• Bulletin of the Korean Chemical Society
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• 제30권10호
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• pp.2299-2302
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• 2009

By controlling the number of electrons transferred to the emitting layer, highly efficient three-wavelength WOLEDs were fabricated. Such WOLEDs are different from those made using simple stacking of RGB emitting layers in that the movement distribution of electrons transferred to emitting layer could be adjusted using the difference in LUMO energy level and that lights of all 3 wavelengths could be emitted through appropriate arrangement of RGB emitting layers. WOLED device with the structure of m-MTDTA (40 nm)/NPB (10 nm)/ Coumarin6 doped $Alq_3$ (3%) (8 nm)/ Rubrene doped NPB (5%) (15 nm)/NPB (2 nm)/ DPVBi (20 nm)/$Alq_3$ (20 nm)/LiF (1 nm)/Al (200 nm) showed high luminance efficiency of 8.9 cd/A and color purity of (0.31, 0.40). In addition, WOLED device with the thickness of non-doped NPB layer increased from 2 nm to 3 nm to increase blue light emission showed a luminance efficiency of 7.6 cd/A and color purity of (0.28, 0.36).

• 대한전자공학회논문지SD
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• 제37권8호
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• pp.48-56
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• 2000

회절격자의 인접한 반주기 길이 사이에 음의 상관관계가 있는 회절격자 반주기의 랜덤 변이가 QWS-DFB 레이저의 특성에 미치는 영향을 유효 굴절률 전달 매트릭스 방법을 이용하여 해석하였다. 상관계수가 0에서 -1로 가까이 감에 따라 랜덤 변이에 의한 회절격자 주기의 오차가 감소하면서 단일모드 안정성과 파장 정확도의 저하가 덜 심각해진다. 이는 랜덤 변이의 크기가 같다면 상관관계가 없는 전자빔 lithography 법으로 회절격자를 만들기보다는 optical lithography 법으로 만드는 것이 회절격자 주기 랜덤 변이의 영향을 줄이는 데에 유리함을 의미한다. 그리고 전자빔 lithography를 이용하여 DFB 레이저를 만들 때에 랜덤 변이의 영향을 줄이려면 분해능을 높이거나, 인접 반주기 길이의 랜덤 변이에 음의 상관관계를 주어야 한다.

• 한국재료학회지
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• 제16권10호
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• pp.624-628
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• 2006

In this study, divalent europium-activated $NaCaPO_4$ green phosphor powders were prepared by the chemical synthetic method followed by heat treatment in reduced atmosphere, and the crystal structures, morphologies and photoluminescent properties of the powders were investigated by x-ray powder diffraction, scanning electron microscope and spectrometer for the first time. The effects of Ca/P and Na/Ca mole ratios on the final products were also investigated. The influences of input amount change of europium as the activator on the light emission intensity were studied, and the resulting concentration quenching phenomenon was observed. The optimized synthesis conditions obtained in this study were Ca/P mole ratio 1.2, Na/Ca mole ratio 3.0 and 4 mole%Eu. The peak wavelength was 505 nm for all the samples. The result of excitation spectrum measurement indicated that the excitation efficiency was high for the long-wavelength UV region. It was thus concluded that the samples prepared in this study can be successfully applied for the light-emitting devices such as LED excited with long-wavelength UV light sources.

• Current Applied Physics
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• 제18권11호
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• pp.1381-1387
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• 2018

One dimensional (1D) grating has been fabricated (using focused ion beam) on 50 nm gold (Au) film deposited on higher refractive index Gallium phosphate (GaP) substrate. The sub-wavelength periodic metal nano structuring enable to couple photon to couple with the surface plasmons (SPs) excited by them. These grating devices provide the efficient control on the SPs which propagate on the interface of noble metal and dielectric whose frequency is dependent on the bulk electron plasma frequency of the metal. For a fixed periodicity (${\Lambda}=700 nm$) and slit width (w = 100 nm) in the grating device, the efficiency of SPP excitation is about 40% compared to the transmission in the near-field. Efficient coupling of SPs with photon in dielectric provide field localisation on sub-wavelength scale which is needed in Heat Assisted Magnetic recording (HAMR) systems. The GaP is also used to emulate Vertical Cavity Surface emitting laser (VCSEL) in order to provide cheaper alternative of light source being used in HAMR technology. In order to understand the underlying physics, far-and near-field results has been compared with the modelling results which are obtained using COMSOL RF module. Apart from this, grating devices of smaller periodicity (${\Lambda}=280nm$) and slit width (w = 22 nm) has been fabricated on GaP substrate which is photoluminescence material to observe amplified spontaneous emission of the SPs at wavelength of 805 nm when the grating device was excited with 532 nm laser light. This observation is unique and can have direct application in light emitting diodes (LEDs).

• 대한금속재료학회지
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• 제49권11호
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• pp.900-904
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• 2011

We have synthesized core-shell structured nanocrystals based on chalcopyrite-type $Cu_{0.2}InS_2$. The photoluminescence of the nanocrystals shows a significant blueshift in the emission wavelength by shell capping with ZnS layers. This shift can be explained with the compressive stress to core nanocrystals applied by the formation of a ZnS shell layer with a large lattice mismatch with the core. In this study, the emission wavelength could be tuned by changing the composition of the shell layers. Nanocrystals with emission wavelength ranging from 575 nm through 630 nm were synthesized by varying the portion of cadmium compared with zinc in the shell layers.

• 한국표면공학회지
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• 제49권1호
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• pp.92-97
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• 2016

The plasma has been used in various industrial fields of semiconductors, displays, transparent electrode and so on. Plasma diagnostics is critical to the uniform process and the product. We use the electron temperature of the various plasma parameters for the diagnosis of plasma. Generally, the range of the electron temperature which is used in a semiconductor process used the range of 1 eV to 10 eV. The difference of electron temperature of 0.5 eV has a influence in plasma process. The electron temperature can be measured by the electrical method and the optical method. Measurement of electron temperature for various gas flow rates was performed in DC-magnetron sputter and Inductively Coupled Plasma. The physical properties of the thin film were also determined by changing electron temperatures. The transmittance was measured using the integrating sphere, and wavelength range was measured at 300 ~ 1100 nm. We obtain the thin film of the mobility, resistivity and carrier concentration using the hall measurement system. As to the electron temperature increase, optical and electrical properties decrease. We determine it was influenced by the oxygen flow ratio and plasma.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.475-475
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• 2010

We have generated Ar plasma in dense plasma focus device with coaxial electrodes for extreme ultraviolet (EUV) lithography and investigated an emitted visible light for electro-optical plasma diagnostics. We have applied an input voltage 4.5 kV to the capacitor bank of 1.53 uF and the diode chamber has been filled with Ar gas of pressure 8 mTorr. The inner surface of the cylindrical cathode has been attatched by an acetal insulator. Also, the anode made of tin metal. If we assumed that the focused plasma regions satisfy the local thermodynamic equilibrium (LTE) conditions, the electron temperature and density of the coaxial plasma focus could be obtained by Stark broadening of optical emission spectroscopy (OES). The Lorentzian profile for emission lines of Ar I of 426.629 nm and Ar II of 487.99 nm were measured with a visible monochromator. And the electron density has been estimated by FWHM (Full Width Half Maximum) of its profile. To find the exact value of FWHM, we observed the instrument line broadening of the monochromator with a Hg-Ar reference lamp. The electron temperature has been calculated using the two relative electron density ratios of the Stark profiles. In case of electron density, it has been observed by the Stark broadening method. This experiment result shows the temporal behavior of the electron temperature and density characteristics for the focused plasma. The EUV emission signal whose wavelength is about 6 ~ 16 nm has been detected by using a photo-detector (AXUV-100 Zr/C, IRD). The result compared the electron temperature and density with the temporal EUV signal. The electron density and temperature were observed to be $10^{16}\;cm^{-3}$ and 20 ~ 30 eV, respectively.

• 한국전기전자재료학회논문지
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• 제17권1호
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• pp.70-74
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• 2004

We investigated transmittance, surface characteristics, and resistivity according to bending of ITO(indium tin oxide) film with four other multi -harrier film). Transmission data of ITO film with four ITO films showed there was about large 90％ transmission above 550nm wavelength at three multi-barrier structures. But, both-side hard coated structure showed relatively low 75％ transmission above 550nm wavelength. And, surface images measured from SEM (scanning electron microscope) showed both-side hard coated structure have a tendency of more roughness. Also, resistivity change of four other multi-barrier film showed there was the lowest change at one-side hardcoated structure. Subsequently, with result of resistivity change according to position, we knew the resistivity change of the center increased rapidly than that of the edge.

• JSTS:Journal of Semiconductor Technology and Science
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• 제5권2호
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• pp.127-130
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• 2005

The structural and electrical properties of InN/GaN multiple quantum wells, which were grown by metalorganic chemical vapor deposition, were characterized by transmission electron microscopy and electroluminescence measurements. As the quantum well growth time was changed, the wavelength was varied from 451 to 531 nm. In the varied current conditions, the blue LED with the InN MQW structures did not have the wavelength shift. With this result, we can expect that the white LEDs with the InN MQW structures do not show the color temperature changes with the variations of applied currents.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2007년도 추계학술대회 논문집
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• pp.264-267
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• 2007

It is important to reduce optical losses from front surface reflection to improve the efficiency of crystalline silicon solar cells. Surface texturing by isotropic etching with acid solution based on HF and $HNO_3$ is one of the promising methods that can reduce surface reflectance. Anisotropic texturing with alkali solution is not suitable for multicrystalline silicon wafers because of its various grain orientations. In this paper, we textured multicrystalline silicon wafers by simple wet chemical etching using acid solution to reduce front surface reflectance. After that, surface morphology of textured wafer was observed by Scanning Electron Microscope(SEM) and Atomic Force Microscope(AFM), surface reflectance was measured in wavelength from 400nm to 1000nm. We obtained 29.29% surface reflectance by isotropic texturing with acid solution in wavelength from 400nm to 1000nm for fabrication of multicrystalline silicon solar cells.