscopy ,Thin film ,Quantum tunnelling - Abstract
We have studied the effects of fluorine inclusion on the electrical transport characteristics and interface structure of the hafnium oxide barrier in a magnetic tunnel junction. The tunneling magnetoresistance (TMR) and resistance-area (RA) as a function of oxidation time show that the TMR ratio of the hafnium oxyfluoride barrier is higher (8.3%) than that of the hafnium oxide barrier (5.7%) at their optimum conditions, and the oxyfluoride barrier junctions maintain a high TMR ratio even when the RA product increases by three orders of magnitude. X-ray photoelectron spectroscopy analysis shows that the fluorine atoms in the oxyfluoride barrier play an important role in the formation of a barrier with uniform composition. We believe that the initial fluoride layer is causing the subsequent oxygen diffusion to slow down, resulting in the formation of a defect-free hafnium oxide layer. These results are consistent with what we have found for aluminum oxyfluoride barriers. more...
- Published
- 2004
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33. Characterization of aluminum oxyfluoride barrier in magnetic tunnel junctions
- Author
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Kookrin Char, D. S. Kim, and Y. Y. Yu
- Subjects
Materials science ,Magnetoresistance ,Silicon ,business.industry ,General Physics and Astronomy ,chemistry.chemical_element ,Nuclear magnetic resonance ,Ferromagnetism ,X-ray photoelectron spectroscopy ,chemistry ,Transmission electron microscopy ,Aluminium ,Electrode ,Optoelectronics ,business ,Quantum tunnelling - Abstract
The electrical characteristics and the interface structure of magnetic tunnel junctions with aluminum oxyfluoride barrier were studied. Compared to conventional junctions with aluminum oxide tunnel barrier, junctions with aluminum oxyfluoride barrier exhibit larger and nearly constant tunneling magnetoresistance (TMR) values over a wide range of junction resistance and show a smaller bias dependence of TMR, a smaller temperature dependence of junction resistance, and higher effective barrier height. The cross sectional TEM image demonstrates that the junction with oxyfluoride barrier has excellent barrier flatness and smooth interfaces. X-ray photoelectron spectroscopy indicates that the fluorine forms an aluminum oxyfluoride barrier together with oxygen and that the growth of fluorine-rich oxyfluoride layer near the top surface of the barrier plays an important role in the formation of the highly insulating barrier, resulting in nearly ideal barrier/electrode interfaces without a detrimental magnetically dead layer. more...
- Published
- 2004
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- View/download PDF
34. Evolution of Electrical Properties of Magnetic Tunnel Junction through Successive Dielectric Breakdowns
- Author
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Kookrin Char, Daeshik Kim, Seong-Soo Kim, Yuyeon Yu, Tesu Kim, and Jun Hyok Kong
- Subjects
Tunnel magnetoresistance ,Materials science ,Tunnel barrier ,Physics and Astronomy (miscellaneous) ,Magnetoresistance ,Condensed matter physics ,Dielectric strength ,Tunnel junction ,General Engineering ,General Physics and Astronomy ,Dielectric ,Series and parallel circuits ,Quantum tunnelling - Abstract
We have fabricated a cross-strip-type Ni81Fe19/Co60Fe40/AlOX/Co60Fe40 magnetic tunnel junction (MTJ) and examined the changes of electrical properties through successive dielectric breakdowns. As the successive breakdowns progressed, both junction resistance and tunneling magnetoresistance (TMR) decreased and the temperature dependence of the junction resistance (R–T) shifted from insulating to metal-like behavior. These results can be explained by formation of increasingly conducting but nonmagnetoresistive channels in the barrier. These electrical properties after breakdowns can be described quantitatively with a parallel circuit model. more...
- Published
- 2003
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35. Observation of the Ni2 O3 phase in a NiO thin-film resistive switching system
- Author
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Deok-Hwang Kwon, Yongseok Choi, Miyoung Kim, Seung Ran Lee, Kyu Hwan Oh, Seung-Beom Son, and Kookrin Char
- Subjects
010302 applied physics ,Materials science ,business.industry ,Non-blocking I/O ,02 engineering and technology ,Memristor ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,law.invention ,Transmission electron microscopy ,law ,Phase (matter) ,Resistive switching ,0103 physical sciences ,Optoelectronics ,General Materials Science ,Thin film ,0210 nano-technology ,business - Published
- 2017
- Full Text
- View/download PDF
36. Interface chemistry and electrical properties of SrVO3/LaAlO3 heterostructures
- Author
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Kookrin Char, Dae Ho Kim, Ki Bong Lee, Hyeong Do Kim, Joonbum Park, Dong-Wook Kim, and Tae-Hee Noh
- Subjects
Surface diffusion ,business.industry ,Chemistry ,Analytical chemistry ,General Physics and Astronomy ,Heterojunction ,Substrate (electronics) ,X-ray photoelectron spectroscopy ,Electrical resistivity and conductivity ,X-ray crystallography ,Optoelectronics ,business ,Layer (electronics) ,Molecular beam epitaxy - Abstract
SrVO3 films were grown by laser molecular beam epitaxy on LaAlO3 substrates. For a 10-nm-thick film, its resistivity could be reduced by a factor of 4 by inserting a single La–O atomic layer on an oxygen-annealed LaAlO3 substrate. X-ray diffraction and x-ray photoelectron spectroscopy measurements revealed that oxygen defect concentrations could be varied significantly by controlling the substrate terminations, i.e., interface chemistry. It was suggested that the interface chemistry could influence formation of extended defects and result in changes in electrical properties. more...
- Published
- 2000
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- View/download PDF
37. Electronic transport inBa1−xKxBiO3single crystals
- Author
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Alan B. Kaiser, G. C. McIntosh, Linlin Zhao, Daoben Zhu, Kookrin Char, J. H. Lee, and Youngju Park
- Subjects
Superconductivity ,Physics ,Condensed matter physics ,Electrical resistivity and conductivity ,Condensed Matter::Superconductivity ,Seebeck coefficient ,Phase (matter) ,Doping ,Condensed Matter::Strongly Correlated Electrons ,Cuprate - Abstract
We report measurements of the thermopower and resistivity of two superconducting ${\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{K}}_{x}{\mathrm{BiO}}_{3}$ single crystals with $x\ensuremath{\sim}0.4$ (close to optimal doping), and analyze these data together with earlier data for K concentrations that span the accessible metallic and superconducting phase $0.37lxl0.55.$ The thermopower S for temperatures below 120 K exhibits similar behavior to that seen for the cuprates close to optimal doping: the thermopower is positive for temperatures just above ${T}_{c}$ but decreases with increasing temperature. A change of slope appears in the thermopower data at T\ensuremath{\sim}120--150 K, with an increase in $dS/dT$ above this temperature. We show that all the data can be accounted for by a two-band model similar to that used by Hashimoto et al. to explain the thermopower of the related superconductor, ${\mathrm{BaPb}}_{0.75}{\mathrm{Bi}}_{0.25}{\mathrm{O}}_{3},$ and are consistent with the reported persistence of the charge-density-wave gap in the superconducting phase near the metal-semiconductor transition. more...
- Published
- 2000
- Full Text
- View/download PDF
38. The effect of microstructure on the electrical properties of YBCO interface-engineered Josephson junctions
- Author
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Karl L. Merkle, B.H. Moeckly, Y. Huang, and Kookrin Char
- Subjects
Josephson effect ,Materials science ,business.industry ,Energy Engineering and Power Technology ,Plasma ,Crystal structure ,Condensed Matter Physics ,Microstructure ,Epitaxy ,Electronic, Optical and Magnetic Materials ,Barrier layer ,Transmission electron microscopy ,Optoelectronics ,Electrical and Electronic Engineering ,business ,Layer (electronics) - Abstract
The microstructure of interface engineered ramp-edge Josephson junctions in YBCO has been studied by transmission electron microscopy (TEM). The junctions are distinctly different from the structures found in heterophase SNS junctions. This structural difference can be directly related to the improved electrical properties of interface engineered junctions. The plasma treatment used in the interface engineering method forms a continuous barrier layer of 2 to 3 nm in thickness, much thinner than the deposited heterophase layers in SNS junctions. The layer, which separates the two YBCO layers, is crystalline, but has a crystal structure different from YBCO. The main factors responsible for the improved junction properties and their good reproducibility are: small barrier thickness, small thickness variation, weak interfacial strain fields, flat and nearly defect-free barrier/YBCO interfaces and good epitaxy of the second YBCO layer with few defects. Possible mechanisms for the formation of the large junction resistance are discussed. more...
- Published
- 1999
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- View/download PDF
39. Scanning probe microscopy for the imaging and control of ferroelectric oxides
- Author
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Thomas Tybell, Robert Hammond, Ø. Fischer, Kookrin Char, Louis Antognazza, M. R. Beasley, Chong H. Ahn, Jean-Marc Triscone, and O. Kuffer
- Subjects
Materials science ,Mechanical Engineering ,Analytical chemistry ,Field effect ,Mineralogy ,Condensed Matter Physics ,Epitaxy ,Ferroelectricity ,law.invention ,Scanning probe microscopy ,Piezoresponse force microscopy ,Mechanics of Materials ,law ,Microscopy ,General Materials Science ,Scanning tunneling microscope ,Sheet resistance - Abstract
Using a combination of scanning probe techniques, including contact mode atomic force microscopy, electric force microscopy, piezoelectric microscopy, and scanning tunneling microscopy, the ferroelectric properties of ferroelectric/metallic oxide heterostructures (Pb(Zr 0.52 Ti 0.48 )O 3 /SrRuO 3 and Sr(Ru 0.37 Ti 0.63 )O 3 /Pb(Zr 0.2 Ti 0.8 )O 3 ) and atomically smooth epitaxial ferroelectric oxides (Pb(Zr 0.2 Ti 0.8 )O 3 and Pb(Zr 0.52 Ti 0.48 )O 3 ) have been studied. Ferroelectric domains in as-grown films were imaged with nanometer resolution, and the domain structure could be modified locally and reversibly. Using the local polarization field of the ferroelectric, nonvolatile, reversible field effects were induced in SrRuO 3 at the submicron level, changing its sheet resistance by up to 300 ohms per square in a fashion that does not require any permanent electrical contacts or associated lithographic processing. more...
- Published
- 1998
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40. Local, Nonvolatile Electronic Writing of Epitaxial Pb(Zr 0.52 Ti 0.48 )O 3 /SrRuO 3 Heterostructures
- Author
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O. Fischer, Thomas Tybell, Jean-Marc Triscone, Chong H. Ahn, Kookrin Char, Robert Hammond, L. Antognazza, and M. R. Beasley
- Subjects
Multidisciplinary ,Materials science ,business.industry ,Analytical chemistry ,Heterojunction ,Epitaxy ,Ferroelectricity ,Electrical contacts ,Scanning probe microscopy ,Optoelectronics ,business ,Lithography ,Sheet resistance ,Electronic density - Abstract
A scanning probe microscope was used to induce local, nonvolatile field effects in epitaxial, ferroelectric Pb(Zr 0.52 Ti 0.48 )O 3 /SrRuO 3 heterostructures. Field-effected regions with linewidths as small as 3500 angstroms were written by locally switching the polarization field of the Pb(Zr 0.52 Ti 0.48 )O 3 layer; the electronic density of the underlying metallic SrRuO 3 layer was modified and the sheet resistance was changed by up to 300 ohms per square. This procedure is completely reversible and allows submicrometer electronic features to be written directly in two dimensions, with no external electrical contacts or lithographic steps required. more...
- Published
- 1997
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- View/download PDF
41. Nanosession: Mott Insulators and Transitions
- Author
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Eva Pavarini, N. Egetenmeyer, Yoshinori Tokura, John L. Sarrao, Tai Hoon Kim, Evgeny Gorelov, Keisuke Shibuya, Claude Ederer, Hyung J. Kim, Myung-Hwan Whangbo, Useong Kim, Simon Gerber, Chanjong Ju, Etienne Janod, Michel Kenzelmann, Masashi Kawasaki, Cristian Vaju, Vincent Guiot, E. Dorolti, Masaki Nakano, Byung-Gu Jeon, Hoon Kim, Jorge L. Gavilano, Joe D. Thompson, Laurent Cario, Roman Kovacik, Benoit Corraze, Roman Movshovich, Daisuke Okuyama, M. A. N. Araújo, J. M. P. Carmelo, Christof Niedermayer, Kee Hoon Kim, Andrea Bianchi, Eric Ressouche, Takafumi Hatano, Erik Koch, Woong-Jhae Lee, Guoren Zhang, Shimpei Ono, Eric D. Bauer, Kookrin Char, Hyun-Joo Koo, S. W. White, E. Kan, Kwang Taek Hong, Hyo Sik Mun, Yoshihiro Iwasa, and Philipp Werner more...
- Subjects
Materials science ,Condensed matter physics ,Mott insulator ,Metal–insulator transition - Published
- 2013
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- View/download PDF
42. Properties of cobalt-doped YBa2Cu3O7−δ thin films
- Author
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Brian H. Moeckly and Kookrin Char
- Subjects
Materials science ,Doping ,Analytical chemistry ,Energy Engineering and Power Technology ,chemistry.chemical_element ,Yba2cu3o7 δ ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Pulsed laser ablation ,Pulsed laser deposition ,chemistry ,Electrical and Electronic Engineering ,Thin film ,Cobalt ,Deposition (law) - Abstract
We show that the properties of YBa 2 (Cu 1− x Co x ) 3 O 7−δ films ( x = 0 to 0.14) deposited by pulsed laser ablation are sensitive to the growth conditions. We describe the behavior of T c , ϱ ( T ), J c ( T ), and X-ray measurements as a function of cobalt content and deposition parameters. Over a range of deposition parameters for which these properties of undoped YBa 2 Cu 3 O 7−δ are hardly altered, the values for cobalt-doped films may vary greatly. We explain this behavior in terms of the way cobalt is incorporated into the films, thereby altering their structural and transport properties. more...
- Published
- 1996
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43. Pair Tunneling fromc-AxisYBa2Cu3O7−xto Pb: Evidence fors-Wave Component from Microwave Induced Steps
- Author
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Bin Chen, S. I. Woods, R. Kleiner, M. B. Maple, R. Summer, Kookrin Char, John Clarke, D. A. Gajewski, S. H. Han, A. S. Katz, R. C. Dynes, E. Dantsker, and A. G. Sun
- Subjects
Physics ,Josephson effect ,Condensed matter physics ,Component (thermodynamics) ,Tunnel junction ,Condensed Matter::Superconductivity ,Pairing ,S-wave ,General Physics and Astronomy ,Order (ring theory) ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Quantum tunnelling ,Microwave - Abstract
In heavily twinned crystals or films of ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}x}$ (YBCO), ${d}_{{x}^{2}{\ensuremath{-}y}^{2}}$ pairing symmetry is expected to cause the cancellation of first-order Josephson tunneling through a YBCO-Pb tunnel junction grown on an a-b face; any residual tunneling is thus second order. As a result, microwaves at frequency f are predicted to induce steps on the current-voltage characteristic at voltages that are multiples of $\frac{1}{2}(hf/2e)$. Experimentally, steps are observed only at multiples of $hf/2e$, suggesting that s-wave pairing is present in YBCO; however, the simultaneous presence of d-wave pairing is by no means ruled out. more...
- Published
- 1996
- Full Text
- View/download PDF
44. High-k perovskite gate oxide BaHfO3
- Author
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Youjung Kim, Kookrin Char, Juyeon Shin, Namwook Kim, Chulkwon Park, Useong Kim, Young Mo Kim, Jae Hoon Kim, Jaejun Yu, and Taewoo Ha
- Subjects
010302 applied physics ,Materials science ,business.industry ,lcsh:Biotechnology ,Gate dielectric ,General Engineering ,Field effect ,02 engineering and technology ,Substrate (electronics) ,Dielectric ,021001 nanoscience & nanotechnology ,01 natural sciences ,lcsh:QC1-999 ,Gate oxide ,lcsh:TP248.13-248.65 ,0103 physical sciences ,Optoelectronics ,General Materials Science ,Field-effect transistor ,0210 nano-technology ,business ,lcsh:Physics ,Perovskite (structure) ,High-κ dielectric - Abstract
We have investigated epitaxial BaHfO3 as a high-k perovskite dielectric. From x-ray diffraction measurement, we confirmed the epitaxial growth of BaHfO3 on BaSnO3 and MgO. We measured optical and dielectric properties of the BaHfO3 gate insulator; the optical bandgap, the dielectric constant, and the breakdown field. Furthermore, we fabricated a perovskite heterostructure field effect transistor using epitaxial BaHfO3 as a gate insulator and La-doped BaSnO3 as a channel layer on SrTiO3 substrate. To reduce the threading dislocations and enhance the electrical properties of the channel, an undoped BaSnO3 buffer layer was grown on SrTiO3 substrates before the channel layer deposition. The device exhibited a field effect mobility value of 52.7 cm2 V−1 s−1, a Ion/Ioff ratio higher than 107, and a subthreshold swing value of 0.80 V dec−1. We compare the device performances with those of other field effect transistors based on BaSnO3 channels and different gate oxides. more...
- Published
- 2017
45. Electrical characteristics and interface structure of magnetic tunnel junctions with aluminum oxyfluoride barrier
- Author
-
Kookrin Char, D. S. Kim, Y. Y. Yu, and J. H. Ham
- Subjects
Materials science ,Physics and Astronomy (miscellaneous) ,Magnetoresistance ,business.industry ,Analytical chemistry ,chemistry.chemical_element ,Electron spectroscopy ,X-ray photoelectron spectroscopy ,chemistry ,Aluminium ,Electrode ,Fluorine ,Optoelectronics ,business ,Layer (electronics) ,Quantum tunnelling - Abstract
The effects of fluorine inclusion in the aluminum oxide tunnel barrier on the electrical characteristics and the interface structure of magnetic tunnel junctions were studied. Compared with conventional junctions without fluorine, the fluorine-containing junctions exhibit larger and nearly constant tunneling magnetoresistance (TMR) values over a wide range of oxidation times and exhibit a smaller bias dependence for TMR. X-ray photoelectron spectroscopy indicates that the fluorine forms an aluminum oxyfluoride barrier together with an oxygen and that the fluorine-rich oxyfluoride layer at the barrier top surface plays an important role in the formation of the highly insulating barrier, resulting in nearly ideal barrier/electrode interfaces without a detrimental magnetically dead layer. more...
- Published
- 2004
- Full Text
- View/download PDF
46. High mobility BaSnO3 films and field effect transistors on non-perovskite MgO substrate
- Author
-
Chulkwon Park, Young Mo Kim, Kookrin Char, Youjung Kim, and Juyeon Shin
- Subjects
010302 applied physics ,Electron mobility ,Materials science ,Physics and Astronomy (miscellaneous) ,business.industry ,Band gap ,Doping ,Field effect ,Nanotechnology ,02 engineering and technology ,Substrate (electronics) ,021001 nanoscience & nanotechnology ,Epitaxy ,01 natural sciences ,Transmission electron microscopy ,0103 physical sciences ,Optoelectronics ,0210 nano-technology ,business ,Perovskite (structure) - Abstract
(Ba,La)SnO3 is a wide bandgap semiconducting perovskite oxide with high electron mobility and excellent oxygen stability. The carrier modulation of (Ba,La)SnO3 channel by field effect on perovskite SrTiO3 substrates has been demonstrated in the recent reports. Here we report that (Ba,La)SnO3 on non-perovskite MgO substrate can also exhibit a high electron mobility and excellent carrier modulation by field, an important step towards scaling up for wafer-size processing. We optimized the undoped buffer layer thickness and measured the transport properties as a function of the La doping. The maximum mobility is 97.2 cm2/Vs at 2.53×1020/cm3. The transmission electron microscope images show that the films are epitaxial with about 2×1011/cm2 threading dislocation density. The field effect device based on the (Ba,La)SnO3 channel on MgO substrates is modulated with a high mobility of 43.9 cm2/Vs and Ion/Ioff of about 3.0×107. more...
- Published
- 2016
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- View/download PDF
47. Magnetoresistance properties of thin films of the metallic oxide ferromagnetSrRuO3
- Author
-
S. C. Gausepohl, Mark Lee, Kookrin Char, Chang-Beom Eom, and R. A. Rao
- Subjects
Phase transition ,Materials science ,Condensed matter physics ,Magnetoresistance ,Magnetic field ,Condensed Matter::Materials Science ,symbols.namesake ,Ferromagnetism ,Electrical resistivity and conductivity ,Saturation (graph theory) ,symbols ,Curie temperature ,Condensed Matter::Strongly Correlated Electrons ,Lorentz force - Abstract
The magnetoresistance of epitaxial thin films (250 to 1000 \AA{} thick) of the metallic oxide ferromagnet ${\mathrm{SrRuO}}_{3}$ has been measured at temperatures ranging from well below to just above the Curie point (\ensuremath{\approxeq}160 K). Measurements using both transverse (nonzero Lorentz force) and longitudinal (zero Lorentz force) geometries cleanly distinguish between an orbital contribution, present only at low temperature, and a spin-flip scattering contribution, present at all temperatures, to the resistivity in magnetic field. The magnetoresistance also shows strongly hysteretic behavior with high coercive and saturation fields. Through the Curie point, the magnetoresistance magnitude shows a maximum, which results from the suppression of the phase transition in magnetic field. The temperature derivative of the zero-field resistivity also shows a discontinuous jump, as predicted by standard theory. more...
- Published
- 1995
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48. Conducting interface states at LaInO3/BaSnO3 polar interface controlled by Fermi level
- Author
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Juyeon Shin, Chulkwon Park, Useong Kim, Young Mo Kim, and Kookrin Char
- Subjects
Electron mobility ,Materials science ,Condensed matter physics ,Band gap ,Doping ,Fermi level ,General Engineering ,Conductance ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,symbols.namesake ,0103 physical sciences ,symbols ,General Materials Science ,Diffusion (business) ,010306 general physics ,0210 nano-technology ,Polarization (electrochemistry) ,Perovskite (structure) - Abstract
We report on a new polar interface state between two band insulators: LaInO3 and BaSnO3, where the sheet conductance enhancement in the interface reaches more than the factor of 104 depending on the La doping concentration in BaSnO3 layer, by monitoring the conductance change before and after the polar interface formation as a function of La doping in BaSnO3. By eliminating the possibilities of oxygen vacancy involvement and cation diffusion, we show that the conductance enhancement is due to electronic reconstruction in the interface. Furthermore, we have found that the interfaces between BaSnO3 and the larger bandgap non-polar perovskites BaHfO3 and SrZrO3 did not show such a conductance enhancement. We discuss a model for the interface state where the Fermi level plays a critical role and the conductance enhancement is due to the existence of polarization in the polar perovskite, LaInO3. more...
- Published
- 2016
- Full Text
- View/download PDF
49. Correlation of Vortex Motion in High-TcSuperconductors
- Author
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Aharon Kapitulnik, Nancy A. Missert, Louis W. Lombardo, David K. Fork, John R. Clem, Thomas Lee, James N. Eckstein, R. B. van Dover, John Clarke, Lise T. Sagdahl, Joseph V. Waszczak, Lynn Schneemeyer, and Kookrin Char more...
- Subjects
Superconductivity ,Physics ,Condensed matter physics ,Condensed Matter::Superconductivity ,Zero (complex analysis) ,General Physics and Astronomy ,Motion (geometry) ,Crystallographic defect ,Noise (radio) ,Magnetic flux ,Vortex ,Magnetic field - Abstract
The magnetic flux noise generated by films and crystals of B${\mathrm{i}}_{2}$S${\mathrm{r}}_{2}$CaC${\mathrm{u}}_{2}$ ${\mathrm{O}}_{8+y}$ and YB${\mathrm{a}}_{2}$C${\mathrm{u}}_{3}$ ${\mathrm{O}}_{7\ensuremath{-}x}$, up to 30 \ensuremath{\mu}m thick and cooled in nominally zero magnetic field, has been measured at opposing surfaces by two dc superconducting quantum interference devices. For both materials, the noise sources at the two surfaces were highly correlated at specific temperatures in a given cooldown. This result suggests that the observed vortices moved as rigid rods. At other temperatures, the noise was mostly uncorrelated, suggesting that the relevant vortices were pinned at more than one point along their length. more...
- Published
- 1995
- Full Text
- View/download PDF
50. Proximity effect inYBa2Cu3O7−δ/YBa2(Cu1−xCox)3O7−δ/YBa2Cu3O7−δ junctions: From the clean limit to the dirty limit the clean limit to the dirty limit with pair breaking
- Author
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Louis Antognazza, Kookrin Char, T. H. Geballe, and Berkowitz Sj
- Subjects
Delta ,Materials science ,Condensed matter physics ,Proximity effect (superconductivity) ,Limit (mathematics) - Published
- 1995
- Full Text
- View/download PDF
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