• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.1864-1865
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• 2007

In this paper, we proposed pre-filter algorithms which using frequency domain analysis method, for the detections of defects in large-sized Thin Film Transistor-Liquid Crystal Display(TFT-LCD) panel surfaces. We performed frequency analysis with 1-D, 2-D FFT methods for extract periodic patterns of lattice structures in TFT-LCDs. To remove this patterns, band-stop filters were used for eliminating specific frequency components. In order to acquire only defected images, we used 2-D inverse FFT methods which can be reverts images that remains defects.

• 한국전기전자재료학회논문지
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• 제32권3호
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• pp.192-195
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• 2019

Single-crystal diamond obtained by chemical vapor deposition (CVD) exhibits great potential for use in next-generation power devices. Low defect density is required for the use of such power devices in high-power operations; however, plastic deformation and lattice strain increase the dislocation density during diamond growth by CVD. Therefore, characterization of the dislocations in CVD diamond is essential to ensure the growth of high-quality diamond. In this work, we analyze the characteristics of the dislocations in CVD diamond through synchrotron white beam X-ray topography. In estimate, many threading edge dislocations and five mixed dislocations were identified over the whole surface.

• Bulletin of the Korean Chemical Society
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• 제11권4호
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• pp.339-342
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• 1990

$Gd_2O_3-ThO_2$ solid solutions containing 8,10 and 12 mol % $ThO_2$ were synthesized with spectroscopically pure $Gd_2O_3,$ and $ThO_2$ polycrystalline powders. X-ray diffraction revealed that all synthesized specimens have the modified fluorite structure, and the lattice parameter of $Gd_2O_3$ is nearly unchanged with increasing $ThO_2$ mol %. Both ac and dc conductivities were measured in the temperature range $500-1100^{\circ}C$ under $Po_2's$ from $10^{-6}$ to $10^{-1}$ atm. The dc conductivities are nearly independent of $Po_2,$ and agree with the ac values. This implies that the solid solutions are ionic conductors. The conductivity increases with increasing $ThO_2$ mol % with an average activation energy of 1.23 eV. An oxygen interstitial defect and ionic hopping conduction are suggested.

• 대한화학회지
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• 제31권6호
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• pp.491-497
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• 1987

고순도의 $ThO_2$와 $Tm_2O_3$로부터 대기압, 1,700$^{\circ}$C 이상에서 직접 고체상반응을 통하여 1,3,5,8,10 및 15 mol% $Tm_2O_3$를 함유하는 $ThO_2-Tm_2O_3$ (TDT)계들을 제조하였다. X-선 회절분석결과 TDT계들은 형석구조를 이루고 있음을 확인하였다. 또한, 도입된 $Tm_2O_3$의 양에 따라 격자상수의 값이 감소됨을 보였다. 그러나, 7mol% 이상의 $Tm_2O_3$를 함유하는 TDT계에서는 어떠한 직선관계도 나타나지 않았으므로 이러한 계들은 불완전 고용체를 형성하고 있다고 결론내렸다. X-선 강도 분석 결과로 부터 구한 잔류인자(R)는 모든 시료에 대하여 0.13이하의 값을 나타내었다. DTA 및 TGA 분석결과 실험온도범위 내에서는 어떠한 상전이도 나타나지 않는 것이 확인 되었다. X-선 회절 데이타로 부터 구한 격자상수와 비중병 밀도 측정결과와의 비교로부터 본시료들의 주 결함은 산소 공위임을 확인하였다.

• 한국결정성장학회지
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• 제30권1호
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• pp.1-6
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• 2020

본 연구에서는 패턴화된 사파이어 기판 위에 HVPE(Hydride Vapor Phase Epitaxy System) 법에 의해 50 nm 두께의 AlN thin film을 증착한 뒤, 에피층 구조가 MO CVD에서 성장되었다. AlN 버퍼층 박막의 표면형상이 SEM, AFM에 의해서, 에피층 구조의 GaN 박막의 결정성은 X-선 rocking curve에 의해 분석되었다. 패턴화된 사파이어 기판 위에 증착된 GaN 박막은, 사파이어 기판 위에 증착된 GaN 박막의 경우보다 XRD 피크 세기가 다소 높은 결과를 나타냈다. AFM 표면 형상에서 사파이어 기판 위에 AlN 박막이 증착된 경우, GaN 에피층 박막의 p-side 쪽의 v-pit 밀도가 상대적으로 낮았으며, 결함밀도가 낮게 관찰되었다. 또한, AlN 버퍼층이 증착된 에피층 구조는 AlN 박막이 없는 에피층의 광출력에 비해 높은 값을 나타냈다.

• 한국결정성장학회:학술대회논문집
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• 한국결정성장학회 1999년도 PROCEEDINGS OF 99 INTERNATIONAL CONFERENCE OF THE KACG AND 6TH KOREA·JAPAN EMG SYMPOSIUM (ELECTRONIC MATERIALS GROWTH SYMPOSIUM), HANYANG UNIVERSITY, SEOUL, 06월 09일 JUNE 1999
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• pp.187-207
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• 1999

The thermal distributions near the growth interface of 150mm CZ crystals were measured by three thermocouples installed at the center, middle (half radius) and edge (10m from surface) of the crystals. The results show that larger growth rates produced smaller thermal gradients. This contradicts the widely used heat flux balance equation. Using this fact, it si confirmed in CZ crystals that the type of point defects created is determined by the value of the thermal gradient (G) near the interface during growth, as already reported for FZ crystals. Although depending on the growth systems the effective lengths of the thermal gradient for defect generation are varied, were defined the effective length as 10mm from the interface in this experiment. If the G is roughly smaller than 20C/cm, vacancy rich CZ crystals are produced. If G is larger than 25C/cm, the species of point defects changes dramatically from vacancies to interstitial. The experimental results which FZ and CZ crystals are detached from the melt show that growth interfaces are filled with vacancy. We propose that large G produces shrunk lattice spacing and in order to relax such lattice excess interstitial are necessary. Such interstitial recombine with vacancies which were generated at the growth interface, next occupy interstitial sites and residuals aggregate themselves to make stacking faults and dislocation loops during cooling. The shape of the growth interface is also determined by the distributions of G across the interface. That is, the small G and the large G in the center induce concave and convex interfaces to the melt, respectively.

• 한국초전도ㆍ저온공학회논문지
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• 제18권4호
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• pp.15-20
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• 2016

The effects of electron beam (EB) irradiation on the superconducting critical temperature ($T_c$) and critical current density ($J_c$) of YBCO films were studied. The YBCO thin films were irradiated using a KAERI EB accelerator with an energy of 0.2 MeV and a dose of $10^{15}-10^{16}e/cm^2$. A small $T_c$ decrease and a broad superconducting transition were observed as the EB dose increased. The value of $J_cs$ (at 20 K, 50 K and 70 K) increased at doses of $7.5{\times}10^{15}$ and $2.2{\times}10^{16}e/cm^2$. However, $J_cs$ decreased as the dose increased further. The X-ray diffraction (XRD) analysis showed that the c axis of YBCO was elongated and the full width at half maximum (FWHM) increased as the dose increased, which is strong evidence of the atomic displacement by EB irradiation. The transmission electron microscopy (TEM) showed that the amorphous layer formed in the vicinity of the surfaces of the irradiated films. The amorphous phase was often present as an isolated form in the interior of the films. In addition to the formation of the amorphous phase, many striations running along the a-b direction of YBCO were observed. The high magnification lattice image showed that the striations were stacking faults. The enhancement of $J_c$ by EB irradiation is likely to be due to the lattice distortion and the formation of defects such as vacancies and stacking faults. The decrease in $J_c$ at a high EB dose is attributed to the extension of the amorphous region of a non-superconducting phase.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제52권7호
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• pp.275-281
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• 2003

$Zn_{0.5}Cd_{0.5}Al_{2}Se_{4}$ and $Zn_{0.5}Cd_{0.5}Al_{2}Se_{4}$:$Co^{2+}$ single crystals were grown by CTR method. The grown single crystals have defect chalcopyrite structure with lattice constant a=5.5966$\AA$, c=10.8042$\AA$ for the pure, a=5.6543$\AA$, c=10.8205$\AA$ for the Co-doped single crystal, respectively. The optical energy band gap was given as indirect band gap. The optical energy band gap was decreased according to add of Co-impurity Temperature dependence of optical energy band gap was fitted well to the Varshni equation. From this relation, we can deduced the entropy, enthalpy and heat capacity. Also, we can observed the Co-impurity optical absorption peaks assigned to the $Co^{2+}$ ion sited at the $T_{d}$ symmetry lattice and we consider that they were attributed to the electron transitions between energy levels of ions.

• 한국재료학회지
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• 제34권9호
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• pp.448-455
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• 2024

We conducted a study on excessive doping of the Cr and In elements in Bi-Sb-Te materials satisfying the Hume-Rothery rule, and investigated the resulting electrical and thermal properties. From X-ray diffraction (XRD) results, we confirmed the formation of a single phase even with excessive doping. Through analysis of electrical properties, we observed the highest enhancement in electrical characteristics at y = 0.2, suggesting that the appropriate ratio of Bi-Sb significantly influences this enhancement. Using the Callaway-von Baeyer (CvB) model to assess scattering due to point defects, we calculated the experimental point defect scattering factor (Γ_CvB.exp), which was notably high due to the substantial differences in volume and atomic weight between the substituted (Cr, In) and original (Bi, Sb) elements. Additionally, we conducted a single parabolic band (SPB) modeling analysis of materials with compositions y = 0.1 and 0.2, where, despite a decrease in density-of-states effective mass (m_d^*) during the enhancement process from y = 0.1 to 0.2, a sharp increase in non-degenerate mobility (μ₀) led to an 88 % increase in weighted mobility (μ_w). Furthermore, analyzing zT with respect to n_H revealed a 51 % increase in zT at a composition of y = 0.2. This study confirmed a significant reduction in lattice thermal conductivity with the co-doping strategy, and with further compositional studies to improve electrical properties, we anticipate achieving high zT.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 하계학술대회 논문집
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• pp.327-327
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• 2009

ZnO with a large band gap (~3.37 eV) and exciton binding energy (~60 meV), is suitable for optoelectronic applications such as ultraviolet (UV) light emitting diodes (LEDs) and detectors. However, the ZnO-based p-n homojunction is not readily available because it is difficult to fabricate reproducible p-type ZnO with high hall concentration and mobility. In order to solve this problem, there have been numerous attempts to develop p-n heterojunction LEDs with ZnO as the n-type layer. The n-ZnO/p-GaN heterostructure is a good candidate for ZnO-based heterojunction LEDs because of their similar physical properties and the reproducible availability of p-type GaN. Especially, the reduced lattice mismatch (~1.8 %) and similar crystal structure result in the advantage of acquiring high performance LED devices. In particular, a number of ZnO films show UV band-edge emission with visible deep-level emission, which is originated from point defects such as oxygen vacancy, oxygen interstitial, zinc interstitial[1]. Thus, defect-related peak positions can be controlled by variation of growth or annealing conditions. In this work, the undoped ZnO film was grown on the p-GaN:Mg film using RF magnetron sputtering method. The undoped ZnO/p-GaN:Mg heterojunctions were annealed in a horizontal tube furnace. The annealing process was performed at $800^{\circ}C$ during 30 to 90 min in air ambient to observe the variation of the defect states in the ZnO film. Photoluminescence measurements were performed in order to confirm the deep-level position of the ZnO film. As a result, the deep-level emission showed orange-red color in the as-deposited film, while the defect-related peak positions of annealed films were shifted to greenish side as increasing annealing time. Furthermore, the electrical resistivity of the ZnO film was decreased after annealing process. The I-V characteristic of the LEDs showed nonlinear and rectifying behavior. The room-temperature electroluminescence (EL) was observed under forward bias. The EL showed a weak white and strong yellowish emission colors (~575 nm) in the undoped ZnO/p-GaN:Mg heterojunctions before and after annealing process, respectively.