• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.454-454
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• 2011

Graphene shows unusual electronic properties, such as carrier mobility as high as 10,000 $cm^2$/Vs at room temperature and quantum electronic transport, due to its electronic structure. Carrier mobility of graphene is ten times higher than that of Silicon device. On the one hand, quantum mechanical studies have continued on graphene. One of them is quantum Hall effect which is observed in graphene when high magnetic field is applied under low temperature. This is why two dimension electron gases can be formed on Graphene surface. Moreover, quantum Hall effect can be observed in room temperature under high magnetic field and shows fractional quantization values. Quantum Hall effect is important because quantized Hall resistances always have fundamental value of h/$e^2$ ~ 25,812 Ohm and it can confirm the quantum mechanical behaviors. The value of the quantized Hall resistance is extremely stable and reproducible. Therefore, it can be used for SI unit. We study to measure quantum Hall effect in CVD graphene. Graphene devices are made by using conventional E-beam lithography and RIE. We measure quantum Hall effect under high magnetic field at low temperature by using He4 gas closed loop cryostat.

• 한국초전도학회:학술대회논문집
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• 2009.07a
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• pp.59-59
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• 2009

• Progress in Superconductivity and Cryogenics
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• v.25 no.1
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• pp.1-5
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• 2023

The study of two-dimensional electron systems with extraordinarily low levels of disorder was, for a long time, the exclusive privilege of the epitaxial thin film research community. However, the successful isolation of graphene by mechanical exfoliation has truly disrupted this field. Furthermore, the assembly of heterostructures consisting of several layers of different 2D materials in arbitrary order by exploiting van der Waals forces has been a game-changer in the field of low-dimensional physics. This technique can be generalized to the large class of strictly 2D materials and offers unprecedented parameters to play with in order to tune electronic and other properties. It has led to a paradigm shift in the field of 2D condensed matter physics with bright prospects. In this review article, we discuss three device fabrication techniques towards high mobility devices: suspended structures, dry transfer, and pick-up transfer methods. We also address state-of-the-art device structures, which are fabricated by the van der Waals pick-up transfer method. Finally, we briefly introduce correlated ground states in the fractional quantum Hall regime.

• Journal of the Korean Physical Society
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• v.80
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• pp.415-419
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• 2022

Ultrathin Pt less than 10 nm thick is widely used in spintronic devices including spin Hall current. The transport property and underlying physics however have not been much studied for ultrathin films. Classical theories are analyzed to find that they cannot be applied to ultrathin films. Quantum mechanical size effect theory was applied to analyze Pt and Pt/CoFeB film sets. The quantum mechanical theory explained the conductance variation for both films along with roughness remarkably well.

• Proceeding of EDISON Challenge
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• 2014.03a
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• pp.516-520
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• 2014

Fractional quantum Hall Effect (FQSH) is one of most fundamental issues in condensed matter physics, and the Topological insulator becomes its prominent applications. This article reviews the general frameworks of these development and the physical properties. FQSH states and topological insulators are supposed to be topologically invariant under the minor change of geometrical shape or internal impurities. The phase transitions involved in this phenomena are known not to be explained in terms of symmetry breaking or Landau-Ginsburg theory. The new type of phase transitions related to topological invariants has acquired new name - topological phase transition. The intuitive concepts and the other area having same type of phase transitions are discussed.

• Journal of the Korean Vacuum Society
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• v.10 no.2
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• pp.262-266
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• 2001

We have presented the electrical properties of the quantum wire fabricated by split gate on GaAs/AlGaAs heterostructures by using the Shubnikov de Haas oscillation and quantum Hall effect measurements. We observed the 1D properties of the sample as increasing gate voltage. The misfit between quantum Hall plateau and minima in Shubnikov do Haas oscillations are interpreted as Landauer-B$"{u}$ tikker formula based on the edge state transport.port.

• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.2
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• pp.81-92
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• 1990

We developed the technologies of wuperlattice and HEMT structures grown by MOCVD, and their characterization. In the case of GaAs/AlGaAs superlattice, the periodicity, interface abruptness and Al compositional uniformity were confirmed through the shallow angle lapping technique and double crystal x-ray measurement. Photoluminesence spectra due to quantum size effect of isolated quantum wells were also observed. The heterojunction abruptness was estimated to be within 1 monolayer fluctuation by the analysis of the relation between PL FWHM(Full Width at Half Maximum) and well width. HEMT structure was successfully grown by MOCVD. The 2 dimensional electron gas formation at heterointerface in HEMT structure were evidenced through the C-V profile, SdH (Shubnikov-de Haas)oscillation and low temperature Hall measurement. Low field mobility were as high as $69,000cm^2/v.sec$ for a sheet carrier density of $5.5{\times}10^{11}cm^-2$ at 15K, and $41,200cm^2/v.sec$ for a sheet carrier density of $6.6{\times}10^{11}cm^-2$ at 77K. In addition, well defined SdH oscillation and quantized Hall plateaues were observed.

• Journal of the Korean Vacuum Society
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• v.8 no.2
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• pp.148-152
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• 1999

the low temperature magnetoresistance effect, electron mobilities, and 2 Dimensional electron Gases (2DEG) properties were investigated in $Si/Si_{1-x}Ge_x$ quantum well devices. N-type $Si/Si_{1-x}Ge_x$ structures were fabricated by utilizing a gas source Molecular Beam Epitaxy (GSMBE). Thermal oxidation was carried out in a dry O atmosphere at $700^{\circ}C$ for 7 hours. Electron mobilities were measured by using a Hall effect and a magnetoresistant effect at low temperatures down to 0.4K. Pronounced Shubnikov-de Haas (SdH) oscillations were observed at a low temperature showing two dimensional electron gases (2DEG) in s tensile strained Si quantum well. The electron sheet density (ns) of $1.5\times10^{12}[\textrm{cm}^{-2}]$ and corresponding electron mobility of 14200 $[\textrm{cm}^2V^{-1}s^{-1}]$ were obtained at a low temperature of 0.4K from $Si/Si_{1-x}Ge_x$ structures with thermally grown oxides.

• Applied Science and Convergence Technology
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• v.23 no.1
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• pp.1-13
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• 2014

Semiconductor quantum structures are often characterized by their energy gaps which are modified by the quantum size effect. Energy levels in semiconductors can be realized by optical transitions within confined structures. Photoluminescence spectroscopy in magnetic fields at low temperatures has proved to be a powerful technique for investigating the electronic states of quantum semiconductor heterostructures and offers a complimentary tool to electrical transport studies. In this review, we examine comprehensive investigations of magneto-excitonic and Landau transitions in a large variety of undoped and doped quantum-well structures. Strong magnetic fields change the diamagnetic energy shift of free excitons from quadratic to linear in B in undoped single quantum well samples. Two-dimensional electron gas induced by modulation doping shows pronounce quantum oscillations in integer quantum Hall regime and discontinuous transition at ${\nu}=1$. Such discontinuous transition can be explained as the formation of spin waves or Skyrmions.

• Korean Journal of Materials Research
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• v.12 no.3
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• pp.195-199
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• 2002

Planar Hall effect of ferromagnetic GaMnAs thin films was investigated for the first time. The films were grown in an optimized growth condition via molecular beam epitaxy at low temperatures. For the optimization of the growth conditions, we used reflection high-energy electron diffraction, electrical conductivity, double crystal x-ray diffraction, and superconducting quantum interference device measurements techniques. We observed that the difference between the longitudinal resistance and the transverse resistance matches the planar Hall resistance. The ratio of the planar Hall resistance at saturation magnetic field to that at zero reached above 500%.