• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.347-348
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• 2013

To obtain high conversion efficiency in InGaN-based solar cells, it is critical to grow high indium (In) composed InGaN layer for increasing sun light absorption wavelength rage. At present, most InGaN-based solar cells adopt InGaN/GaN multi-quantum-well (MQW) structure for high crystalline quality of InGaN with high In composition. In this study, we fabricated and compared the performances of two types of InGaN/GaN MQW solar cells which have the 15% (SC 15) and 25% (SC 25) of In composition at quantum well layer. Although both devices showed similar dark current density and leakage current, SC 15 showed better performance under AM 1.5G illumination as shown in Fig. 1. It is interesting to note that SC 25 showed severe current density decrease as increasing voltages. As a result, it lowered short circuit current density and fill factor of the device. However, SC 15 showed steady current density and over 75 % of fill factor. To investigate these differencesmore clearly, we analyzed their photoluminescence (PL) spectra under various applied voltages as shown in Fig. 2. At the same time, photocurrent, which was generated by PL excitation, was also measured as shown in Fig. 3. Further, we investigated the relationship between piezoelectric field and performance of InGaN based solar cell varying indium composition.

• Korean Journal of Optics and Photonics
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• v.18 no.2
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• pp.155-161
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• 2007

A new and simple method of 3-dimensional circuit modeling and analysis is proposed and verified experimentally for the first time by determining 3-dimensional current flow and 2-dimensional light distribution in blue InGaN/GaN multi-quantum well (MQW) light emitting diode (LED) devices. Circuit parameters of the LED consist of the resistance of the metallic film and epitaxial layer, and the intrinsic diode which represents the active region emitting the light. The circuit parameters are extracted from the transmission line model (TLM) and current-voltage relation. We applied the >> proposed method and extracted circuit parameters to obtain the light emission pattern in a top-surface emitting-type LED. The current spreading effect is analyzed theoretically and quantitatively with a variation of the resistance of metallic and epitaxial layers. The emitting-light distribution of the fabricated blue LED showed a good agreement with the analyzed result, which shows the dark emission intensity at the corner of the p-electrode.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.469-470
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• 2009

본 논문은 전류의 변화에 따른 태양전지 모듈의 열 분포에 대하여 실험하였다. 태양전지 모듈의 경우 내구성의 문제가 대두되고 있는데 그 중에 열에 의한 노화현상이 가장 큰 문제이다. 실제적으로 태양전지 모듈에서 저 전류와 고 전류의 경우에서 서로 상이한 열 분포가 이루어지고 있다. 이번 연구를 통해 열 해석에 있어서 전류에 따른 태양전지 모듈에서의 열에 의한 노화현상을 좀 더 정확히 예측 할 수 있을 것이다.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.19 no.4
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• pp.47-54
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• 2005

The improvement of perspectives on dark and limited underground space could be an important factor in successful underground space development. The Current trend in the apartment underground parking garages requires not only quantitatively energy efficient design and operation but also qualitative improvement of the space. For this, we need to consider two factors: Firstly, to understand the characteristics of the lamps; Secondly, to improve the uniformity ratio of illuminance. In a winter season, a way to keep the uniformity and a method not to lower the indoor illuminance level by cold ambient air should be established. Therefore, a change in interval and arrangement of the lighting fixtures is required. Also, in their operations, the current time-fixed control method needs to be changed into the control which method considers the use pattern.

• Progress in Superconductivity
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• v.4 no.2
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• pp.99-103
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• 2003

We studied the nonequilibrium superconductivity due to tunnel injection of polaronic quasiparticle (QP) from organic photoconductor. The transport properties of an organic copper (II) phthalocyanine (Cu -Pc)/d-wave superconductor were investigated in dark and under ultraviolet (UV) radiation for performance of a novel $high -T_{c}$ superconducting three terminal device. We observed that the injection of polaronic QP from the organic Cu -Pc film into the $Bi_2$S $r_2$$CaCuO_{8+{\delta}}$ film generated a substantially larger nonequilibrium effect as compared to the normal QP injection current. We could increase the current gain by UV excitation of the organic photoconductor injector. The tunneling spectroscopy of a Cu -Pc/BSCCO junction exhibited a small enhancement of the zero bias conductance peak under the W excitation. The above phenomena are of importance in developing optically controlled three terminal superconducting device.e.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.1
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• pp.123-127
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• 2007

Up sizing of dye-sensitized solar cell(DSC) is the important technology to bring about commercialization of DSC. Several studies to obtain a stable large area DSC have been investigated in overseas laboratories, but have been hardly done in our country. In this study, up sizing technology of dye sensitized solar cells(DSCs) was investigated. We investigated low dark current materials for the current collecting grid. From the result, a new DSC module with metal grid was designed, and fabricated. For a new interconnection, both working and counter electrodes are alternately coupled on 10[cm]$\times$7[cm] substrate. We have achieved 68% of fill factor and photoelectric conversion efficiency of around 2.6% as the best results of new designed DSC structure.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.12
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• pp.1140-1143
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• 2006

We report on the fabrication of P3HT-based thin-film transistors (TFTs) for liquid crystal display that consist of $NiO_x$, poly-vinyl phenol (PVP), and Ni for the source-drain (S/D) electrodes, gate dielectric layer, and gate electrode, respectively The $NiO_x$ S/D electrodes of which the work function is well matched to that of P3HT are deposited on a P3HT channel by electron-beam evaporation of NiO powder. The maximum saturation current of our P3HT-based TFT is about $15{\mu}A$ at a gate bias of -30 V showing a high field effect mobility of $0.079cm^2/Vs$ in the dark, and the on/off current ratio of our TFT is about $10^5$. It is concluded that jointly adopting $NiO_x$ for the S/D electrodes and PVP for gate dielectric realizes a high-quality P3HT-based TFT.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.25-28
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• 2004

Photocurrent spectrum, photoresponse, and I-V measurements were made for close-packed HgTe nanoparticles without organic capping materials to investigate their photocurrent characteristics in the infrared range. In absorption and photoluminescence (PL) spectra taken for the close-packed nanoparticles film, the wavelengths of exciton peaks was red-shifted, compared with organic capped HgTe nanoparticles dispersed in solution. This red-shift is caused by the lessening of the exciton binding energy. The I-V curves and photoresponse for the close-packed nanoparticles film reveal their dark current and fast photoresponse with no current decay, respectively. The observation suggests that the HgTe nanoparticles are a very prospect material applicable for photodetectors in the whole IR range.

• Transactions on Electrical and Electronic Materials
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• v.5 no.4
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• pp.133-137
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• 2004

The development of digital x-ray detector has been extensively progressed for the application of various medical modalities. In this study, we introduce a new hybrid-type x-ray detector to improve problems of a conventional direct or indirect digital x-ray image technology, which composed of multi-layer structure using a CaWO$_4$ phosphor and amorphous selenium (a-Se) photoconductor. The leakage current of our detector was found to be ∼180 pA/cm$^2$ at 10 V/m, which was significantly reduced than that of a single a-Se detector. The x-ray sensitivity was measured as the value of 4230 pC/cm$^2$/mR at 10 V/m. We found that the parylene thin film between a CaWO$_4$ phosphor and an a-Se layer acts as an insulator to prevent charge injection from indium thin oxide (ITO) electrode into an a-Se layer under applied bias.

• Current Optics and Photonics
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• v.3 no.6
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• pp.510-515
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• 2019

In this paper, we introduce a 1.3-㎛ 25-GHz waveguide-integrated vertical PIN type Ge-on-Si photodetector fabricated using a multi-project wafers service based on fringing field analysis in the depletion region. In general, 1.3-㎛ photodetectors fabricated using a commercial foundry service can achieve limited bandwidths because a significant amount of photo-generated carriers are located within a few microns from the input along the device length, and they are influenced by the fringing field, leading to a longer transit time. To estimate the response time, we calculate the fringing field in that region and the transit time using the drift velocity caused by the field. Finally, we compare the estimated value with the measured one. The photodetector fabricated has a bandwidth of 20.75 GHz at -1 V with an estimation error of <3 GHz and dark current and responsivity of 110 nA and 0.704 A/W, respectively.