• Journal of the Korean Physical Society
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• 제73권12호
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• pp.1879-1883
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• 2018

We analyzed the deep-trap states of GaN/InGaN ultraviolet light-emitting diodes (UV LEDs) before and after electrical stress. After electrical stress, the light output power dropped by 5.5%, and the forward leakage current was increased. The optical degradation mechanism could be explained based on the space-charge-limited conduction (SCLC) theory. Specifically, for the reference UV LED (before stress), two sets of deep-level states which were located 0.26 and 0.52 eV below the conduction band edge were present, one with a density of $2.41{\times}10^{16}$ and the other with a density of $3.91{\times}10^{16}cm^{-3}$. However, after maximum electrical stress, three sets of deep-level states, with respective densities of $1.82{\times}10^{16}$, $2.32{\times}10^{16}cm^{-3}$, $5.31{\times}10^{16}cm^{-3}$ were found to locate at 0.21, 0.24, and 0.50 eV below the conduction band. This finding shows that the SCLC theory is useful for understanding the degradation mechanism associated with defect generation in UV LEDs.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.191.2-191.2
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• 2013

The negative photoconductivity was frequently observed in some semiconductors. It was known that the origin of the negative photoresponse from ZnO is molecular chemisorption or the charging effect of nanoparticles in bulk matrix. However, the origin of the negative photoresponse of thin film was not still clear. One of possible explanation is due to the deep level trap scheme, which describes the origin of the negative photoresponse via defect state under illumination of light. However, the defect states below Fermi level have high capture rate by Coulomb effect, so that these states are usually filled by electrons if the defect states have donor-like character. Therefore the condition which the defect states located in below Fermi level should be partially filled by electrons make more difficult to understand of mechanism of the negative photoresponse. In this study, n-ZnO/p-Si heterojunction diodes were fabricated by UHV RF magnetron sputter. Then, some diodes show the negative photoresponse under ultra-violet light illumination. The defect state of the ZnO was analyzed by photoluminescence and deep level transient spectroscopy. To interpret the negative photoconductivity, band diagram was simulated by using SCAPS program.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2006년도 6th International Meeting on Information Display
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• pp.718-722
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• 2006

The dependence of n-channel 2 shot SLS poly-Si TFT characteristics on the DOS (density of states) parameters was investigated by using a device simulation. Device performances were most sensitive to the DOS of poly-Si/gate insulator (GI) interface and poly-Si active layer. Deep level states at the poly-Si/GI interfaces strongly affect the subthreshold slope.

• Bulletin of the Korean Chemical Society
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• 제19권6호
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• pp.628-634
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• 1998

The properties of the n-type impurities nitrogen and phosphorus in diamond have been investigated by means of electronic band structure calculations within the framework of the semiempirical extended Huckel tight-binding method. For diamond with the nitrogen and phosphorus substitutional impurities, calculated density of states shows the impurity level deep in the band gap. This property can be derived from the substantial <111> relaxation of the impurity and nearest-neighbor carbon atoms, which is associated with the population of an antibonding orbital between them. The passivated donor property of the P-vacancy complex which lies deep in the gap is also discussed.

• Structural Monitoring and Maintenance
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• 제4권3호
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• pp.269-299
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• 2017

This paper presents a Level III damage evaluation methodology, which simultaneously, identifies the location, the extent, and the severity of stiffness damage in deep beams. Deep beams are structural elements with relatively high aspect (depth-to-length) ratios whose response are no longer based on the simplified Euler-Bernoulli theory. The proposed methodology is developed on the bases of the force-displacement relations of the Timoshenko beam theory and the concept of invariant stress resultants, which states that the net internal force existing at any cross-section of the beam is not affected by the inflicted damage, provided that the external loadings in the undamaged and damaged beams are identical. Irrespective of the aspect ratios, local changes in both the flexural and the shear stiffnesses of beam-type structures may be detected using the approach presented in this paper.

• 한국진공학회지
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• 제19권3호
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• pp.199-205
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• 2010

수열합성법(hydrothermal) 방식으로 성장한 ZnO 기판에 고에너지의 전자빔을 조사시킨 후 쇼트키(Schottky)다이오드를 제작하여 결함상태와 전기적 특성 변화를 조사하였다. 1 MeV 및 2 MeV 전자빔으로 $1{\times}10^{16}$ electrons/$cm^2$ dose로 기판의 Zn 면에 조사하였다. 1 MeV 전자빔이 조사된 시료에서는 표면에 전자빔 유도결함을 형성시켜 누설전류를 증가시켰고, 2 MeV 전자빔의 경우는 오히려 다이오드 누설절류 감소와 on/off 특성을 향상시키는 것으로 나타났다. 이들 시료에 대한 DLTS (deep level transient spectroscopy) 측정결과 전자빔 조사에 따른 전기적 물성변화는 활성화에너지와 포획단면적이 각각 $E_c$-0.33 eV 및 $2.97{\times}10^{15}\;cm^{-2}$인 O-vacancy가 주된 연관성을 보였으며, 활성화에너지 $E_v$+0.8 eV인 결함상태도 새롭게 완성되었다.

• 정보과학회 논문지
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• 제44권6호
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• pp.607-612
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• 2017

도시에서 홍수 피해를 방지하기 위한 침수를 예측하기 위해 본 논문에서는 딥러닝(Deep Learning) 기법을 적용한다. 딥러닝 기법 중 시계열 데이터 분석에 적합한 Recurrent Neural Networks (RNNs)을 활용하여 강의 수위 관측 데이터를 학습하고 침수 가능성을 예측하였다. 예측 정확도 검증을 위해 사용한 데이터는 미국의 트리니티강의 데이터로, 학습을 위해 2013 년부터 2015 년까지 데이터를 사용하였고 평가 데이터로는 2016 년 데이터를 사용하였다. 입력은 16개의 레코드로 구성된 15분단위의 시계열 데이터를 사용하였고, 출력으로는 30분과 60분 후의 강의 수위 예측 정보이다. 실험에 사용한 딥러닝 모델들은 표준 RNN, RNN-BPTT(Back Propagation Through Time), LSTM(Long Short-Term Memory)을 사용했는데, 그 중 LSTM의 NE(Nash Efficiency)가 0.98을 넘는 정확도로 기존 연구에 비해 매우 높은 성능 향상을 보였고, 표준 RNN과 RNN-BPTT에 비해서도 좋은 성능을 보였다.

• 방사성폐기물학회지
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• 제15권4호
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• pp.301-312
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• 2017

The concept of deep borehole disposal (DBD) for high-level nuclear wastes has been around for about 40 years. Now, the Department of Energy (DOE) in the United States (U.S.) is re-examining this concept through recent studies at Sandia National Laboratory and a field test. With DBD, nuclear waste will be emplaced in boreholes at depths of 3 to 5 km in crystalline basement rocks. Thinking is that these settings will provide nearly intact rock and fluid density stratification, which together should act as a robust geologic barrier, requiring only minimal performance from the engineered components. The Nuclear Waste Technical Review Board (NWTRB) has raised concerns that the deep subsurface is more complicated, leading to science, engineering, and safety issues. However, given time and resources, DBD will evolve substantially in the ability to drill deep holes and make measurements there. A leap forward in technology for drilling could lead to other exciting geological applications. Possible innovations might include deep robotic mining, deep energy production, or crustal sequestration of $CO_2$, and new ideas for nuclear waste disposal. Novel technologies could be explored by Korean geologists through simple proof-of-concept experiments and technology demonstrations.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.314-314
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• 2012

The dilute magnetic semiconductors (DMS) have been developed to multi-functional electro-magnetic devices. Specially, the Si based DMS formed by ion implantation have strong advantages to improve magnetic properties because of the controllable effects of carrier concentration on ferromagnetism. In this study, we investigated the deep level states of Fe- and Co-ions implanted Si wafer during rapid thermal annealing (RTA) process. The p-type Si (100) wafers with hole concentration of $1{\times}10^{16}cm^{-3}$ were uniformly implanted by Fe and Co ions at a dose of $1{\times}10^{16}cm^{-2}$ with an energy of 60 keV. After RTA process at temperature ranges of $500{\sim}900^{\circ}C$ for 5 min in nitrogen ambient, the Au electrodes with thickness of 100 nm were deposited to fabricate a Schottky contact by thermal evaporator. The surface morphology, the crystal structure, and the defect state for Fe- and Co- ion implanted p-type Si wafers were investigated by an atomic force microscopy, a x-ray diffraction, and a deep level transient spectroscopy, respectively. Finally, we will discuss the physical relationship between the electrical properties and the variation of defect states for Fe- and Co-ions implanted Si wafer after RTA.

• 한국초등수학교육학회지
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• 제20권2호
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• pp.239-257
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• 2016

미국의 새 수학과 규준인 Common Core State Standards for Mathematics는 잘 알려진 것처럼 모든 학생이 대학에 진학하거나 직업에 종사하기위한 준비를 위해 명료하고 일관된 틀을 제공하는 것을 목표로 개발되어, 현재 40개의 주가 이 새로운 규준을 채택하고 있다. 이 규준에 관한 최근 우리나라의 선행연구들은 규준을 Cluster Heading 수준에서 소개하고 있고, 규준의 수준에서 우리나라의 교육과정과 비교하고 있다. 그러니 실제로 각 세부 규준의 내용을 상세하게 해석한 내용은 수면 아래의 모습을 보여 준다. 캘리포니아 주의 수학과 규준의 내용을 상세하게 해석한 책이 Mathematics Framework for California Public Schools이다. 이 연구는 미국 캘리포니아 주의 수학과 규준인 California Common Core State Standards(CA CCSSM)와 이 규준의 해설서라고 부르기에 적당한 Mathematics Framework for California Public Schools에서 제시한 초등학교 도형영역을 상세하게 살펴보는 것이 목적이다.