• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.11
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• pp.120-127
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• 1996

In the WKB analysis, we propose the new forms of the trial eigenfunctions which not only converge at the turning points but also approximate to the conventional WKB solutions away from the turning points. The eigenvalue equation of multiple waveguides with graded index profile are derived by using the proposed WKB analysis and the transfer matrix method. The drived equation sare represented in the recursive form. The results of the eigenvalue equation sare comapred with those of the FDM, one of the well-known computational methods, for a three-waveguide coupler.

• Proceedings of the Optical Society of Korea Conference
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• 2001.08a
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• pp.254-255
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• 2001

No Abstract.See Full-text

• Proceedings of the Optical Society of Korea Conference
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• 1996.09a
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• pp.99-99
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• 1996

• Proceedings of the Korean Vacuum Society Conference
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• 2002.06a
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• pp.65-65
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• 2002

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.243.1-243.1
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• 2016

Recently, many groups have attempted to fabricate 3-dimensional (3D) structures of GaN such as pyramids, rods, stripes and annulars. Since quantum structures on non-polar and semi-polar planes of 3D structures have less influence of internal electric filed, multi quantum wells (MQWs) formed on those planes have high quantum efficiency. Especially, pyramidal and annular structures consist of various crystal planes with different emission wavelength, providing a possibillity of phosphor-free white light emtting diodes (WLEDs).[1] However, it still has problem to obtain high color rendering index (CRI) number because of narrow-band emission and poor indium composition caused by the formation of few number of facets during metal-organic chemical vapor deposition growth.[2] If we can fabricate 3D structure having more various facets, we can make broad-band emittied WLEDs and improve CRI number. In this study, we suggest a simple method to fabricate 3D structures having various facet and containing high indium composition by means of a combination of metal-organic chemical vapor deposition and wet chemical etching techniques.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.1
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• pp.89-93
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• 2004

Piezoelectric fields built in I $n_{x}$G $a_1$$_{-x}$N/GaN (x=0.06∼0.1) quantum wells (QWs) have been estimated by comparing the transition energies, both calculated and measured by photoluminescence (PL). The calculation was numerically carried out with a rectangular QW model, where the effective bandgap considering a bowing facto, energy levels quantized for the lowest lying electrons and heavy holes (1e-lhh), and biaxial compressive strain were included except for the piezoelectric fields. The calculated values were observed to be larger (9∼15 meV) than the measured values by PL, which was considered to be caused by the piezoelectric fields built in InGaN/GaN QW interface. In addition, we observed the energy shift by measuring the EPDPL (excitation power-dependent PL), which was compared with the energy difference caused by the piezoelectric fields.

• Korean Journal of Optics and Photonics
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• v.14 no.3
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• pp.279-285
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• 2003

Wide- and flat-gain laser diodes were designed and fabricated from asymmetric multiple quantum well (AMQW) structures which consist of three compressively strained InGaAsP wells of different thicknesses. For a 400 ${\mu}{\textrm}{m}$-long lasers with as-cleaved facets, -1 ㏈ and -3 ㏈ gain bandwidth were 45 nm and 80 nm, respectively. For this AMQW structure, calculated gain spectra with various line broadening functions were compared with experimental results. We confirmed the calculated gain spectra using an asymmetric line broadening function were in good agreement with the measured data.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.225-225
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• 2016

PHOLED devices which have the structure of ITO/HAT-CN(5nm)/NPB(50nm)/EML(47nm)/TPBi(10nm)/Alq3(20nm)/LiF(0.8nm)/Al(100nm) are fabricated to investigate the diffusion length of the triplet exciton by using double-quantum-well(DQE) EML structure. To fabricate DQW structures, Ir(ppy)3(2% wt) and Ir(btp)2(8% wt) are used as green and red emission zones, respectively. In DQW structured EML, as shown in Fig. 1, 1nm thick layers of green and red emission zones are located middle of the EML, and the distance between these wells(x) is changed from 0nm to 10nm. As shown in Fig. 2, the emission spectra from DQW PHOLED devices are changed with different x. The intensity of the green emission(520nm) is decreased when x is decreased, and it goes to near zero when x=0nm. This behavior can be identified as the diffusion of the triplet excitons from Ir(ppy)3 to Ir(btp)2 by the Dexter energy transfer(DET). From the external quantum efficiency(EQE) of the red emission, as shown in Fig. 3, the diffusion length of the triplet excitons can be determined by the equation of DET rate, R=A Exp(-2RDA/L), where RDA is donor-acceptor distance and L is the sum of the van der Wals radii. As a result, the measured data of the red EQEs with different x are identified to theoretical result from the equation of DET rate(Fig. 4). From this results, we could confirm that the diffusion length of the triplet excitons can be determined by using DQW structure and this method is very useful to investigate the behavior of the excitons in PHOLEDs.

• New Physics: Sae Mulli
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• v.68 no.11
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• pp.1183-1191
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• 2018

The plasmon behaviors in a superlattice of $GaAs/Al_xGa_{1-x}As$ multiple quantum wells with a half-parabolic confining potential due to different dielectric interfaces are studied under magnetic and electric fields perpendicular and parallel to the superlattice axis by using a previously published theoretical framework. From the density-density correlation functions by considering the intrasubband and the inter-subband transitions under the random phase approximation, we calculate the dispersion energies of the surface and the bulk states as functions of the composition of the multiple quantum well structure and of the magnetic field strength and the average electric field strength over the quantum well. The Raman intensities for various magnetic field strengths and average electric field strengths over the quantum well are also obtained as a function of the energy of the incoming light for these states.

• Journal of Environmental Health Sciences
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• v.46 no.1
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• pp.88-95
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• 2020

Object: The purpose of this study was to select priority points for soil management using the location of groundwater and to suggest this method for soil contamination surveys. Method: Groundwater impact range was set to an area of 100 to 500 meters from the center point of agricultural groundwater wells. Data on industrial complex and factory areas, areas of stored or used ores and scrap metals, areas associated with waste and recycling, and traffic-related facilities areas were collected and checked for whether they fall within the groundwater impact range. Longitude and latitude coordinates of these data were mapped on the groundwater impact range using QGIS (Quantum Geographic Information System). Results: Considering the groundwater impact range, the points were selected as follows: 589 points were selected from 6,811 factories and 259 points were selected from 1,511 recycling business points. Traffic-related facility areas were divided between gas stations, bus depots, and auto mechanics. Thirty-four points were selected from 149 bus depots and 573 points were selected from 6,013 auto mechanic points. From the 2,409 gas station points, 323 were selected. Conclusion: Contaminated soil influences groundwater and crops, which can harm human health. However, soil pollution is not easily identified, so it is difficult to determine what has occurred. Pollution must be prevented beforehand and contaminated soil found. By selecting and investigating soil contamination survey points in consideration of the location of groundwater wells, we can safely manage water resources by preventing groundwater contamination in advance.