• Journal of IKEEE
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• v.27 no.1
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• pp.19-24
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• 2023

Since silicon having a band gap energy of about 1.12 eV are limited to a maximum operating temperature of less than 250 ℃, the sample with MIS structure based on the SiC substrate of wide-band gap energy was manufactured and the hydrogen response characteristics at high temperatures were investigated. The dielectric layer applied here is a tantalum oxide layer that is highly permeable to hydrogen gas and shows stability at high temperatures. It was formed by RTO at a temperature of 900 ℃ with tantalum. The thickness, depth profiles, and leakage current of the tantalum oxide layer were analyzed through TEM, SIMS, and leakage current characteristics. For the hydrogen gas response characteristics, the capacitance change characteristics were investigated in the temperature range from room temperature to 400 ℃ for hydrogen gas concentrations from 0 to 2,000 ppm. As a result, it was confirmed that the sample exhibited excellent sensitivity and a response time of about 60 seconds.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.82.1-82.1
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• 2010

수소화된 비정질 실리콘 박막을 이용한 반도체는 현재 태양전지, 트랜지스터, 매트릭스 배열 및 이미지 센서 등의 분야에서 이용되고 있다. 자세히 이야기 하면, 여러 가지의 광전효과 물질에 대한 특성이 있으며, 가시광선영역에 대하여 > $10^5cm^{-1}$이상의 매우 높은 광흡수계수와 낮은 온도를 갖는 증착공정 등이 있다. 박막의 밴드갭은 약 1.6~1.8eV로서 태양전지의 흡수층과 passivation층으로 적절하다. 여러 가지 종류의 태양전지 중 비정질 실리콘 박막/결정질 실리콘 기판의 구조로 이루어진 이종접합 태양전지는 저온에서 공정이 가능한 대표적인 것으로서 HIT(Heterojunction with Intrinsic Thin layer)구조로 산요사에 의해 제안된 것이다. 이것은 결정질 실리콘 기판과 도핑된 비정질 실리콘 박막사이에 얇은 진성층 비정질실리콘 박막을 삽입함으로서, 캐리어 전송을 좋게하여 실리콘 기판 표면의 passivation효과를 증대시키는 결과를 가지고 온다. 실험실 규모에서는 약 20%이상의 효율을 보이고 있으며, 모듈에서는 19.5%의 높은 효율을 보이고 있어 실리콘 기판을 이용한 고효율 태양전지로서 각광을 받고 있다. 이러한 이종접합 태양전지의 대부분은 단결정 실리콘을 사용하고 있는데, 점차적으로 다결정 실리콘 기판으로 추세가 바뀌고 있어, 여기에 맞는 표면 passivation 공정 및 분석이 필요하다. 본 발표에서는 다결정 실리콘 기판위에 진성층 비정질 실리콘 박막을 유도결합 플라즈마 화학기상 증착법(ICP-CVD)을 이용하여 제조하여 passivation 효과를 분석한다. 일반적으로 ICP는 CCP(coupled charged plasma)에 비해 약 100배 이상 높은 플라즈마 밀도를 가지고 있으며, 이온 충돌같은 표면으로 작용하는 것들이 기존 방식에 비해서 작다라는 장점이 있다. 먼저, 유리기판을 사용하여 ICP-CVD 챔버내에 이송 한 후 플라즈마 파워, 온도 및 가스비(SiH4/H2)에 따른 진성층 비정질 실리콘 박막을 증착 한 후, 밴드갭, 전도도 및 결합구조 등에 대한 결과를 분석한 후, 최적의 값을 가지고 250um의 두께를 갖는 다결정 실리콘을 기판위에 증착을 한다. 두께(1~20nm)에 따라 표면의 passivation이 되는 정도를 QSSPCD(Quasi steady state Photoconductive Decay)법에 의하여 소수캐리어의 이동거리, 재결합율 및 수명 등에 대한 측정 및 분석을 통하여 다결정 실리콘 기판의 passivation effect를 확인한다. 제시된 데이터를 바탕으로 향후 다결정 HIT셀 제조를 통해 태양전지 효율에 대한 특성을 비교하고자 한다.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.163-163
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• 2010

중적외선 영역 ($3{\sim}5\;{\mu}m$)은 공기 중에 존재하는 이산화탄소나 수증기에 의해 흡수가 일어나지 않기 때문에 군사적으로 중요한 파장 영역이며, 야간에 적을 탐지하는데 응용되고 있다. InSb는 77 K에서 중적외선 파장 흡수에 적합한 밴드갭 에너지 (0.228 eV)를 갖고 있으며, 다른 화합물 반도체와 달리 전하 수송자 이동도 (전자: $10^6\;cm^2/Vs$, 정공: $10^4\;cm^2/Vs$)가 매우 빠르기 때문에 적외선 화상 감지기 재료로 매우 적합하다. 또한 현재 중적외선 영역대에서 널리 사용되는 HgCdTe (MCT)와 대등한 소자 성능을 나타냄과 동시에 낮은 기판 가격, 소자의 제작 용이성 때문에 MCT를 대체할 물질로 주목 받고 있다. 하지만, 기판과 절연막의 계면에 존재하는 결함 때문에 에너지 밴드갭 내에 에너지 준위를 형성하여 높은 누설 전류 특성을 보인다. 따라서 InSb 적외선 소자의 구현을 위하여 고품질의 절연막의 연구가 필수적이라고 할 수 있겠다. 절연막의 특성을 알아보기 위해, n형 InSb 기판에 플라즈마 화학 기상 증착법 (PECVD)을 이용하여 $SiO_2$, $Si_3N_4$를 증착하였으며, 증착 온도를 $120^{\circ}C$에서 $240^{\circ}C$까지 $40^{\circ}C$ 간격으로 변화하여 증착온도가 미치는 영향에 대하여 알아보았다. 절연막과 기판의 계면 특성을 분석하기 위하여 77 K에서 커패시턴스-전압 (C-V) 분석을 하였으며, 계면 트랩 밀도는 Terman method를 이용하여 계산하였다 [1]. $Si_3N_4$를 증착하였을 경우, $120{\sim}240^{\circ}C$의 증착 온도에서 $2.4{\sim}4.9{\times}10^{12}\;cm^{-2}eV^{-1}$의 계면 트랩 밀도를 가졌으며, 증착 온도가 증가할수록 계면 트랩 밀도가 증가하는 경향을 보였다. 또한 모든 증착 온도에서 flat band voltage가 음의 전압으로 이동하였다. $SiO_2$의 경우 $120{\sim}200^{\circ}C$의 증착온도에서 $7.1{\sim}7.3{\times}10^{11}\;cm^{-2}eV^{-1}$의 계면 트랩 밀도 값을 보였으나, $240^{\circ}C$ 이상에서 계면 트랩밀도가 $12{\times}10^{11}\;cm^{-2}eV^{-1}$로 크게 증가하였다. $SiO_2$ 절연막을 사용함으로써, $Si_3N_4$ 대비 약 25% 정도 낮은 계면 트랩 밀도를 얻을 수 있었으며, 모든 증착 온도에서 양의 전압으로 flat band voltage가 이동하였다. 두 절연막에 대한 계면 트랩의 원인을 분석하기 위하여 XPS 측정을 진행하였으며, 깊이에 따른 조성 분석을 하였다. 본 실험에서 최적화된 $SiO_2$ 절연막을 이용하여 InSb 소자의 pn 접합 연구를 진행하였다. Be+ 이온 주입을 진행하고, 급속열처리(RTA) 공정을 통하여 p층을 형성하였다. -0.1 V에서 16 nA의 누설 전류 값을 보였으며, $2.6{\times}10^3\;{\Omega}\;cm^2$의 RoA (zero bias resistance area)를 얻을 수 있었다.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.4
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• pp.121-127
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• 2022

β-Gallium oxide (Ga₂O₃), an ultra-wide bandgap semiconductor, has attracted great attention due to its promising applications for high voltage power devices. The most stable phase among five different polytypes, β-Ga₂O₃ has the wider bandgap of 4.9 eV and higher breakdown electric field of 8 MV/cm. Furthermore, it can be grown from melt source, implying higher growth rate and lower fabrication cost than other wide bandgap semiconductors such as SiC, GaN and diamond for the power device applications. In this study, β-Ga₂O₃ bulk crystals were grown by the edge-defined film-fed growth (EFG) process. The growth direction and the principal surface were set to be the [010] direction and the (100) plane of the β-Ga₂O₃ crystal, respectively. The spectra measured by Raman an alysis could exhibit the crystal phase an d impurity dopin g in the β-Ga₂O₃ ingot, and the crystallinity quality and crystal direction were analyzed using high-resolution X-ray diffraction (HRXRD). The crystal quality and various properties of as-grown β-Ga₂O₃ ribbon was systematically analyzed in order to investigate the spatial variation in entire crystal grown by EFG method.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.4
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• pp.871-877
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• 2008

It is important to investigate the relationship between weld process parameters and weld bead geometry for adaptive arc robot welding. Howeve, it is difficult to predict an exact back-bead owing to gap in process of butt welding. In this paper, the quantitative prediction system to specify the relationship external weld conditions and weld bead geometry was developed to get suitable back-bead in butt welding which is widely applied on industrial field. Multiple regression analysis for the prediction of process parameters was used as the research method. And, the results of the prediction method were compared and analyzed.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1988.05a
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• pp.33-34
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• 1988

Recent developments in characterization techniques for solar cells are reviewed. First, general rules of material selection for solar cells such as $CuInSe_2$ and amorphous silicon of photovoltaic application are studied. Secondly, a method to obtain correct cell efficiency measurements under AM1 condition is introduced. Thirdly, various characterization techniques for solar cells are discussed. A special emphasis is given to up-scaling and computer control of the characterizations in the following systems; cell I-V characteristics for cell efficiency and other cell parameters, spectral response for quantum efficiency, surface photovoltage for diffusion length of minority carriers, and photothermal deflection for density of states in energy gaps.

• Journal of dental hygiene science
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• v.2 no.1
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• pp.1-9
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• 2002

The objection of this present study are (1) measurement of patient's expectation toward quality care of dental services. (2) Analysis of differential expectation of dental service by the patient characteristics and (3) presentation of measurement implication for better dental service at the dental clinic. The data used in the study were collected from April 25 to June 9, 2001 and for 77 patients of university dental hospital and 102 patients of dental clinic. The study found, in general, that patient's expectation on the clinic environmental factor was most highly scored followed by dental human factors. The convenience of transportation from the patient's residence to the clinic was highly concerned as be an important factor in dental service utilization.

• KDI Journal of Economic Policy
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• v.34 no.4
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• pp.117-156
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• 2012

This paper decomposes and estimates trend/cyclical components of some key macro variables-GDP, inflation, and interest rate, using a simple DSGE model along with flexible trend specification. The extracted cyclical components of output and interest rate are similar to HP-filtered counterparts, despite some differences in persistence and volatility, while inflation resembles that from BK filtering. This implies that the usual practice of applying a single filtering method to the data of interest may be problematic. When the baseline model is extended to incorporate consumption habit and price indexation, habit turns out to be important in explaining the persistence of business cycles. Comparison of several alternative models shows that the usual practice of estimation of DSGE model using filtered data leads to biased results. Finally, various sensitivity analyses illustrate that (1) allowing for correlation between structural cyclical shocks and trend shocks and (2) including irregular components (in inflation rate) may deliver interesting/important implication for gap estimates.

• Korea Trade Review
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• v.41 no.3
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• pp.27-42
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• 2016

This study is to investigate seaport clustering by using meta-frontier and cross-efficiency models. Data covers the 13 Asian ports during 2009, 2010 and 2013 with 3 inputs(depth, total area, and number of cranes) and 1 output(TEU). Correlations coefficient from cross-efficiency matrix are used for measuring clustering dendrogram. After that, meta-frontier analysis for investigating whether the clustering using cross-efficiency method increases the meta-efficiency. Empirical main results are as follows: First, group efficiencies of Busan, Incheon, and Gwangyang ports are increased. Second, meta and group efficiencies of China ports are greater than those of Korean ports. Third, distortion of technology gap of Gwangyang is lower than that of Busan and Incheon. Fourth, Gwangyang, clustering with Ningbo, Chingtao, Tokyo and Caosung ports in 2009 and with Dubai port in 2013 can increase the efficiency. Fifth, to enhance the efficiency, Busan port should be clustered to group 2 in 2010 and group 1 in 2013, and Incheon port clustered to group 2 in 2010 and 2013. Fifth, it is empirically investigated that Busan, Incheon and Gwangyang ports can increase the efficiency by using Cross-efficiency and Meta-frontier models. Port policy planner should promote the clustering policy for Busan with Hong Kong, Shanghai, and Singapore, Incheon and Gwangyang with Chingtao, Nagoya, Ningbo, Tokyo, and Kaoshung ports.

• Economic Analysis
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• v.25 no.2
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• pp.1-53
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• 2019

This paper examines monetary policy quantitatively in a two-agent and small-scale New-Keynesian economy with debt-constrained households that cannot smooth their consumption intertemporally and frictionlessly since highly indebted households are not allowed to borrow above a certain debt ceiling in incomplete financial markets without additional risk premiums due to information asymmetry between savers and borrowers. We find that, in the event of cost shocks, the asymmetric responses of borrowing households without, and saving households with, dividend incomes lead to different labor supplies and consumptions over heterogeneous households, and eventually to an extension of the monetary policy transmission channels. The income effect and low elasticity of the labor supply play key roles in such asymmetric responses over heterogeneous households. We also find that the social welfare in a flexible inflation targeting (FIT) monetary policy, in which both the inflation gap and the output gap are considered in an integrated manner when policy-making, is similar to that of the Ramsey optimal monetary policy (ROP), in which the shares of debt-constrained households, as well as all economic states, including both the inflation gap and output gap, are considered comprehensively for policy-making, and that it is greater than that of simple inflation targeting (SIT) monetary policy, in which only the inflation gap is considered mechanically for policy-making. Such social welfare implies that a FIT policy may still work even in an economy with a sizable number of debt-constrained households. Further, the responses of cost shocks to consumption and labor supply are dying out more slowly under FIT and ROP policies than under an SIT policy.