• Journal of the Korean Vacuum Society
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• v.15 no.1
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• pp.81-88
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• 2006

Laterally self-aligned InGaAs/GaAs quantum-dots (QDs) have been fabricated by using a multilayer stacking technique. For the growth optimization, we vary the number of stacks and the growth temperature in the ranges of 1-15 periods and $500-540^{\circ}C$. respectively, Atomic force microscope (AFM) images and photoluminescence (PL) spectra reveal that the lateral alignment of QDs is enhanced in extended length by an increased stack period, but severely degrades into film-like wires above a critical growth temperature. The morphological and the photoluminescence characteristics of laterally self-aligned InGaAs QDs have been analyzed through mutual comparisons among four samples with different parameters. An anisotropic arrangement develops with increasing number of stacks, and high-temperature capping allows isolated QDs to be spontaneously organized into a one-dimensionally aligned chain-like shape over a few ${\mu}m$, Moreover, the migration time allowed by growth interruption plays an additional important role in the chain arrangement of QDs. The QD chains capped at high temperature exhibit blue shifts in the emission energy, which may be attributed to a slight outdiffusion of In from the InGaAs QDs.

• Journal of the Korean Vacuum Society
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• v.22 no.6
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• pp.327-334
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• 2013

Long-wave infrared detectors using the type-II InAs/GaSb strained superlattice (T2SL) material system with the nBn structure were designed and fabricated. The band gap energy of the T2SL material was calculated as a function of the thickness of the InAs and GaSb layers by the Kronig-Penney model. Growth of the barrier material ($Al_{0.2}Ga_{0.8}Sb$) incorporated Te doping to reduce the dark current. The full width at half maximum (FWHM) of the $1^{st}$ satellite superlattice peak from the X-ray diffraction was around 45 arcsec. The cutoff wavelength of the fabricated device was ${\sim}10.2{\mu}m$ (0.12 eV) at 80 K while under an applied bias of -1.4 V. The measured activation energy of the device was ~0.128 eV. The dark current density was shown to be $1.0{\times}10^{-2}A/cm^2$ at 80 K and with a bias -1.5 V. The responsivity was 0.58 A/W at $7.5{\mu}m$ at 80 K and with a bias of -1.5 V.

• Journal of the Korean Vacuum Society
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• v.20 no.1
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• pp.22-29
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• 2011

An infrared thermographic imaging module of [$320{\times}256$] focal-plane array (FPA) based on [InAs/GaSb] strained-layer superlattice (SLS) was fabricated, and its images were demonstrated. The p-i-n device consisted of an active layer (i) of 300-period [13/7]-ML [InAs/GaSb]-SLS and a pair of p/n-electrodes of (60/115)-period [InAs:(Be/Si)/GaSb]-SLS. FTIR photoresponse spectra taken from a test device revealed that the peak wavelength (${\lambda}_p$) and the cutoff wavelength (${\lambda}_{co}$) were approximately $3.1/2.7{\mu}m$ and $3.8{\mu}m$, respectively, and it was confirmed that the device was operated up to a temperature of 180 K. The $30/24-{\mu}m$ design rule was applied to single pixel pitch/mesa, and a standard photolithography was introduced for [$320{\times}256$]-FPA fabrication. An FPA-ROIC thermographic module was accomplished by using a $18/10-{\mu}m$ In-bump/UBM process and a flip-chip bonding technique, and the thermographic image was demonstrated by utilizing a mid-infrared camera and an image processor.

• Journal of the Korean Vacuum Society
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• v.20 no.1
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• pp.35-41
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• 2011

In this study, the interface soaking effect in InAs/GaAs strained-layer superlattice (SLS) on crystalline phase modulation has been analyzed by the x-ray diffraction (XRD) curve. The strain variation induced by As and/or Sb soaking was determined by the separation angle between the substrate peak and the 0th-order superlattice satellite peak in the XRD spectra. Contrated that the As/InAs soaking arises minor GaAs-like interfacial layer, the Sb/GaSb soaking induces InSb-like one. The Fourier-transformed curves of the Pendellosung interference oscillation shows that the optimum soaking times of As/InAs and Sb/GaSb are 2 sec and 12 sec, at which the highest crystallineity has, respectively. An anomalous twin-peak phenomenon that a satellite peak splits into two peaks was observed in the SLS structure co-soaked by As and Sb at InAs${\rightarrow}$GaSb interfaces. We suggest that it may be resulted from coexistence of two kinds crystalline phases of InAsSb and GaAsSb due to intermixing of In${\leftrightarrow}$Ga and Sb${\leftrightarrow}$As.

• Journal of the Korean Vacuum Society
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• v.20 no.5
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• pp.361-366
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• 2011

An in-situ, real-time monitoring of GaN epilayers grown by low pressure metalorganic chemical vapor deposition system modified for spectral reflectance was performed. Reflectance spectrums from 190~861 nm were observed using p-polarized light with incident angle of $75^{\circ}$. All reflectance spectrums showed interference oscillation caused by multiple reflection within GaN epilayers, and the spectrum from GaN with low crystalline quality showed weak reflectance intensity and much low amplitude of the oscillation because many defects in GaN resulted in light scattering and absorption. Signal variation of reflected light which was selected around strong constructive wavelength range was also observed during $NH_3$ supplying and $NH_3$ cut-off. There was no significant change in signal intensity when $NH_3$ cut-off for 10 sec, but it showed higher intensity when $NH_3$ was cut off for over 30 sec and its intensity kept unchanged. This result indicates that GaN surface was N-terminated during $NH_3$ supplying but Ga-terminated during $NH_3$ cut-off because of high nitrogen equilibrium vapor pressure of GaN, and metallic Ga-terminated surface caused slightly higher reflectance intensity.

• Korean Journal of Environmental Agriculture
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• v.17 no.4
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• pp.352-357
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• 1998

This experiment was conducted to find out the effects of major nutrient levels(N, P, K) on ozone susceptibility of tomato plants(Lycopersicon esculentum Mill, cv. Pink Glory). Plants were grown in water culture system. A half-strength of Hoagland's nutrient solution was considered as a standard formulation($N_{100}$ $P_{100}$ $K_{100}$). The levels of major nutrients were adjusted through addition or removal of several fertilizer salts from the standard solution. Top growth was significantly decreased at the low nitrogen level or phosphorus removal condition. P- and K-contents of leaves were greatly decreased by removal of salts containing P and K from the nutrient solution. The rate of ozone injury was significantly increased when potassium was removed. However, the influence of nitrogen and phosphorus levels or high potassium level on injury occurrence did not show statistical significance compared to the standard solution. Ozone exposure resulted in reduction of chlorophyll, and increase of ethylene production, electrolyte leakage and malondialdehyde(MDA) contents. These changes were much more enhanced in plants grown at the potassium removal solution. Whereas the activity of superoxide dismutase(SOD) was low at the potassium removal treatment and this tendency remained after ozone exposure. These results indicated that potassium nutrient level in tomato plants is closely associated with the susceptibility to ozone injury.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.4
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• pp.110-115
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• 2010

Transparent conducting gallium-doped zinc oxide (GZO) thin films which were deposited on Corning glass substrate using an Gun-type rf magnetron sputtering deposition technology. The GZO thin films were fabricated with an GZO ceramic target (Zn : 97[wt%], $Ga_2O_3$ : 3[wt%]). The GZO thin films were deposited by varying the growth conditions such as the substrate temperature, oxygen pressure. Among the GZO thin films fabricated in this study, the one formed at conditions of the substrate temperature of 200[$^{\circ}C$], Ar flow rate of 50[sccm], $O_2$ flow rate of 5[sccm], rf power of 80[W] and working pressure of 5[mtorr] showed the best properties of an electrical resistivity of $2.536{\times}10^{-4}[{\Omega}{\cdot}cm]$, a carrier concentration of $7.746{\times}10^{20}[cm^{-3}]$, and a carrier mobility of 31.77[$cm^2/V{\cdot}S$], which indicates that it could be used as a transparent electrode for thin film transistor and flat panel display applications.

• The Korean Journal of Pharmacology
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• v.24 no.2
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• pp.197-201
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• 1988

Effects of high concentration of KC1 and caffeine on cytosolic $Ca^{2+}$ level $([Ca^{2+}]_{cyt})$, measured simultaneously with muscle tension using a fluorescent intracellular $Ca^{2+}$ indicator fura 2, were examined in isolated smooth muscle of rat aorta. High $K^+$ (72.7 mM) solution induced sustained increase in both $([Ca^{2+}]_{cyt})$ and tension. In contrast to this, caffeine (20 mM) induced a rapid increase in $([Ca^{2+}]_{cyt})$ followed by a decrease to a level which was higher than the resting level. However, muscle tension showed only a transient increase followed by a decrease below the resting level. In a $Ca^{2+}-free$ solution, high $K^+-induced$ neither $([Ca^{2+}]_{cyt})$ nor tension, whereas caffeine induced a transient increase in both $([Ca^{2+}]_{cyt})$ and muscle tension. These results suggest that high $K^+-induced$ contraction in vascular smooth muscle of rat aorta is due to $Ca^{2+}$ influx whereas caffeine-induced contraction is due to $Ca^{2+}$ release from cellular store. Further, caffeine seems to have an additional effect to decrease the sensitivity of the contractile elements to $Ca^{2+}$.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.443-443
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• 2014

CIS 박막을 제조하기 위한 방법으로 셀렌화(selenization)방식, MOCVD방식, 동시진공증발(co-evaporation)방식, 전착(electrodeposition)방식 등이 있으나, 이러한 방식을 이용하여 CuInSe2 박막을 제조하는 경우 어떤 방법으로든 다원화합물의 조성 및 결정성을 조절하기가 매우 어려운 단점이 있었다. 기판의 온도를 일정 온도로 유지하도록 하고, 증발원을 가열하여 이에 내포된 물질(이원화합물 또는 단일원소)을 증발시켜 기판에 증착이 이루어지도록 하거나, 기판의 온도를 승온시키고 구리 이원화합물을 내포한 증발원을 가열해 물질을 증발시켜 기판에 증착이 이루어지도록 하는 방법으로 기판에 박막이 형성되도록 한다. 기판의 대면적화로 인해 균일한 박막의 형성이 어려워지고 있으며, 이중 15% 이상의 고효율을 보인 방법은 3-stage process를 이용한 동시진공증발방식으로, Cu, In, Ga, Se 등의 각 원소를 동시에 진공 증발시키면서 조성을 조절하여 태양전지에 적절한 전기적, 광학적 특성을 가지는 Cu(In,Ga)Se2 (CIGS)박막을 증착시키는 방법이다. 일반적으로, 실험실에서 연구되고 있는 장비의 구조는 증발원이 아래에 장착되어서 상향 증착되는 방식이다. 본 연구에서 사용된 장비는 하향 증발원이 측면에 장착되어서 하향 증착되는 방식으로 구성하였다. 증착되는 면방향으로, 적외선온도계(pyrometer)가 설치된 시창(viewport)의 오염 등으로 인하여, 지속적인 공정이 이루어지기 힘든 점을 개선하여 증착기판의 후면에 적외선 온도계를 설치하여 기판의 온도변화를 감지하여 공정에 반영할 수 있도록 하였다. 본 연구에서는 하향식 진공 증발원, 기판후면 온도모니터링모듈 등을 개발 장착하여, CIGS 박막을 제조하였으며, 버퍼층은 moving 스퍼터링법으로 ZnS를 증착하였고, 투명전극층은 PLD(Pulsed Laser Deposition)를 이용하여 제조하였다. 가장 높은 광변환효율을 보인 Al/ZnO/CdS/Mo/SLG박막시료는 유효면적 $0.45cm^2$에 광변환효율 15.65 %, Jsc : $33.59mA/cm^2$, Voc : 0.64 V, FF : 73.09 %를 얻을 수 있었으며, CdS를 ZnS로 대체한 Al/ZnO/ZnS/Mo/SLG박막시료는 유효면적 $0.45cm^2$에 광변환효율 12.45 %, Jsc : $33.62mA/cm^2$, Voc : 0.59 V, FF : 62.35 %를 얻을 수 있었다.

• Journal of the Korean Chemical Society
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• v.35 no.5
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• pp.480-486
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• 1991

The solubilities of ethyl bromide in aniline and o-chloroaniline have been measured at 5, 15$^{\circ}$ and 25$^{\circ}$C in the presence and the absence of gallium bromide. When gallium bromide does not exist in the system, the solubility of ethyl bromide in o-chloroaniline is greater than in aniline, indicating a stronger interaction of ethyl bromide with o-chloroaniline than that with aniline. It could be thought that ethyl bromide forms unstable complex with gallium bromide in the presence of gallium bromide in the system. This complex has been assumed in various ways and evaluated, that instability constant (K value) is relatively constancy under the assumption of 1 : 1 complex, $C_2H_5Br{\cdot}GaBr_3$. Therefore, the complex forms the following equilibrium in the solution: $C_2H_5Br{\cdot}GaBr_3\;{\rightleftharpoons}\;C_2H_5Br +1/2Ga_2Br_6$ The instability of the complex of ethyl bromide with gallium bromide is compared with similar complexes of gallium bromide with methyl bromide. The changes of enthalpy, free energy and entropy fcor the dissociation of the complex are also calculated.