• Title/Summary/Keyword: self-consistent method

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Epitaxial Structure Optimization for High Brightness InGaN Light Emitting Diodes by Using a Self-consistent Finite Element Method

  • Kim, Kyung-Soo;Yi, Jong Chang
    • Journal of the Optical Society of Korea
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    • v.16 no.3
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    • pp.292-298
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    • 2012
  • The epitaxial layer structures for blue InGaN light emitting diodes have been optimized for high brightness applications with the output power levels exceeding 1000 $W/cm^2$ by using a self-consistent finite element method. The light-current-voltage relationship has been directly estimated from the multiband Hamiltonian for wurtzite crystals. To analyze the efficiency droop at high injection levels, the major nonradiative recombination processes and carrier spillover have also been taken into account. The wall-plug efficiency at high injection levels up to several thousand $A/cm^2$ has been successfully evaluated for various epilayer structures facilitating optimization of the epitaxial structures for desired output power levels.

A Green's-Matrix Approach to Chemisorption

  • Jang, Yun-Hee;Kim, Ho-Jing
    • Bulletin of the Korean Chemical Society
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    • v.14 no.2
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    • pp.238-243
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    • 1993
  • A self-consistent-field Green's matrix method for the calculation of electronic properties of chemisorbed system is devised and applied to the methanol on copper(110) surface. The method is based on CNDO Hartree-Fock approximation. Contour integration in the complex energy plane is used for an efficient calculation of the charge-density bond-order matrix. The information on each fragment prior to chemisorption is efficiently used and a small number of iterations are needed to reach the self-consistency. The changes of density of states and other quantities of methanol due to chemisorption are consistent with reported experimental results.

A Theoretical Study on the Dispersion of Elastic Waves in Particulate Composites (입자복합재료 내부의 탄성파 분산에 관한 이론적 연구)

  • 김진연;이정권
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.7
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    • pp.1697-1704
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    • 1994
  • Elastic wave propagation in discrete random medium studies to predict dynamic effective properties of composite materials containing spherical inclusions. A self-consistent method is proposed which is analogous to the well-known coherent potential approximation. Three conditions that must be satisfied by two effective elastic moduli and effective density are derived for the time without limit of frequency. The derived self-consistency conditions have the physical meaning that the scattering of coherent wave by the constituents in effective medium is vanished on the average. The frequency-dependent complex effective wave speed and coherent attenuation can be obtained by solving the derived self-consistency conditions numerically. The wave speed and attenuation obtained from present theory are shown to be in the better agreements with previous experimental observations than the previous theory.

Self-consistent Solution Method of Multi-Subband BTE in Quantum Well Device Modeling (양자 우물 소자 모델링에 있어서 다중 에너지 부준위 Boltzmann 방정식의 Self-consistent한 해법의 개발)

  • Lee, Eun-Ju
    • Journal of the Institute of Electronics Engineers of Korea SD
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    • v.39 no.2
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    • pp.27-38
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    • 2002
  • A new self-consistent mathematical model for semiconductor quantum well device was developed. The model was based on the direct solution of the Boltzmann transport equation, coupled to the Schrodinger and Poisson equations. The solution yielded the distribution function for a two-dimensional electron gas(2DEG) in quantum well devices. To solve the Boltzmann equation, it was transformed into a tractable form using a Legendre polynomial expansion. The Legendre expansion facilitated analytical evaluation of the collision integral, and allowed for a reduction of the dimensionality of the problem. The transformed Boltzmann equation was then discretized and solved using sparce matrix algebra. The overall system was solved by iteration between Poisson, Schrodinger and Boltzmann equations until convergence was attained.

Numerical Analysis of I-V Curves of RTDs with AlGaAs/GaAs Structure by Self-consistent Method (Self-consistent법에 의한 AlGaAs/GaAs구조 공명터널링 다이오드의 전기적 특성 해석)

  • Kim, S.J.;Park, G.Y.;Yoo, H.S.;Yi, S.H.;Choi, B.G.;Sung, Y.K.
    • Proceedings of the KIEE Conference
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    • 1993.07b
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    • pp.1280-1282
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    • 1993
  • We investigated theoretically the current-voltage characteristics of resonant tunneling diodes with a single quantum well structure, using a self-consistent method. This method is a numerical analysis which is able to include the effects of the undoped spacer layer and the band bending by charge accumulation and depletion on the contact layers, so that it is better suited to explain experimental results. The structure used is an $Al_{0.5}Ga_{0.5}$As/GaAs/$Al_{0.5}Ga_{0.5}As$ single quantum well. In this work, we estimate the theoretical current-voltage characteristics, and then, the dependence of the current-voltage curves on the thickness of undoped spacer layers.

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Dependence of the Thickness of Spacer Layers on the Current Voltage Characteristics of DB Resonant Tunneling Diodes Analyzed with a Self-Consistent Method (스페이서층 두께변화에 따른 공명터널링 다이오드에서 전류-전압 특성의 자기무모순법에 의한 해석)

  • 김성진;이상훈;성영권
    • Journal of the Korean Institute of Telematics and Electronics A
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    • v.31A no.3
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    • pp.46-52
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    • 1994
  • We investigated theoretically the current-voltage characteristics of resonant tunneling diodes with a single quantum well structure. using a self-consistent method. This method is a numerical analysis which is able to include the effects of the undoped spacer layer and the band bending by charge accumulation and depletion on the contact layers which have not been considered in the flat-band model reported by Esaki. so that it is better suited to explain experimental results. The structure used is an $AL_{0.5}Ga_{0.5}AS/GaAs/Al_{0.5}Ga_{0.5}AS$ single quantum well. In this work. we estimate the theoretical current-voltage characteristics of the same structure, and then, the dependence of the current-voltage curves on the thickness of undoped spacer layers sandwiched between the barrier and highly n-doped GaAs contact layer.

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Extended Additional Layer Method for the Calculation of TM mode coupling coefficient for Trapezoidal Gratings (확장된 새로운 층 방법을 이용한 사다리꼴 회절격자의 TM 모드의 결합계수 계산)

  • 조성찬;이동찬;김부균
    • Journal of the Korean Institute of Telematics and Electronics D
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    • v.35D no.9
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    • pp.87-92
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    • 1998
  • TM mode coupling coefficients for a generic five-layer DFB structure with trapezoidal and triangular gratings are calculated using the extended additional layer method. To determine the unperturbed field distributions of TM modes, a grating region is replaced by a new uniform layer whose inverse dielectric constant is the average value of the inverse dielectric constant of grating region in both longitudinal and transverse directions. Based on the self-consistent check, the validity of this method is established by comparing the results calculated by partitioning the grating region up to six uniform layers.

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The DC Characteristics of Submicron MESFEFs (서브미크론 MESFET의 DC 특성)

  • 임행상;손일두;홍순석
    • Electrical & Electronic Materials
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    • v.10 no.10
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    • pp.1000-1004
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    • 1997
  • In this paper the current-voltage characteristics of a submicron GaAs MESFET is simulated by using the self-consistent ensemble Monte Carlo method. The numerical algorithm employed in solving the two-dimensional Poisson equation is the successive over-relaxation(SOR) method. The total number of employed superparticles is about 1000 and the field adjusting time is 10fs. To obtain the steady-state results the simulation is performed for 10ps at each bias condition. The simulation results show the average electron velocity is modified by the gate voltage.

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Analysis of Invesion Layer Quantization Effects in NMOSFETs (NMOSFET의 반전층 양자 효과에 관한 연구)

  • Park, Ji-Seon;Sin, Hyeong-Sun
    • The Transactions of the Korean Institute of Electrical Engineers C
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    • v.51 no.9
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    • pp.397-407
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    • 2002
  • A new simulator which predicts the quantum effect in NMOSFET structure is developed. Using the self-consistent method by numerical method, this simulator accurately predicts the carrier distribution due to improved calculation precision of potential in the inversion layer. However, previous simulator uses analytical potential distribution or analytic function based fitting parameter Using the developed simulator, threshold voltage increment and gate capacitance reduction due to the quantum effect are analyzed in NMOS. Especially, as oxide thickness and channel doping dependence of quantum effect is analyzed, and the property analysis for the next generation device is carried out.