• Journal of the Korean Institute of Telematics and Electronics D
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• v.34D no.4
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• pp.62-72
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• 1997

The optical power splitter/couplers based on MMI(multimode interference) in GaAs/AlGaAs are studied. We presetn a design of optical power splitter/couplers, which have deeply etched multimode waveguide. The properties and fabrication tolerance on the etching depth, multimode waveguide width are simulatedusing a FD-BPM (finite difference beam propgation method). Proposed 1*N optical of designed device is 0.7dB smaller than the optical power splitter with a shallowly etched MMI section. For 0.5dB excess loss, the predicted fabrication tolerance is 0.6.mu.m on the multimode waveguide width of the 14 optical power splitter with a deeply etched MMI section. Also excess loss and uniformity of poposed 32*32 optical power coupler are below 0.3dB. The excess loss of proposed 32*32 optical power coupler is 2dB smaller than the optical power coupler with a shallowly etched MMI section. It is shown that the optical power splitters/couplers with a deeply etched mMI section have low loss, good uniformity, and improved fabriction tolerance.

• Proceedings of the Korean Vacuum Society Conference
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• 2007.08a
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• pp.359-359
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• 2007

• Korean Journal of Materials Research
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• v.28 no.11
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• pp.659-662
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• 2018

We report the properties of infrared photodetectors based on two kinds of quantum dots(QDs): i) 2.0 ML InAs QDs by the Stranski-Krastanov growth mode(SK QDs) and ii) sub-monolayer QDs by $4{\times}[0.3ML/1nm\;In_{0.15}Ga_{0.85}As]$ deposition(SML QDs). The QD infrared photodetector(QDIP) structure of $n^+-n^-(QDs)-n^+$ is epitaxially grown on GaAs (100) wafers using molecular-beam epitaxy. Both the bottom and top contact GaAs layers are Si doped at $2{\times}10^{18}/cm^3$. The QD layers are grown with Si doping of $2{\times}10^{17}/cm^3$ and capped by an $In_{0.15}Ga_{0.85}As$ layer at $495^{\circ}C$. The photoluminescence peak(1.24 eV) of the SML QDIP is blue-shifted with respect to that (1.04 eV) of SK QDIPs, suggesting that the electron ground state of SML QDIP is higher than that of the SK QDIP. As a result, the photoresponse regime(${\sim}9-14{\mu}m$) of the SML QDIP is longer than that (${\sim}6-12{\mu}m$) of the SK QDIP. The dark current of the SML QDIP is two orders of magnitude smaller value than that of the SK QDIP because of the inserted $Al_{0.08}Ga_{0.92}As$ layer.

• Clean Technology
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• v.18 no.1
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• pp.83-88
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• 2012

In order to improve the stability of ${\gamma}-Al_2O_3$ on hydrolysis of $SF_6$, the catalytic promoters were investigated in this study. The crystal phase of ${\gamma}-Al_2O_3$ is transformed to their ${\alpha}$-phase during hydrolysis of $SF_6$. Various metal oxides were applied as the promoter material that is Ga, Mg, and Zn and the promoter of 1, 5, and 10 wt% was impregnated over ${\gamma}-Al_2O_3$ by the impregnation method. Specially, it were confirmed in the catalytic activity tests and XRD analysis that ZnO/${\gamma}-Al_2O_3$ catalyst had the high activity for decomposition of $SF_6$ by catalytic hydrolysis and the crystal phase of ZnO promoted ${\gamma}-Al_2O_3$ was not transformed. From these results, it could be known that the stability of ${\gamma}-Al_2O_3$ is enhanced with the catalytic promotion of ZnO impregnated over the surface of catalyst.

• Proceedings of the IEEK Conference
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• 2006.06a
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• pp.471-472
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• 2006

The passivation technology is very important, because this technology can protect a device against the influence of ambient environment, and prevent the performance reduction. In this paper, we fabricated the $0.1{\mu}m\;{\Gamma}$-gate InAlAs/InGaAs metamorphic high electron mobility transistors (MHEMTs) on GaAs substrates using the low-k benzocyclobutene (BCB) and $Si_3N_4$ as a passivation and we performed the comparisons of characteristics of the MHEMTs. After passivation, the DC and RF measurement results were decreased either the conventional Si3N4 or BCB layers. The decrement of the BCB passivation was smaller than the $Si_3N_4$ passivation.

• Journal of the Korean Vacuum Society
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• v.19 no.1
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• pp.10-13
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• 2010

We studied the effect of $O_2$ plasma treatments on the electrical property of Ti / Al ohmic contacts to N-face n-type GaN. The surface of N-face, n-type GaN has been treated with $O_2$ plasma for 120 s before the deposition of bilayered electrodes, Ti (50 nm) / Al (35 nm), and its contact resistance was compared with that of the reference sample without $O_2$ plasma. As a result, we found that the ohmic contact was reduced from $4.3\;{\times}\;10^{-1}\;{\Omega}cm^2$ to $1.25\;{\times}\;10^{-3}\;{\Omega}cm^2$ by applying $O_2$ plasma on the surface of n-type GaN, which was attributed to the reduction in the Schottky barrier height (SBH), caused by nitrogen vacancies formed during the $O_2$ plasma process.

• Nuclear Engineering and Technology
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• v.54 no.7
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• pp.2579-2585
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• 2022

Ceramics of quaternary garnets (Gd,Y)₃Al₂Ga₃O₁₂ doped with Ce, Tb have been fabricated and evaluated as prospective materials for indirect energy converters of α-and β-voltaic. Samples were characterized at excitation with an X-ray source and an intense 150 keV electron beam and showed good temperature stability of their emission and tolerance to irradiation. The role of X-rays accompanied the α-particle emitting in the increase of the conversion efficiency is clarified. The garnet-type structure of the matrix in the developed materials allows the production of quality crystalline mass with a light yield exceeding that of the commonly used YAG: Ce scintillator by a factor of two times.

• Journal of The Korean Astronomical Society
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• v.36 no.spc1
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• pp.93-99
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• 2003

Various attempts have been made to explain the: pronounced seasonal and universal time (UT) variations of geomagnetic indices. As one of such attempts, we analyze the hourly-averaged auroral electroject indices obtained during the past 20 years. The AU and AL indices maximize during summer and equinoctial months, respectively. By normalizing the contribution of the solar conductivity enhancement to the AU index, or to the eastward electrojet, it is found that the AU also follows the same semiannual variation pattern of the AL index, suggesting that the electric field is the main modulator of the semiannual magnetic variation. The fact that the variation pattern of the yearly-mean AU index follows the mirror image of the AL index provides another indication that the electric field is the main modulator of magnetic disturbance. The pronounced UT variations of the auroral electrojet indices are also noted. To determine the magnetic activity dependence, the probability of recording a given activity level of AU and AL during each UT is examined. The UT variation of the AL index, thus obtained, shows a maximum at around 1200-1800 UT and a minimum around 0000-0800 UT particularly during winter. It is closely associated with the rotation of the geomagnetic pole around the rotational axis, which results in the change of the solar-originated ionospheric conductivity distribution over the polar region. On the other hand the UT variation is prominent during disturbed periods, indicating that the latitudinal mismatch between the AE stations and the auroral electrojet belt is responsible for it. Although not as prominent as the AL index, the probability distribution of the AU also shows two UT peaks. We confirm that the Dst index shows more prominent seasonal variation than the AE indices. However, the UT variation of the Dst index is only noticeable during the main phase of a magnetic storm. It is a combined result of the uneven distribution of the Dst stations and frequent developments of the partial ring current and substorm wedge current preferentially during the main phase.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.6
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• pp.372-375
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• 2017

ZnO thin films were deposited by RF magnetron sputtering and then diffused by using an As source in the ampouletube. Also, the ZnO p-n homojunction was made by using As-doped ZnO thin films, and its properties were analyzed. After the As doping, the surface roughness increased, the crystal quality deteriorated, and the full width at half maximum was increased. The As-doped ZnO thin films showed typical p-type properties, and their resistivity was as low as $2.19{\times}10^{-3}{\Omega}cm$, probably because of the in-diffusion from an external As source and out-diffusion from the GaAs substrate. Also, the ZnO p-n junction displayed the typical rectification properties of a p-n junction. Therefore, the As diffusion method is effective for obtaining ZnO films with p-type properties.

• Journal of the Korean Vacuum Society
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• v.19 no.2
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• pp.141-147
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• 2010

In this study, high-k oxide films like $Al_2O_3$, $TiO_2$, $HfO_2$ were deposited on Si, $SiO_2$/Si, GaAs wafers, and then the thermal conductivity was measured by using thermo-reflectance method which utilizes the reflectance variation of the film surface produced by the periodic temperature variation. The result shows that high-k oxide films with 50 nm thickness have high thermal conductivity of 0.80~1.29 W/(mK). Therefore, effectively dissipate the heat generated in the electric circuit such as CMOS memory device, and the heat transfer changes according to the micro grain size.