• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.138-138
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• 2009

Recently, thin-film solar cells of Cu(In,Ga)$Se_2$(CIGS) have reached a high level of performance, which has resulted in a 19.9%-efficient device. These conventional devices were typically fabricated using chemical bath deposited CdS buffer layer between the CIGS absorber layer and ZnO window layer. However, the short wavelength response of CIGS solar cell is limited by narrow CdS band gap of about 2.42 eV. Taking into consideration the environmental aspect, the toxic Cd element should be replaced by a different material. It is why during last decades many efforts have been provided to achieve high efficiency Cd-free CIGS solar cells. In order to alternate CdS buffer layer, ZnS buffer layer is grown by using chemical bath deposition(CBD) technique. The thickness and chemical composition of ZnS buffer layer can be conveniently by varying the CBD processing parameters. The processing parameters were optimized to match band gap of ZnS films to the solar spectrum and exclude the creation of morphology defects. Optimized ZnS buffer layer showed higher optical transmittance than conventional thick-CdS buffer layer at the short wavelength below ~520 nm. Then, chemically deposited ZnS buffer layer was applied to CIGS solar cell as a alternative for the standard CdS/CIGS device configuration. This CIGS solar cells were characterized by current-voltage and quantum efficiency measurement.

• Journal of Sensor Science and Technology
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• v.31 no.5
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• pp.337-342
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• 2022

Hydrogen (H₂) gas is widely preferred for use as a renewable energy source owing to its characteristics such as environmental friendliness and a high energy density. However, H₂ can easily reverse or explode due to minor external factors. Therefore, H₂ gas monitoring is crucial, especially when the H₂ concentration is close to the lower explosive limit. In this study, metal oxide materials and their p-n heterojunctions were synthesized by a hydrothermal-assisted dip-coating method. The synthesized thin films were used as sensing materials for H₂ gas. When the H₂ concentration was varied, all metal oxide materials exhibited different gas sensitivities. The performance of the metal oxide gas sensor was analyzed to identify parameters that could improve the performance, such as the choice of the metal oxide material, effect of the p-n heterojunctions, and operating temperature conditions of the gas sensor. The experimental results demonstrated that a CuO/ZnO gas sensor with a p-n heterojunction exhibited a high sensitivity and fast response time (134.9% and 8 s, respectively) to 5% H₂ gas at an operating temperature of 300℃.

• Proceedings of the KIEE Conference
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• 2004.07c
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• pp.2105-2107
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• 2004

In this study, Spiral inductors on the $SiO_2$/Si(100) substrate were fabricated by the magnetron sputtering method. Cu thin film with the thickness of 2 ${\mu}m$ was deposited on the substrate. Also we fabricated square inductors through the wet chemical etching technique. The inductors are completely specified by the turn width and the spacing between spirals. Both the width and spacing between spirals were varied from 10 to 60 ${\mu}m$ and from 20 to 70 ${\mu}m$, respectively. Inductance and Q factor dependent on the RF frequency were investigated to analyze performance of inductor arrays. Also, We recommend that the reasonable Q-factors, spec's turns and thickness of the coil for inductors cab be set to be ideal condition.

• Progress in Superconductivity
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• v.5 no.1
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• pp.45-49
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• 2003

We have designed and fabricated the single-layer high $T_{c}$ SQUID magnetometer consisting of a directly coupled grain boundary junction SQUID with an inductance of 100 pH and 16 nested parallel pickup coils with the outermost dimension of 8.8 mm ${\times}$ 8.8 mm. The magnetometer was formed from a YBCO thin film deposited on an STO(100) bicrystal substrate with a misorientation angle of $30^{\circ}$. The SQUID magnetometer was further improved by optimizing the multi-loop pickup coil design for use in unshielded environments. Typical characteristics of the dc SQUID magnetometer had a modulation voltage of 40 $\mu\textrm{V}$ and a white noise of $30fT/Hz^{1}$2/. The SQUID magnetometer exhibited a 1/f noise level at 10 Hz reduced by a factor of about 3 compared with that of the conventional solid type pickup coil magnetometers and a very stable flux locked loop operation in magnetically disturbed environments.s.

• 한국신재생에너지학회:학술대회논문집
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• 2009.06a
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• pp.23-23
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• 2009

CIGS 박막 태양전지는 제조단가가 낮고 박막 태양전지 중에서 변환효율이 가장 높아 발전 가능성이 큰 태양전지로 인식되고 있다. 이미 일본, 독일, 미국을 비롯한 선진국에서는 30-50 MW 급의 양산 라인이 구축되고 있어 2010년 이후에는 본격적인 상용화가 진행될 것으로 보인다. CIGS 광흡수층은 진공증발, 셀렌화, 나노입자, 전기도금등 다양한 방식으로 제조가 가능한데 이 중에서도 동시진공증발공정은 고효율 CIGS 박막 태양전지 제조에 적합하다. 본 연구에서는 동시진공증발법을 이용하여 CIGS 박막을 증착하였으며 소다회유리/Mo/CIGS/CdS/i-ZnO/n-ZnO/Al/AR 구조의 태양전지를 제조하였다. 기판온도 모니터링을 통한 Cu 이차상 조절 기술을 이용하여 결정립이 매우 큰 CIGS 박막을 증착하였으며 Ga/(In+Ga) 조성비의 조절을 통하여 밴드갭 에너지를 최적화하였다. 또한 QCM 장치를 활용하여 용액 속에서 성장되는 CdS 박막의 두께와 특성을 조절하였다. 이러한 공정최적화를 통하여 개방전압 0.65 V, 단락전류밀도 38.8 $mA/cm^2$, 충실도 0.74 그리고 변환효율 18.8% 의 CIGS 박막 태양전지를 얻었다.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.05a
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• pp.77-81
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• 2006

We report the performance of a four-element, 11.67 GHz, high-Tc superconducting (HTS) microstrip antenna array with corporate feed network and circular polarization for direct broadcasting satellite (DBS) system. Our array antennas were designed and built on a 0.5 mm thick MgO substrate. To compare the superconducting antennas with normal conducting counterpart, One antenna pattern was fabricated from gold thin film, and a second pattern was fabricated from $YBa_2Cu_3O_{7-x}$ (YBCO) superconducting thin film. To improve the axial ratio of circularly polarized arrays, sequential rotation technique were used. Efficiency, radiation pattern, return loss and bandwidth were measured for both antennas at room temperature and at cryogenic temperature. The array produced good circular polarization, and the gain of the array at 77 K, relative to a copper array at room temperature was approximately 1.54 dB. The measured return loss of our HTS antenna array was 35.79 dB at the resonant frequency of 11.67 GHz and The total effective bandwidth was about 3.4 %. The results showed that high-temperature superconductors, when used in microstrip arrays, improved the efficiency of the HTS antenna array for circularly polarization.

• Progress in Superconductivity
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• v.3 no.2
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• pp.188-192
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• 2002

To introduce flux pinning center in HTS-BSCCO system, nano-size MgO particles were uniformly distributed within the Bi-2223 grain by partial hydration of MgO. The existing method MgO doped Bi-2223 used nato-size MgO powders, which resulted in agglomeration during mixing or grain growth during heat-treatment due to the high surface energy of the fine particles. By hydration of the MgO surface, the agglomeration of the MgO powders was avoided and the size of remaining MgO core was controlled by changing hydration medium and time. The thin film obtained by spin coating of (Bi_$1.8/Pb_{0.4}$)$Sr_2$$_{Ca}$$2.2/Cu_3$ $O_{y}$ nitrate solution mixed with hydrated MgO showed the even distribution of nano-size MgO particles in the Bi-2212 grains.s.s.

• Proceedings of the KIEE Conference
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• 1997.07d
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• pp.1436-1438
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• 1997

In this paper, CdS thin films, which were widely used window layer of the CdS/CdTe and the CdS/$CuInSe_2$ heterojunction solar cell, were grown by chemical bath deposition, and The properties were investigated in detail. Cadmium acetate and thiourea were used as cadmium and sulfur source, respectively. And Ammonium acetate was used as the buffer solution. Also Ammonia was used for controlling pH concentration. The reaction velocity was increased with increasing reaction temperature and decreasing pH concentration. The crystal structure of CdS films grown with various pH concentration had the hexagonal structure with (002) plane peak. In the range of pH $9{\sim}9.5$, the intensity of the peak was highest, and as increasing pH concentration, decreased the intensity of the peak except pH12.

• Journal of the Korean Magnetics Society
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• v.12 no.5
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• pp.184-188
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• 2002

The Cu/Ni/Cu(002)/Si(100) films which have perpendicular magnetic anisotropy were deposited by e-beam evaporation methods. From the reflection high energy electron diffraction pattern, the films were confirmed to be grown epitaxially on silicon. After 2X lots ions/$\textrm{cm}^2$ C+ irradiation, magnetic easy-axis was changed from surface normal to in-plane as shown in the hysteresis loop of magneto-optical Kerr effects. It became manifest from analysis of X-ray reflectivity and grazing incident X-ray diffraction that even though interface between top Cu layer and Ni layer became rougher, the contrast of Cu and Ni's electron density became manifest after ion irradiation. In addition, the strain after deposition of the films was relaxed after ion irradiation. Strain relaxation related with change of magnetic properties and mechanism of intermixed layer's formation was explained by thermo-chemical driving force due to elastic and inelastic collision of ions.

• Journal of Sensor Science and Technology
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• v.10 no.6
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• pp.328-337
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• 2001

The stochiometric mix of evaporating materials for the $CdGa_2Se_4$ single crystal thin films was prepared from horizontal furnace. To obtain the single crystal thin films, $CdGa_2Se_4$ mixed crystal was deposited on thoroughly etched semi-insulating GaAs(100) substrate by the Hot Wall Epitaxy (HWE) system. The source and substrate temperature were $630^{\circ}C$ and $420^{\circ}C$, respectively. The crystalline structure of single crystal thin films was investigated by the photoluminescence and double crystal X-ray diffraction (DCXD). The carrier density and mobility of $CdGa_2Se_4$ single crystal thin films measured from Hall effect by van der Pauw method are $8.27{\times}10^{17}cm^{-3}$, $345\;cm^2/V{\cdot}s$ at 293 K, respectively. From the photocurrent spectrum by illumination of perpendicular light on the c-axis of the $CuInSe_2$ single crystal thin film, we have found that the values of spin orbit splitting ${\Delta}So$ and the crystal field splitting ${\Delta}Cr$ were 106.5 meV and 418.9 meV at 10 K, respectively. From the photoluminescence measurement on $CdGa_2Se_4$ single crystal thin film, we observed free excition ($E_x$) existing only high quality crystal and neutral bound exiciton ($D^{\circ}$, X) having very strong peak intensity. Then, the full-width-at -half-maximum(FWHM) and binding energy of neutral donor bound excition were 8 meV and 13.7 meV, respectivity. By Haynes rule, an activation energy of impurity was 137 meV.