• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1996.11a
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• pp.128-134
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• 1996

In this study, the thermal and optical properties of multicomponent glass optical fiber by adding heavy metal oxide Ga$_2$O$_3$were investigated. The fiber samples were made by rod in tube method. The optical loss of fiber was measured in 0.3~1.8${\mu}{\textrm}{m}$ wavelength region. As Ga$_2$O$_3$increased up to 20wt%, the transition and softening temperature of bulk glass were increased from 495$^{\circ}C$ to 579$^{\circ}C$ and from 548$^{\circ}C$ to 641$^{\circ}C$respectively. Whereas the thermal expansion coefficient was decreased from 102 to 79.1$\times$10$^{-7}$ $^{\circ}C$. The refractive index was increased from 1.621 to 1.665, and IR cut-off wavelength was enlarged from 4.64${\mu}{\textrm}{m}$ to 6.1${\mu}{\textrm}{m}$. The optical loss of fiber was decreased and more remarkably decreased in 1.146${\mu}{\textrm}{m}$~1.8${\mu}{\textrm}{m}$ wavelength region.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.8
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• pp.752-758
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• 2004

This paper reports on the DC and RF characteristics of AlGaN/InGaN/GaN high electron-mobility transistors (HEMTs) grown by molecular beau epitaxy(MBE) on sapphire substrates. The devices with a 0.5 ${\mu}$m gate-length exhibited relatively flat transconductance(g$\_$m/), which results from the enhanced carrier confinement of the InGaN channel. The maximum drain current was 880 mA/mm with a peak g$\_$m/ of 156 mS/mm, an f$\_$T/ of 17.3 GHz, and an f$\_$MAX/ or 28.7 GHz. In addition to promising DC and RF results, pulsed I-V and current-switching measurements showed little dispersion in the unpassivated AlGaN/InGaN HEMTs. These results suggest that the addition of In to the GaN channel improves the electron transport characteristics as well as suppressing current collapse that is related to the surface trap states.

• Korean Journal of Materials Research
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• v.7 no.6
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• pp.492-497
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• 1997

HVPE를 이용하여 sapphire기판 위에서 후막 GaN의 성장특성을 조사하였다. 성장온도가 100$0^{\circ}C$에서 110$0^{\circ}C$로 증가하여도 성장속도는 영향을 받지않고 50-60$\mu\textrm{m}$/hr의 성장속도를 나타내었으나 표면특성과 결정성은 향상되었다. 110$0^{\circ}C$에서 성장된 후막 GaN는 DCXRD측정결과 451arcsec의 반티폭을 나타내었으며, PL측정결과 10K에서 19meV의 반치폭을 나타내었다. Ga 공급원의 온도가 93$0^{\circ}C$에서 77$0^{\circ}C$로 감소하여도 성장속도는 영향을 받지 않았으나, 77$0^{\circ}C$의 온도에서 GaN의 결정성이 향상되었다. HCI의 양이 5sccm에서 20sccm으로 증가함에 따라 성장속도가 15$\mu\textrm{m}$/hr에서 60$\mu\textrm{m}$/hr으로 증가하였으며, 표면특성도 향상되었다.

• YAKHAK HOEJI
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• v.35 no.3
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• pp.174-181
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• 1991

These experiments were conducted to investigate the effects of glycyrrhizin(GL) and glycyrrhetinic acid(GA) on histamine synthesis, lymphocyte blastogenesis in C57BL/6J mice splenocytes, IL-1 production, $Ca^{2+}$ uptake by macrophage-like P388D$_{1}$ cells and plaque forming cell assay against SRBC. Histamine contents, lymphocyte blastogenesis, IL-1 activity, $Ca^{2+}$ uptake and plaque forming cell were determined by enzyme isotope method, [sup 3/H]-thymidine incorporation, C3H/HeJ mouse thymocytes proliferation, the addition of 5 $\mu$Ci/ml $^{45}$Ca$^{2+}$ to P388D$_{1}$, cell suspension and assay to sheep red blood cell, respectively. Cytotoxicity, which was expressed as 50% mortality, was occurred by the addition of GL(10$^{-3}$M) and GA(10$^{-4}$M). Histamine production in mouse spleen cell culture was significantly increased by the addition of 0.25 $\mu\textrm{g}$/ml of Con A, after 48 hour incubation. Con A dependent T-lymphocyte proliferation was also enhanced by the addition of 0.25 .mu.g/ml of Con A. The effects of GL on histamine contents and T-lymphocyte proliferation were significantly decreased at high dose (10$^{-5}$M), while IL-1 activity was remarkably suppressed by 10$^{-8}$~10$^{-4}$M of GL. $Ca^{2+}$ uptake was not changed, but antibody production was increased by GL(10 mg/kg). GA inhibited histamine contents at 10$^{-9}$~10$^{-7}$ and depressed Con A (0.25 $\mu\textrm{g}$/ml) dependent T-lymphocyte proliferation at 10$^{-7}$~10$^{-5}$M of GA, but increased suboptimal dose (Con A 0.1 $\mu\textrm{g}$/ml) at 10$^{-9}$~10$^{-7}$M of GA. IL-1 activity was suppressed by 10$^{-8}$~10$^{-4}$M of GA and $Ca^{2+}$ uptake was enhanced by 10$^{-9}$~10$^{-6}$ of GA, but antibody production was not changed by GA. From the above results, it is suggested that GL and GA have immuno-regulatory action. GL decreased cell-mediated immune response, and increased humoral immune response at high dose. On the other hand, low dose of GA enhanced cell-mediated immune response, while high doses of GA decreased humoral immune reaction.

• Journal of Sensor Science and Technology
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• v.8 no.5
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• pp.421-426
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• 1999

In this paper, we present p-channel GaAs MOSFET having $Al_2O_3$ as gate insulator fabricated on a semi-insulating GaAs substrate, which can be operated in the depletion mode. $1\;{\mu}m$ thick undoped GaAs buffer layer, $4000\;{\AA}$ thick p-type GaAs epi-layer, undoped $500{\AA}$ thick AlAs layer, and $50\;{\AA}$ thick GaAs cap layer were subsequently grown by molecular beam epitaxy(MBE) on (100) oriented semi-insulating GaAs substrate and this wafer was oxidized. AlAs layer was fully oxidized as a $Al_2O_3$ thin film. The I-V, $g_m$, breakdown charateristics of the fabricated GaAs MOSFET showed that wet thermal oxidation of AlAs/GaAs epilayer/S I GaAs was successful in realizing depletion mode p-channel GaAs MOSFET.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.5
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• pp.7-13
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• 1997

A X-band 3-stage monolithic LNA (low noise amplifier) with series feedback has been successfully desined and demonstrated by suign 0.5-$\mu\textrm{m}$ GaAs MESFET. In the design of the 3-stage LNA, the effects of series feedback to the noise figure, the gain, and the stability have been investigated ot find the optimal short stub length. As a result, the inductive series feedback topology which has 10degree short stub in the GaAs MESFET source lead, has been employed in the 1-st stage. The fabricated MMIC LNA's chip size is only 1mm$^{2}$/stage, which is smaller than the previously reported X-band MMIC input/output return losses are less than -10dB and -15dB, respectively. The noise figure (NF) is less than 2.6dB. The measured data show good agreement with the simulated values.

• Proceedings of the Optical Society of Korea Conference
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• 1991.06a
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• pp.139-143
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• 1991

GRIN-SCH quantum well structured Laser Diode were fabricated using MOCVD and operated as CW at room temperature. The threshold current density of the LD with 670${\mu}{\textrm}{m}$ cavity length was 530 A/$\textrm{cm}^2$. For the ridge waveguide type index guiding structured LD with 6${\mu}{\textrm}{m}$ stripe width and 240${\mu}{\textrm}{m}$ cavity length, the threshold current was 50㎃. The maximum differential quantum efficiency was 0.95W/A when the optical output was 60mW. The lasing wavelength of QW LD was 865nm. In the L-I measurement. TE mode was superior to TM mode. From the near field pattern, single lateral mode operation was observed.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.146-147
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• 2012

InP 기판위에 자발성장법으로 성장된 InAs 양자점은 $1.55{\mu}m$ 영역에서 발진하는 양자점 반도체 레이저 다이오드 및 광 증폭기를 제작할 수 있기 때문에 많은 관심을 받고 있다. 광통신 대역의 $1.55{\mu}m$ 반도체 레이저 다이오드 및 광 증폭기 분야에서 InAs/InP 양자점이 많은 관심을 받고 있으나, InAs/GaAs 양자점에 비해 제작이 어려운 단점을 가지고 있다. InAs/InP 양자점은 InAs/GaAs 양자점에 비해 격자 불일치가 작아 양자점의 크기가 크고 특히 As 계 박막과 P 계박막의 계면에서 V 족 원소 교환 반응으로 계면 특성 저하가 발생하여 성장이 까다롭다. As 과 P 간의 교환반응은 성장온도와 V/III 에 의해 크게 영향을 받는 것으로 보고되었다. 그러나, P계 InGaAsP 박막 위에 InAs 성장 시 발생하는 As/P 교환반응에 대한 연구는 매우 적다. 본 연구에서는 InGaAsP 박막 위에 InAs 양자점 성장 시 GI (growth interruption)에 의한 As/P 교환반응이 InAs 양자점의 형상 및 광학적 특성에 미치는 영향을 연구하였다. 시료는 수직형 저압 Metal Organic Chemical Vapor Deposition (MOCVD)를 이용하여 $520^{\circ}C$의 온도에서 성장하였다. 그림1(a) 구조의 양자점은 InP (100) 기판위에 InP buffer layer를 성장한 후 InP와 격자상수가 일치하는 $1.1{\mu}m$ 파장의 InGaAsP barrier를 50 nm 성장하였다. 그 후 As 분위기 하에서 다양한 GI 시간을 주었고 그 위에 InAs 양자점을 성장하였다. 양자점 성장 후 InGaAsP barrier를 50 nm, InP capping layer를 50 nm 성장하였다. AFM측정을 위해 InP capping layer 위에 동일한 GI 조건의 InAs/InGaAsP 양자점을 성장하였고 양자점 성장 후 As분위기 하에 온도를 내려주었다. 그림1(b) 구조의 양자점은 그림1(a) 와 모든 조건은 동일하나 InAs 양자점과 InGaAsP barrier 사이에 GaAs 2ML를 삽입한 구조이다. 양자점 형상 특성 평가는 Atomic force microscopy를 이용하였으며, 광특성 분석은 Photoluminescence를 이용하였다.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.1
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• pp.1-7
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• 2000

In this paper, we present n-channel GaAs MOSFET having $Al_2O_3$ as gate in insulator fabricated on a semi-insulating GaAs substrate. 1 ${\mu}$m thick undoped GaAs buffer layer, 1500 ${\AA}$ thick n-type GaAs, undoped 500 ${\AA}$ thick AlAs layer, and 50 ${\AA}$ GaAs caplayer were subsequently grown by molecular beam epitaxy(MBE) on (100) oriented semi-insulating GaAs substrate oxidized. When it was wet oxidized, AlAs layer was fully converted $Al_2O_3$. The I-V, $g_m$, breakdown charateristics of the fabricated GaAs MOSFET showed that wet thermal oxidation of AlAs/GaAs epilayer/S${\cdot}$I GaAs was suitable in realizing depletion mode GaAs MOSFET.

• Korean Journal of Materials Research
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• v.8 no.9
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• pp.860-864
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• 1998

We investigated the photoluminescence and the crystalline properties with Ga doping concentrations (0-12 mol%) in $\textrm{Zn}_{1.98}\textrm{Mn}_{0.02}\textrm{SiO}_{4}$ green phosphors prepared by the solid state reaction. The photoluminescence was improved by a doping of Ga element in $\textrm{Zn}_{1.98}\textrm{Mn}_{0.02}(\textrm{Si_{1-x}\textrm{Ga}_{x})\textrm{O}_{4}$ phosphors which showed the highest emission intensity and good color purity in the doping concentration of x=0.08. The emission intensity of $\textrm{Zn}_{1.98}\textrm{Mn}_{0.02}(\textrm{Si_{1-x}\textrm{Ga}_{x})\textrm{O}_{4}$(x= 0.08) phosphors was increased to 7 times with increasing the sintering temperatures from $1100^{\circ}C$ to $1400^{\circ}C$, showing the improved crystalline quality. The decay time was not affected by Ga doping concentrations with constant values around 24ms. It was found from SEM and PSA analyses that the phosphors were composed of a large number of small grains around 1-3$10\mu\textrm{m}$ with a small amounts of agglomerated particles above $10\mu\textrm{m}$.