• Journal of the Microelectronics and Packaging Society
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• v.28 no.1
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• pp.13-20
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• 2021

GaN has shown good potential owing to its better chemical stability than other materials and tunable bandgap with materials such as InN and AlN. Tunable bandgap allows GaN to make the maximum utilization of the solar spectrum, thus improves the solar-to-hydrogen (STH) efficiency. In addition, GaN band gap contains the oxidation and reduction level of water, so it can split water without external voltage. However, STH efficiency using GaN itself is low and has been actively studied recently to improve it. In this thesis, we have summarized the studies related to the use of GaN as a photoelectrode for photoelectrochemical water splitting.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.35 no.3
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• pp.308-310
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• 2022

Ultrawide bandgap gallium oxide (Ga₂O₃) semiconductors are known to have excellent photocatalytic properties due to their high redox potential. In this study, CO₂ reduction is demonstrated using nanostructured Ga₂O₃ photocatalyst under ultraviolet (254 nm) light source conditions. After the CO₂ reduction, C₂H₄ remained as a by-product in this work. Nanostructured Ga₂O₃ photocatalyst also showed an excellent endurance characteristic. Photogenerated electron-hole pairs boosted the CO₂ reduction to C₂H₄ via nanostructured Ga₂O₃ photocatalyst, which is attributed to the ultrawide and almost direct bandgap characteristics of the gallium oxide semiconductor. The findings in this work could expedite the realization of CO₂ reduction and a simultaneous C₂H₄ production using a low cost and high performance photocatalyst.

• Korean Chemical Engineering Research
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• v.56 no.4
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• pp.585-591
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• 2018

Characteristics of nano-structured $SiO_2:Zn$ hollow powders prepared in the micro drop fluidized reactor process were investigated with respect to bandgap energy and surface activity. The $SiO_2:Zn$ hollow powders were successfully prepared continuously in the one step process with reasonable production efficiency, with varying the amount of THAM (tris(hydroxymethyl)-aminomethane) additive and concentration of $Zn^{2+}$ ions. The doping of $Zn^{2+}$ ions into $SiO_2$ lattice led to the reduction of bandgap energy by forming the acceptor level of $Zn^{2+}$ below the conduction band of $Si^{4+}$ ions. The hollow shape also contributed to reduce the bandgap energy of $SiO_2:Zn$ powders. The doping of $Zn^{2+}$ ions into $SiO_2$ hollow powders could enhance the surface activity by forming SiO-H stretching and oxygen vacancies at the surface of $SiO_2:Zn$ powders.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.3 s.94
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• pp.300-310
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• 2005

In this paper we propose the compact three-layer EBG structure. The unit cell of the proposed EBG structure is composed of a square patch in the upper layer and a square ring stripline in the lower layer that are connected to the ground plane through conducting vias. Reflection phase analysis method and tangential transmission method were considered to accomplish effective EM simulation and measurement. EM simulation results indicate that bandgap characteristics of the EBG structure using both methods is nearly identical. Parametric studies have been performed with the EM simulator to analyze the properties of the EBG structure by investigating the phase shift of the normally incident plane wave, and the transmission measurements between simple monopole antennas positioned near the EBGstructure have been done. The operating fiefuency bandgap of the proposed EBG structure is about 34 $\%$ lower than the conventional EBG structure with the same size. Measured results show bandgap from 0.930 GHz to 0.945 GHz.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.4
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• pp.121-127
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• 2022

β-Gallium oxide (Ga₂O₃), an ultra-wide bandgap semiconductor, has attracted great attention due to its promising applications for high voltage power devices. The most stable phase among five different polytypes, β-Ga₂O₃ has the wider bandgap of 4.9 eV and higher breakdown electric field of 8 MV/cm. Furthermore, it can be grown from melt source, implying higher growth rate and lower fabrication cost than other wide bandgap semiconductors such as SiC, GaN and diamond for the power device applications. In this study, β-Ga₂O₃ bulk crystals were grown by the edge-defined film-fed growth (EFG) process. The growth direction and the principal surface were set to be the [010] direction and the (100) plane of the β-Ga₂O₃ crystal, respectively. The spectra measured by Raman an alysis could exhibit the crystal phase an d impurity dopin g in the β-Ga₂O₃ ingot, and the crystallinity quality and crystal direction were analyzed using high-resolution X-ray diffraction (HRXRD). The crystal quality and various properties of as-grown β-Ga₂O₃ ribbon was systematically analyzed in order to investigate the spatial variation in entire crystal grown by EFG method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.3A
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• pp.430-434
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• 2000

In this paper, a novel photonic bandgap(PBG) structure is proposed for increasing stropband of lowpass filter without the size increment of circuit for application in microstrip circuits. The proposed structure is connected in parallel two periodic structures which have different center frequency of the stopband. The wide stopband is achieved by two periodic structures of two different stopbands. We also show the performance improvement of microstrip patch antenna by etching of the proposed structure in ground plane.

• Proceedings of the Korean Vacuum Society Conference
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• 2009.08a
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• pp.204-204
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• 2009

• 한국정보통신설비학회:학술대회논문집
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• 2003.08a
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• pp.20-22
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• 2003

본 논문에서는 Photonic Bandgap(PBG)를 공진 특성을 이용하여 마이크로파 발진기의 위상잡음을 줄이기 위한 기술을 제시한다. 마이크로스트립 라인으로 구현한 공진기는 낮은 Q(Quality factor)를 가진다. PBG를 적용했을 때 공진기의 Q값을 높여줌으로써 발진기의 위상잡음 특성이 향상됨을 보이고자 한다.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2002.11a
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• pp.34-38
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• 2002

기존에 제안된 도파관 스위치의 경우, 도파관의 E-plane에 PBG 기판을 내장하게 되는데, 이 경우 PBG 기판의 저항값을 조절해주는 MEMS 스위치의 바이어스 라인에 대한 문제점이 발생한다 본 논문에서는 PBG 기판을 도파관의 H-plane에 놓음으로써 바이어스 라인을 RF로부터 쉽게 분리하고, 또한 단일 공진 주파수를 갖는 PBG의 경우에 제한된 기판의 길이로 인하여 bandwidth가 좁아지는 문제점을 서로 다른 공진 주파수를 갖는 PBG 기판의 연결을 통해서 bandwidth를 약 80%이상 증가시킬 수 있음을 보였다.

• Proceedings of the IEEK Conference
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• 2003.07a
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• pp.354-357
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• 2003

The low noise and balanced amlifier has been designed by using PBG. Usually balanced LNAis used to matching the input and output mismatching that caused by matching the low noise matching point. And the PBG supresses the harmoincs. This paper proposed balanced LNA by using PBG. And this configuration improve the performance - noise figure, VSWR.