• JSTS:Journal of Semiconductor Technology and Science
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• 제10권2호
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• pp.100-106
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• 2010

The impact of surface quantization on device parameters of a Si metal oxide semiconductor (MOS) capacitor has been analyzed in the present work. Variation of conduction band bending, position of discrete energy states, variation of surface potential, and the variation of inversion carrier concentration at charge centroid have been analyzed for different gate voltages, substrate doping concentrations and oxide thicknesses. Oxide thickness calculated from the experimental C-V data of a MOS capacitor is different from the actual oxide thickness, since such data include the effect of surface quantization. A correction factor has been developed considering the effect of charge centroid in presence of surface quantization at strong inversion and it has been observed that the correction due to surface quantization is crucial for highly doped substrate with thinner gate oxide.

• 대한전자공학회논문지
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• 제24권2호
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• pp.260-264
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• 1987

Gaussian $n^{+}$-p집합에 대해 위치함수인 유전율을 고려한 Poisson's equation의 일반적인 형태를 수치적으로 풀어 접합깊이가 전하밀도에 미치는 영향을 살펴 보았다. 또한 유전율의 변화에 기인한 전하 쌍극자의 해석적인 모델을 제시하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.246-246
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• 2016

Tungsten-nitrogen (W-N) co-doping has been known to enhance the photocatalytic activity of anatase titania nanoparticles by utilizing visible light. The doping effects are, however, largely dependent on calcination or annealing conditions, and thus, the massive production of quality-controlled photocatalysts still remains a challenge. Using density functional theory (DFT) thermodynamics and time-dependent DFT (TDDFT) computations, we investigate the atomic structures of N doping and W-N co-doping in anatase titania, as well as the effect of the thermal processing conditions. We find that W and N dopants predominantly constitute two complex structures: an N interstitial site near a Ti vacancy in the triple charge state and the simultaneous substitutions of Ti by W and the nearest O by N. The latter case induces highly localized shallow in-gap levels near the conduction band minimum (CBM) and the valence band maximum (VBM), whereas the defect complex yielded deep levels (1.9 eV above the VBM). Electronic structures suggest that substitutions of Ti by W and the nearest O by N improves the photocatalytic activity of anatase by band gap narrowing, while defective structure degrades the activity by an in-gap state-assisted electron-hole recombination, which explains the experimentally observed deep level-related photon absorption. Through the real-time propagation of TDDFT (rtp-TDDFT), we demonstrate that the presence of defective structure attracts excited electrons from the conduction band to a localized in-gap state within a much shorter time than the flat band lifetime of titania. Based on these results, we suggest that calcination under N-rich and O-poor conditions is desirable to eliminate the deep-level states to improve photocatalysis.

• 한국정보통신학회논문지
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• 제16권4호
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• pp.793-798
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• 2012

본 연구에서는 이중게이트(Double Gate; DG) MOSFET에서 채널 내 도핑분포 및 채널구조에 따른 문턱전압이하 전류의존성을 분석하고자 한다. 전위분포를 구하기 위하여 포아송방정식을 풀 때 전하분포는 가우스분포함수를 이용할 것이며 이의 타당성은 이미 여러 논문에서 입증하였다. 이중게이트 MOSFET는 게이트전압에 의한 전류제어능력의 증가로 단채널 효과를 감소시킬 수 있어 문턱전압이하 특성을 향상시킬 수 있다. 문턱전압이하 영역에서 전류제어는 고집적회로에서 소비전력의 감소와 관계된 매우 중요한 요소이다. 게이트전압에 따른 문턱전압이하 전류의 변화를 이용하여 문턱전압의 변화를 정량적으로 분석할 것이다. 문턱전압이하 전류는 채널 내 도핑분포 및 채널크기에 의하여 영향을 받는다. 그러므로 본 연구에서는 채널길이 및 채널두께의 변화가 전류흐름에 미치는 영향을 채널도핑농도, 도핑분포함수 등에 따라 분석할 것이다.

• 한국응용과학기술학회지
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• 제32권1호
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• pp.1-6
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• 2015

본 연구에서는 발광층의 전자와 정공의 재결합 영역을 확인하고, 단계적 도핑구조를 이용하여 여기자들의 효율적인 분배를 통해 roll-off 효율을 감소시켜서 녹색 인광 유기발광다이오드의 수명 증가를 나타냈다. 발광층 내 호스트는 양극성의 4,4,N,N'-dicarbazolebiphenyl (CBP)를 사용하여 전하의 이동을 원활하게 하였다. 발광층을 네 구역으로 분할하여 각각 소자를 제작하였고, 네 구역의 도판트 농도에 따라 발광효율과 수명 향상을 보였다. 이로써 발광층 내의 단계적 도핑구조를 이용하여 캐리어와 여기자들이 원활하게 분배된 것을 확인하였다. 기준소자 대비 발광층의 도판트 농도를 5, 7, 11, 9% 순서로 단계적 도핑구조를 적용한 device C의 수명이 약 73.70% 증가하였고, 휘도 효율은 51.10 cd/A와 외부 양자 효율은 14.88%의 성능을 보였다.

• Bulletin of the Korean Chemical Society
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• 제34권2호
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• pp.384-388
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• 2013

Fluorine-doping on the $Li_{1+x}Mn_{1.9-x}Al_{0.1}O_4$ spinel cathode materials is found to alter crystal shape, and enhance initial interfacial reactivity and solid electrolyte interphase (SEI) formation, leading to improved initial coulombic efficiency in the voltage region of 3.3-4.3 V vs. Li/$Li^+$ in the room temperature electrolyte of 1 M $LiPF_6$/EC:EMC. SEM imaging reveals that the facetting on higher surface energy plane of (101) is additionally developed at the edges of an octahedron that is predominantly grown with the most thermodynamically stable (111) plane, which enhances interfacial reactivity. Fluorine-doping also increases the amount of interfacially reactive $Mn^{3+}$ on both bulk and surface for charge neutrality. Enhanced interfacial reactivity by fluorine-doping attributes instant formation of a stable SEI layer and improved initial cyclic efficiency. The data contribute to a basic understanding of the impacts of composition on material properties and cycling behavior of spinel-based cathode materials for lithium-ion batteries.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2008년도 International Meeting on Information Display
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• pp.1319-1322
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• 2008

$CsN_3$ was developed as a novel n doping material with air stability and low deposition temperature. Evaporation temperature of $CsN_3$ was similar to that of common hole injection material and it worked well as a n dopant in electron transport layer. Driving voltage was lowered and high power efficiency was obtained in green phosphorescent devices by using $CsN_3$ as a dopant in electron transport layer. It could also be used as a charge generation layer in combination with $MoO_3$. In addition, n doping mechanism study revealed that $CsN_3$ is decomposed into Cs and $N_2$ during evaporation. This is the first work reporting air stable and low temperature evaporable n dopant in organic light-emitting diodes.

• 한국표면공학회지
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• 제49권6호
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• pp.490-497
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• 2016

In this study, 3-dimensional ripple structured anion (chlorine) doped ZnO thin film are developed, and used as electron transporting layer (ETL) in inverted organic photovoltaics (I-OPVs). Optical and electrical characteristics of ZnO:Cl ETL are investigated depending on the chlorine doping ratio and optimized for high efficient I-OPV. It is found that optimized chlorine doping on ZnO ETL enhances the ability of charge transport by modifying the band edge position and carrier mobility without decreasing the optical transmittance in the visible region, results in improvement of power conversion efficiency of I-OPV. The highest performance of 8.79 % is achieved for I-OPV with ZnO:Cl-x (x=0.5wt%), enhanced ~10% compared to that of ZnO:Cl-x (x=0wt%).

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2007년도 7th International Meeting on Information Display 제7권2호
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• pp.1650-1653
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• 2007

We demonstrate fluorescent green organic lightemitting diodes employing a rhenium oxide ($ReO_3$)-doped N,N-diphenyl-N,N'-bis(1,1'-biphenyl)-4,4'-diamine (NPB) hole transporting layer (HTL). The devices exhibit significantly reduced driving voltages as well as prolonged lifetime. Details of $ReO_3$ doping effects are described in terms of charge transfer complex and stabilization of HTL morphology.

• Progress in Superconductivity
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• 제10권2호
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• pp.123-127
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• 2009

NaFeAs recently observed superconductivity with the maximum $T_c{\approx}25$ K is investigated using first principles approach. We will address briefly the electronic structure and contrast other superconducting pnictides. This system shows strong two-dimensionality and reduction of flatness in the Fermi surfaces undermines tendencies of magnetic or charge instabilities. As observed in other superconducting pnictides, $Q_M=(\pi,\pi,0)$ antiferromagnetic ordering, which has not been observed clearly yet in this compound, is energetically favored. However, contrast to other superconducting pnictides, the density of states in this ordering shows considerable electron-hole asymmetry, implying efficiency of hole-doping than electron-doping to enhance $T_c$.