• Journal of the Korean Applied Science and Technology
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• v.34 no.3
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• pp.562-567
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• 2017

The organic light-emitting diodes are fabricated with six anthracene derivatives containing simple substituents such as phenyl or naphthyl group. The device structure is as in the following: Indium tin oxide (ITO) (180 nm)/4,4-4,4',4"-tris[N-(1-naphthyl)-N-phenylamino]triphenylamine (2-TNATA) (30 nm)/4,4'-bis[N-(1-naphthyl)-N-phenyl-1-amino] biphenyl (NPB) (20 nm)/Emitting compound (30 nm)/2,2',2"-(1,3,5-Benzinetriyl)-tris (1-phenyl-1-H-benz-imidazole) TPBi (40 nm)/lithium quinolate (Liq) (2 nm)/Al (100 nm). In the emitting layer the anthracene derivatives are used without any dopant. All the six devices show blue emissions. Among the tested diodes, the one with 9-(2-naphthyl)-10-(p-tolyl) anthracene (2-NTA) exhibited luminous efficiency, power and external quantum efficiencies of 3.26 cd/A, 0.98 lm/A, 2.8 % at $20mA/cm^2$.

• Current Optics and Photonics
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• v.2 no.1
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• pp.79-84
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• 2018

We present a novel and simple method to enable spatially selective $ZnAl_2O_4$ nanocrystal formation on the surface of $B_2O_3$-$Al_2O_3$-ZnO-CaO-$K_2O$ glass by employing localized laser heating. Optimized precipitation of glass-ceramics containing nanocrystals doped with $Eu^{3+}$ and $Yb^{3+}$ ions was performed by controlling $CO_2$ laser power and scan speed. Micro-x-ray diffraction and transmission electron microscopy revealed the mean size and morphology of nanocrystals, and energy dispersive x-ray spectroscopy showed the lateral distribution of elements in the imaged area. Laser power and scan speed controled annealing temperature for crystalization in the range of 1.4-1.8 W and 0.01-0.3 mm/s, and changed the size of nanocrystals and distribution of dopant ions. We also report more than 20 times enhanced downshift visible emission under ultraviolet excitation, and 3 times increased upconversion emission from $Eu^{3+}$ ions assisted by efficient sensitizer $Yb^{3+}$ ions in nanocrystals under 980 nm excitation. The confocal microscope revealed the depth profile of $Eu^{3+}$ ions by showing their emission intensity variation.

• Particle and aerosol research
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• v.5 no.1
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• pp.1-7
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• 2009

Fe- and V-doped titanium dioxide nanoparticles consisting of spherical primary nanoparticles were synthesized from a mixed liquid precursor by using the flame spray pyrolysis. The effects of dopant concentration on the powder properties such as morphology, crystal structure, and light adsorption were analyzed by TEM, XRD, and UV-Vis spectrophotometer, respectively. As the V/Ti molar ratio increased, pure anatase particles were synthesized. On the contrary, rutile phase particles were synthesized as the Fe/Ti ratio increased. Photocatalytic property of as-prepared $TiO_2:Fe,V$ nanoparticles was investigated by measuring the removal efficiency for volatile organic compounds (VOCs) under the irradiation of visible light. After 2 hrs under visible light, the removal efficiencies of benzene, p-xylene, ethylbenzene, and toluene were reached to 21.9%, 21.4%, 19.8% and 17.6% respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.11b
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• pp.492-496
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• 2001

Due to their better photosensitivity in X-ray, the amorphous selenium based photoreceptor is widely used on the X-ray conversion materials. It was possible to control the charge carrier transport of amorphous selenium by suitably alloying a-Se with other elements(e,g. As, Cl). In this paper, We investigated dopants(As, Cl) composition rate to improve dark resistivity and transport properties of charge carrier in amorphous selenium using by direct X-ray conversion material. Alloying a-Se with As inhibits the recrystallization of a-Se but introduces undesirable deep hole traps. then doping with Cl(in the ppm range) compensates for the deep hole traps. We investigated their composition rate in various doping conditions and then obtained optimum dopant composition rate. The result was Se-As 0.3%-c] 30 ppm and X-ray Sensitivity was 0.57 pC/$pixel{\cdot}mR$ at $137{\mu}m{\times}137{\mu}m$ Pixel area.

• Electrical & Electronic Materials
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• v.10 no.9
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• pp.909-915
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• 1997

To improve the electro-induced strain and to decease the hysteresis of that W $O_3$dopant of which amount is 0~0.8wt% was added to (P $b_{0.73}$/B $a_{0.27}$)(Z $r_{0.75}$/ $Ti_{0.25}$) $O_3$+0.1wt% $Y_{2}$/ $O_3$ceramics. At the specimen with 0.4 wt% W $O_3$the electromechanical coupling coefficient( $K_{31}$ ) showed the maximum value of 23.6% at D.C 10 kV/cm electric field. At the same W $O_3$addition amount the piezoelectric constant( $d_{31}$ ) and the electro-induced strain($\Delta$$\ell$/$\ell$)showed the highest values of 182$\times$10$^{-12}$ [C/N] 210$\times$10$^{-6}$ $\Delta$$\ell$/$\ell$at D.C. 10 kV/cm electric field. respectively0 kV/cm electric field. respectivelyvely.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.420-420
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• 2011

결정질 태양전지에서 고효율 달성을 위한 LBC(Local Back Contact) 구조의 중요성이 강조되고 있다. LBC 구조에서 후면 passivation 형성을 위한 SiNX layer를 PECVD로 형성 시, 실리콘 bulk 내로 H+ 원자가 침투하여 Boron과 결합하게 되면 Boron이 bulk 내에서 dopant로 작용을 하지 못하게 되어, 후면에서 p-층을 형성하고, 이는 VOC의 저하를 야기 시킨다. 본 연구에서는 LBC 구조에서 후면 passivation 시 bluk 내 B-H결합으로 인한 태양전지 특성 저하 문제를 해결하기 위해, SiNX를 증착하기 전에 얇은 산화막 barrier를 성장시켜 Bulk 내에 H+ 침투를 최소화 하였다. PECVD를 이용한 N2O 플라즈마 처리, HNO3 Wet Chemical Oxidation의 방법을 통해 substrate와 SiNX 사이에 얇은 oxide 층을 형성하였으며, 각각의 조건에 대해 lifetime 측정을 실시하였다. 그 결과 SiON/SiNx를 이용한 막의 lifetime이 $94.5{\mu}s$로 가장 우수하였고, Reference에 비해 25.4% 증가함을 확인할 수 있었다. 그러나 HNO3/SiNx에서는 30.6%, SiON에서는 84.3% 감소함을 확인하였다. Voc 측정 결과 또한 SiON/SiNx를 이용한 막이 670mV로 가장 우수함을 확인할 수 있었다. 본 연구를 통해 LBC구조에서 후면에 얇게 SiON/SiNx막을 형성함으로서 H+이온의 침투를 저지하여 후면 B-H결합을 막아 태양전지 특성 저하를 감소시키는 것을 확인할 수 있었다.

• Bulletin of the Korean Chemical Society
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• v.29 no.2
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• pp.335-338
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• 2008

New efficient red emitter having short p?-conjugation length and asymmetric bulky structure, 2-(7-diphenylamino-benzo[1,2,5]thiadiazole-4-ylmethylene)-malononitrile, was synthesized and characterized. Using this material as a dopant, we fabricated electroluminescence device with a structure of ITO/DNTPD/NPD/BTZA (5 wt% in Alq3)/Alq3/LiF/Al. The device exhibited a high brightness of 761 cd/m2 at a driving voltage of 4.8 V, and current efficiency is 0.75 cd/A. The Commission International de IEclairage (CIE) coordinates of the EL device were found to be (0.62, 0.37) at 10 mA/cm2.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1791-1793
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• 2000

본 연구에서는 다결정 실리콘 박막 트랜지스터(poly-Si TFTs)에서의 소오스 및 드레인 영역 형성을 위해 PSG (phosphosilicate glass)와 BSG (borosilicate glass) 박막을 도핑 물질(dopant)로 하여 저온에서 엑시머 레이저(eximer laser)로 활성화하는 공정을 제안한다. 이 실험을 통해 소스 가스인 $PH_3$와 $SiH_4$의 유량비, 레이저 에너지 밀도와 레이저 조사 횟수를 변화시키면서 면저항(sheet resistance)과 불순물의 확산 깊이(diffusion depth)를 성공적으로 조절하였다. 불순물의 확산 깊이와 표면 농도는 레이저 에너지 밀도와 조사 횟수를 증가시킴에 따라 증가하였으며 그 결과 최소 면저항 값은 인(P)의 경우 450$\Omega/\square$을 얻었고 붕소(B)의 경우 1100$\Omega/\square$을 얻었다. 이러한 실험결과는 제안된 방법을 통해 poly-Si TFTs 에서 소오스, 드레인 영역의 도핑 공정을 수행할 수 있음을 보여준다.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.3
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• pp.130-136
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• 1989

Electrical transport and thermally induced metastability in hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs) using boron-doped amorphous silicon as an active layer have been studied. The device characteristics n-channel and p-channel operations. The thermal quenching experiments on amorphous silicon-silicon nitride ambipolar TFT give clear evidence for the co-existence of two distinct metastable changes. The densities of metastable active dopants and dangling bonds increase with the quenching temperature. On the other hand, the interface state density appears to decrease with increasing quenching temperature.

• Applied Science and Convergence Technology
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• v.23 no.5
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• pp.221-239
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• 2014

The global demand for energy has been increasing since past decades. Various technologies have been working to find a suitable alternative for the generation of sustainable energy. Photovoltaic technologies for solar energy conversion represent one of the significant routes for the green and renewable energy production. Despite of remarkable improvement in solar cell technologies, the generation of power is still suffering with lower energy conversion efficiency, high production cost, etc. The major problem in improving the PV efficiency is spectral mismatch between the incident solar spectrum and bandgap of a semiconductor material used in solar cell. Luminescent materials such as rare-earth doped phosphor materials having the quantum efficiency higher than unity can be helpful for photovoltaic applications. Quantum cutting phosphors are the most suitable candidates for the generation of two or more low-energy photons for the absorption of every incident high-energy photons. The phosphors which are capable of converting UV photon to visible and near-IR (NIR) photon are studied primarily for photovoltaic applications. In this review, we will survey various near IR quantum cutting phosphors with respective to their synthesis method, energy transfer mechanism, nature of activator, sensitizer and dopant materials incorporation and energy conversion efficiency considering their applications in photovoltaics.