• 한국재료학회:학술대회논문집
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• 한국재료학회 2009년도 춘계학술발표대회
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• pp.29.1-29.1
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• 2009

Fabrication of good quality P-type GaN remained as a challenge for many years which hindered the III-V nitrides from yielding visible light emitting devices. Firstly Amano et al succeeded in obtaining P-type GaN films using Mg doping and post Low Energy Electron Beam Irradiation (LEEBI) treatment. However only few region of the P-GaN was activated by LEEBI treatment. Later Nakamura et al succeeded in producing good quality P-GaN by thermal annealing method in which the as deposited P-GaN samples were annealed in N2 ambient at temperatures above $600^{\circ}C$. The carrier concentration of N type and P-type GaN differs by one order which have a major effect in AlGaN based deep UV-LED fabrication. So increasing the P-type GaN concentration becomes necessary. In this study we have proposed a novel method of activating P-type GaN by electrochemical potentiostatic method. Hydrogen bond in the Mg-H complexes of the P-type GaN is removed by electrochemical reaction using KOH solution as an electrolyte solution. Full structure LED sample grown by MOCVD serves as anode and platinum electrode serves as cathode. Experiments are performed by varying KOH concentration, process time and applied voltage. Secondary Ion Mass Spectroscopy (SIMS) analysis is performed to determine the hydrogen concentration in the P-GaN sample activated by annealing and electrochemical method. Results suggest that the hydrogen concentration is lesser in P-GaN sample activated by electrochemical method than conventional annealing method. The output power of the LED is also enhanced for full structure samples with electrochemical activated P-GaN. Thus we propose an efficient method for P-GaN activation by electrochemical reaction. 30% improvement in light output is obtained by electrochemical activation method.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2008년도 추계학술발표대회 및 제15회 신소재 심포지엄
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• pp.11.1-11.1
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• 2008

• 한국전기전자재료학회논문지
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• 제18권10호
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• pp.945-949
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• 2005

We have grown GaN layers with in-situ SiN mask by metal organic chemical vapor deposition (MOCVD) and study the physical properties of the GaN layer. We have also fabricate PN junction light emitting diode (LED) to investigate the effect of the SiN mask on its optical property By inserting a SiN mask, (102) the full width at half maximum (FWHM) decreased from 480 arcsec to 409 arcsec and threading dislocation (TD) density decreased from $3.21{\times}10^9\;cm^{-2}$ to $9.7{\times}10^8\;cm^{-2}$. The output power of the LED with a SiN mask increased from 198 mcd to 392 mcd at 20 mA. We have thus shown that the SiN mask improved significantly the physical and optical properties of the GaN layer.

• 한국산학기술학회논문지
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• 제10권7호
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• pp.1514-1519
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• 2009

400nm 파장을 방출하는 GaN LED를 제조하여, n-GaN층과 p-GaN층의 위에 있는 ITO층 표면에 패턴을 만들어 광 추출 효율을 향상시켰다. 추가적으로, n과 p패드 아래와 칩의 바닥면에 각각 광반사 금속을 설치하였다. 광 추출 효율은 20mA에서 n-GaN의 텍스쳐링에 의해 20% 증가되었고 ITO의 텍스쳐링에 의해 18% 증가되었다. 표면 처리가 않된 LED와 비교해서 n-GaN와 ITO를 함께 표면 텍스쳐링 했을때의 광 추출 효율은 20mA에서 32% 증가되었다.

• 한국재료학회지
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• 제23권3호
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• pp.161-167
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• 2013

The ZnO thin films were grown on GaN template substrates by RF magnetron sputtering at different RF powers and n-ZnO/p-GaN heterojunction LEDs were fabricated to investigate the effect of the RF power on the characteristics of the n-ZnO/p-GaN LEDs. For the growth of the ZnO thin films, the substrate temperature was kept constant at $200^{\circ}C$ and the RF power was varied within the range of 200 to 500W at different growth times to deposit films of 100 nm thick. The electrical, optical and structural properties of ZnO thin films were investigated by ellipsometry, X-ray diffraction (XRD), atomic force microscopy (AFM), photoluminescence (PL) and by assessing the Hall effect. The characteristics of the n-ZnO/p-GaN LEDs were evaluated by current-voltage (I-V) and electroluminescence (EL) measurements. ZnO thin films were grown with a preferred c-axis orientation along the (0002) plane. The XRD peaks shifted to low angles and the surface roughness became non-uniform with an increase in the RF power. Also, the PL emission peak was red-shifted. The carrier density and the mobility decreased with the RF power. For the n-ZnO/p-GaN LED, the forward current at 20 V decreased and the threshold voltage increased with the RF power. The EL emission peak was observed at approximately 435 nm and the luminescence intensity decreased. Consequently, the crystallinity of the ZnO thin films grown with RF sputtering powers were improved. However, excess Zn affected the structural, electrical and optical properties of the ZnO thin films when the optimal RF power was exceeded. This excess RF power will degrade the characteristics of light emitting devices.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.572-572
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• 2013

본 연구에서는 Plasma damage-free 선형 대향 타겟 스퍼터(Linear Facing Target sputtering: LFTS) 시스템을 이용하여 성막시킨 GaN-LED의 투명전극용 Ga-doped ZnO (GZO) 박막의 특성을 연구하였다. LFTS 시스템을 이용한 GZO 성막 공정 중 LED소자의 플라즈마 노출에 의한 데미지를 최소화 하기 위해 일정한 타겟간 거리(Target-to-Target distance: 65 mm)에서 타겟과 기판간 거리(Target-to-Substrate distance)를 50 mm에서 120 mm로 변화시키며 GZO 투명 전극을 성막해 박막의 특성과 소자의 특성을 동시에 분석하였다. LFTS에서 플라즈마는 GZO 타겟 사이에 형성된 일방향의 자장에 의해 효과적으로 구속되기 때문에 기판과 타겟 거리를 최적화 할 경우 플라즈마 데미지를 최소화하며 GaN-LED의 제작이 가능하다. 기판과 타겟 사이의 거리가 120 mm에서 최적화된 200 nm 두께의 GZO 투명 전극은 DC 파워 250 W, 공정 압력 0.3 mTorr, Ar 20 sccm 실험 조건하에서 LED 소자 위해 성막되었으며, 이후 $600^{\circ}C$ 수소 분위기에서 1분간 급속 열처리하였고 면저항(37 Ohm/sq.)과 450 nm 파장에서의 투과도(83%)를 나타냄을 확인할 수 있었다. LED 소자와 타겟 사이의 거리가 50 mm에서 120 mm로 증가할수록 성막공정 중 LED 소자에 미치는 플라즈마 데미지의 감소로 인해 GaN-LED 소자의 turn on voltage가 8.2 V에서 3.4 V로 감소한 것을 확인하였으며, 또한 radiant intensity는 20 mA의 전류를 인가하였을 시 0.02 mW/sr에서 8 mW/sr로 400배 향상되었다. 이러한 소자 특성은 대향 타겟 스퍼터 시스템으로 성장시킨 GZO 투명전극이 LED 소자의 투명 전극 층(Transparent Conductive Layer: TCL)에 적용될 수 있음을 말해준다.

• 한국반도체및디스플레이장비학회:학술대회논문집
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• 한국반도체및디스플레이장비학회 2005년도 추계 학술대회
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• pp.59-62
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• 2005

백색 LED 램프를 제조하는 공정에서 램프간의 전기적 개방상태의 절연상태를 유지하기 위해 사파이어 기판 위에 성장된 GaN 계 반도체 에피박막층을 제거하기 위해 유도 결합형 플라즈마 식각 공정을 이용하였다. 4 미크론의 두께를 갖는 GaN 층을 식각하는데 있어 식각 방지 마스킹 물질로 포토레지스트, $SiO_2,\;Si_{3}N_4$ 및 $Al_{2}O_3$를 시험하였다. 동일한 전력 및 가스유량상태에서 $Al_{2}O_3$만 에피층을 보호할 수 있음을 확인하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.313-313
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• 2012

In recent years there have been many studies of InGaN/GaN based light emitting diodes (LEDs) in order to progress the performance of luminescence. Many previous literatures showed the performance of LEDs by changing the LED structures and substrates. However, the studies carried out by the researchers so far were very complicated and sometimes difficult to apply in practice. Therefore, we propose one simple method of changing the thickness and the numbers of multiple quantum wells (MQWs) in order to optimize their effects. In our research, we investigated electrical and optical properties by changing the well thickness and the number of quantum well (QW) pair in LED structures by growing the structure -inch Si (111) wafer. We defined the samples from LED_1 to LED_3 according to MQW structure. Samples LED_1, LED_2 and LED_3 consist of 5-pair InGaN/GaN (3.5 nm/ 4.5 nm), 5-pair InGaN/GaN (3 nm/4.5 nm) and 7-pair InGaN/GaN (3.5 nm/4.5 nm), respectively. We characterized electrical and optical properties by using electroluminescence (EL) measurement. Also, Efficiency droop was analyzed by calculating external quantum efficiency (EQE) with varying injection current. The EL spectra of three samples show different emission wavelength peaks, FWHM and the blueshift of wavelength caused by screening the internal electric field because of the effect of different MQW structure. The results of optical properties show that the LED_2 sample reduce the internal electric field in QW than LED_1 from EL spectra. the increase in the number of QW pairs reduces the strain and increase the In composition in MQW. And, the points of efficiency droop's peak show different trend from LED_1 to LED_3. It is related with the carrier density in active region. Thus, from the results of experiments, we are able to achieve high performance LEDs and a reduction of efficiency droop and emission wavelength blueshift by optimizing MQWs structure.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2011년도 춘계학술대회 및 Fine pattern PCB 표면 처리 기술 워크샵
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• pp.180-181
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• 2011

기존의 GaN LED에 사용되어지고 있는 p형 GaN 반도체의 Ni/Au 투명 접촉 전극을 제조할 때 발생하는 오염과 공정을 줄이고 발광효율을 향상시킬 수 있는 투명 접촉 전극을 제작하기 위해 마그네트론 2원 동시 방전법을 사용하여 AZO-NiO 박막을 증착 하였다. Al 원자 함량에 따른 AZO-NiO 박막의 구조적, 전기적, 광학적 특성을 조사하였다.

• Bulletin of the Korean Chemical Society
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• 제30권2호
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• pp.419-422
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• 2009

The luminescence intensity of calcium sulfide codoped with $Eu^{2+},\;Si^{4+}\;and\;Ga^{3+}$ was investigated as a function of the dopant concentration. An enhancement of the red luminescence resulted from the incorporation of $Si^{4+}\;and\;Ga^{3+}\;into\;CaS:Eu^{2+}.\;The\;non-codoped\;CaS:Eu^{2+}$ converted only 3.0% of the absorbed blue light into luminescence. As the $Si^{4+}\;and\;Ga^{3+}$ were embedded into the host lattice, the luminescence intensity increased and reached a maximum of Q = 10.0% at optimized concentrations of the codopants in CaS. Optimized CaS:$Eu^{2+},Si^{4+},Ga^{3+}$ phosphors were fabricated with blue GaN LED and the chromaticity index of the phosphor-formulated GaN LED was investigated as a function of the wt% of the optimized phosphor.