• Journal of the Microelectronics and Packaging Society
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• v.28 no.4
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• pp.85-89
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• 2021

AlGaN-based UV-C light-emitting diodes (LEDs) were applied for p-type activation by electrochemical potentiostatic activation (EPA). The p-type activation efficiency was increased by removing hydrogen atoms through EPA treatment using a neutral Mg-H complex that causes high resistance and low conductivity. A neutral Mg-H complex is decomposed into Mg^- and H⁺ depending on the key parameters of solution, voltage, and time. The improved hole carrier concentration was confirmed by secondary ion mass spectroscopy (SIMS) analysis. This mechanism eventually improved the internal quantum efficiency (IQE), the light extraction efficiency, the leakage current value in the reverse current region, and junction temperature, resulting in better UV-C LED lifetime. For systematic analysis, SIMS, Etamax IQE system, integrating sphere, and current-voltage measurement system were used, and the results were compared with the existing N₂-annealing method.

• Journal of the Semiconductor & Display Technology
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• v.16 no.1
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• pp.40-44
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• 2017

The effect of weak dielectric silicone dioxide($SiO_2$) embedded in polyfluorene(PFO) emitting layer of polymer-based multi structure OLED was investigated. Indium tin oxide(ITO)/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)/poly(9,9-di-n-octylfluorenyl-2,7-diyl)(PFO)/2,2,2"-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi)/aluminum(Al) structure OLED was fabricated by spin-coating method. Applied electric field causes some effect on $SiO_2$ in PFO layer. Thus, interaction between polymers and affected $SiO_2$ might generate electrical and luminance properties change. Experimental results, show the reduced threshold voltage of 6 V(from 23 V to 17 V). The maximum current density was rather increased from $71A/m^2$ to $610A/m^2$ and maximum brightness was also increased from $7.19cd/m^2$ to $41.03cd/m^2$, 9 and 6 times each. Additionally we obtained colour broadening result due to the increasing of blue-green band emission. Consequently we observed that electrical and luminance properties are enhanced by adding $SiO_2$ and identified the possibility of controlling the emission colour of OLED device according to colour broadening.

• Journal of the Semiconductor & Display Technology
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• v.7 no.4
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• pp.19-22
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• 2008

Thin film has been an increasing important subject of intensive research, owing to the fact that these films possess desirable optical, electrical and electrochemical properties for uses in many semi-conducting nano-crystal applications, such as light-emitting diodes, lasers and solar cell applications. Here, ZnSe thin films were deposited by electrochemical method for the applications of light emitting diode. Electrochemical deposition of ZnSe thin film is not easy, because of the high difference of reduction potential between zinc ion and selenium acid. In order to handle the band gap of ZnSe crystal thin films easily, electrochemical methods are promising to manufacture these films economically. Therefore we have investigated the present study to characterize zinc selenide thin films deposited on ITO glass plates electrochemically. The luminescent properties of ZnSe films have been evaluated by UV-Vis spectrometer and luminescence spectrometer. And the morphology of the film surface has been discussed qualitatively from SEM images.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.618-619
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• 2010

LED는 기존의 발광원에 비해 훨씬 높은 파워와 효율성으로 인해 최근 들어 각종 조명이나 교통신호 등에서 사용이 급증하고 있다. LED 재료를 위해 지금까지 여러가지가 연구되어 왔는데, 갈륨 질화물 (Gallium Nitride, GaN)에 기반한 시스템이 최근들어 가장 큰 관심을 받고 있다. GaN 방식은 열적으로 매우 안정성이 있고, 1.9 ~ 6.2 eV 범위의 넓은 밴드의 Gap, 그리고 인듐이나 알루미늄과 결합하여 청, 녹, 백색등의 다양한 빛을 발생할 수 있는 장점을 가지고 있다. 예를 들어 청색 LED는 광학 방식의 기록매체에, 백색 LED는 기존의 조명램프의 대체용으로 활용이 가능하다. 이러한 장점 덕분에 GaN기반 LED 시장은 1994년에 최초로 상용화 된 이래 최근 급격한 성장을 보여 왔다. 그러나 GaN은 다른 III~V 타입의 반도체 재료와는 달리 재료가 성장하기 위해 사파이어와 같은 별도의 기판을 필요로 하는 문제가 있다. 이것은 결국 전위발생과 같은 격자의 부조화 같은 문제를 야기하여 결국 LED의 성능을 떨어뜨리는 요인이 된다. 이러한 문제를 해결하기 위해 HVPE(Hydride Vapor Phase Epitaxy) 방법이 개발되었는데, 이 방법은 시간당 100 미크론의 매우 빠른 성장속도로 높은 두께의 레이어를 만드는 장점이 있다. 이렇게 성장된 GaN 레이어는 베이스 기판에서 쉽게 분리되어 활용이 가능하다. 그러나 HVPE 기술은 성장 공정에서 두께를 균일하게 만들도록 제어하는 것이 매우 어렵다는 문제가 있다. 따라서 HVPE 방식에서는 이러한 조건을 만족시키기 위해 반응현상에 대한 물리적 해석을 토대로 공정조건을 정밀하게 설계해야 한다. 이를 위해 최근에 실험 또는 시뮬레이션을 활용하여 이러한 공정조건을 향상시키기 위한 여러 연구가 진행되었다. 본 연구에서는 이러한 연구의 일환으로 반응로에 투입되는 여러 기체의 유량과 존별 주변온도 조건을 입력변수로 하고, 이들이 GaN 성장에 미치는 영향을 분석하였다. HVPE 시스템에서 가장 이상적인 목표는 반응기체가 층류유동을 유지하면서 대부분의 반응이 기판위에서 이뤄지며, 기판위에서 성장되는 재료의 두께가 균일하게 되는 것이다. 입력변수들이 이러한 결과에 어떠한 영향을 미치는 지 분석하기 위해 전산유체역학(CFD, Computational Fluid Dynamics)을 수행하는 상용코드 FLUENT를 사용하였다. 보다 실제에 가까운 해석을 위해서는 기체간의 화학반응을 포함해야 하나, 해석의 편의와 효율을 위해 본 연구에서는 열 및 유동해석만을 수행하였다. 한편 실제 반응로의 우수성은 성장속도와 두께분포의 균일도를 통해 평가된다. CFD 해석을 통해 이들을 분석하기 위해 기존에 수행한 실험조건을 해석하고 해석결과의 유동패턴/압력분포를 실험결과의 성장속도/두께분포와 비교하고, 이중에서 관련성이 높은 해석결과변수를 우수성 평가에 활용하였다. 기존의 실험결과를 토대로 이러한 중요 결과변수와 함께 이들에 대한 목표값이 도출되고 나면, 입력 공정조건 - 사용기체의 유량과 주변온도 조건 - 에 대해 실험계획(DOE,Design of Experiment)을 수립하고 목표성능을 구현하기 위한 최적설계를 수행할 수 있다. 일반적으로 CFD를 통해 최적의 설계나 공정조건을 탐색하는 작업은 1회의 CFD 계산시간이 매우 오래 소요되기 때문에 쉽지 않다. 그러나 본 연구에서는 CFD와 DOE의 적절한 조합을 통해 적은 수의 해석을 가지고도 원하는 결과를 효율적으로 얻는 것이 가능함을 입증하고자 한다. 본 발표에서는 아직 이러한 연구가 완성되지 않은 시점에서 제반 연구개요를 소개하고 현 시점까지의 연구 결과 및 향후 계획을 소개하고자 한다.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.6
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• pp.169-180
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• 2018

White light-emitting diodes (LEDs) are more economical than fluorescent lights, and provide high brightness, a high lifetime expectancy, and greater durability. As LEDs are closely connected with people's daily lives, dimming control of LED is an important component in providing energy savings and improving quality of life. In visible light communications systems using these LEDs, multiple input multiple output (MIMO) technology has attracted a lot of attention, in that it can attain the channel capacity in proportion to the number of antennas. This paper analyzes the power performance of three kinds of modulation in visible light communications (VLC) systems applied space-time block code (STBC) techniques. The modulation schemes are return-to-zero on-off keying (RZ-OOK), variable pulse position modulation (VPPM), and overlapping pulse position modulation (OPPM), and dimming control was applied. The power requirements and power consumption were used as metrics to compare the power efficiency in $2{\times}2$ STBC-VLC environments under the three kinds of modulation. We confirm that dimming control affects the communications performance of each modulation scheme. VPPM showed greater consumption among the three modulations, and OPPM showed energy savings comparable to VPPM.

• Journal of the korean academy of Pediatric Dentistry
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• v.36 no.2
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• pp.199-208
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• 2009

This study was performed to improve the conventional $DIFOTI^{TM}$ system(EOS Inc., USA) by developing the prototype of DIFOTI system which consists of light emitting diode(LED) and digital camera. The images of enamel surfaces treated under Carbopol 907 de-mineralizing solution were taken daily during 7 days of experimental periods by both DIFOTI systems. The results of comparative analyses of obtained images can be summarized as follows: 1. Trans-illumination indices of images taken from sample enamel surfaces were decreased with time in both systems. 2. The difference of intensity of luminance between sound and de-mineralized enamel surface in prototype DIFOTI system was shown to be relatively smaller than conventional $DIFOTI^{TM}$ system. The application of LED light source in prototype DIFOTI system could possibly reduce the amount of current consumption and that could ultimately lead us to the successful development of wireless model with battery. The innovative development of digital camera is undoubtedly expected to create much clearer image despite of wireless transfer. LED and digital camera can be combined into a smaller size but a very important task of improving image manager and analyzing program into a simpler and easier one to manipulate has to be solved.

• Horticultural Science & Technology
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• v.29 no.4
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• pp.352-357
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• 2011

Rose seed shows low germination percentages (about 20%) because it has a high amount of substances that inhibit germination in the pericarp. We investigated the effect of orientation of achene, the day after pollination (DAP), and cold storage with or without half-cut in achene for the germination percentage in R. rugosa. Germination percentages of intact or half-cut achenes were investigated in a 16-hour photoperiod at $25^{\circ}C$ room on basal MS medium for two weeks. In germination percentage, maximum 100% was measured within one week when half-cut achenes were cultured on an orientation that the embryos facing to the light. Half-cut achenes at 90 DAP were germinated 100% regardless of cold storage. Various LED lights (red, blue, yellow, green, and white) were illuminated over the half-cut achenes to gain the effect of light color. Germination percentage of R. rugosa seeds under blue LED reached the greatest with 90% within one week of culture and these seedlings were the best with a steady growth rate. It is concluded that half-cut achenes would be an effective method to improve seed germination in R. rugosa without stratification or scarification. This system could be applied to breeding studies in rose cultivars.

• Journal of Radiation Protection and Research
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• v.37 no.1
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• pp.10-15
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• 2012

Design and performance test results of a newly developed optically stimulated luminescence (OSL) measurement system are presented in this paper. Generally, different types of optical filters are used in OSL reader system to minimize the interference of the stimulation light in the OSL signal. For optically stimulation of $Al_2O_3:C$, we have arrived at an optimal combination of the filters, i.e., GG420 filter for filtering the stimulating light source, and a combined UG11 and BG39 filter at the detecting window (PMT). By using a high luminance blue LED (Luxeon V), sufficient luminous intensity could be obtained for optically stimulation. By using various control boards, the OSL reader device was successfully interfaced with a personal computer. A software was developed to deliver required commands to operate the OSL reader by using the LabView program (National Instruments, Inc.). In order to evaluate the reliability and the reproducibility of newly designed-OSL reader. Performance testing of the OSL reader was carried out for OSL efficiency, OSL decay curve and signal to noise ratio of the standard $Al_2O_3:C$ OSL material. It was found to be comparable with that of commercial Riso reader system.

• Science of Emotion and Sensibility
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• v.24 no.2
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• pp.25-38
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• 2021

The aim of this study is to protect workers and pedestrians from accidents at night or bad weather by attaching optical fiber to existing safety clothing that is made only with fluorescent fabrics and retroreflective materials. A safety vest was designed and manufactured by applying optical fiber, and energy-harvesting technology was developed. The safety vest was designed to emit light using the automatic flashing of optical fibers attached to the film, and an energy harvester was manufactured and attached to drive the light emission of the optical fiber more continuously. As a result, first, the vest wearer' body was recognized from a distance through the optical fiber and retroreflection, which helped prevent accidents. Thus, this concept helps in saving lives by preventing accidents during night-time work on the roadside or activities of rescue crew and sports activities, or by quickly finding the point of an accident with a signal that changes the optical fiber light emission. Second, to use the wasted energy, a piezoelectric-element power generation system was developed and the piezoelectric-harvesting device was mounted. Potentially, energy was efficiently produced by activating the effective charging amount of the battery part and charging it auxiliary. In the existing safety vest, detecting the person wearing the vest is almost impossible in the absence of ambient light. However, in this study, the wearer could be found within 100 m by the light emission from the safety vest even with no ambient light. Therefore, in this study, we will help in preventing and reducing accidents by developing smart safety clothing using optical fiber and energy harvester attached to save lives.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2021.10a
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• pp.606-608
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• 2021

Humans and various devices are interconnected using the Internet of Things and are used in various ways. In this study, a synchronization control system with remote locations was constructed using ICT, and a signal system for pedestrians was implemented using the system. PLC circuits were used to implement controllers, through which wireless control signal transmission and reception, LED lamp emission control, and power control were performed. It was confirmed that signal synchronization from the main controller to the remote sub-controller was possible by establishing a controller and pedestrian traffic light system, and lamp signal synchronization of the pedestrian traffic light system installed on both sides of the road was implemented. As a result, it was confirmed that 1:1 remote control or 1:N remote group control was possible, and this result can be used in various fields.