• Journal of the Korea Academia-Industrial cooperation Society
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• v.7 no.6
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• pp.1056-1063
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• 2006

Thermal evaporated 10 nm-Ni/l nm-Ir/(or polycrystalline)p-Si(100) and 10 nm-$Ni_{50}Co_{50}$/(or polycrystalline)p-Si(100) films were thermally annealed using rapid thermal annealing fur 40 sec at $300{\sim}1200^{\circ}C$. The annealed bilayer structure developed into Ni(Ir or Co)Si and resulting changes in sheet resistance, microstructure, phase and composition were investigated using a four-point probe, a scanning electron microscopy, a field ion beam, an X-ray diffractometer and an Auger electron spectroscope. The final thickness of Ir- and Co-inserted nickel silicides on single crystal silicon was approximately 20$\sim$40 nm and maintained its sheet resistance below 20 $\Omega$/sq. after the silicidation annealing at $1000^{\circ}C$. The ones on polysilicon had thickness of 20$\sim$55 nm and remained low resistance up to $850^{\circ}C$. A possible reason fur the improved thermal stability of the silicides formed on single crystal silicon substrate is the role of Ir and Co in preventing $NiSi_2$ transformation. Ir and Co also improved thermal stability of silicides formed on polysilicon substrate, but this enhancement was lessened due to the formation of high resistant phases and also a result of silicon mixing during high temperature diffusion. Ir-inserted nickel silicides showed surface roughness below 3 nm, which is appropriate for nano process. In conclusion, the proposed Ir- and Co- inserted nickel silicides may be superior over the conventional nickel monosilicides due to improved thermal stability.

• New Physics: Sae Mulli
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• v.68 no.12
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• pp.1308-1314
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• 2018

$Er^{3+}$ and $Yb^{3+}$ co-doped $Y_3Ga_5O_{12}$ polycrystalline powders were prepared by using a solid-state reaction method, and their crystallinities were measured using X-ray diffraction. According to the results of X-ray diffraction, the powders showed a polycrystalline tetragonal structure. The photoluminescence and the upconversion luminescence properties of the $(Y_{0.85-x}Yb_{0.15})_3Ga_5O_{12}:Er^{3+}_x$ (x = 0.03, 0.06, 0.09, 0.12 and 0.15) phosphors were investigated in detail. Green and red upconversion emissions were observed for the phosphors excited by 980 nm radiation from a semiconductor laser. The powders exhibited strong green and weak red upconversion emission peaks at 553 and 660 nm, respectively. Also, their upconversion processes were explained using an energy-diagram analysis and the strongest upconversion intensity was emitted by the powder with a 0.12 mol $Er^{3+}$ ion concentration.

• Electronic Materials Letters
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• v.14 no.6
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• pp.718-724
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• 2018

With the development of photovoltaic industry, the cost of photovoltaic power generation has become the significant issue. And the metallization process has decided the cost of original materials and photovoltaic efficiency of the solar cells. Nowadays, double printing process has been introduced instead of one-step printing process for front contact of polycrystalline silicon solar cells, which can effectively improve the photovoltaic conversion efficiency of silicon solar cells. Here, the relative cheap Cu paste has replaced the expensive Ag paste to form Ag/Cu composite front contact of silicon solar cells. The photovoltaic performance and the cost of photovoltaic power generation have been investigated. With the optimization on structure and height of Cu finger layer for Ag/Cu composite double-printed front contact, the silicon solar cells have exhibited a photovoltaic conversion efficiency of 18.41%, which has reduced 3.42 cent per Watt for the cost of photovoltaic power generation.

• Korean Journal of Materials Research
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• v.21 no.4
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• pp.216-219
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• 2011

Perovskite manganites such as $RE_{1-x}A_xMnO_3$ (RE = rare earth, A = Ca, Sr, Ba) have been the subject of intense research in the last few years, ever since the discovery that these systems demonstrate colossal magnetoresistance (CMR). The CMR is usually explained with the double-exchange (DE) mechanism, and CMR materials have potential applications for magnetic switching, recording devices, and more. However, the intrinsic CMR effect is usually found under the conditions of a magnetic field of several Teslas and a narrow temperature range near the Curie temperature ($T_c$). This magnetic field and temperature range make practical applications impossible. Recently, another type of MR, called the low-field magnetoresistance(LFMR), has also been a research focus. This MR is typically found in polycrystalline half-metallic ferromagnets, and is associated with the spin-dependent charge transport across grain boundaries. Composites with compositions $La_{0.7}(Ca_{1-x}Sr_x)_{0.3}MnO_3)]_{0.99}/(BaTiO_3)_{0.01}$ $[(LCSMO)_{0.99}/(BTO)_{0.01}]$were prepared with different Sr doping levels x by a standard ceramic technique, and their electrical transport and magnetoresistance (MR) properties were investigated. The structure and morphology of the composites were studied by X-ray diffraction (XRD) and scanning electronic microscopy (SEM). BTO peaks could not be found in the XRD pattern because the amount of BTO in the composites was too small. As the content of x decreased, the crystal structure changed from orthorhombic to rhombohedral. This change can be explained by the fact that the crystal structure of pure LCMO is orthorhombic and the crystal structure of pure LSMO is rhombohedral. The SEM results indicate that LCSMO and BTO coexist in the composites and BTO mostly segregates at the grain boundaries of LCSMO, which are in accordance with the results of the magnetic measurements. The resistivity of all the composites was measured in the range of 90-400K at 0T, 0.5T magnetic field. The result indicates that the MR of the composites increases systematically as the Ca concentration increases, although the transition temperature $T_c$ shifts to a lower range.

• Journal of the Korean Vacuum Society
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• v.6 no.3
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• pp.235-241
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• 1997

The crystallinity and the structure of heteroepitaxially grown $Y_2O_3$ films on the silicon substrates deposited by Ultra High Vacuum Ionized Cluster Beam(UHV-ICB) were investigated by Back-scattering Spectroscopy(BS)/channeling. The channeling minimum values, $X_{min}$, of the $Y_2O_3$ films deposited by other methods were 0.8~0.95 up to the present, which indicates amorphous or highly polycrystalline nature of the $Y_2O_3$ films. On the contrary, the channeling minimum value of heteroepitaxially grown $Y_2O_3$ films on Si(100) and Si(111) deposited by UHV-ICB are 0.28 and 0.25 respectively. These results point out fairly good crystalline quality. It is also observed that the top region of $Y_2O_3$ films have less crystalline defects than the bottom region regardless of the crystal direction of the Si substrates. The axis of $Y_2O_3$<111> epitaxially grown on Si(111) is tilt by $0.1^{\circ}$ with respect to Si<111>. That of $Y_2O_3$<110> on Si(100) is parallel to the Si<001>. The $Y_2O_3$ film on Si(100) grew with single domain structure and that on Si(111) grew with double domain structure. From the result of oxygen resonance BS/channeling, the oxygen atoms in heteroepitaxially grown $Y_2O_3$ film on Si(111) substrate have the crystallinity, but that on Si(100) shows almost channeling amorphous state.

• Journal of the Microelectronics and Packaging Society
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• v.30 no.2
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• pp.71-75
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• 2023

In this study, inorganic perovskite films with different compositions were grown by thermal chemical vapor deposition depending on the substrate and their optical properties were compared. Inorganic perovskite crystals were grown on SiO₂/Si and c-Al₂O₃ substrates using CsBr and PbBr₂, respectively, under the same growth conditions. Cs₄PbBr₆-CsPbBr₃ crystallites were grown on the SiO₂ with polycrystalline structure, while a CsPbBr₃ (100) dominant thin film was formed on the c-Al₂O₃ substrate with single crystal structure. From the photoluminescence measurement, CsPbBr₃ showed typical green emission centered at 534 nm with a full width at half maximum (FWHM) of about 91 meV. The Cs₄PbBr₆-CsPbBr₃ mixed structure exhibits blue-shifted emission at 523 nm with a narrow FWHM of 63 meV and a fast decay time of 6.88 ns. These results are expected to be useful for application in photoelectric devices such as displays, solar cells, and light sensors based on inorganic metal perovskites.

• Korean Journal of Materials Research
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• v.18 no.12
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• pp.655-659
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• 2008

The NO gas sensing properties of ZnO-carbon nanotube (ZnO-CNT) composites fabricated by the coaxial coating of single-walled CNTs with ZnO were investigated using pulsed laser deposition. Upon examination, the morphology and crystallinity of the ZnO-CNT composites showed that CNTs were uniformly coated with polycrystalline ZnO with a grain size as small as 5-10 nm. Gas sensing measurements clearly indicated a remarkable enhancement of the sensitivity of ZnO-CNT composites for NO gas compared to that of ZnO films while maintaining the strong sensing stability of the composites, properties that CNT-based sensing materials do not have. The enhanced gas sensing properties of the ZnO-CNT composites are attributed to an increase in the surface adsorption area of the ZnO layer via the coating by CNTs of a high surface-to-volume ratio structure. These results suggest that the ZnO-CNT composite is a promising template for novel solid-state semiconducting gas sensors.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.61.1-61.1
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• 2010

$CuIn_{1-x}-GaxSe_2$ based materials with direct bandgap and high absorption coefficient are promising materials for high efficiency hetero-junction solar cells. CIGS champion cell efficiency(19.9%, AM1.5G) is very close to polycrystalline silicon(20.3%, AM1.5G). A reduction in the price of CIGS module is required for competing with well matured silicon technology. Price reduction can be achieved by decreasing the manufacturing cost and by increasing module efficiency. Manufacturing cost is mostly dominated by capital cost. Device properties of CIGS are strongly dependent on doping, defect chemistry and structure which in turn are dependent on growth conditions. The complex chemistry of CIGS is not fully understood to optimize and scale processes. Control of the absorber grain size, structural quality, texture, composition profile in the growth direction is important to achieving reliable device performance. In the present work, CIS nanoparticles were prepared by a simple wet chemical synthesis method and their structural and optical properties were investigated. XRD patterns of as-grown nanopowders indicate CIS(Cubic), $CuSe_2$(orthorhombic) and excess selenium. Further, as-grown and annealed nanopowders were characterized by HRTEM and ICP-OES. Grain growth of the nanopowders was followed as a function of temperature using HT-XRD with overpressure of selenium. It was found that significant grain growth occurred between $300-400^{\circ}C$ accompanied by formation of ${\beta}-Cu_{2-x}Se$ at high temperature($500^{\circ}C$) consistent with Cu-Se phase diagram. The result suggests that grain growth follows VLS mechanism which would be very useful for low temperature, high quality and economic processing of CIGS based solar cells.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.73.1-73.1
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• 2010

For the successful cold starting of a fuel cell engine, either internal of external heat supply must be made to overcome the formation of ice from water below the freezing point of water. In the present study, switchable vanadium oxide compounds as variable temperature-electrical resistance materials onto the surface of flat metallic bipolar plates have been prepared by a dip-coating technique via an aqueous sol-gel method. Subsequently, the chemical composition and micro-structure of the polycrystalline solid thin films were analyzed by X-ray diffraction, X-ray fluorescence spectroscopy, and field emission scanning electron microscopy. In addition, it was carefully measured electrical resistance hysteresis loop over a temperature range from $-20^{\circ}C$ to $80^{\circ}C$ using the four-point probe method. The experimental results revealed that the thin films was mainly composed of Karelianite $V_2O_3$ which acts as negative temperature coefficient materials. Also, it was found that thermal dissipation rate of the vanadium oxide thin films partially satisfy about 50% saving of the substantial amount of energy required for ice melting at $-20^{\circ}C$. Moreover, electrical resistances of the vanadium-based materials converge on an extremely small value similar to that of pure flat metallic bipolar plates at higher temperature, i.e. $T{\geq}40^{\circ}C$. As a consequence, experimental studies proved that it is possible to apply the variable temperature-electrical resistance material based on vanadium oxides for the cold starting enhancement of a fuel cell vehicle and minimize parasitic power loss and eliminate any necessity for external equipment for heat supply in freezing conditions.

• Current Photovoltaic Research
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• v.2 no.1
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• pp.1-7
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• 2014

We developed a method of growing thin Si film at $600^{\circ}C$ by hot wire CVD using a very thin large-grained poly-Si seed layer for thin-film Si solar cells. The seed layer was prepared by crystallizing an amorphous Si film by vapor-induced crystallization using $AlCl_3$ vapor. The average grain size of the p-type epitaxial Si layer was about $20{\mu}m$ and crystallographic defects in the epitaxial layer were mainly low-angle grain boundaries and coincident-site lattice boundaries, which are special boundaries with less electrical activity. Moreover, with a decreasing in-situ boron doping time, the mis-orientation angle between grain boundaries and in-grain defects in epitaxial Si decreased. Due to fewer defects, the epitaxial Si film was high quality evidenced from Raman and TEM analysis. The highest mobility of $360cm^2/V{\cdot}s$ was achieved by decreasing the in-situ boron doping time. The performance of our preliminary thin-film solar cells with a single-side HIT structure and $CoSi_2$ back contact was poor. However, the result showed that the epitaxial Si film has considerable potential for improved performance with a reduced boron doping concentration.