• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.32 no.5
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• pp.426-431
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• 2019

In this study, we report the effect of pre-treatment of alpha-$Ga_2O_3$ grown on a sapphire substrate by halide vapor phase epitaxy (HVPE). During the pre-treatment process, 10 sccm of GaCl gas was injected to the sapphire substrate at $470^{\circ}C$. The surface morphologies of the alpha-$Ga_2O_3$ layers grown with various pre-treatment time (3, 5, and 10 min) were flat and crack-free. The transmittance of the alpha-$Ga_2O_3$ epi-layers was measured to analyze their optical properties. The transmittance was over 80% within the range of visible light. The strain in the alpha-$Ga_2O_3$ grown with a pre-treat 5 min was measured, and was found to be close to the theoretical XRD peak position. This can be explained by the reduction of strain having caused a lattice mismatch between the alpha-$Ga_2O_3$ layer and sapphire substrate. The calculated dislocation density of the screw and edge were $2.5{\times}10^5cm^{-2}$ and $8.8{\times}10^9cm^{-2}$, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.135-135
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• 2010

본 연구에서는 ZnO를 기반으로 하여 $In_2O_3$, $Ga_2O_3$를 혼합한 IGZO 박막의 물성들을 분석하였다. 광학적 특성 결과 가시광 영역에서 모두 80%이상의 투과율을 나타내었으며, 전기적 특성을 조사한 결과 $In_2O_3:Ga_2O_3$:ZnO (1:9:90 wt.%)의 IGZO박막에서 $1.90{\times}10^{-3}\;\Omega/cm$의 비저항을 확인 할 수 있었다. 또한 상온에서 $400^{\circ}C$로 기판온도에 변화를 주어 실험하였으며, 결정성을 분석하기 위하여 XRD (PANALYTICAL CO.)를 사용하였고, SEM (JEOL CO.) 을 이용하여 IGZO박막의 미세 구조를 확인하였다. UV-ViS spectrophotometer (SHIMADZU CO.) 을 사용하여 광학적 특성을 측정하였으며, Hall effect측정 장비를 이용하여 캐리어 농도 및 Hall이동도 변화에 따른 비저항을 비교 분석하였다.

• Proceedings of the KIEE Conference
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• 2006.10a
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• pp.48-49
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• 2006

Highly conductive and transparent films of Ga-doped ZnO have been prepared by pulsed laser deposition using a ZnO target with 3 wt% ${Ga_2}{O_3}$ dopant. Films with the resistivity as low as $3.3{\times}10^{-4}{\Omega}cm$ and the transmittance above 80 % at the wavelength of 400 to 800 nm can be fabricated on glass substrate at room temperature. It is shown that a stable resistivity for the use in oxidation ambient at high temperature can be obtained for the films. Heat treatments were performed to examine the thermal stability of ZnO and GZO films at ptemperature range from $100^{\circ}C$ to $400^{\circ}C$ in $O_2$ ambient for 30 minutes. The resistivity of ZnO film annealed at $400^{\circ}C$ increased by two orders of magnitude, in case of GZO film was relatively stable up to at $400^{\circ}C$. For practical applications at high temperatures the thermal stability of resistivity of GZO thin films might become an advantage for transparent electrodes.

• Journal of Radiation Industry
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• v.10 no.4
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• pp.189-192
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• 2016

$^{68}Ga$ has emerged as a promising candidate for non-invasive diagnostic imaging within Positron Emission Tomography (PET) because of its advantageous radiochemical characteristics ($t_{1/2}=68min$, ${\beta}^+$ yield ~89%). $^{68}Ga$ forms a stable chelation with various ligands and it is possible to be quickly and easily study using a $^{68}Ge/^{68}Ga$ generator. Commercial $^{68}Ge/^{68}Ga$ generators are chromatographic system using the inorganic materials such as alumina and tin dioxide which are employed as column matrixes for $^{68}Ge$. In this study, we tried out to make $^{68}Ge/^{68}Ga$ generator system with the $^{68}GeO_2$ microstructures for column matrix. $^{68}Ge$ tends to have stable bond with oxide as $^{68}GeO_2$ microstructures. The $^{68}GeO_2$ has been synthesized by hydrolysis of $GeCl_4$ (sol-gel method) and characterized by X-ray diffraction and scanning electron microscope for geometrical analysis. The stability of $GeO_2$ was tested using eluents with diverse solvents(water, ethanol and 0.1 N HCl). The radioactivity of $^{68}Ga^{3+}$ in eluate through $GeO_2$ was measured to prove a function as column material for a generator.

• Korean Journal of Materials Research
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• v.19 no.8
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• pp.417-420
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• 2009

This study develops a highly transparent ohmic contact using phosphorus doped ZnO with current spreading for p-GaN to increase the optical output power of nitride-based light-emitting diodes (LEDs). The phosphorus doped ZnO transparent ohmic contact layer was prepared by radio frequency magnetron sputtering with post-deposition annealing. The transmittance of the phosphorus doped ZnO exceeds 90% in the region of 440 nm to 500 nm. The specific contact resistance of the phosphorus doped ZnO on p-GaN was determined to be $7.82{\times}10^{-3}{\Omega}{\cdot}cm^2$ after annealing at $700^{\circ}C$. GaN LED chips with dimensions of $300\times300{\mu}m$ fabricated with the phosphorus doped ZnO transparent ohmic contact were developed and produced a 2.7 V increase in forward voltage under a nominal forward current of 20 mA compared to GaN LED with Ni/Au Ohmic contact. However, the output power increased by 25% at the injection current of 20 mA compared to GaN LED with the Ni/Au contact scheme.

• Journal of the Korean Ceramic Society
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• v.38 no.2
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• pp.107-111
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• 2001

Sr$_{(1-x)}$Ca$_{x}$TiO$_3$: Pr$^{3+}$ , Ga$^{3+}$ (0$\leq$x$\leq$1) 형광체의 여기 및 발광 스펙트럼과 분광 반사율을 조사하여 발광 메커니즘을 규명하고자 하였다. 발광 스펙트럼에서는 611~614nm 사이에서 peak을 가지는 하나의 적색 발광 밴드가 관찰되었으며, 조성에 따라 발광밴드의 모양이 달랐다. 이는 조성에 따른 모체의 결정 구조 변화 때문으로 생각된다. 여기 스펙트럼 끝단과 분광 반사율 스펙트럼의 흡수단은 서로 일치하였으며, 이 결과로부터 모체에 흡수된 에너지가 Pr$^{3+}$ 에 전달되어 적색광을 방출하는 것이 주된 메커니즘으로 생각된다. 한편 120$0^{\circ}C$에서 4시간동안 열처리하여 합성한 Sr$_{0.4}$Ca$_{0.6}$TiO$_3$:(0.1 mol%)Pr$^{3+}$ , (0.2 mol%)Ga$^{3+}$ 는 우수한 색순도와 휘도를 나타내었다.다.

• Journal of the Korean Electrochemical Society
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• v.6 no.1
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• pp.59-64
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• 2003

We fabricated mixed ionic-electronic conducting membranes, $CH_4\;Using\;{0.7}Sr_{0.3}Ga_{0.6}Fe_{0.4}O_{3-\delta}$, by solid state reaction method for solid oxide fuel cell. The membranes consisted of single perovskite phase and exhibited high relative density, $>95\%$. We coated $La_{0.6}Sr_{0.4}CoO_{3-\delta}$ layer using screen printing method in order to improve surface reactivity of the $La_{0.7}Sr_{0.3}Ga_{0.6}Fe_{0.4}O_{3-\delta}$. As a result, the oxygen permeation flux of the coated $La_{0.7}Sr_{0.3}Ga_{0.6}Fe_{0.4}O_{3-\delta}$ showed higher value, $0.5ml/min{\cdot}cm^2\;at\;950^{\circ}C$ than the uncoated one. Higher oxygen permeation was observed in the porously coated Lao $La_{0.7}Sr_{0.3}Ga_{0.6}Fe_{0.4}O_{3-\delta}$membranes with larger grain sizes. Syngas, $CO+H_2$, was successfully obtained from methane gas, $CH_4$, using the $La_{0.6}Sr_{0.4}CoO_{3-\delta}$ coated $La_{0.7}Sr_{0.3}Ga_{0.6}Fe_{0.4}O_{3-\delta}$, with over $40\%\;of\;CH_4$ conversion and syngas yield. $La_{0.7}Sr_{0.3}Ga_{0.6}Fe_{0.4}O_{3-\delta}$ membrane was stable even when it was exposed to the reducing environment, methane, for 600 hrs at $950^{\circ}C$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.574-577
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• 2001

GaN thin films on sapphire were grown by rf magnetron sputtering with ZnO buffer layer. The dependence of GaN film quality on ZnO buffer layer was investigated by X-ray diffraction(XRD). The improved film quality has been obtained by using thin ZnO buffer layer. Using Auger electron spectroscopy(AES), it was observed that the annealing process improved the GaN film quality. The surface roughness according to the annealing temperatures(700, 900, 1100$^{\circ}C$) were investigated by AFM(atomic force microscopy) and it was confirmed that the crystallization was improved by increasing the annealing temperature. Photoluminescence at 8K shows a near-band-edge peak at 3.2eV with no deep level emission.

• Transactions of the Korean hydrogen and new energy society
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• v.12 no.2
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• pp.137-146
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• 2001

고상 반응법을 이용하여 $La_{0.7}Sr_{0.3}Ga_{0.6}Fe_{0.4}O_{3-{\delta}}$ 분말을 합성하고 혼합전도체 분리막을 소결하여 제조하였다. 제조된 분리막은 $LaGaO_3$에 일치하는 폐롭스카이트 결정구조를 나타내었으며 95% 이상의 높은 상대밀도를 나타내었다. 스크린 프린팅 방법으로 $La_{0.6}Sr_{0.4}CoO_{3-{\delta}}$ 후막을 disk의 양 표면에 코팅하였으며 코팅 막은 비교적 치밀한 미세구조를 나타내었다. 코팅되지 않은 분리막과 코팅된 분리막의 산소투과 성능을 비교 실험한 결과 $850^{\circ}C$에서 동일한 두께의 코팅된 분리막의 정상상태 산소 투과 유속이 $0.7{m{\ell}}/min.cm^2$ 정도로 코팅되지 않은 분리막에 비해 약 2~3배로 높게 나타났다.

• Journal of the Korean Ceramic Society
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• v.41 no.8
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• pp.573-577
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• 2004

We have synthesized a Eu$^{2＋}$-activated Sr$_3$MgSi$_2$ $O_{8}$ blue phosphor and investigated an attempt to develop blue LEDs by combining it with a InGaN blue LED chip (Len=405 nm). The InGaN-based Sr$_3$MgSi$_2$ $O_{8}$：Eu LED Lamp shows two bands at 405 nm and 460 nm. The 405 nm emission band is due to a radiative recombination from a InGaN active layer. This 405 nm emission was used as an optical transition of the Sr$_3$MgSi$_2$ $O_{8}$：Eu phosphor. The 460 m emission band is ascribed to a radiative recombination of Eu$^{2＋}$ impurity ions in the Sr$_3$MgSi$_2$ $O_{8}$ host matrix. As a consequence of a preparation of W blue LED Lamp using the Sr$_3$MgSi$_2$ $O_{8}$：Eu blue phosphor, the highest luminescence efficiency was obtained at the ration of epoxy/blue phosphor(1/0,202). At this time, the CIE chromaticity was x=0.1417 and y=0.0683.