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Metal Organic Chemical Vapor Deposition법을 이용한 Germanium 전구체의 증착 특성 연구
김선희,김봉준,김도형,이준기,Kim, Sun-Hee,Kim, Bong-June,Kim, Do-Heyoung,Lee, June-Key 한국재료학회 2008 한국재료학회지 Vol.18 No.6
Polycrystalline germanium (Ge) thin films were grown by metal organic chemical vapor deposition (MOCVD) using tetra-allyl germanium [$Ge(allyl)_4$], and germane ($GeH_4$) as precursors. Ge thin films were grown on a $TiN(50nm)/SiO_2/Si$ substrate by varying the growth conditions of the reactive gas ($H_2$), temperature ($300-700^{\circ}C$) and pressure (1-760Torr). $H_2$ gas helps to remove carbon from Ge film for a $Ge(allyl)_4$ precursor but not for a $GeH_4$ precursor. $Ge(allyl)_4$ exhibits island growth (VW mode) characteristics under conditions of 760Torr at $400-700^{\circ}C$, whereas $GeH_4$ shows a layer growth pattern (FM mode) under conditions of 5Torr at $400-700^{\circ}C$. The activation energies of the two precursors under optimized deposition conditions were 13.4 KJ/mol and 31.0 KJ/mol, respectively.
고투과율 광학유리(SF57HHT) 초정밀절삭의 실험적 연구
김민재(Min-Jae Kim),이준기(June-Key Lee),황연(Yeon Hwang),김혜정(Hye-Jeong Kim),김정호(Jeong-Ho Kim) 한국생산제조학회 2012 한국생산제조학회지 Vol.21 No.2
Heavy flint optical glass(SF57HHT) is new material that has extremely high transmittance. Due to brittleness and high hardness, optical glass is one of the most difficult to materials for ultra-precision turning. According to the hypothesis of ductile machining, all materials, regardless of their hardness and brittleness, will undergo transition from brittle to ductile machining region below critical undefromed chip thickness. In this study, cutting test was carried out to evaluate cutting performance of heavy flint glass using ultra-precision machine with single crystal diamond bite. The machined workpiece surface topography, tool wear and surface roughness were examined using AFM and SEM. The experimental results indicate that the machining mode become the brittle mode to ductile mode, when the maximum undeformed chip thinkness is large than critical value. Tool wear mainly occurs on the flank face and its wear mechanism is dominated by abrasion. This study demonstrates the feasibility of SF57HHT by diamond turning.
전기화학적 정전위 활성화를 사용한 수소 제거에 의한 AlGaN기반의 UV-C 발광 다이오드의 p-형 활성화
이고은(Koh Eun Lee),최낙준(Rak Jun Choi),찬드라 모한 마노즈 쿠마르(Chandra Mohan Manoj Kumar ),강현웅(Hyunwoong Kang),조제희(Jaehee Cho),이준기(June Key Lee) 한국마이크로전자및패키징학회 2021 마이크로전자 및 패키징학회지 Vol.28 No.4
AlGaN 기반 UV-C 발광다이오드(LEDs)에 전기화학적 전위차 활성화(EPA)에 의한 p-형 활성화를 진행하였다. 높은 저항과 낮은 전도도를 유발하는 중성 Mg-H의 복합체의 수소원자를 EPA를 이용하여 제거하여 p-형 활성화 효율을 높였다. 중성 Mg-H 복합체는 주요 매개 변수인 용액, 전압, 시간에 의해 Mg-과 H+로 분해되며, 2차 이온질량 분광법(SIMS) 분석을 통하여 개선된 정공 캐리어의 농도를 확인할 수 있었다. 이 메커니즘은 결국 내부 양자효율(IQE)의 증가, 광 추출 효율 향상, 역 전류 영역의 누설전류 값 개선, 접합 온도 개선 등을 이루어 결과적으로 UV-C LED의 수명을 향상시켰다. 체계적인 분석을 위해 SIMS, Etamax IQE 시스템, 적분구, 전류-전압(I-V) 측정 등을 사용하였으며, 그 결과를 기존의 N2-열 처리 방법과 비교 평가하였다. AlGaN-based UV-C light-emitting diodes (LEDs) were applied for p-type activation by electrochemical potentiostatic activation (EPA). The p-type activation efficiency was increased by removing hydrogen atoms through EPA treatment using a neutral Mg-H complex that causes high resistance and low conductivity. A neutral Mg-H complex is decomposed into Mg- and H+ depending on the key parameters of solution, voltage, and time. The improved hole carrier concentration was confirmed by secondary ion mass spectroscopy (SIMS) analysis. This mechanism eventually improved the internal quantum efficiency (IQE), the light extraction efficiency, the leakage current value in the reverse current region, and junction temperature, resulting in better UV-C LED lifetime. For systematic analysis, SIMS, Etamax IQE system, integrating sphere, and current-voltage measurement system were used, and the results were compared with the existing N2-annealing method.
김민재(Min Jae Kim),이준기(June Key Lee),윤영곤(Yeong Gon Yun),이현성(Hyeon Sung Lee),황연(Yeon Hwang),김혜정(Hye Jeong Kim),김정호(Jeong Ho Kim) 한국생산제조학회 2011 한국생산제조학회지 Vol.20 No.4
There is an immense need to obtain nanometric surface finish on optical glass owing to the advantage of improved performance of the components. But owing to brittleness and hardness, optical glass is one of the materials that is difficult to ultra-precision turning. According to the hypothesis of ductile mode machining, regardless of their hardness and brittleness, will undergo a transition from brittle to ductile machining region below a critical undeformed chip thickness. Below this threshold, it is suggested that the energy required for plastic formation. Thus, plastic deformation is the predominant mechanism of material removal in machining these materials in this mode. An experimental study is conducted diamond cutting for machining BK7 glass. The investigation presents the feasibility of achieving nanometric surface and the understanding the mechanism of cutting glass, proving the cutting edge radius effect.
나노 구조의 패턴을 갖는 n-type GaN 기판을 이용한 380 nm UV-LED의 광 추출 효율 개선
백광선,조민성,이영곤,송영호,김승환,김재관,전성란,이준기,Baek, Kwang-Sun,Jo, Min-Sung,Lee, Young-Gon,Sadasivam, Karthikeyan Giri,Song, Young-Ho,Kim, Seung-Hwan,Kim, Jae-Kwan,Jeon, Seong-Ran,Lee, June-Key 한국재료학회 2011 한국재료학회지 Vol.21 No.5
Ultraviolet (UV) light emitting diodes (LEDs) were grown on a patterned n-type GaN substrate (PNS) with 200 nm silicon-di-oxide (SiO2) nano pattern diameter to improve the light output efficiency of the diodes. Wet etched self assembled indium tin oxide (ITO) nano clusters serve as a dry etching mask for converting the SiO2 layer grown on the n-GaN template into SiO2 nano patterns by inductively coupled plasma etching. PNS is obtained by n-GaN regrowth on the SiO2 nano patterns and UV-LEDs were fabricated using PNS as a template. Two UV-LEDs, a reference LED without PNS and a 200 nm PNS UV-LEDs were fabricated. Scanning Electron microscopy (SEM), Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD), Photoluminescence (PL) and Light output intensity- Input current- Voltage (L-I-V) characteristics were used to evaluate the ITO-$SiO_2$ nanopattern surface morphology, threading dislocation propagation, PNS crystalline property, PNS optical property and UVLED device performance respectively. The light out put intensity was enhanced by 1.6times@100mA for the LED grown on PNS compared to the reference LED with out PNS.
김영복(Young Bok Kim),이의삼(Wee Sam Lee),한승헌(Seung Heon Han),이동길(Dong Kil Lee),이준기(June Key Lee) 한국생산제조학회 2021 한국생산제조학회지 Vol.30 No.3
Machining experiments were conducted to improve the surface morphology of a microlens array using the raster milling method. Three types of raster milling methods were investigated in this study: parallel, tilted, and single-point raster milling. Further, the characteristics of the machined surfaces were analyzed. In parallel raster milling, hump formation on the machined surface was promoted by the tool’s run-out deviation. In tilted raster milling, tool marks occurred on the machined surfaces owing to tool wear. In single-point raster milling, wherein the tool axis rotated according to the lens curvature during machining, the form accuracy of peak-to-valley was confirmed to improve from 0.46 to 0.07 μm. Therefore, single-point raster milling was validated as a highly robust machining method because the surface morphology was rarely affected by tool errors.