In_xGa_1-xN/GaN 다중양자우물 구조의 광학적 성질 연구

김기홍,김인수,박헌보,배인호,유재인,장윤석,Kim, Ki-Hong,Kim, In-Su,Park, Hun-Bo,Bae, In-Ho,Yu, jae-In,Jang, Yoon-Seok 한국진공학회 2009 Applied Science and Convergence Technology Vol.18 No.1

$In_xGa_{1-x}N$/GaN 다중양자우물 구조의 EL 특성을 온도와 주입전류 변화에 따른 특성을 조사하였다 저전류와 고전류 주입시 EL 효율의 온도 의존 변화는 매우 다르게 나타나는데, 이러한 온도와 전류의 변화에 의한 독특한 EL 효율의 변화는 내부전기장의 존재 하에 순방향 바이어스에 기인한 외부전기장의 영향인 것으로 볼 수 있다. 그리고 $In_xGa_{1-x}N$/GaN 다중양자우물 구조에서 In 성비의 증가는 발광파장위치의 적색이동을 보였다. 15K에서 주입 전류의 증가에 따라 녹색 양자우물 구조는 80 meV와 청색 양자우물 구조는 22 meV의 청색 편이를 하였다. 이는 전류의 증가에 의해 단위 시간당 생성되는 캐리어 수가증가하게 되고 그에 따라 subband가 급격히 채워지는 band filling 현상이 일어나게 되어 짧은 파장에서 재결합이 증가하기 때문이다. 그리고 청색과 녹색 다중 양자우물구조의 짧은 파장 쪽으로의 편이 차이는 In 농도에 기인한 것으로 In 농도가 높으면 양자우물 깊이가 증가되어 더 강한 양자속박효과가 작용하여 캐리어 구속력이 증가하기 때문 것으로 볼 수 있다. Temperature and injection current dependence of electroluminescence(EL) spectral intensity of the $In_xGa_{1-x}N$/GaN multi-quantum wells(MQW) have been studied over a wide temperature range and as a function of injection current level. It is found that a temperature-dependent variation pattern of the EL efficiency under very low and high injection currents shows a drastic difference. This unique EL efficiency variation pattern with temperature and current can be explained field effects due to the driving forward bias in presence of internal(piezo and spontaneous polarization) fields. Increase of the indium content in $In_xGa_{1-x}N$/GaN multiple quantum wells gives rise to a redshift of 80 meV and 22 meV for green and blue MQW, respectively. It can be explained by carrier localization by potential fluctuation of multiple quantum well and MQW structures also shows a keen difference owing to the different indium content in InGaN/GaN MQW.

n-GaAs 구조에서의 ArF excimer laser annealing에 따른 Photoreflectance 특성 연구

김기홍,유재인,심준형,배인호,임진환,김진희,유재용,Kim, Ki-Hong,Yu, Jae-In,Sim, Jun-Hyoung,Bae, In-Ho,Lim, Jin-Hwan,Kim, Jin-Hi,Yu, Jae-Yong 한국진공학회 2007 Applied Science and Convergence Technology Vol.16 No.2

n-GaAs의 시료를 furnace annealing 처리와 laser annealing 처리를 한 후, PR 방법으로 비교 조사하였다. 시료는 Furnace annealing을 5 분간 $400{\sim}800^{\circ}C$에서 처리한 시료와 ArF excimer laser($30{\sim}50\;W$)로 5 분간 Laser annealing 처리 한 시료로 준비하였다. Furnace로 annealing을 한 경우에 주 신호(정점)는 1.43 eV에서 관측되었는데 비해 laser로 annealing 한 샘플은 1.42 eV로 0.01 eV가 더 작게 관측되었다. 이는 laser annealing이 furnace annealing 보다 표면과 내면에서 일어나는 열처리 효과가 더 고르게 일어나가 때문이다. We investigated variation of the photoreflectance(PR) signals for n-GaAs furnace and laser annealed. The samples were annealed by using ArF excimer laser(5 min, $30{\sim}50\;W$) and furnace(5 min $400{\sim}700^{\circ}C$). The PR signals(top point) measured from the ArF excimer laser annealed sample showed 1.42 eV and furnace annealed sample showed 1.43 eV. This result is ArF excimer laser annealed sample was uniform annealed surface and inter state.

AlAs 에피층 위에 성장된 InAs 양자점의 Photoluminescence 특성연구

김기홍,심준형,배인호,Kim, Ki-Hong,Sim, Jun-Hyoung,Bae, In-Ho 한국재료학회 2009 한국재료학회지 Vol.19 No.7

The optical characterization of self-assembled InAs/AlAs Quantum Dots(QD) grown by MBE(Molecular Beam Epitaxy) was investigated by using Photoluminescence(PL) spectroscopy. The influence of thin AlAs barrier on QDs were carried out by utilizing a pumping beam that has lower energy than that of the AlAs barrier. This provides the evidence for the tunneling of carriers from the GaAs layer, which results in a strong QD intensity compared to the GaAs at the 16 K PL spectrum. The presence of two QDs signals were found to be associated with the ground-states transitions from QDs with a bimodal size distribution made by the excitation power-dependent PL. From the temperature-dependent PL, the rapid red shift of the peak emission that was related to the QD2 from the increasing temperature was attributed to the coherence between the QDs of bimodal size distribution. A red shift of the PL peak of QDs emission and the reduction of the FWHM(Full Width at Half Maximum) were observed when the annealing temperatures ranged from 500 $^{\circ}C$ to 750 $^{\circ}C$, which indicates that the interdiffusion between the dots and the capping layer was caused by an improvement in the uniformity size of the QDs.

자연 성장된 InAs/AlAs 양자점의 Photoreflectance 특성

김기홍,심준형,배인호,Kim, Ki-Hong,Sim, Jun-Hyoung,Bae, In-Ho 한국진공학회 2009 Applied Science and Convergence Technology Vol.18 No.3

MBE법으로 성장된 InAs/AlAs 양자점(quantum dots; QD) 구조의 광학적 특성을 photoreflectance(PR) 이용하여 조사하였다. Wetting layer(WL) 두께에 따른 전체 장벽의 폭이 달라짐에 따라 GaAs 완충층 및 WL 신호의 세기가 변화되었다. QD 층이 식각된 시료의 상온 PR측정 결과로부터 $1.1{\sim}1.4\;eV$ 영역의 완만한 신호는 InAs QDs과 WL에 관련된 신호임을 알았다. 온도 $450{\sim}750^{\circ}C$범위에서 열처리 시켰을 때 WL층의 PR 신호가 red shift하였는데, 이는 열처리 후 InAs WL와 AlAs층 사이에 Al과 In의 내부 확산에 의해 양자점의 크기가 균일하게 재분포 되고, WL의 임계 두께가 증가하였음을 나타낸다. The optical characterization of self-assembled InAs/AlAs quantum dots(QD) grown by MBE were investigated using photoreflectance spectroscopy. The intensities of the signals of the GaAs buffer and wetting layer(WL) changed with the width of the WL layer. The PR spectrum for the sample, in which QDs layer were etched off at room temperature, indicated that the broadened signal ranging $1.1{\sim}1.4\;eV$ was originated from InAs QDs and WL. The intensities of signals of GaAs buffer and the WL changed with the WL width. A red shift of the PR peak of WL are observed when the annealing temperatures range from $450^{\circ}C$ to $750^{\circ}C$, which indicates that the interdiffusion between dots and capping layer is caused by improvement in size uniformity of QDs.

표면조도 특성에 따른 저항 점 용접성 평가 및 너깃 형성 고찰

김기홍,최영민,김영석,임영목,유지훈,강남현,박영도,Kim, Ki-Hong,Choi, Yung-Min,Kim, Young-Seok,Rhym, Young-Mok,Yu, Ji-Hun,Kang, Nam-Hyun,Park, Yeong-Do 대한용접접합학회 2008 대한용접·접합학회지 Vol.26 No.5

With the increased use of surface textured steel sheet in body-in-white assembly, resistance spot weldability of these steels is considered to be an important subject. This study evaluated nugget formation and weldability by measuring dynamic resistance with various weld pressure, current, and weld time for steel sheet with two different surface roughnesses. The surface roughness for T-H steel ($R_{a}=1.70\;{\mu}m$) was higher than that for T-L steel ($R_{a}=1.33\;{\mu}m$), and resulted in increased contact resistance and heating for T-H steel spot welding. Therefore, at low weld current and weld cycle ranges, the T-H steel showed better weldability over the T-L steel. The evaluations of weld interface showed that the fusion zone in the T-H steel sheet was continuous in contrast to discontinuous fusion zone for T-L steel sheet at the same welding conditions. A comparison of dynamic resistance and tensile-shear strength (TSS) between T-H and T-L steel sheet suggested that high surface roughness provided larger heating at early cycle of welding and larger TSS.

Benedenia derzhavini (Trematoda : Monogenea) from Cultured Korean Rockfish, Sebastes schlegeli, in Korea

김기홍,권세련,Kim, Ki-Hong,Kwon, Se-Ryun 한국어병학회 1998 한국어병학회지 Vol.11 No.1

The benedeniine monogenean Benedenia derzhabini (Layman, 1930) Meserve, 1938 from cultured Korean rockfish, Sebastes schlegeli, is described and reported for the first time in Korea. The parasite was recovered from the gills and inner wall of operculum. B. derzhavini is distinguished from B. seriolae and B. sebastodis by the relative shape and length between the accessory sclerites and the hamuli. Benedeniidae과에 속하는 단생흡충류인 Benededia derzhavini(Layman, 1930) Meserve, 1938가 양식 조피볼락의 아가미와 아가미 뚜껑 내벽에 기생하고 있음을 국내에서 처음으로 보고하며, 아울러 이 종의 형태학적 특징을 자세히 기술하였다. B. derzhayini는 B. seriolae 및 B. sebastodis 등의 종들과 accessory sclerite와 hamuli의 형태 및 상대적인 길이 비율 차이에 의해서 구별되었다.

극저온 환경에 적용되는 INCONEL 718합금의 Gas Tungsten Arc Welding 기계적 특성 평가

김기홍,문인상,문일윤,이병호,Kim, Ki-Hong,Moon, In-Sang,Moon, Il-Yoon,Rhee, Byung-Ho 한국재료학회 2009 한국재료학회지 Vol.19 No.12

Inconel 718 alloy has excellent mechanical properties at room temperature, high temperature and cryogenic conditions. UTS of base metal is about 900MPa at room temperature; this is increased up to 1300MPa after heat treatment & aging-hardening. Mechanical properties of Inconel 718 Alloy were similar to those shown in the the results for tensile test; mechanical properties of Inconel 718 alloy's GTAW were similar to those of base metal's properties at room temperature. Mechanical properties at cryogenic conditions were better than those at room temperature. Heat-treated Inconel 718, non- filler metal GTAW on Inconel 718 and GTAW used filler metal on Inconel 718's UTS was 1400MPa at cryogenic condition. As a result, the excellent mechanical properties of Inconel 718 alloy under cryogenic conditions was proved through tensile tests under cryogenic conditions. In addition, weldability of Inconel 718 alloy under cryogenic conditions was superior to that of its base-metal. In this case, UTS of hybrid joint (IS-G) at -100$^{\circ}C$ was 900MPa. Consequently, UTS of Inconel 718 alloy is estimated to increase from -100$^{\circ}C$ to a specific temperature below -100$^{\circ}C$. Therefore, Inconel 718 alloy is considered a pertinent material for the production of Lox Pipe under cryogenic conditions.

Spatial distribution of Microcotyle sebastis (Monogenea: Microcotyliidae) on Gills of the Cultured Korean Rockfish, Sebastes schlegeli

김기홍,최은석,지보영,Kim, Ki-Hong,Choi, Eun-Seok,Ji, Bo-Young 한국어병학회 1998 한국어병학회지 Vol.11 No.1

Distribution of a monogenean helminth Microcotyle sebastis on the gills of cultured Korean rockfish (Sebastes schlegeli) was investigated with regard to gill arches, sides of gill hemibranches (anterior or posterior), and their sections (dorsal, medial and ventral). M. sebastis has a significant preference for the second and third pair of gills, and shows marked affinity for anterior hemibranches of each gill branch, and medial sections of each gill hemibranch. The results suggest that the larger volume of water flows and surface area of the second and third pair of gills might affect the distribution of M. sebastis, and the concentrated distribution of M. sebastis on the anterior medial section of gills would be related with the increasing chances of mating by niche restriction. 양식 조피볼락에 기생하는 단생흡충류인 Microcotyle sebastis의 분포패턴을 아가미 새궁별, 새엽별(전방과 후방) 및 등면, 중앙면, 복면으로 구분하여 조사하였다. 조사 결과 M. sebastis는 제 2 및 제 3 새궁에 유의성 있는 선호도를 나타냈으며, 후방보다는 전방부의 새엽과 중앙 부위에서 집중적으로 발견되었다. 이러한 결과로 부터 각 아가미 새엽으로 들어오는 물의 양과 아가미의 표면적이 M. sebastis의 분포에 영향을 미칠 수 있는 것으로 여겨지며, 또한 전방 중앙부에 집중적으로 기생하는 원인은 미소서식처의 범위를 좁힘으로써 개체간의 접촉을 증가시기고, 이를 통해 교미의 효율을 높이기 위한 것으로 사료된다.

감자튀김시 Silicone Oil 의 튀김유 산화방지효과에 관한 연구

김기홍,정병상,심중환,배재오 ( Ki Hong Kim,Byoung Sang Chung,Joong Hwan Sim,Jae Oh Bae ) 한국유화학회 1993 한국응용과학기술학회지 Vol.10 No.2

탄화실 부착카본 제거장치 개발

김기홍,이용국 ( Ki Hong Kim,Yong Kuk Lee ) 한국화학공학회 1995 화학공학의이론과응용 Vol.1 No.2