Photoluminescence of Zn1-xBexSe Films Grown by Using Molecular Beam Epitaxy

황영훈,Youngho Um,Hyekyeong Kim,J.K Furdyna 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.3

We report a systematic investigation of band-edge photoluminescence of the II-VI wide band-gap semiconductor Zn$_{1-x}$Be$_{x}$Se for a series of Be compositions (0 $<$ $x$ $<$ 0.4). The specimens investigated were in the form of thin films fabricated by using molecular beam epitaxy (MBE). The near band-edge emissions of free excitons (designated as FX) were systematically investigated as a function of temperature and of alloy composition. From the temperature dependence of the free exciton peak, the Varshni temperature parameters $\alpha$ and $\beta$ were found to increase with increasing Be concentration $x$. From the temperature dependence of the FWHM of the free exciton FX emission line, the broadening factors $\Gamma (T)$ were determined from a fit to the data. Furthermore, the activation energies of thermal quenching for the E$_A$ peak were obtained from the temperature dependence of the free exciton peaks, and were found to decrease with increasing Be concentration.

Magnetic, Structural, and Electrical Properties of Si1?xMnx Single Crystals

황영훈,Youngho Um,Hyekyeong Kim,Soon Cheol Hong,Sunglae Cho 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.4

We have investigated the magnetic and the electrical transport properties of Si1.xMnx (x = 0.5 and 0.75) single crystals grown by using the vertical Bridgman method. The alloys with the Mn concentration x = 0.5 have weak ferromagnetic ordering around TC ' 30 K. However, Si0.25Mn0.75 alloys show weak ferromagnetic ordering at 70 K and antiferromagnetic ordering at 104 K, which is confirmed by magnetization, electrical transport, and neutron diffraction studies. The conductivities appear to be n-type for samples with x = 0.5 and p-type for x = 0.75.

Structural, Electrical and Magnetic Properties of Diluted Magnetic Semiconductor Si1-xMnxTe1.5 Single Crystals

황영훈,Youngho Um,Hyekyeong Kim,Sunglae Cho 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.6

We studied the dependence of the magnetic properties on the Mn concentration of IV-VI diluted magnetic semiconductor Si1.xMnxTe1.5 single crystals prepared by using the vertical Bridgman technique. X-ray studies showed that the crystal structure was hexagonal. The magnetization measurement of Si1.xMnxTe1.5 showed a ferromagnetic ordering up to 80 K. With increasing Mn concentration, the saturation magnetization increased and the coercive field increased, as shown in the hysteresis loop. For x = 0.20 and 0.31, a slope change in the resistivity was observed around 80 K and corresponded to a ferromagnetic (FM)-paramagnetic (PM) phase transition.

Spectral Dependence of the Dielectric Function of Quaternary CdMnCoTe by Spectroscopic Ellipsometry

황영훈,Youngho Um,Hyekyeong Kim,Hyoyeol Park 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.III

Spectroscopic ellipsometry measurements of the complex dielectric function of a series of Cd$_{0.63-y}$Mn$_{0.37}$Co$_y$Te single crystals grown by the vertical Bridgman method have been performed in the 1.5 $\sim$ 5.5 eV energy range at room temperature. The measurement data were analyzed by fitting the second-derivative spectra ($d^2 \varepsilon$/$d \omega^2$) with a theoretical model, namely, the standard critical-point (SCP) line shapes. The $E_1$, $E_1$+$\Delta_1$ and $E_2$ energies decreased with increasing Co composition $y$, which is due to the hybridization effect of the valence and conduction bands in Cd$_{1-x}$Mn$_x$Te with Co $3d$ levels.

Optical Absorption of Zn1−xMnxSiAs2 Single Crystals : Variation of theEnergy Gap with Composition and Temperature

황영훈,Youngho Um,Hyekyeong Kim,Sunglae Cho,Sungyeol Choi 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.4

We have investigated the Mn composition x and the temperature (12 K T 300 K) dependences of the energy gap of Zn1−xMnxSiAs2 crystals. Single crystals were grown by using the vertical Bridgman method for a series of Mn compositions x. The variation of the enery gap, Eg, with temperature follows the Varshni’s relation for all compositions. The energy gap decreased up to x 0.04. Thereafter, it increased with x. The energy gap bowing effect is related to the sp-d exchange interaction between the 3d electrons of magnetic Mn ions and the band electrons and to magnetic and chemical disorder.

Optical, Electrical, and Magneto-Optical Properties for Bulk Cd0.63-yMn0.37HgyTe Single Crystals

황영훈,Youngho Um,Hyekyeong Kim,Hyoyeol Park,Sunglae Cho 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.3

We investigated the magneto-optical properties of diluted magnetic semiconductor Cd$_{0.63-y}$ Mn$_{0.37}$Hg$_{y}$Te single crystals grown using a vertical Bridgman method. This material crystallizes in the zinc-blende structure for values of $y$ $\leq$ 0.07. The band gap energy increases with increasing for $y$ $\leq$ 0.03, while decreasing with increasing for $y$ $\geq$ 0.03. An anomalous behavior was also observed in the magnetic susceptibility and the electrical resistivity. The Verdet dispersion curves were enhanced near the fundamental band gap energy. The Verdet constant showed a maximum for the sample with $y$ = 0.03, and the value was approximately four times larger than that of the Cd$_{0.63}$Mn$_{0.37}$Te crystal. The Verdet constant had a maximum around Hg compositions with $y~\sim$ 0.03, and this result agrees well with the behavior of the magnetic susceptibility. This result reflects that Hg ion mediates and enhances the spin-spin interaction between Mn$^{2+}$ ions with increasing Hg composition up to $y~\sim$ 0.03.

Structural, Optical, and Magneto-Optical Properties in Diluted Magnetic Semiconductors Cd0.63-yMn0.37CoyTe Single Crystals

황영훈,Youngho Um,Hyekyeong Kim,Hyoyeol Park,Sunglae Cho 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.3

We investigated the magneto-optical properties of diluted magnetic semiconductor Cd$_{0.63-y}$ Mn$_{0.37}$Co$_{y}$Te single crystals grown using a vertical Bridgman method. From the temperature dependence of the band-gap energy, the Varshni temperature parameter $\alpha$ was found to increase linearly with increasing Co concentration $y$ while $\beta$ decreased with $y$. The Faraday rotation as a function of photon energy with various Co compositions for CdMnCoTe in the temperature range of 10 to 300 K was measured. The Verdet dispersion curves were enhanced near the fundamental band gap energy. The Verdet constant becomes larger since because the effect of the $sp$-$d$ exchange interaction is enhanced as the temperature is lowered. At 10 K, the Verdet constants of the Faraday rotation for the samples with $y$ = 0, 0.01, 0.02, and 0.04 were observed to be --0.94, --1.41, --1.69, and --2.11 deg/G cm at 610 nm, respectively. The Verdet constant showed a maximum for the sample with $y$ = 0.04, and the value was approximately 2.3 times larger than that of the Cd$_{0.63}$Mn$_{0.37}$Te crystal. The Faraday rotation increased as Co content was increased, and the origin of the enhancement of the Faraday rotation in CdMnCoTe crystals could be explained in terms of the magnetization.

re3data.org의 데이터 리포지터리 인증 현황 분석

신영호(Youngho Shin),엄정호(Hungho Um),신성호(Sungho Shin),서동민(Dongmin Seo) 한국콘텐츠학회 2022 한국콘텐츠학회 종합학술대회 논문집 Vol.2022 No.7

한국 산업클러스터 정책의 전개와 새로운 경향

엄창옥(ChangOk Um),이요한(YoHan Lee),최용호(YoungHo Choi),박우식(WooSik Park) 한국경제통상학회 2009 경제연구 Vol.27 No.4

This study is to analyze the formation and the development process of industrial cluster of Korea in a view point of 'advantage of interaction' between economic actors, "advantage of integration' or 'advantage of embeddedness' based on local resources, and in line with this, review the development process of Korean industrial cluster. At the same time, how the policies of Korean industrial cluster has effect on the development of the industrial cluster was analyzed. As a result of this analysis, the following conclusions were induced. First, it turned out that Korean industrial cluster is in the middle stage of 'organic cluster' in general. Second, in the concept of 'reverse institutionalization' , the policy of Korean industrial cluster helped to form the network between businesses which is located in the industrial complex, thereby contributing to promoting the technological innovative activities solving the technical problems based on this network. Due to the over 50 years' policy of industrial cluster from 1964 to the present day, Korean industrial cluster has been evolving and three new trends are shown in this process. First trend is 'the expansion', which means the closed industrial cluster is changing into the openness. Second trend is 'the fusion'. As diversity in industrial cluster increases and social capital is accumulated, new industrial area is being created by fusion between specified industries. Third trend is 'the embeddedness', which means that the isolated business in industrial complex take root in local community and utilizing local innovative capacities for business innovative activities. From this point of view, the policy of industrial cluster in the future should be carried out within the scope of not interfering with self-evolution of industrial cluster. Thus the new policy of industrial cluster in the autonomic and endogenous direction is required to develop the present stage of industrial cluster into 'innovative stage' and 'embeddedness stage'. 본 논문은 산업클러스터의 형성과 발전과정을 지리적으로 집적한 기업이 기업간의 ‘상호작용의 이익’과 지역자원 기반의 ‘집적의 이익’ 혹은 ‘착근화의 이익’을 향유해가는 과정으로 해석하고, 이런 관점에서 한국의 산업클러스터 발전과정을 재검토하였다. 동시에 한국의 산업클러스터 정책이 산업클러스터 발전에 어떤 영향을 주었는지 분석하고자 하였다. 이 분석을 통해 우리는 몇 가지의 결론을 도출할 수 있었다. 첫째, 한국의 산업클러스터는 전반적으로 유기적 클러스터 단계(The stage of Organic Cluster)의 중간영역에 와 있음을 알 수 있었다. 둘째, ‘역분해 제도화'(reverse institutionalization)라는 개념으로 볼 때, 한국의 산업클러스터 정책은 단순집적지에 지나지 않았던 공업단지의 입주 기업들간에 취약하나마 상당한 네트워크를 형성하게 하였으며, 이 네트워크를 기반으로 하여 현장애로기술을 해결해나가는 기술혁신활동을 추진하는데 기여하고 있음을 알 수 있었다. 1964년부터 현재에 이르기까지 50년이 넘는 산업클러스터 정책으로 인해 한국의 산업클러스터는 자기진화를 지속해오고 있고 그 과정 속에서 세 가지의 새로운 경향을 보이고 있음을 분석하였다. 첫째는 광역화 경향이다. 폐쇄적인 산업클러스터가 개방화되고 있다는 점이다. 둘째는 융합화의 경향이다. 산업클러스터 내에 다양성이 증가하고 사회적 자본이 축적됨에 따라 특정산업 간의 융합이 발생하여 새로운 산업영역을 창출하고 있다는 점이다. 셋째는 착근화의 경향이다. 아주 미약하지만 고립된 산업클러스터 내의 기업이 지역에 뿌리를 내리고 지역혁신역량을 기업혁신활동에 이용하려는 경향을 보인다는 점이다. 이러한 관점에서 볼 때, 앞으로 산업클러스터 정책은 산업클러스터의 자기진화를 방해하지 않는 방향에서 이루어져야 한다는 점을 지적하고자 한다. 한국의 현단계의 산업클러스터가 ‘혁신적 클러스터 단계’와 ‘착근적 클러스터 단계’로 발전하기 위해서는 자율적·내생적 방향에서의 새로운 산업클러스터 정책을 필요로 한다는 점이다.

Composition-dependent Magnetic Properties of Si<SUB>1-x</SUB>Mn<SUB>x</SUB> (0.1 < x < 0.9) Single Crystals

Younghun Hwang,Youngho Um,Hyo-yeol Park 한국자기학회 2010 Journal of Magnetics Vol.15 No.2

In this study, we investigated the optical, magnetic, and electrical transport properties of Si1-xMnx (0.1 < x < 0.9) single crystals grown by the vertical Bridgman method. The alloys with a Mn concentration of up to 64% demonstrated weak ferromagnetic ordering around TC = 30 K. The Si0.25Mn0.75 and Si0.18Mn0.82 alloys showed weak ferromagnetic ordering at 70 K and antiferromagnetic ordering at 104 K, as confirmed by magnetization, neutron diffraction, and transport studies.