• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.10
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• pp.799-802
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• 2011

In this study, SiC single-crystal ingots were prepared on two seed crystals with different doping level by using the physical vapor transport (PVT) technique; then, SiC crystal wafers sliced from the grown SiC ingot were systematically investigated to find the effect of seed doping level on the doping concentration and crystal quality of the SiC. To exclude extra effects induced by adjustment of the process parameters, we simultaneously grew the SiC crystals on two seed crystals with different level, which were fabricated from previous two SiC crystal ingots.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.10
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• pp.775-778
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• 2011

TBP (tertiarybutylphosphine), a relatively new material for phosphorus, has been studied with EDMIn (ethyldimethylindium) as an indium source for the growth of InP by MOVPE (metalorganic vapor phase epitaxy). Mirror smooth and good crystalline InP layers were obtained at $500-600^{\circ}C$ with the TBP/EDMIn molar ratio as low as 21. The deposited InP layers are all n-type with the electron concentration in the range of (5-10)${\times}10^{16}\;cm^{-3}$, which is a lot higher than those from $PH_3$. This high concentration is due presumably to the high concentration of donor impurities in TBP. And it has been found that the formation of adduct occurs between EDMIn and TBP at room temperature when the partial pressure of EDMIn in the reactant mixture is above $1{\times}10^{-2}$ Torr. The high concentration of impurities in TBP and the adduct formation between EDMIn and TBP are major obstacles in replacing $PH_3$ and TMIn for the growth of device quality InP layers.

• Proceedings of the KSRS Conference
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• 2000.04a
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• pp.49-54
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• 2000

Conventional methods for measuring winds provide wind velocity observations over limited area and time period. The use of satellite imagery for measuring wind velocity overcomes some of these limitations by providing wide area and near condinuous coverage. And its accurate depiction is essential for operational weather forecasting and for initialization of NWP models. GMS-5 provides full disk images at hourly intervals. At four times each day - 0500, 1100, 1700, 2300 hours UTC-a series of three images is received, separated by thirty minutes, centered at the four times. The current wind system generates winds from sets of 3 infrared(IR) images, separated by an hour, four times a day. It also produces visible(VIS) and water vapor(WV) image-based winds from half-hourly imagery four times a day. The derivation of wind from satellite imagery involves the identification of suitable cloud targets. tracking the targets on sequential images, associating a pressure height with the derived wind vector, and quality control. The aim of this research is to incorporate imagery from other available spectral channels and examine the error characteristics of winds derived from these images.

• Journal of Korean Vacuum Science & Technology
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• v.4 no.3
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• pp.81-85
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• 2000

The effects of $NH_3$ flow rate and reactor pressure on Al composition and the interface of AlGaN/GaN heterostructure were studied. Equilibrium partial pressure of Ga and Al over AiGaN alloy was calculated as a function of growth pressure, $NH_3$flow rate and temperature. It was found equilbrium vapor pressure of Al is significantly lower than that of Ga, thus, the alloy composition mainly controlled by Ga partial pressure. We believe that more decomposition of Ga occur at lower $NH_3$ flow rate and higher growth pressure leads to preferred Al incorporation into AlGaN. The alloy composition gradient became larger at AlGaN/GaN heterointerface at higher reactor pressures, higher Al composition and low $NH_3$ flow rate. This composition gradient lowered sheet carrier concentration and electron mobility as well. We obtained an AlGaN/GaN heterostructure with sheet carrier density of ${\sim}2{\times}10^{13}cm^{-2}$ and mobility of 1250 and 5000 $cm^2$/Vs at 300 K and 100 K, respectively.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.170-170
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• 2010

a-plane 혹은 m-plane면을 사용하는 무분극 GaN LED는 c축 방향으로 발생하는 분극의 영향을 받지 않기 때문에 분극 GaN LED에 비해 높은 내부 양자효율을 가진다. 또한 무분극 GaN는 상대적으로 고농도의 p-type 도핑이 가능하기 때문에 광효율을 높일 수 있다. 하지만 이와 같은 장점에도 불구하고 무분극 GaN는 성장모드의 비대칭으로 인해 높은 결정성과 mirror-like한 표면을 얻기가 힘들다. 본 논문에서는 Metalorganic chemical-vapor deposition (MOCVD) 장비를 사용하여 r-plane 사파이어 기판위에 a-plane GaN을 성장시켰다. 일반적으로 사용하는 저온에서의 nucleation layer 성장 대신 $1050^{\circ}$의 고온에서 성장 시킨후 일반적으로 사용하는 two-step 성장방법으로 그위에 5.5um정도의 GaN을 성장시켰다. 성장시 Trimethylgallium(TMGa)와 암모니아를 각각 Ga과 N 소스로 이용하였고 캐리어 가스는 수소를 사용하였다. 비대칭 결정성을 줄이기 위해 3D island growth mode에서의 성장조건을 바꾸어 c축과 m축 방향으로의 X-ray 결정성(FWHM) 차이가 564 arcsec에서 206 arcsec로 변화 시켰다. Normarski 현미경으로 표면을 관찰한 결과 v-defect이 없고 a-plane GaN에서 볼 수 있는 전형적인 줄무늬 패턴을 가지는 표면을 얻었으며 광학적 특성을 보기 위해 Photoluminescence (PL)을 측정하였다.

• Journal of Welding and Joining
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• v.30 no.4
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• pp.24-30
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• 2012

Laser welding by fiber laser accompanied by a lot of spatter and humping bead. This is because the deep and narrow keyhole usually form due to high beam quality. So the weld bead is formed defects, because the plasma jet with a high vapor pressure make the molten pool on keyhole wall scattered. For such a reason, unstable behavior of keyhole is difficult to monitor laser welding by using the laser induced plasma. Mostly, fiber laser welding of thick plates most be influenced by this effect. Therefore, fiber laser welding has been difficult to apply the sole. Thus, laser welding monitoring based on plasma measurements have much difficulty in measurements and analysis of signal. In this study, influence of the plasma emission signal according to welding speed and laser power in fiber laser welding analysed by using RMS and FFT analysis. We can verify that RMS value of the plasma emission signal changes with welding parameters in fiber laser welding, and aspect ratio greater than 1, the peak of FFT frequency had been moved in accordance with welding parameter.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.3
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• pp.38-43
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• 2004

This paper describes the construction of a circular polariscope. Generally, a circular polariscope contains four optical elements and a light source. The first element following the light source is called the linear polarizer. It converts the ordinary light into plane-polarized light. The second element is a quarter wave plate which converts the plane-polarized light into circularly polarized light. Following the quarter wave plate, a specimen made of transparent photoelastic material is located in a loading device. The second quarter wave plate is set and the last element is the analyzer. These polarizing elements, two quarter wave plates and two linear polarizing filters, were purchased from the USA. Frames and other structures for holding polarizing filters were machined and assembled to be rotated. Light box, which includes four incandescent lamps and two sodium-vapor lamps, was made. In order to proof the function of the newly built polariscope, Tardy compensation test was applied to a rectangular shaped specimen made of poly-carbonate material (PSM 1). The error of the fringe constant, which was measured by the newly built polariscope, was within 4.4 percent compared to the standard value of this material. It is possible to make a good quality of polariscope if accurate polarizing filters will be used.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.05a
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• pp.37-37
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• 2012

The coated steels, mainly with zinc by either hot-dip galvanizing or electroplating, are widely used for panels of automotive, electrical appliances and construction, whose size of world market have reached 130 million tons in 2008. Current issues for the coated steels can be integrated in terms of high functionality, low cost, environment-friend and available resource. The best solution can be provided if thin layer coating with higher quality is produced by an eco-friendly process, and PVD, physical vapor deposition, can be an alternative practice to existing coating processes. PVD technologies have been very common ones in electronic and semiconductor industries, but recognized as non-profitable processes for the coated steels due to low process speed and lack of continuous operation skills. Systematic researches from 1990s in Europe, even though discouraged by a shutdown of the first Japanese PVD coating plant in 1999, have realized several continuous PVD coating plants, and also enhanced launching of developments in steel industries. To be successful with PVD coating technologies over existing ones, productivity to meet economics should be created from a highly sophisticated process. Some PVD technologies fit for the high-speed process will be introduced together with experiences from industrial applications.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.1107-1112
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• 2006

The purpose of this study is a heat transfer coefficient test of evaporator tube in shell and tube heat exchanger by shapes, using R-404A. The experimental apparatus is designed to simulate the real heat transfer rate in one shell and tube heat exchanger. The test section is formed four type tubes that are Inner ridged tube, Corrugated tube, Turbo-C tube, Inner fin tube and shell type is formed by electrical heater. All tests were performed at a fixed refrigerant evaporator temperature at $1.5^{\circ}C,\;-3^{\circ}C$ and with mass fluxes of 29, 25 kg/hr. Heat transfer rate is calculated a enthalpy difference in test section. In experiment, heat transfer coefficient measured one by one and electrical heaters are supplemented by evaporator.

• Current Photovoltaic Research
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• v.7 no.1
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• pp.15-20
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• 2019

Most high-efficiency n-type silicon solar cells are based on the high quality surface passivation and ohmic contact between the emitter and the metal. Currently, various metalization methods such as screen printing using metal paste and physical vapor deposition are being used in forming electrodes of n-type silicon solar cell. In this paper, we analyzed the degradation factors induced by the front electrode formation process using e-beam evaporation of double passivation structure of p-type emitter and $Al_2O_3/SiN_x$ for high efficiency solar cell using n-type bulk silicon. In order to confirm the cause of the degradation, the passivation characteristics of each electrode region were determined through a quasi-steady-state photo-conductance (QSSPC).