• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.196-199
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• 2009

We report the multiple quantum well (MQW) structure for highly efficient red phosphorescent OLEDs. Various triplet quantum well devices from a single well to five quantum wells are realized using a wide band-gap hole and electron transporting layers, narrow band-gap host and dopant material, and charge control layers (CCL). The maximum external quantum efficiency of 14.8 % with a two quantum well device structure is obtained, which is the highest value among the red phosphorescent OLEDs using same dopant.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.347-347
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• 2012

Nickel Oxide (NiO) is a transition metal oxide of the rock salt structure that has a wide band gap of 3.5 eV. It has a variety of specialized applications due to its excellent chemical stability, optical, electrical and magnetic properties. In this study, we concentrated on the application of NiO thin film for transparent conducting oxide. The energy band structure, electronic and optical properties of Nickel Oxide (NiO) thin films grown on Si by using electron beam evaporation were investigated by X-Ray Photoelectron Spectroscopy (XPS), Reflection Electron Energy Loss Spectroscopy (REELS), and UV-Spectrometer. The band gap of NiO thin films determined by REELS spectra was 3.53 eV for the primary energies of 1.5 keV. The valence-band offset (VBO) of NiO thin films investigated by XPS was 3.88 eV and the conduction-band offset (CBO) was 1.59 eV. The UV-spectra analysis showed that the optical transmittance of the NiO thin film was 84% in the visible light region within an error of ${\pm}1%$ and the optical band gap for indirect band gap was 3.53 eV which is well agreement with estimated by REELS. The dielectric function was determined using the REELS spectra in conjunction with the Quantitative Analysis of Electron Energy Loss Spectra (QUEELS)-${\varepsilon}({\kappa},{\omega})$-REELS software. The Energy Loss Function (ELF) appeared at 4.8, 8.2, 22.5, 38.6, and 67.0 eV. The results are in good agreement with the previous study [1]. The transmission coefficient of NiO thin films calculated by QUEELS-REELS was 85% in the visible region, we confirmed that the optical transmittance values obtained with UV-Spectrometer is the same as that of estimated from QUEELS-${\varepsilon}({\kappa},{\omega})$-REELS within uncertainty. The inelastic mean free path (IMFP) estimated from QUEELS-${\varepsilon}({\kappa},{\omega})$-REELS is consistent with the IMFP values determined by the Tanuma-Powell Penn (TPP2M) formula [2]. Our results showed that the IMFP of NiO thin films was increased with increasing primary energies. The quantitative analysis of REELS provides us with a straightforward way to determine the electronic and optical properties of transparent thin film materials.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2016.05a
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• pp.83-84
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• 2016

A wideband stacked patch antenna with parasitic elements, rectangular and triangle shaped patches, is proposed. Two different shaped parasitic elements are placed in the above of main rectangular microstrip patch antenna in order to achieve wide bandwidth for 860 MHz band. Coupling between the main patch and parasitic patches is realized by thick air gap. The gap and locations of parasitic patches are found to be the main factor of the wideband impedance matching. The proposed antenna is designed on a ground plane with small size of $119mm{\times}109mm$ for application of compact transceivers. And the impedance bandwidth of the antenna should satisfied CDMA band to the 780MHz~890MHz.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.6
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• pp.376-379
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• 2016

In this paper, the efficiency improvement of the heterojunction with intrinsic thin layer (HIT) solar cells is obtained by optimization process of p-type a-SiC:H as emitter. The optoelectronic of p-type a-SiC:H layers including the optical band-gap and conductivity under the methane gas content variation is conducted in detail. A significant increase in the Jsc by $1mA/cm^2$ and Voc by 30 mV are attributed to enhanced photon-absorption due to broader band-gap of p-a-SiC:H and reduced band-offsets at p-side interface, respectively of HIT solar cells.

• Journal of IKEEE
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• v.24 no.4
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• pp.1122-1128
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• 2020

Bandwidth Extension refers to restoring and expanding a narrow band signal(NB) that is damaged or damaged in the encoding and decoding process due to the lack of channel capacity or the characteristics of the codec installed in the mobile communication device. It means converting to a wideband signal(WB). Bandwidth extension research mainly focuses on voice signals and converts high bands into frequency domains, such as SBR (Spectral Band Replication) and IGF (Intelligent Gap Filling), and restores disappeared or damaged high bands based on complex feature extraction processes. In this paper, we propose a model that outputs an bandwidth extended signal based on an autoencoder among deep learning models, using the residual connection of one-dimensional convolutional neural networks (CNN), the bandwidth is extended by inputting a time domain signal of a certain length without complicated pre-processing. In addition, it was confirmed that the damaged high band can be restored even by training on a dataset containing various types of sound sources including music that is not limited to the speech.

• Advances in materials Research
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• v.2 no.2
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• pp.77-91
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• 2013

High quality nanoparticles of neodymium barium niobium ($NdBa_2NbO_6$) perovskites have been synthesized using an auto ignition combustion technique for the first time. The nanoparticles thus obtained have been characterized by powder X-ray diffraction, thermo gravimetric analysis, differential thermal analysis, Fourier transform infrared spectroscopy, Raman spectroscopy and transmission electron microscopy. UV-Visible absorption and photoluminescence spectra of the samples are also recorded. The structural analysis shows that the nano powder is phase pure with the average particle size of 35 nm. The band gap determined for $NdBa_2NbO_6$ is 3.9 eV which corresponds to UV-radiation for optical inter band transition with a wavelength of 370nm. The nanopowder could be sintered to 96% of the theoretical density at $1325^{\circ}C$ for 2h. The ultrafine cuboidal nature of nanopowders with fewer degree of agglomeration improved the sinterability for compactness at relatively lower temperature and time. During the sintering process the wide band gap semiconducting behavior diminishes and the material turns to a high permittivity dielectric. The microstructure of the sintered surface was examined using scanning electron microscopy. The striking value of dielectric constant ${\varepsilon}_r=43$, loss factor tan ${\delta}=1.97{\times}10^{-4}$ and the observed band gap value make it suitable for many dielectric devices.

• Korean Chemical Engineering Research
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• v.57 no.3
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• pp.331-337
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• 2019

Titania has become the most applicable material for photocatalytic application. Nevertheless, titania has the weak point in its wide band gap energy that is mainly activated by UV irradiation. There have been vast research challenges in order to make the wide band gap energy of titania narrow that could be activated in the presence of visible light. Various modifications of titania surface were popular because titania needs to change its surface to respond in visible light. Among the methodological approaches, N-doping to titania can be the alternative candidate because it is facile process and eco-friendly. The activated electron from valence band in N-doped $TiO_2$ migrates to conduction band in the presence of visible light irradiation, which shows photocatalytic activity as well. In this study, focused on the evaluation of nitrogen state after N-doping through brief review. Arguments are still existed in nitrogen states and their different effects on photocatalytic activity. In particular, two nitrogen states are generally reported; substitutional and interstitial states. The research articles regarding N-doped $TiO_2$ are continuously appearing because the potential application of water split in visible light is still fascinate. The future of N-doped $TiO_2$ is also presented by referrals based on various literature.

• Current Photovoltaic Research
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• v.1 no.1
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• pp.38-43
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• 2013

$Cu(In,Ga)_3Se_5$ is a candidate material for the top cell of $Cu(In,Ga)Se_2$ tandem cells. This phase is often found at the surface of the $Cu(In,Ga)Se_2$ film during $Cu(In,Ga)Se_2$ cell fabrication, and plays a positive role in $Cu(In,Ga)Se_2$ cell performance. However, the exact properties of the $Cu(In,Ga)_3Se_5$ film have not been extensively studied yet. In this work, $Cu(In,Ga)_3Se_5$ films were fabricated on Mo-coated soda-lime glass substrates by a three-stage co-evaporation process. The Cu content in the film was controlled by varying the deposition time of each stage. X-ray diffraction and Raman spectroscopy analyses showed that, even though the stoichiometric Cu/(In+Ga) ratio is 0.25, $Cu(In,Ga)_3Se_5$ is easily formed in a wide range of Cu content as long as the Cu/(In+Ga) ratio is held below 0.5. The optical band gap of $Cu_{0.3}(In_{0.65}Ga_{0.35})_3Se_5$ composition was found to be 1.35eV. As the Cu/(In+Ga) ratio was decreased further below 0.5, the grain size became smaller and the band gap increased. Unlike the $Cu(In,Ga)Se_2$ solar cell, an external supply of Na with $Na_2S$ deposition further increased the cell efficiency of the $Cu(In,Ga)_3Se_5$ solar cell, indicating that more Na is necessary, in addition to the Na supply from the soda lime glass, to suppress deep level defects in the $Cu(In,Ga)_3Se_5$ film. The cell efficiency of $CdS/Cu(In,Ga)_3Se_5$ was improved from 8.8 to 11.2% by incorporating Na with $Na_2S$ deposition on the CIGS film. The fill factor was significantly improved by the Na incorporation, due to a decrease of deep-level defects.

• Bulletin of the Korean Chemical Society
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• v.33 no.3
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• pp.1075-1077
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• 2012

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07a
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• pp.379-382
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• 2002

GaAs has wide band gap, Therefore that malarial can used high Temperature application. in this paper explain to current-voltage characteristics of thermal effect. we experiment on thermal test of current-voltage characteristics and gate leakage current with real device. As a result, we propose a current-volatage characteristics model. that model base on gate leakage current, and gate leakage current influence gate source voltage.