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Park J.-H.,Toyohashi University of Technology | Wakahara A.,Toyohashi University of Technology | Okada H.,Toyohashi University of Technology | Sekiguchi H.,Toyohashi University of Technology | And 5 more authors.
Japanese Journal of Applied Physics | Year: 2011

The growth mode of europium (Eu)-doped GaN epitaxial films grown on a GaN template by rf plasma-assisted molecular beam epitaxy (PAMBE) was investigated with different III/V ratios under a constant Eu beam equivalent pressure ratio [PEu/(PEu + PGa)]. The reflection high-energy electron diffraction (RHEED) patterns and atomic force microscopy (AFM) images revealed the transition of the growth mode from threedimensional (3D) to step-flow/two-dimensional (2D) by increasing the III/V ratio. When the films were grown in the 3D growth mode, Eu concentrations estimated by Rutherford backscattering spectrometry/channeling (RBS/channeling) were almost constant, although the III/V ratios varied. However, when the growth mode was transferred from 3D to step-flow/2D, precipitates on the surface abruptly increased while the Eu concentration abruptly decreased, indicating the abrupt degradation of Eu-incorporation in the film. Luminescence sites of Eu3+ were sensitive to the III/V ratio, and Eu atoms have different luminescence sites in both growth modes. Furthermore, luminescence efficiency abruptly increased when the growth mode was transferred from 3D to step-flow/2D. © 2011 The Japan Society of Applied Physics.

Kim D.G.,Korea Photonics Technology Institute | Oh G.Y.,Chung - Ang University | Kim H.J.,Korea Photonics Technology Institute | Kim S.H.,Korea Photonics Technology Institute | And 7 more authors.
Electronics Letters | Year: 2010

A novel triangular resonator with a long evanescent field around the critical angle has been analysed and demonstrated for the first time. The sensitivity of the resonance shift used for changing the refractive index of 1×10-5 at the incidence angle of 18° is 1.04×10 -7nm/RIU for transverse magnetic polarised light. An extinction ratio of 6dB was observed near 1550nm, where the incidence angle of the total internal reflection mirror inside the resonator was 18°. © 2010 The Institution of Engineering and Technology.

Kritzinger R.,South Optical Technology | Burger J.,South Optical Technology | Meyer J.,University of Johannesburg
SAIEE Africa Research Journal | Year: 2012

A discrete inverse scattering method, known as layer-peeling, is used to synthesise a LPFG (long-period fibre grating) from a desired complex spectrum by a direct solution of the coupled-mode equations, while simultaneously determining the physical properties of the layered structure. The physical properties of the grating structure are determined in a recursive layer-by-layer manner by using causality arguments to design LPFGs exhibiting a flat-top spectral profile. The results obtained from the layer-peeling method are optimised using the flip-flop method to ease the fabrication process. We found that the layer-peeling method has the highest performance and executes in the least amount of time. A discussion of possible applications where optimised broadband LPFGs could be utilised in the field of telecommunications and sensing demonstrates the importance of the results.

Lee J.M.,Hanyang University | Yi J.,Hanyang University | Lee W.W.,Hanyang University | Jeong H.Y.,Hanyang University | And 3 more authors.
Applied Physics Letters | Year: 2012

One-dimensional and two-dimensional hybrid structures, composed of vertical ZnO nanorods grown on large-area graphene, are successfully integrated onto the GaN/InGaN light emitting diodes (LEDs). Compared with GaN LED without transparent conducting electrode, current injection and light emission increased almost 2-3 times, respectively, by the introduction of graphene based conducting electrode. Additional ∼66 increase in light emission was achieved by growing the ZnO nanorods on the graphene, which is consistent with the finite difference time domain modeling result. Furthermore, electroluminescence intensity profiles confirm the uniform light emission with high brightness in GaN LED with the ZnO nanorods-graphene hybrid electrode. © 2012 American Institute of Physics.

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