• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 추계학술대회 논문집 Vol.16
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• pp.412-414
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• 2003

This paper is about research of scintillator layer, which is used for Hybrid method to increase electric signals in a-Se, the material of Direct method. In case of the thermal evaporation, CsI has column structure which is an disadvantage as scintillator. But it decreases scattering of incident X-ray, has better Light output intensity than other scintillation materials. CsI was made by Thermal evaporation. The Doping material, Na, 0.1, 0.3, 0.5, 0.7g were added in each sample. Analysis of absorbed wavelength, PL(Photoluminescence), Light output intensity, SEM, and XRD analysis were performed to analyze optical characteristics. Doping rate of CsI:Na to use as scintillation layer in a-Se based detector could be optimized.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.69-69
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• 2010

The research is the structural and optical characteristics of the Cadmium Sulfide(CdS) film, nanowires and nanobelts grown on the $Al_2O_3$ substrate using the vapor phase epitaxy method. The field-emission scanning electron microscopy(FE-SEM) were used to identify the shape of the surface of the nanostructures and x-ray diffraction(XRD) and transmission electron microscopy (TEM) were used to evaluate the structural characterisitcs. As a result, the XRD was confirmed the CdS peak and the substrate peak and TEM showed single crystals with wurtzite hexagonal structure on the nanostructures. As for the optical characteristic of the nanostructures, photoluminescence(PL) and micro-raman spectrum were measured. The PL measurements confirmed the emission peak related bound exciton to neutral donor($D^0X$) peak and free exciton(FX) peak. The micro-raman spectrum showed that the peak of the nanostructures were similar to the pure crystalline CdS peak and each peak were overtone of LO phonon of the hexagonal CdS of the longitudinal optical(LO) phonon mode. Therefore, it is confirmed that the CdS nanostructures grown in this research have superior crystallinity.

• 한국재료학회지
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• 제18권10호
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• pp.511-514
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• 2008

We have synthesized $Eu^{3+}$-doped $YVO_4$ phosphors by using a hydrothermal method and investigated their luminescent properties. Aqueous solutions of $Y_2O_3,\;V_2O_5,\;Eu_2O_3$, and nitric acid with various pH values were used as the precursors. The crystallinity, surface condition, and emission characteristics were examined using XRD, FT-IR, and photo-excited spectrometer. $Eu^{3+}$ incorporation followed by the efficient red emission strongly depends on the acidity of solution media. The emission intensity becomes stronger as the pH values increase to 7 and then gradually decreases. This phenomenon might be related to the hydroxyl quenching effect, which is induced by surface bound OH-groups.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2012년도 춘계학술발표회 논문집
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• pp.236-237
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• 2012

ZnO nanorods were grown on R-plane sapphire substrates with the seed layers annealed at different temperature. The effects of annealing temperature for the seed layers on the properties of the ZnO nanorods were investigated by scanning electron microscopy, X-ray diffraction, UV-visible spectroscopy, and photoluminescence. For the as-prepared seed layers, the ZnO nanorods and the ZnO nanosheets were observed. Only the ZnO nanorods were grown as the annealing temperature was above $700^{\circ}C$. The optical transmittance in the UV region was almost zero while that in the visible region was gradually increased as the annealing temperature increased to $700^{\circ}C$. The optical band gap of the ZnO nanorods was increased as the annealing temperature increased to $700^{\circ}C$. In the visible region, the refractive index was decreased with increasing the wavelength, and the extinction coefficient was decreased as the annealing temperature increased to $700^{\circ}C$. The non-linear exciton radiative life time of the FX emission peak was established by cubic equation. The values of Varshni's empirical equation fitting parameters were ${\alpha}=4{\times}10^{-3}eV/K$, ${\beta}=1{\times}10^4K$, and $E_g(0)=3.335eV$ and the activation energy was found to be about 94.6 meV.

• Journal of Ceramic Processing Research
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• 제19권5호
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• pp.439-443
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• 2018

The outstanding characteristics of high quality GaN single crystal substrates make it possible to apply the manufacture of high brightness light emitting diodes and power devices. However, it is very difficult to obtain high quality GaN substrate because the process conditions are hard to control. In order to effectively control the formation of GaN polycrystals during the bulk GaN single crystal growth by the HVPE (hydride vapor phase epitaxy) method, a quartz ring was introduced in the edge of substrate. A variety of evaluating method such as high resolution X-ray diffraction, Raman spectroscopy and photoluminescence was used in order to measure the effectiveness of the quartz ring. A secondary ion mass spectroscopy was also used for evaluating the variations of impurity concentration in the resulting GaN single crystal. Through the detailed investigations, we could confirm that the introduction of a quartz ring during the GaN single crystal growth process using HVPE is a very effective strategy to obtain a high quality GaN single crystal.

• 대한금속재료학회지
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• 제46권4호
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• pp.217-222
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• 2008

Characteristics of etching and induced surface morphology variation by wet-etching of n-face n-type GaN were investigated using KOH solutions. It was observed that hexagonal pyramids were formed on the etched surface regardless of etching conditions. However, the size of the hexagonal pyramids was changed as the etching time and temperature increased, respectively. Initially, as the etching time and concentration of KOH solution increased, the hexagonal pyramid was observed to be dissociated into smaller pyramids. However, as the etching time increased further, the size of the hexagonal pyramids increased again, indicating that the etching of N-face n-type GaN by KOH solutions proceeded through the evolution of hexagonal pyramids, such as formation, dissociation and enlargement of pyramids. Furthermore, it was also observed that there is a correlation between the photoluminescence intensity of the etched surface and the value of root-mean-square roughness. The intensity of PL increased as the roughness value increased due to the enhancement of the extraction efficiency of the generated photons.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.184-184
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• 2012

Recently, InGaN/GaN multi-quantum well grown on GaN pyramid structures have attracted much attention due to their hybrid characteristics of quantum well, quantum wire, and quantum dot. This gives us broad band emission which will be useful for phosphor-free white light emitting diode. On the other hand, by using quantum dot emission on top of the pyramid, site selective single photon source could be realized. However, these structures still have several limitations for the single photon source. For instance, the quantum efficiency of quantum dot emission should be improved further. As detection systems have limited numerical aperture, collection efficiency is also important issue. It has been known that micro-cavities can be utilized to modify the radiative decay rate and to control the radiation pattern of quantum dot. Researchers have also been interested in nano-cavities using localized surface plasmon. Although the plasmonic cavities have small quality factor due to high loss of metal, it could have small mode volume because plasmonic wavelength is much smaller than the wavelength in the dielectric cavities. In this work, we used localized surface plasmon to improve efficiency of InGaN qunatum dot as a single photon emitter. We could easily get the localized surface plasmon mode after deposit the metal thin film because lnGaN/GaN multi quantum well has the pyramidal geometry. With numerical simulation (i.e., Finite Difference Time Domain method), we observed highly enhanced decay rate and modified radiation pattern. To confirm these localized surface plasmon effect experimentally, we deposited metal thin films on InGaN/GaN pyramid structures using e-beam deposition. Then, photoluminescence and time-resolved photoluminescence were carried out to measure the improvement of radiative decay rate (Purcell factor). By carrying out cathodoluminescence (CL) experiments, spatial-resolved CL images could also be obtained. As we mentioned before, collection efficiency is also important issue to make an efficient single photon emitter. To confirm the radiation pattern of quantum dot, Fourier optics system was used to capture the angular property of emission. We believe that highly focused localized surface plasmon around site-selective InGaN quantum dot could be a feasible single photon emitter.

• 한국결정성장학회지
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• 제9권1호
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• pp.107-112
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• 1999

고주파 반응성 스퍼터링에 의하여 ZnSe/GaAs 박막을 성장하였다. 박막성장을 위한 본 시스템에서의 최적조건을 찾기 위하여 Ar 압력, sputter 입력전력, 기판온도, 기판과 target 간격의 변화 등을 시도하였다. 성장된 결정의 표면과 격면을 전자현미경으로 관찰했을 때 표면이 균일하게 성장되었으며 기판과 박막의 계면이 평활함을 알 수 있었다. DCRC 측정에 의해 격자 부정합에 의한 변형과 부정합률을 구했다. Photoluminescence 측정으로부터 질소를 주입하지않고 성장한 ZnSe/GaAs 시료는 bound exciton $I_2$세기가 $I_1$보다 우세하게 나타났고 bound exciton $I_2$은 깊은 받개준위인 $I_1\;^d$를 나타냄을 확인할 수 있었다. 성장 중에 질소를 주입한 ZnSe/GaAs 시료에서는 $I_1$ 봉우리가 $I_2$봉우리보다 세기가 매우 컸으며 반폭치값도 작게 나타났다. 이때 bound exciton $I_1$의 근원은 질소의 doping으로 인하여 방출되는 봉우리이며 p형 ZnSe/GaAs 박막으로 성장되었음을 확인하였다.

• 한국결정성장학회지
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• 제20권3호
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• pp.113-116
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• 2010

본 논문에서는 Sb를 촉매제로 이용하는 경우의 InGaN 나노구조의 성장과 구조적 특징 및 광학적 특성에 대해서 연구하였다. 결정성장에 있어서 촉매제의 사용은 성장 모드의 변화와 결정 결함의 감소 등을 위한 목적으로 많이 사용되어왔다. 본 연구에서는 혼합소스 HVPE(hydride vapor phase epitaxy) 사용하여 (0001) 사파이어 기판 위에 InGaN 나노구조를 성장하였고, 구조적 및 광학적 특성은 scanning electron microscope(SEM)과 photoluminescence(PL)를 통해 평가하였다. Sb이 첨가되지 않은 경우에는 InGaN 나노구조가 c-축 방향으로 정렬되는 경향을 보이지만 Sb이 첨가된 경우에는 InGaN 나노구조의 c-축 방향이 기판에 대해 평행하거나 경사진 방향으로 정렬되고 있는 것을 관찰할 수 있었다. In의 조성은 Sb 의 첨가 여부에 관계없이 약 3.2% 정도로 계산되었다. 이러한 결과들로부터 측면 배향된 나노입자를 활성층으로 하는 광소자에 적용할 경우 압전 전계를 완화할 수 있기 때문에 광소자의 발광 성능을 향상시킬 수 있을 것으로 기대된다.

• 대한전자공학회논문지SD
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• 제43권2호
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• pp.8-12
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• 2006

졸-겔 법으로 $Pt/TiO-2/SiO_2/Si$ 기판 위에 ZnO 박막을 제작하여, 열처리 온도에 따른 박막의 결정화 특성 및 미세구조와 광학적 특성을 조사하였다. XRD 측정 결과로부터, 열처리 온도가 $600^{\circ}C$ 일때 가장 우수한 c-축 배향성을 나타냈으며, 이때 반가폭은 $0.4360^{\circ}C$ 이었다. AFM 으로 ZnO 박막의 표면형상과 표면 거칠기를 관찰한 결과, $600^{\circ}C$ 열처리 온도에서 입자가 고르게 성장하여 치밀한 박막이 형성되었음을 관찰할 수 있었고, 표면 거칠기도 1.048nm 로 가장 우수한 값을 나타내었다. ZnO 박막의 열처리 온도에 따른 PL 특성을 조사한 결과, $600^{\circ}C$로 열처리된 ZnO 박막에서 자외선 영역의 발광 피크 (378nm)는 가장 크게 가시광 영역의 발광 피크 (510nm)는 가장 작게 관찰되었다. 가시광 영역의 발광 피크가 작은 것은 산소 공공 또는 불순물이 매우 적다는 것을 의미하므로, $600^{\circ}C$로 열처리된 ZnO 박막은 비교적 화학양론적으로 성장되었음을 확인할 수 있었다.