• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.78.2-78.2
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• 2010

Cu(In,Ga)Se2 (CIGS)박막태양전지는 간단한구조와 가격경쟁력 및 고효율화 가능성에 대한 기대감에 의해 많은 연구가 수행되어오고 있다. 특히 높은 흡수계수와 적절한 밴드갭, 큰 결정크기와 같은 물질의 특성들이 장점으로 작용하고 있기 때문이다. 또한 CIGS박막태양전지는 다른 태양전지에 비해 광열화가 적다는 장점도 가지고 있다. CIGS 박막은 CuInSe2내의 In 사이트에 Ga을 도핑함으로서 형성이 되는데 그때의 밴드갭은 약 1.4eV이며 이를 형성하기 위해 많은 방법들이 제안되고 있는데, CIGS박막 형성 시 가장 중요시 여겨야 될 인자는 구성원소로부터 최적화된 조성비를 찾는 것이다. 이러한 관점에서 볼때 evaporation법이나 sputtering법같은 진공방식의 공정법이 비진공방식에 비해 최적의 조성비를 찾는 것이 수월할 것으로 생각된다. selenization을 하기전에, 동시증착이나 다층박막형성을 통해 Cu-In-Se의 조합이 일반적으로 이루어진다. 어떤방법이든 Se의 부가적인 공급이 이루어지는데 시작 전구체의 조합에서 그 해법을 제시하는 것에 대한 논의가 많이 부족한 현실로서, CuInSe2의 단일전구체에 의한 박막형성과 특성평가에 대해 구체적인 논의가 필요하다. 본 실험에서는 Cu-In-Se 전구체를 CuInSe2 단일 타겟에서부터 RF 마그네트론 스퍼터링법을 이용하여 박막증착을 하여 Se의 Rapid Thermal Process(RTA)법을 통해 Se이 순차적으로 공급되었다. 이때 형성되는 박막의 태양전지 흡수층 적용을 위한 광학적, 전기적 및 구조적에 대한 논의된다. Soda lime glass(SLG)와 Corning 1737 유리를 기판으로 하여 아세톤-에탄올을 이용, 초음파세척을 실시하였다. 스퍼터 공정을 하기전에 흡착된 물분자를 제거하기 위하여 약 30분간 $120^{\circ}C$로 열을 가해주었으며, 공정을 위한 총 아르곤 가스의 양은 약 50sccm이며 이때의 공정압력은 20mtorr로 고정하였다. 우선 RF power와 기판온도에 따른 단일전구체 형성을 관찰하기 위하여 각각 30~80W, RT~$400^{\circ}C$로 변화를 주어 박막을 형성한 후 모든 sample에 대하여 $500^{\circ}C$분위기에 effusion cell을 이용하여 Se 분위기에서 결정화를 실시하였다. 샘플의 두께는 Surface profiler로 측정하였고 단면은 전자주사현미경으로 관찰되었다. 동시에 SEM이미지를 통하여 morphology와 grain size 및 EDX를 통하여 조성분석을 하였다. 밴드갭, 투과율 및 흡수계수는 UV-VIS-NIR분광분석법을 통하여 수행되었으며, 전기적 특성분석을 위해 4-point-probe와 Hall effect측정을 수행하였다. 공정변수에 따른 단일타겟으로 얻어 결정화된 CuInSe2박막의 자세한 결과와 논의에 대하여 발표한다.

• Journal of the Korean Vacuum Society
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• v.22 no.3
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• pp.119-125
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• 2013

In this study, we studied the properties of ZnO(Al) and ZnO(AlGa) thin film according to film thickness deposited on SLG by In-line magnetron sputtering system. XRD, FESEM, 4-point probe, Hall measurement system and UV/Vis-NIR spectrophotometer were employed to analyze the properties of ZnO(Al) and ZnO(AlGa) thin film. The all films exhibited (002) preferential orientation with clear peak shape and high intensity. The carrier concentration and Hall mobility of ZnO(Al) and ZnO(AlGa) thin film were improved with increasing thickness. The resistivity of both films decreased when the film thickness was raised from 500 nm to 1,450 nm. And then relatively the resistivity of ZnO(AlGa) film was lower than that of ZnO(Al) film. The transmittance of the films decreased with increasing film thickness but all films exhibited optical transmittances of over 83.3% in the visible region.

• Journal of the Korean Ceramic Society
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• v.56 no.2
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• pp.178-183
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• 2019

A process of fabricating the foamed glass that has closed pores with 8 ~ 580 ㎛ sizes without a blowing agent by sintering 10 ㎛ boron-free glass powder composed of CaO, MgO, SO₃, Al₂O₃-83 wt% SiO₂ at a molding pressure of 0 ~ 120 MPa and a sintering temperature of 750 ~ 1000℃ was investigated. To analyze the glass transition temperature of glass powder, thermogravimetric analysis-differential thermal analysis (TGA-DTA) method were used. The microstructure and pore size of foamed glass were examined using the optical microscopy and field emission scanning electron microscopy (FE-SEM). For the thermal diffusivity and color of the fabricated samples, a heat flow meter and ultraviolet-visible-near-infrared (UV-VIS-NIR)-colormetry were used, respectively. In the TGA-DTA result, the glass transition temperature of glass powder was confirmed to be 626℃. In the microstructure result, closed pores of 7 ~ 20 ㎛ were formed at 750 ~ 900℃, and they were not affected by the molding pressure and sintering temperature. However, at 1,000℃, when there was 0 MPa molding pressure, closed pores of 580 ㎛ were confirmed, and the pore size decreased as the molding pressure increased. Moreover, at a molding pressure of 30 MPa or higher, closed pores of approximately 400 ㎛ were formed. The porosity showed an increasing trend of smaller molding pressure and larger sintering temperature, and it was controllable in the range of 5.69 ~ 68.45%. In the thermal diffusivity result, there was no change according to the molding pressure, and, by increasing the sintering temperature, up to 0.115 W/m·K could be obtained. The Lab color index (CIE-Lab) results all showed a similar translucent white color regardless of molding pressure and sintering temperature. Therefore, based on the foamed glass without boron and blowing agent, it was confirmed that white foamed glass, which has closed pores of 8 ~ 580 ㎛ and a thermal diffusivity characteristic of 0.115 W/m·K, can be fabricated by changing the molding pressure and sintering temperature.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.264-264
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• 2010

Single-walled carbon nanotubes (SWCNTs) were grown on a Si wafer by using thermal chemical vapor deposition (t-CVD). We investigated the effect of the catalyst deposition rate on the types of CNTs grown on the substrate. In general, smaller islands of catalyst occur by agglomeration of a catalyst layer upon annealing as the catalyst layer becomes thinner, which results in the growth of CNTs with smaller diameters. For the same thickness of catalyst, a slower deposition rate will cause a more uniformly thin catalyst layer, which will be agglomerated during annealing, producing smaller catalyst islands. Thus, we can expect that the smaller-diameter CNTs will grow on the catalyst deposited with a lower rate even for the same thickness of catalyst. The 0.5-nm-thick Fe served as a catalyst, underneath which Al was coated as a catalyst support as well as a diffusion barrier on the Si substrate. The catalyst layers were. coated by using thermal evaporation. The deposition rates of the Al and Fe layers varied to be 90, 180 sec/nm and 70, 140 sec/nm, respectively. We prepared the four different combinations of the deposition rates of the AI and Fe layers. CNTs were synthesized for 10 min by flowing 60 sccm of Ar and 60 sccm of $H_2$ as a carrier gas and 20 sccm of $C_2H_2$ as a feedstock at 95 torr and $810^{\circ}C$. The substrates were subject to annealing for 20 sec for every case to form small catalyst islands prior to CNT growth. As-grown CNTs were characterized by using field emission scanning electron microscopy, high resolution transmission electron microscopy, Raman spectroscopy, UV-Vis NIR spectroscopy, and atomic force microscopy. The fast deposition of both the Al and Fe layers gave rise to the growth of thin multiwalled CNTs with the height of ${\sim}680\;{\mu}m$ for 10 min while the slow deposition caused the growth of ${\sim}800\;{\mu}m$ high SWCNTs. Several radial breathing mode (RBM) peaks in the Raman spectra were observed at the Raman shifts of $113.3{\sim}281.3\;cm^{-1}$, implying the presence of SWCNTs (or double-walled CNTs) with the tube diameters 2.07~0.83 nm. The Raman spectra of the as-grown SWCNTs showed very low G/D peak intensity ratios, indicating their low defect concentrations.

• Journal of the Korean Vacuum Society
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• v.17 no.1
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• pp.23-27
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• 2008

We have investigated the effect of annealing on the structural and optical properties of polycrystalline Ga doped ZnO (GZO) films grown on glass substrates by RF-magnetron sputter at room temperature. The structural and optical properties of as-grown GZO films were characterized and then samples were annealed at $400{\sim}600^{\circ}C$ in $N_2$ ambient for 30, 60 minutes, respectively. The field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) were used to measure the grain size and the crystalline quality of the films. We found that the crystalline quality was improved and the grain size tends to be increased. The optical properties of GZO thin films were analyzed by UV-VIS-NIR spectrophotometers. It is found that optical properties of thin films are increased by annealing and can be used for transparent electrode application. We believe that the appropriate post-growth heat treatment could be contributed to the improvement of GZO-based devices.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.454-454
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• 2014

Silicon microwire array is one of the promising platforms as a means for developing highly efficient solar cells thanks to the enhanced light trapping efficiency. Among the various fabrication methods of microstructures, deep reactive ion etching (DRIE) process has been extensively used in fabrication of high aspect ratio microwire arrays. In this presentation, we show precisely controlled Si microwire arrays by tuning the DRIE process conditions. A periodic microdisk arrays were patterned on 4-inch Si wafer (p-type, $1{\sim}10{\Omega}cm$) using photolithography. After developing the pattern, 150-nm-thick Al was deposited and lifted-off to leave Al microdisk arrays on the starting Si wafer. Periodic Al microdisk arrays (diameter of $2{\mu}m$ and periodic distance of $2{\mu}m$) were used as an etch mask. A DRIE process (Tegal 200) is used for anisotropic deep silicon etching at room temperature. During the process, $SF_6$ and $C_4F_8$ gases were used for the etching and surface passivation, respectively. The length and shape of microwire arrays were controlled by etching time and $SF_6/C_4F_8$ ratio. By adjusting $SF_6/C_4F_8$ gas ratio, the shape of Si microwire can be controlled, resulting in the formation of tapered or vertical microwires. After DRIE process, the residual polymer and etching damage on the surface of the microwires were removed using piranha solution ($H_2SO_4:H_2O_2=4:1$) followed by thermal oxidation ($900^{\circ}C$, 40 min). The oxide layer formed through the thermal oxidation was etched by diluted hydrofluoric acid (1 wt% HF). The surface morphology of a Si microwire arrays was characterized by field-emission scanning electron microscopy (FE-SEM, Hitachi S-4800). Optical reflection measurements were performed over 300~1100 nm wavelengths using a UV-Vis/NIR spectrophotometer (Cary 5000, Agilent) in which a 60 mm integrating sphere (Labsphere) is equipped to account for total light (diffuse and specular) reflected from the samples. The total reflection by the microwire arrays sample was reduced from 20 % to 10 % of the incident light over the visible region when the length of the microwire was increased from $10{\mu}m$ to $30{\mu}m$.

• Korean Journal of Materials Research
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• v.25 no.2
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• pp.61-67
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• 2015

$Fe_2O_3$ coated plate mica($Fe_2O_3$/mica) for infrared reflectance red pigment was prepared under hydrothermal treatment. $Fe_2O_3$ was perfectly coated on mica via the difference of surface charge between $Fe_2O_3$ and mica particles at pH 3. $Fe_2O_3$/mica was then calcined at $800^{\circ}C$ to stabilize the coated layer on mica. The infrared(IR) reflectance pigments were characterized by X-ray diffraction, FE-SEM, zeta potential, and a UV-Vis-NIR spectrophotometer. In particular, the CIE color coordinate and IR reflectance properties of $Fe_2O_3$/mica pigments were investigated in relation to the thickness variation of the $Fe_2O_3$ layer coated on mica of various lateral sizes. The isolation-heat red paints containing the pigments were prepared and optimized with a thinner, settling agent, and dispersant. Then, the films were made. The thermal property of isolation-heat on these films was observed through the relationship of the IR reflectance value, which was based on the variation of the $Fe_2O_3$ layer's thickness coated on mica and mica's lateral size as IR reflectance pigment. With an increase in IR reflectance on these films, the thermal property of isolation-heat was effectively enhanced.

• Korean Journal of Materials Research
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• v.23 no.12
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• pp.672-679
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• 2013

$Fe_4[Fe(CN)_6]_3$ coated on a mica or $TiO_2$/mica surface as infrared reflective blue pigment was prepared by a hydrothermal method. $Fe_4[Fe(CN)_6]_3$, used as coloring agent, was uniformly coated on mica or $TiO_2$/mica under the optimized condition of a 1.2 : 1 weight ratio between iron(III) chloride hexahydrate and potassium ferrocyanidetrihydrate at the initial pH level of 4.5 at $70^{\circ}C$. The infrared (IR)-reflective pigments were characterized by SEM, Zeta-potenial, FT-IR, and UV-VIS NIR spectrophotometry. Especially the CIE color coordinate and total solar reflectance(TSR) properties of the pigments were investigated in relation to variation of the coating and coated substrate thicknesses. Isolation-heat paint was prepared with 20 wt% blue pigments fully dispersed in acryl-urethane resin and several additives to coat the film uniformly. The films were also measured with CIE color coordinate, TSR, and the surface temperature was recorded by an isolation-heat measuring system. The pigments and films of $Fe_4[Fe(CN)_6]_3$ coated on mica and $TiO_2$/mica showed high TSR values compared with the TSR value of $Fe_4[Fe(CN)_6]_3$ itself. According to the increase of TSR value, the property of isolation-heat is effective. To realize the optimal blue color, we applied the the pigment to $TiO_2$ coated mica(TM(b)) which has blueish interference color. The pigment of $Fe_4[Fe(CN)_6]_3$ coated on TM(b) shows a strong blue color compared with that of $Fe_4[Fe(CN)_6]_3$ coated on $TiO_2$/Mmca(TM(w)), which has a whitish interference color.