• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.51-51
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• 2010

Group III-nitride semiconductors have been widely studied as the materials for growth of light emitting devices. Currently, GaN devices are predominantly grown in the (0001) c-plane orientation. However, in case of using polar substrate, an important physical problem of nitride semiconductors with the wurtzite crystal structure is their spontaneous electrical polarization. An alternative method of reducing polarization effects is to grow on non-polar planes or semi-polar planes. However, non-polar and semipolar GaN grown onto r-plane and m-plane sapphire, respectively, basically have numerous defects density compared with c-plane GaN. The purpose of our work is to reduce these defects in non-polar and semi-polar GaN and to fabricate high efficiency LED on non/semi-polar substrate. Non-polar and semi-polar GaN layers were grown onto patterned sapphire substrates (PSS) and nano-porous GaN/sapphire substrates, respectively. Using PSS with the hemispherical patterns, we could achieve high luminous intensity. In case of semi-polar GaN, photo-enhanced electrochemical etching (PEC) was applied to make porous GaN substrates, and semi-polar GaN was grown onto nano-porous substrates. Our results showed the improvement of device characteristics as well as micro-structural and optical properties of non-polar and semi-polar GaN. Patterning and nano-porous etching technologies will be promising for the fabrication of high efficiency non-polar and semi-polar InGaN LED on sapphire substrate.

• Journal of Ceramic Processing Research
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• v.13 no.spc1
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• pp.93-95
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• 2012

We report on the growth and characterization of the nano- and micro scale GaN structures selectively grown on the vertex of GaN stripes using the metal organic vapor phase epitaxy method and conventional photolithography technique. The triangular shaped nano- and micro GaN structures which have semi-polar {11-22} facets were formed only on the vertex of the lower GaN stripes. Crystalline defects reduction was observed by transmission electron microscopy for upper GaN stripes. We also have grown the InGaN/GaN multi-quantum well structures on the semi-polar facets of the upper GaN stripes. Cathodoluminescence images were taken at 366, 412 and 555 nm related to GaN band edge, InGaN/GaN layer and defects, respectively.

• Proceedings of The Korean Society of Agricultural and Forest Meteorology Conference
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• 2017.11a
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• pp.83-83
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• 2017

• Ocean and Polar Research
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• v.24 no.3
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• pp.237-247
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• 2002

We report all sky camera and Fabry-Perot interferometer (FPI) observations of mesospheric gravity waves and a 12-hour wave at Resolute $(75^{\circ}N)$ and a joint observation of 10-hour wave with Eureka $(80^{\circ}N)$. All sky camera observations showed a low occurrence of mesosphere gravity waves during equinoxes, which is similar to the mid-latitude region. A slightly higher occurrence near solstice appears to indicate that gravity waves are not filtered out by the neutral wind in the winter. The FPI observation of a 12-hour wave showed amplitude variations from day to day. The phase of the wave is mostly stable and consistent with the GSWM prediction in the winter. The phase shifts with season as predicted by the GSWM. Four events of the 12-hour wave were found in spring with amplitudes larger than the GSW predictions. The FPls at Resolute and Eureka also observed a wave with period close to 10 hours. The 10-hour wave maybe the result of the non-linear interaction between the semi-diurnal tide and the quasi-two day wave. Further studies are under way. Overall, the combined Resolute and Eureka observation have revealed some new fractures about the mesospheric gravity wave, tidal wave, and other oscillations.

• Journal of IKEEE
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• v.23 no.4
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• pp.1288-1294
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• 2019

The channel-achieving property made the polar code show to advantage as an error-correcting code. However, sufficient error-correction performance shows the asymptotic property that is achieved when the length of the code is long. Therefore, efficient architecture is needed to realize the implementation of very-large-scale integration for the case of long input data. Although the most basic fully parallel encoder is intuitive and easy to implement, it is not suitable for long polar codes because of the high hardware complexity. Complementing this, a partially parallel encoder was proposed which has an excellent result in terms of hardware area. Nevertheless, this method has not been completely generalized and has the disadvantage that different architectures appear depending on the hardware designer. In this paper, we propose a hardware design scheme that applies the proposed systematic approach which is optimized for bit-dimension permutations. By applying this solution, it is possible to design a generalized partially parallel encoder for long polar codes with the same intuitive architecture as a fully parallel encoder.

• Communications of the Korean Mathematical Society
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• v.12 no.3
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• pp.597-602
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• 1997

Let H be a separable complex Hilbert space and L(H) be the *-algebra of all bounded linear operators on H. For $T \in L(H)$, we construct a pair of semi-positive definite operators $$ $\mid$T$\mid$_r = (T^*T)^{\frac{1}{2}} and $\mid$T$\mid$_l = (TT^*)^{\frac{1}{2}}. $$ An operator T is called a semi-hyponormal operator if $$ Q_T = $\mid$T$\mid$_r - $\mid$T$\mid$_l \geq 0. $$ In this paper, by using a technique introduced by Berberian [1], we show that the approximate point spectrum $\sigma_{ap}(T)$ of a semi-hyponomal operator T is empty.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.21 no.3
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• pp.114-118
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• 2011

We report on the growth and characterization of nano and micro scale GaN structures selectively grown on the vertex of hexagonal GaN pyramids. $SiO_2$ near the vertex of hexagonal GaN pyramids was removed by optimized photolithgraphy process and followed by a selective growth of nano and micro scale GaN structures by metal organic vapor phase epitaxy (MOVPE). The pyramidal GaN nano and micro structures which have crystal facets of semi-polar {1-101} facets were formed only on the vertex of GaN pyramids and the size of the selectively grown nano and micro GaN structures was easily controlled by growth time. As a result of TEM measurement, Reduction of threading dislocation density was conformed by transmission electron microscopy (TEM) in the selectively grown nano and micro GaN structures. However, stacking faults were newly developed near the edge of $SiO_2$ film because of the roughness and nonuniformity in thickness of the $SiO_2$ film.

• Bulletin of the Korean Space Science Society
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• 2011.04a
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• pp.22.1-22.1
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• 2011

Two dominant components of polar motion are the Chandler and the annual components. Recently, the existence of 500-day period component in the Earth's polar motion has been manifested. But its existence is not clear on Fourier spectrum. One cause of difficulty involved here is that the amplitudes of the two main components are slightly variable in time by certain amounts (Chandler: 0.15~0.28 arcsec, annual: 0.09~0.15 arcsec). A residual polar motion time series excluding the two main components for a time span between 1962 Jan and 2010 Nov from IERS C04 time series dataset was constructed by least square fitting. For faithful fitting, 43 time segments of 6.8 year length (each starts on January 1st of successive years) were separately acquired and later combined together. The period of dominant peak in the spectrum of this residual polar motion time series is 490 days. Next peaks have their periods as semi-annual, 300~330 days, ~560 days, 670 days, and 1360 days.

• 한국가시화정보학회:학술대회논문집
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• 2004.12a
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• pp.81-90
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• 2004

A zonal embedded grid technique has been developed for computation of the two-dimensional Navier-Stokes equations with cylindrical coordinates. The fundamental idea of the zonal embedded grid technique is that the number of azimuthal grids can be made small near the origin of the coordinates so that the grid size is more uniformly distributed over the domain than with the conventional regular-grid system. The code developed using this technique combined with the explicit, finite-volume method was then applied to calculation of the spin-up flows within a semi-circular cylinder. It was shown that the numerical results were in good agreement with the experimental results both qualitatively and quantitatively.

• Transactions on Electrical and Electronic Materials
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• v.7 no.1
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• pp.16-20
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• 2006

In this paper, we investigated the effects of short-term oxygen plasma treatment of semiconducting silicone layer to improve interfacial performances in joints prepared with a insulating silicone materials. Surface characterizations were assessed using contact angle measurement and x-ray photoelectron spectroscopy (XPS), and then adhesion level and electrical performance were evaluated through T-peel tests and electrical breakdown voltage tests of treated semi-conductive and insulating joints. Plasma exposure mainly increased the polar component of surface energy from $0.21\;dyne/cm^2$ to $47\;dyne/cm^2$ with increasing plasma treatment time and then leveled off. Based on XPS analysis, the surface modification can be mainly ascribed to the creation of chemically active functional groups such as C-O, C=O and COH on semi-conductive silicone surface. This oxidized rubber layer is inorganic silica-like structure of Si bound with three to four oxygen atoms ($SiO_x,\;x=3{\sim}4$). The oxygen plasma treatment produces an increase in joint strength that is maximum for 10 min treatment. However, due to brittle property of this oxidized layer, the highly oxidized layer from too much extended treatment could be act as a weak point, decreasing the adhesion strength. In addition, electrical breakdown level of joints with adequate plasma treatment was increased by about $10\;\%$ with model samples of joints prepared with a semi-conducting/ insulating silicone polymer after applied to interface.