Gwangju, South Korea
Gwangju, South Korea

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Kim H.D.,University of Oxford | Kyhm K.,CNRS Neel Institute | Kyhm K.,Pusan National University | Taylor R.A.,University of Oxford | And 4 more authors.
Applied Physics Letters | Year: 2013

We performed spectroscopic studies of a single GaAs quantum ring with an anisotropy in the rim height. The presence of an asymmetric localised state was suggested by the adiabatic potential. The asymmetry was investigated in terms of the polarization dependence of excitons and biexcitons, where a large energy difference (∼ 0.8 meV) in the exciton emission energy for perpendicular polarizations was observed and the oscillator strengths were also compared using the photoluminescence decay rate. For perpendicular polarizations, the biexciton exhibits twice the energy difference seen for the exciton, a fact that may be attributed to a possible change in the selection rules for the lowered symmetry. © 2013 American Institute of Physics.

Kim H.D.,University of Oxford | Kyhm K.,Pusan National University | Kyhm K.,CNRS Neel Institute | Taylor R.A.,University of Oxford | And 6 more authors.
Applied Physics Letters | Year: 2013

We observe excited exciton and biexciton states of localised excitons in an anisotropic quantum ring, where large polarisation asymmetry supports the presence of a crescent-like localised structure. We also find that saturation of the localised ground state exciton with increasing excitation can be attributed to relatively fast dissociation of biexcitons (∼430 ps) compared to slow relaxation from the excited state to the ground state (∼1000 ps). As no significant excitonic Aharonov-Bohm oscillations occur up to 14 T, we conclude that phase coherence around the rim is inhibited as a consequence of height anisotropy in the quantum ring. © 2013 AIP Publishing LLC.

Johnson M.,U.S. Navy | Song J.,Nano Photonics Research Center | Hong J.,Korea University | Chang J.,Spin Convergence Research Center
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2013

We describe the development of a magnetic logic device that is uniquely different from spintronic approaches based on magnetoresistive effects that derive from spin dependent transport of carriers. The core of our device is a thin film avalanche diode channel fabricated as a p-n bilayer. Because of the structural asymmetry, the carriers are sensitive to an in-plane magnetic field and the diode has a large magnetoresistance. We characterize our device as a current switch. The high- and low-current states are well defined and are determined by the magnetic field. Positive or negative field orientation with constant field strength is an appropriate selector. We then describe an integrated avalanche diode logic device in which the magnetic field is provided by the local fringe field from a patterned ferromagnetic film with nanometer dimensions. The magnetization orientation of the nanomagnet, and the sign of the magnetic field, is set by spin torque transfer (STT) using small amplitude current pulses. We describe how simple arrangements of these integrated devices can be used as dynamically reconfigurable logic gates. Reconfigurable Boolean AND/OR gates using early prototype structures with micron dimensions are shown. Scaling arguments that justify the plausibility of fabricating an integrated device with dimensions of 100 nm are presented. These arguments suggest that such a device could produce an output current driving STT write processes and provide fanout capability in an integrated network. © 2013 Copyright SPIE.

Ryu J.H.,IT Convergence Technology Research Laboratory | Lee W.-J.,Nano Photonics Research Center | Lee B.K.,IT Convergence Technology Research Laboratory | Do L.-M.,IT Convergence Technology Research Laboratory | And 3 more authors.
ETRI Journal | Year: 2014

This study proposes a novel optical sensor structure based on a refractometer combining a bend waveguide with an air trench. The optical sensor is a 1 x 2 splitter structure with a reference channel and a sensing channel. The reference channel has a straight waveguide. The sensing channel consists of a U-bend waveguide connecting four C-bends, and a trench structure to partially expose the core layer. The U-bend waveguide consists of one C-bend with the maximum optical loss and three C-bends with minimum losses. A trench provides a quantitative measurement environment and is aligned with the sidewall of the C-bend having the maximum loss. The intensity of the output power depends on the change in the refractive index of the measured material. The insertion loss of the proposed optical sensor changes from 3.7 dB to 59.1 dB when the refractive index changes from 1.3852 to 1.4452. © 2014 ETRI.

Kim I.,Pusan National University | Kiba T.,Hokkaido University | Murayama A.,Hokkaido University | Song J.D.,Nano photonics Research Center | Kyhm K.,Pusan National University
Current Applied Physics | Year: 2015

Optical anisotropy of self-assembled elliptical InP quantum dots has been investigated in terms of the polarization dependence of excitons. Although large size inhomogeneity is present, two kinds of characteristic quantum dots, which are classified into large and small quantum dots, were found in terms of the polarization anisotropy. We have confirmed that the large quantum dots are more pronounced in the polarization anisotropy, where the degree of linear polarization for the large quantum dots is significantly larger (∼60%) than that for the small ones (∼36%). The effective shape of quantum dots is also estimated by using the size dependence of oscillator strength, which is in agreement with the AFM image. We also suggest that the anisotropy of exciton oscillator strength can be modified via the dipole-dipole interaction between nearest exciton dipoles. © 2015 Elsevier B.V. All rights reserved.

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