• 한국응용과학기술학회지
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• 제34권1호
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• pp.50-57
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• 2017

금속산화물 반도체 중 하나인 산화아연은 인체에 무해하고 친환경적이며, 우수한 화학적, 열적 안정성의 특성을 지니며 3.37 eV의 넓은 밴드갭 에너지와 60 meV의 높은 엑시톤 바인딩 에너지로 인해 태양전지, 염료페기물의 분해, 가스센서 등 다양한 분야에 응용이 가능한 물질이다. 산화아연은 입자 형상 및 결정성의 변화에 따라 광촉매 활성이 변하게 된다. 따라서, 다양한 실험변수와 첨가제를 사용하여 입자를 합성하는 것이 매우 중요하다. 본 논문에서는 마이크로파 수열합성법을 사용하여 산화아연을 합성하였다. 전구체로는 질산아연을 사용하였고, 수산화나트륨을 사용하여 용액의 pH를 11로 조정하였다. 첨가제로는 계면활성제인 에탄올아민, 세틸트리메틸암모늄브로마이드, 소듐도데실설페이트, 솔비탄모노올레이트를 첨가하였다. 합성된 입자는 별모양, 원추형, 씨드형태, 박막형태의 구형의 형상을 보였다. 합성된 산화아연의 물리 화학적 특성은 XRD, SEM, TGA을 통하여 확인하였고, 광학적 특성은 UV-vis spectroscopy, PL spectroscopy, Raman spectroscopy으로 확인하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.286-286
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• 2016

Hexagonal boron nitride (hBN) is a dielectric insulator with a two-dimensional (2D) layered structure. It is an appealing substrate dielectric for many applications due to its favorable properties, such as a wide band gap energy, chemical inertness and high thermal conductivity[1]. Furthermore, its remarkable mechanical strength renders few-layered hBN a flexible and transparent substrate, ideal for next-generation electronics and optoelectronics in applications. However, the difficulty of preparing high quality large-area hBN films has hindered their widespread use. Generally, large-area hBN layers prepared by chemical vapor deposition (CVD) usually exhibit polycrystalline structures with a typical average grain size of several microns. It has been reported that grain boundaries or dislocations in hBN can degrade its electronic or mechanical properties. Accordingly, large-area single crystalline hBN layers are desired to fully realize the potential advantages of hBN in device applications. In this presentation, we report the growth and transfer of centimeter-sized, nearly single crystal hexagonal boron nitride (hBN) few-layer films using Ni(111) single crystal substrates. The hBN films were grown on Ni(111) substrates using atmospheric pressure chemical vapor deposition (APCVD). The grown films were transferred to arbitrary substrates via an electrochemical delamination technique, and remaining Ni(111) substrates were repeatedly re-used. The crystallinity of the grown films from the atomic to centimeter scale was confirmed based on transmission electron microscopy (TEM) and reflection high energy electron diffraction (RHEED). Careful study of the growth parameters was also carried out. Moreover, various characterizations confirmed that the grown films exhibited typical characteristics of hexagonal boron nitride layers over the entire area. Our results suggest that hBN can be widely used in various applications where large-area, high quality, and single crystalline 2D insulating layers are required.

• 공업화학
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• 제7권5호
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• pp.954-962
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• 1996

측쇄가 메틸, 페닐 혹은 이들이 혼합된 구조인 4종의 폴리실란계 고분자를 합성하고, 이어서 이들에 요오드를 도핑하여 변형된 폴리실란/$I_2$ 고분자들을 얻었다. 그들의 구조적, 열적, 전기적 특성을 FT-IR, UV/VIS, TGA/DTG,DSC, 전기전도도 측정을 통하여 체계적으로 관찰하였다. FT-IR 스펙트럼들에 의하여 원하는 측쇄를 함유한 폴리실란계 고분자의 합성을 확인하였다. 열분석에 의하여 측쇄그룹이 메틸기에서 페닐기로 치환됨에 따라 열안정성이 증가함을 확인 하였다. UV/VIS 분석에서는 메틸기의 치환체에서 나타나는 350nm의 실리콘 결합의 ${\sigma}-{\sigma}*$ 전이는 페닐기가 치환되면서 장파장쪽으로 이동하였으며 이는 ${\pi}$ 전자의 비편재화에 의한 띠간격의 감소가 발생함을 나타내었다. 요오드로 도핑된 고분자들은 도핑되지 않은 고분자들에 비하여 다단계의 열분해가 일어나며 잔기의 함량도 높았다. 전도도는 폴리실란 고분자에서는 $10^{-5}S/cm$ 범위의 값을 가지고 도핑 폴리실란에서 $10^{-4}S/cm$ 범위의 값들을 나타내었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.345-346
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• 2013

InGaN material is being studied increasingly as a prospective material for solar cells. One of the merits for solar cell applications is that the band gap energy can be engineered from 0.7 eV for InN to 3.4 eV for GaN by varying of indium composition, which covers almost of solar spectrum from UV to IR. It is essential for better cell efficiency to improve not only the crystalline quality of the epitaxial layers but also fabrication of the solar cells. Fabrication includes transparent top electrodes and surface texturing which will improve the carrier extraction. Surface texturing is one of the most employed methods to enhance the extraction efficiency in LED fabrication and can be formed on a p-GaN surface, on an N-face of GaN, and even on an indium tin oxide (ITO) layer. Surface texturing method has also been adopted in InGaN-based solar cells and proved to enhance the efficiency. Since the texturing by direct etching of p-GaN, however, was known to induce the damage and result in degraded electrical properties, texturing has been studied widely on ITO layers. However, it is important to optimize the ITO thickness in Solar Cells applications since the reflectance is fluctuated by ITO thickness variation resulting in reduced light extraction at target wavelength. ITO texturing made by wet etching or dry etching was also revealed to increased series resistance in ITO film. In this work, we report a new way of texturing by deposition of thickness-optimized ITO films on ITO nano dots, which can further reduce the reflectance as well as electrical degradation originated from the ITO etching process.

• 한국결정성장학회지
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• 제16권5호
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• pp.189-197
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• 2006

[$AgGaSe_2$] 단결정 박막을 수평 전기로에서 합성한 $AgGaSe_2$ 다결정을 증발원으로하여, hot wall epitaxy(HWE) 방법으로 증발원과 기판(반절연성-GaAs(100))의 온도를 각각 $630^{\circ}C,\;420^{\circ}C$로 고정하여 성장하였다. 이때 단결정 박막의 결정성은 광발광 스펙트럼과 이중결정 X-선 요동곡선(DCRC)으로 부터 구하였다. $AgGaSe_2$의 광흡수 스펙트럼으로부터 구한 온도에 의존하는 에너지 밴드갭 $E_g(T)$는 Varshni 공식에 fitting한 결과 $E_g(T)=1.9501eV-(8.79x10^{-4}eV/K)T^2(T+250K)$를 잘 만족하였다. 성장된 $AgGaSe_2$ 단결정 박막을 Ag, Ga, Se 분위기에서 각각 열처리하여 10K에서 photoluminescience(PL) spectrum을 측정하여 점 결함의 기원을 알아보았다. PL 측정으로 부터 얻어진 $V_{Ag},\;V_{Se},\;Ag_{int}$, 그리고 $Se_{int}$는 주개와 받개로 분류되어졌다. $AgGaSe_2$ 단결정 박막을 Ag 분위기에서 열처리하면 p형으로 변환됨을 알 수 있었다. 또한, Ga 분위기에서 열처리하면 열처리 이전의 PL 스펙트럼을 보이고 있어서, $AgGaSe_2$ 단결정 박막에서 Ga은 안정된 결합의 형태로 있기 때문에 자연 결함의 형성에는 관련이 없음을 알았다.

• 공업화학
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• 제24권5호
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• pp.537-543
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• 2013

본 연구에서는 유기박막태양전지로 적용 가능한 push-pull 구조의 고분자를 합성하여 그 특성을 확인하였다. 전자주개 물질로는 benzodithiophene 유도체를 도입하였고, 전자받개물질은 benzothiadiazole 유도체를 사용하여 Stille coupling 반응으로 poly{4,8-didodecyloxybenzo[1,2-b;3,4-b]dithiophene-alt-5,6-bis(octyloxy)-4,7-di(thiophen-2-yl)benzo[c][1,2,5]-thiadiazole} (PDBDT-TBTD)를 합성하였다. 각 합성 단계별 단량체의 확인은 $^1H-NMR$과 GC-MS를 통해 이루어졌으며, 합성된 conjugated polymer는 GPC, TGA, UV-Vis, cyclic voltammetry를 이용하여 물리적, 광학적 및 전기화학적 특성을 확인하였다. PDBDT-TBTD의 수평균 분자량은 6200이였으며, 초기 분해온도(5% weight loss temperature, $T_d$)값은 $323^{\circ}C$로 측정 되었다. 박막형태에서의 최대 흡수파장은 599 nm이며, 광학적 밴드갭(${E_g}^{opt}$)은 1.70 eV으로 확인되었다. 유기박막태양전지 소자는 ITO/PEDOT : PSS/PDBDT-TBTD : $PC_{71}BM/BaF_2/Ba/Al$ 구조로 제작하였으며, PDBDT-TBTD와 $PC_{71}BM$를 1 : 2 (w/w)의 비율로 블렌딩하여 광활성층으로 사용하였다. 제작된 소자는 solar simulator으로 광전변환효율을 확인하였고, 최대 광전변환효율은 2.1%이었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.493-493
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• 2014

The manufacturing cost of thin-film photovoltics can potentially be lowered by minimizing the amount of a semiconductor material used to fabricate devices. Thin-film solar cells are typically only a few micrometers thick, whereas crystalline silicon (c-Si) wafer solar cells are $180{\sim}300\mu}m$ thick. As such, thin-film layers do not fully absorb incident light and their energy conversion efficiency is lower compared with that of c-Si wafer solar cells. Therefore, effective light trapping is required to realize commercially viable thin-film cells, particularly for indirect-band-gap semiconductors such as c-Si. An emerging method for light trapping in thin film solar cells is the use of metallic nanostructures that support surface plasmons. Plasmon-enhanced light absorption is shown to increase the cell photocurrent in many types of solar cells, specifically, in c-Si thin-film solar cells and in poly-Si thin film solar cell. By proper engineering of these structures, light can be concentrated and coupled into a thin semiconductor layer to increase light absorption. In many cases, silver (Ag) nanoparticles (NP) are formed either on the front surface or on the rear surface on the cells. In case of poly-Si thin film solar cells, Ag NPs are formed on the rear surface of the cells due to longer wavelengths are not perfectly absorbed in the active layer on the first path. In our cells, shorter wavelengths typically 300~500 nm are also not effectively absorbed. For this reason, a new concept of plasmonic nanostructure which is NPs formed both the front - and the rear - surface is worth testing. In this simulation Al NPs were located onto glass because Al has much lower parasitic absorption than other metal NPs. In case of Ag NP, it features parasitic absorption in the optical frequency range. On the other hand, Al NP, which is non-resonant metal NP, is characterized with a higher density of conduction electrons, resulting in highly negative dielectric permittivity. It makes them more suitable for the forward scattering configuration. In addition to this, Ag NP is located on the rear surface of the cell. Ag NPs showed good performance enhancement when they are located on the rear surface of our cells. In this simulation, Al NPs are located on glass and Ag NP is located on the rear Si surface. The structure for the simulation is shown in figure 1. Figure 2 shows FDTD-simulated absorption graphs of the proposed and reference structures. In the simulation, the front of the cell has Al NPs with 70 nm radius and 12.5% coverage; and the rear of the cell has Ag NPs with 157 nm in radius and 41.5% coverage. Such a structure shows better light absorption in 300~550 nm than that of the reference cell without any NPs and the structure with Ag NP on rear only. Therefore, it can be expected that enhanced light absorption of the structure with Al NP on front at 300~550 nm can contribute to the photocurrent enhancement.

• 공업화학
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• 제28권5호
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• pp.547-553
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• 2017

본 연구는 $TiO_2$ 골격에 Pd을 삽입시켰을 때 나타나는 광 촉매 성능의 차이에 초점을 두고, $TiO_2$와 x mol% $Pd-TiO_2$(x = 0.25, 0.5, 0.75 그리고 1.0)의 5가지 촉매를 제안하였다. 전형적인 졸-겔 방법을 사용하여 촉매를 합성하고 각 촉매의 페놀 광 분해 성능을 평가하였다. XRD, TEM, SEM/EDS, UV/Vis 분광법, 광 발광 분광법 등을 이용하여 촉매의 물리화학적 특성을 확인하였고, 광 발광 분광법 및 광 전류 측정으로 광학적 특성을 확인하였다. Pd 이온을 첨가하면 촉매의 밴드 갭이 감소하고, 광 생성된 전자와 정공 사이의 전하 분리가 쉽게 발생한다. 결과적으로, 0.75 mol% $Pd-TiO_2$ 촉매상의 페놀 광 분해 성능은 순수한 $TiO_2$보다 3배 더 높았는데, 이는 광 촉매 반응 중에 Pd 이온이 전자캡쳐 역할을 하여 일어난 결과로 여겨진다.

• 한국정보통신학회논문지
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• 제12권3호
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• pp.517-526
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• 2008

본 논문에서는 자동차 계기판의 OLED 디스플레이 모듈용 One-chip DC-DC 변환기 회로를 제안하였다. 전하 펌핑 방식의 OLED 패널 구동전압 회로는 PWM(Pulse Width Modulation) 방식을 사용한 DC-DC 변환기 회로에 비해 소형화, 저가격 및 낮은 EMI 특성을 갖는다. 그리고 Bulk-potential 바이어싱 회로를 사용하므로 전하 펌핑 시 기생하는 PNP BJT에 의한 전하 손실을 방지하도록 하였고, 밴드갭 기준전압 발생기의 Start-up 회로에서 전류소모를 기존 BGR 회로에 비해 42% 줄였고 VDD의 링 발진기 회로에 로직전원인 VLP를 사용하여 링 발진기기 레이아웃 면적을 줄였다. 또한 OLED 구동전압인 VDD의 구동 전류는 OLED 패널에서 요구하는 40mA 이상이다. $0.25{\mu}m$ High-voltage 공정을 이용하여 테스트 칩을 제작 중에 있으며, 레이아웃 면적은$477{\mu}m{\times}653{\mu}m$이다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 추계학술대회 논문집
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• pp.114-114
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• 2009

ZnO has received considerable attention due to its potential applicability to optoelectronic devices such as ultraviolet-light emitting diodes (UVLEDs) and laser diodes (LDs). As well known, however, polar ZnO with the growth direction along the c-axis has spontaneous and piezoelectric polarizations that will result in decreased quantum efficiency. Recently, nonpolar ZnO has been studied to avoid such a polarization effect. In order to realize applications of nonpoar ZnO-based films to LEDs, growth of high quality alloys for quantum well structures is one of the important tasks that should be solved. $Mg_xZn_{1-x}O$ and $Cd_xZn_{1-x}O$ is ones of most promising alloys for this application because the alloys of ZnO with MgO and CdO provide a wide range of band-gap engineering spanning from 2.4 to 7.8 eV. In this study, we investigated on $Mg_xZn_{1-x}O$ films grown with various Mg/Zn flux ratios The films were grown on R-plane sapphire substrates by plasma-assisted molecular beam epitaxy (PAMBE). we investigated on $Mg_xZn_{1-x}O$ films grown with various Mg/Zn flux ratios. The films were grown on R-plane sapphire substrates by plasma-assisted molecular beam epitaxy (PAMBE). With the relatively low Mg/Zn flux ratios, a typical striated anisotropic surface morphology which was generally observed from the nonpolar (11-20) ZnO film on r-plane sapphire substrates. By increasing the Mg/Zn flux ratio, however, additional islands were appeared on the surface and finally the surface morphology was entirely changed, which was generally observed for the (0001) polar ZnO films by losing the striated morphology. Investigations by X-ray $\Theta-2{\Theta}$ diffraction revealed that (0002) and (10-11) ZnO planes are appeared in $Mg_xZn_{1-x}O$ films by increasing the Mg/Zn flux ratio. Further detailed investigation by transmission electron microscopy (TEM) and photoluminescence (PL) will be discussed.