• Journal of Korean Ophthalmic Optics Society
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• v.10 no.3
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• pp.193-203
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• 2005

Highly c-axis oriented nanocrystalline ZnO thin films on silica glass substrates were prepared by spin coating-pyrolysis process with a zinc naphthenate precursor. Only the XRD intensity peak of (002) phase was observed for all samples. With an increase in heat treatment temperature, the peak intensity of (002) phase increases. No significant aggregation of particle was present. From scanning probe microscopy analyses, three-dimensional grain growth, which was thought to be due to inhomogeneous substrate surface and c-axis oriented grain growth of the ZnO phase, was independent on heal-treatment temperature. Highly homogeneous surface of the highly-oriented ZnO film was observed at $800^{\circ}C$. All the films exhibited a high transmittance (above 80%) in visible region except film heat treated at $1000^{\circ}C$, and showed a sharp fundamental absorption edge at about $0.38{\sim}0.40{\mu}m$. The estimated energy band gap for all the films were within the range previously reported for films and single crystal. ZnO films, consisting of densely packed grains with smooth surface morphology were obtained by heat treatment at $600^{\circ}C{\sim}800^{\circ}C$, expected to be ideal for practical application, such as transparent conductive film and optical device.

• Korean Journal of Materials Research
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• v.9 no.4
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• pp.349-354
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• 1999

The temperature dependences of the Hall coefficient, carrier mobility, electrical resistivity, Seebeck coefficient, thermal conductivity, and figure-of-merit of the undoped and $CdI_2$-doped 90% $Bi_2Te_3-10% Bi_2Se_3$, single crystals, grown by the Bridgman method, have been characterized at temperatures ranging from 77K to 600K. The saturated carrier concentration and degenerate temperature of the undoped 90% $Bi_2Te_3-10% Bi_2Se_3$ single crystal are $5.85\times10_{18}cm^{-3}$ and 127K, respectively. The scattering parameter of the 90% $Bi_2Te_3-10% Bi_2Se_3$ single crystal is determined to b -0.23, and the electron mobility to hole mobility ratio ($\mu_e/\mu_h)$ is 1.45. The bandgap energy at 0K of the 90% <$Bi_2Te_3-10% Bi_2Se_3$ single crystal is 0.200 eV. Adding $CdI_2$as a donor dopant, a maximum figure-of-merit of $3.2\times10^{-3}/K$$CdI_2$-doped specimen.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.6
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• pp.71-77
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• 2014

In this paper, we investigated the effects of high-energy electron beam irradiation (HEEBI) on the optical transmittance of InGaZnO (IGZO) films grown on transparent Corning glass substrates, with a radio frequency magnetron sputtering technique. The IGZO thin films deposited at low temperature were treated with HEEBI in air at room temperature (RT) with an electron beam energy of 0.8 MeV and doses of $1{\times}10^{14}-1{\times}10^{16}electrons/cm^2$. The optical transmittance of the IGZO films was measured using an ultraviolet visible near-infrared spectrophotometer (UVVIS). The detailed estimation process for separating the transmittance of HEEBI-treated IGZO films from the total transmittance of IGZO films on transparent substrates treated with HEEBI is given in this paper. Based on the experimental results, we concluded that HEEBI with an appropriate dose of $10^{14}electrons/cm^2$ causes a maximum increase in the transparency of IGZO thin films. We also concluded that HEEBI treatment with an appropriate dose shifted the optical band gap ($E_g$) toward the lower energy region from 3.38 to 3.31 eV. This $E_g$ shift suggested that HEEBI in air at RT with an appropriate dose acts like a thermal annealing treatment in vacuum at high temperature.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.4
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• pp.596-601
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• 2020

Silicon carbide is considered a potentially useful material for high-temperature electronic devices because of its large band gap energy and p-type or n-type conduction that can be controlled by impurity doping. Accordingly, the thermoelectric properties of -SiC powder prepared by refined diatomite were investigated for high value-added applications of natural diatomite. -SiC powder was synthesized by a carbothermal reduction of the SiO₂ in refined diatomite using carbon black. An acid-treatment process was then performed to eliminate the remaining impurities (Fe, Ca, etc.). n-Type semiconductors were fabricated by sintering the pressed powder at 2000℃ for 1~5h in an N2 atmosphere. The electrical conductivity increased with increasing sintering time, which might be due to an increase in carrier concentration and improvement in grain-to-grain connectivity. The carrier compensation effect caused by the remaining acceptor impurities (Al, etc.) in the obtained -SiC had a deleterious influence on the electrical conductivity. The absolute value of the Seebeck coefficient increased with increasing sintering time, which might be due to a decrease in the stacking fault density accompanied by grain or crystallite growth. On the other hand, the power factor, which reflects the thermoelectric conversion efficiency of the present work, was slightly lower than that of the porous SiC semiconductors fabricated by conventional high-purity -SiC powder, it can be stated that the thermoelectric properties could be improved further by precise control of an acid-treatment process.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.3
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• pp.29-34
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• 2019

Silicon carbide is considered to be a potentially useful material for high-temperature electronic devices, as its large energy band gap and the p-type and/or n-type conduction can be controlled by impurity doping. Particularly, electric conductivity of porous n-type SiC semiconductors fabricated from ${\beta}-SiC$ powder at $2000^{\circ}C$ in $N_2$ atmosphere was comparable to or even larger than the reported values of SiC single crystals in the temperature region of $800^{\circ}C$ to $1000^{\circ}C$, while thermal conductivity was kept as low as 1/10 to 1/30 of that for a dense SiC ceramics. In this work, for the purpose of decreasing sintering temperature, it was attempted to fabricate porous reaction-sintered bodies at low temperatures ($1400-1600^{\circ}C$) by thermal decomposition of polycarbosilane (PCS) impregnated in n-type ${\beta}-SiC$ powder. The repetition of the impregnation and sintering process ($N_2$ atmosphere, $1600^{\circ}C$, 3h) resulted in only a slight increase in the relative density but in a great improvement in the Seebeck coefficient and electrical conductivity. However the power factor which reflects the thermoelectric conversion efficiency of the present work is 1 to 2 orders of magnitude lower than that of the porous SiC semiconductors fabricated by conventional sintering at high temperature, it can be stated that thermoelectric properties of SiC semiconductors fabricated by the present reaction-sintering process could be further improved by precise control of microstructure and carrier density.

• Journal of IKEEE
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• v.23 no.1
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• pp.14-21
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• 2019

In this paper, we implemented an on-board miniaturization antenna operating 2.4 GHz using MZR(Mu Zero Resonator). It is must be operating under the constraint that the size of the small terminal PCB should be $78{\times}38{\times}0.8mm^3$ and the size of the system should be $63{\times}38{\times}0.8mm^3$ and the size of the radiating part should be $15{\times}38{\times}0.8mm^3$. The feeding structure uses a CPW structure for stable feeding and a feeding point at the upper left of the system board. A magnetic field coupling structure is used for coupling the feeding part and the antenna. The resonance frequency of the MZR is determined by the series inductance and capacitance of the cell, so the gap between the cells, the length of the cell, the length of the interdigital capacitor, and the spacing between the radiation part and the ground plane are analyzed. The antenna was designed and fabricated using the results. The total size of the antenna including the feed structure is $20.8{\times}9.0{\times}0.8mm^3$, and the electrical length is $0.1664{\lambda}_0{\times}0.072{\lambda}_0{\times}0.0064{\lambda}_0$. The measurement result for 10 dB bandwidth, gain and directivity are 440 MHz(18.3%), 0.4405 dB, and 2.722 dB respectively. It is confirmed that the radiation pattern has omnidirectional characteristics and it can be applied to ultra small terminal antenna.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.33 no.2
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• pp.83-90
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• 2023

The β-Ga₂O₃ has the most thermodynamically stable phase, a wide band gap of 4.8~4.9 eV and a high dielectric breakdown voltage of 8MV/cm. Due to such excellent electrical characteristics, this material as a power device material has been attracted much attention. Furthermore, the β-Ga₂O₃ has easy liquid phase growth method unlike materials such as SiC and GaN. However, since the grown pure β-Ga₂O₃ single crystal requires the intentionally controlled doping due to a low conductivity to be applied to a power device, the research on doping in β-Ga₂O₃ single crystal is definitely important. In this study, various source powders of un-doped, Sn 0.05 mol%, Sn 0.1 mol%, Sn 1.5 mol%, Sn 2 mol%, Sn 3 mol%-doped Ga₂O₃ were prepared by adding different mole ratios of SnO₂ powder to Ga₂O₃ powder, and β-Ga₂O₃ single crystals were grown by using an edge-defined Film-fed Growth (EFG) method. The crystal direction, crystal quality, optical, and electrical properties of the grown β-Ga₂O₃ single crystal were analyzed according to the Sn dopant content, and the property variation of β-Ga₂O₃ single crystal according to the Sn doping were extensively investigated.

• Applied Chemistry for Engineering
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• v.22 no.1
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• pp.15-20
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• 2011

Poly[2,3-dimethyl-5,8-dithiophene-2-yl-quinoxaline-alt-9,9-dihexyl-9H-fluorene] (PFTQT) and poly[2,3-dimethyl-5,8-dithiophen-2-yl-quinoxaline-alt-10-hexyl-10H-phenothiazine (PPTTQT) based on 2,3-dimethyl-5,8-dithiophen-2-yl-quinoxaline weresynthesized by Suzuki coupling reaction. All polymers were soluble in common organic solvents such as chloroform, chlorobenzene, o-dichlorobenzene, tetrahydrofuran (THF) and toluene. The maximum absorption wavelength and band gap of PFTQT were 440 nm and 2.30 eV, and PPTTQT were 445 nm and 2.23 eV, respectively. The HOMO and LUMO energy level of PFTQT were -6.05 and -3.75 eV, and PPTTQT were -5,89 and -3.66 eV, respectively. The organic photovoltaic devices based on the blend of polymer and PCBM (1 : 2 by weight ratio) were fabricated. Efficiencies of devices were 0.24% (PFTQT) and 0.16% (PPTTQT), respectively. The short circuit current density ($J_{sc}$), fill factor (FF), and open circuit voltage ($V_{oc}$) of the device with PFTQT were $0.97mA/cm^2$, 29% and 0.86 V, and the device based on PPTTQT were $0.80mA/cm^2$, 28% and 0.71 V, 31% and 0.71 V, respectively, under air mass (AM) 1.5 G and 1 sun condition ($100mA/cm^2$).