Equivalent-circuit Analysis of ITO/Alq3/AlOrganic Light-emitting Diode

Dong-Hoe Chung,Tae Wan Kim 한국전기전자재료학회 2007 Transactions on Electrical and Electronic Material Vol.8 No.3

An ITO/Alq3/Al structure was used to study complex impedance of Alq3 based organic light-emitting diodes. Equivalent circuit was analyzed in a device structure of ITO/Alq3/Al with a thickness layer of Alq3 of 100 nm. The obtained impedance was able to be fitted using equivalent circuit model of parallel combination of resistance Rp and capacitance Cp with a small series resistance of Rs.

Equivalent-circuit Analysis of ITO/Alq₃/Al Organic Light-emitting Diode

Chung, Dong-Hoe,Kim, Tae-Wan The Korean Institute of Electrical and Electronic 2007 Transactions on Electrical and Electronic Material Vol.8 No.3

An $ITO/Alq_3/Al$ structure was used to study complex impedance of $Alq_3$ based organic light-emitting diodes. Equivalent circuit was analyzed in a device structure of $ITO/Alq_3/Al$ with a thickness layer of $Alq_3$ of 100 nm. The obtained impedance was able to be fitted using equivalent circuit model of parallel combination of resistance $R_p$ and capacitance $C_p$ with a small series resistance of $R_s$.

Equivalent Circuit Models in Organic Light-Emitting Diodes Designed Using a Cole-Cole Plot

Han, S. M.,Kim, K. P.,Choo, D. C.,Kim, T. W.,Seo, J. H.,Kim, Y. K. TaylorFrancis 2007 Molecular Crystals and Liquid Crystals Vol.470 No.1

<P> The equivalent circuit models in organic light-emitting diodes (OLEDs) consisting of indium-tin-oxide (ITO)/tris(8-hydroxyquinoline) Aluminum (Alq3)/Aluminum (Al), ITO/Alq3/Lithium quinolate/Al or ITO/N,N-bis-(1-naphthyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB)/Alq3/Al were investigated. The relaxation times were obtained from the impedances as functions of frequencies, and the equivalent circuits in the OLEDs were designed by using the relaxation times of OLEDs determined from the impedance spectroscopies. The Cole-Cole plots calculated from the equivalent circuit models were in reasonable agreements with the experimental results. These results can help designing equivalent circuit models of multilayer OLEDs.</P>

InGaN/GaN 청색 발광다이오드에서 전류 과밀 현상이 운반자 넘침에 미치는 영향에 대한 연구

유혜정,이진규,김태수,오난초,송정훈 한국물리학회 2014 새물리 Vol.64 No.11

Because conventional GaN-based light-emitting diodes (LEDs) grown on the sapphire substrates use a mesa structure for current injection, the current flows have both vertical and horizontal components. In these LEDs, the distribution of the current density in the horizontal direction cannot be totally uniform. The nonuniform current flows may cause nonuniform light emission and degrade the external quantum efficiency. This effect is called the current crowding effect. In this study, we analyzed the degree of current crowding and its effects on the carrier spill-over and the resultant external quantum efficiency in InGaN/GaN blue LEDs. A carrier spill-over that was larger by a factor of 1.7 was observed when the current crowding was measured to be 3.1 times lager, which means current crowding enhances the current overflow. We further show that the nonuniform distribution of carriers results in a different external quantum efficiency (EQE) that is a function of the distance from the p-contact edge, which can have a significant effect on the efficiency droop at high current. Although several mechanisms have been suggested to explain the droop, including electron leakage at heterointerfaces, poor hole injection efficiency, indium-rich regions, we show that the current-crowding effect, which increases with increasing current density is one of the major causes of the efficiency droop. 일반적인 GaN 기반 발광다이오드는 사파이어 기판 위에 성장시킨 메사 구조이다. 발광다이오드는 수직방향과 수평방향으로 전류의 흐름이 생기게 된다. 이때 구조적인 특성으로 인하여 메사 구조로 이루어진 발광다이오드에서는 수평 방향으로의 전류의 흐름에 불균형이 생기게 된다. 수평으로의 불균형한 전류 주입은 위치적으로 불균형한 발광을 유도하게 되고 이러한 현상을 ``전류 과밀 현상 (current crowding effect)''이라 한다. 본 연구에서는 전류 과밀의 정도를 분석하여, 이러한 전류 과밀 현상이 위치에 따른 운반자 넘침과 외부양자효율에 미치는 영향을 측정 분석하였다. 전류 과밀 현상이 큰 영역일수록 운반자 넘침은 커졌다. 이에 전류 과밀 현상은 운반자 손실을 유발하였다. 또한 위치적인 운반자 주입 불균형이 위치적으로 다른 내부양자효율을 초래하였고 그에 따라 실제 소자에 고전류 효율 저하로 이어지는 것을 보일 수 있었다. 고전류 효율 저하에 영향을 미치는 요인으로는 전류 누설, 정공의 주입 효율 감소, 인듐 국소화 등이 알려져 있지만, 전류 밀도가 증가할수록 더 큰 영향을 받는 전류 과밀 현상이 고전류 효율 감소에 매우 중요한 기여를 하고 있음을 보일 수 있었다.

Electrical Properties of Organic Light-Emitting Diodes Fabricated on HfOX-Treated Indium-Tin-Oxide Surfaces by Using an Impedance Spectroscopy Analysis

이준신,조재현,박형준,김현민,손혁주,김재홍,허종규,손선영,박근희,남은경,정동근 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.6

In organic light-emiting diodes (OLEDs), both the electrons and the holes ned to be injected efficiently to obtain the best device performance. This means that a smal injection barier height at the indium-tin oxide (ITO)/organic interface is required. The insertion of an insulating layer betwen the ITO and the organic layers leads to a significant improvement in the charge injection and the electroluminescence output. In this study, the surface of the ITO anode in OLEDs was treated with an HfOX deposition proces by using an atomic-layer chemical- vapor deposition system (ALCVD). The OLEDs fabricated on the HfOX-treated ITO anode showed a lower impedance and a higher conductance and capacitance. The changes in the capacitance, the conductance and the impedance were atributed to the enhanced carier tunneling and to a change in the work function of ITO. In this work, we used an impedance spectroscopy analysis to determine the effect of the HfOX treatment on the surface of ITO and to model the equivalent circuit for OLEDs. Impedance spectroscopy is one of the most powerful tools used to study equivalent circuit models for and the charge carier dynamics and the dielectric properties of organic devices. Devices with an ITO/organic material/Al structure could be modeled as resistances and capacitances aranged in paralel or in series. The number of elements depend on the composition of the structure, esentialy the number of layers and the contacts.

Parameter Analysis of an Organic Light-Emitting Diode (OLED)

이순석 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.2

The contact resistance, the paralel resistance and the paralel capacitance of an organic light- emiting diode (OLED) were analyzed as a function of voltage. A sinusoidal voltage, a direct current (DC)voltage and a designed voltage were applied to obtain the parameters. The contact resistance was 82 Ω and the parallel resistance of the OLED was found to decrease from 28 M to 5 k as the applied voltage was increased from 2.4 V to 6.8 V. The conduction current only flowed through the device during a period of constant voltage and the displacement and the conduction currents flowed during a period of increasing voltage. The parallel capacitance, obtained by using the displacement current, was about 0.71 nF at voltage below 1.8 V and deceased, after showing a peak value of 0.85 nF at 3.3 V, as the applied voltage was increased. The contact resistance, the paralel resistance and the paralel capacitance of an organic light- emiting diode (OLED) were analyzed as a function of voltage. A sinusoidal voltage, a direct current (DC)voltage and a designed voltage were applied to obtain the parameters. The contact resistance was 82 Ω and the parallel resistance of the OLED was found to decrease from 28 M to 5 k as the applied voltage was increased from 2.4 V to 6.8 V. The conduction current only flowed through the device during a period of constant voltage and the displacement and the conduction currents flowed during a period of increasing voltage. The parallel capacitance, obtained by using the displacement current, was about 0.71 nF at voltage below 1.8 V and deceased, after showing a peak value of 0.85 nF at 3.3 V, as the applied voltage was increased.

Dynamic Response of Organic Right-emitting Diodes in ITO/Alq3/Al Structure

Dong-Gyu Lee,이준웅 한국전기전자재료학회 2005 Transactions on Electrical and Electronic Material Vol.6 No.3

Dynamic response of organic light-emitting diodes were analyzed in ITO/Alq3(100 nm)/Al device structure with a variation of voltage an frequency. At low frequency region, complex impedance is mostly governed by resistive component, and at high frequency region by capacitive component. Also, we have evaluated resistance, capacitance and permittivity of devices.

A Bottom-gate Depletion-mode Nanowire Field Effect Transistor (NWFET) Model Including a Schottky Diode Model

유윤섭,이세한,D. S. Kim,Y. C. Jung,황성우,안도열 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.3

We present a compact model for a bottom-gate depletion-mode nanowire field-effect transistor (NWFET) including a Schottky diode model for efficient circuit simulation. The NWFET model is based on an equivalent circuit corresponding to two back-to-back Schottky diodes for the metalsemiconductor (MS) contacts separated by a depletion-mode NWFET for the intrinsic NWFET. The previously developed depletion-mode NWFET model is used for the intrinsic part of the NWFET. The Schottky diode model for the M-S contacts includes the thermionic field emission (TFE) and the thermionic emission (TE) mechanisms for reverse bias and forward bias, respectively. Our newly developed model is integrated into Advanced Design System (ADS), in which the extrinsic part (Schottky diode model) and the intrinsic part of the NWFET are developed by utilizing the symbolically defined device (SDD) for an equation-based nonlinear model. The results simulated from the newly developed NWFET model reproduce the experimental results within 10% errors. The mobilities extracted from the newly developed NWFET model are compared with those extracted from the previously reported NWFET model which replaced the Schottky diodes with series resistances.

Design and analysis of a highly reliable large-area Z-type transparent module for dye-sensitized solar cells

Kim, Hyeongseok,Jo, Jeonghoo,Lee, Ganghoo,Shin, Myunghun,Lee, Joo-Cheol Elsevier 2017 SOLAR ENERGY -PHOENIX ARIZONA THEN NEW YORK- Vol.155 No.-

<P><B>Abstract</B></P> <P>The design methodologies for large-area transparent dye-sensitized solar cells (DSSCs) and modules for building-integrated photovoltaic (BIPV) windows are presented. Using electrochemical impedance spectroscopy and the optical/electrical measurements of a small-sized (∼9×5mm) test cell, the basic circuitry of a DSSC is generated in a unit cell for building the 2-dimensional equivalent circuit model of a large-area Z-type transparent DSSC module (300×300mm) on P-Spice. Based on solar irradiation at a window-side monitored for a year, we have proposed a DSSC module design that generates the maximal electrical energy for the best levelized cost of electricity. While simulations using the developed model estimated a module efficiency of ∼3.23% and an annual electrical energy generation of 448kWh/m<SUP>2</SUP>, the fabricated module with a cell width of ∼18mm exhibited an efficiency of ∼3.19%; the design is also conducive for practical manufacturing and thermal reliability. The developed model demonstrates the operational behaviors of DSSC modules under local shadowing conditions that match with the experiments. The feasibility of the DSSC as a reverse diode, working as a distributed by-pass diode eliminating the current mismatch loss is also demonstrated; this is beneficial for long-term operations. This work can be applied to other types of DSSCs and can be used for producing DSSC-based BIPV windows.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The design methodologies for DSSCs and modules for BIPV windows are presented. </LI> <LI> Equivalent circuit models are established using EIS and the optical/electrical measurements. </LI> <LI> Large-area Z-type transparent DSSC module (300×300mm) are designed and fabricated. </LI> <LI> Annual maximal electricity of 448kWh/m<SUP>2</SUP> are expected for the best LCOE. </LI> </UL> </P>

A Semi-analytical Model for Depletion-mode N-type Nanowire Field-effect Transistor (NWFET) with Top-gate Structure

유윤섭 대한전자공학회 2010 Journal of semiconductor technology and science Vol.10 No.2

We propose a semi-analytical current conduction model for depletion-mode n-type nanowire field-effect transistors (NWFETs) with top-gate structure. The NWFET model is based on an equivalent circuit consisting of two back-to-back Schottky diodes for the metal-semiconductor (MS)contacts and the intrinsic top-gate NWFET. The intrinsic top-gate NWFET model is derived from the current conduction mechanisms due to bulk charges through the center neutral region as well as of accumulation charges through the surface accumulation region, based on the electrostatic method, and thus it includes all current conduction mechanisms of the NWFET operating at various top-gate bias conditions. Our previously developed Schottky diode model is used for the MS contacts. The newly developed model is integrated into ADS, in which the intrinsic part of the NWFET is developed by utilizing the Symbolically Defined Device (SDD) for an equation-based nonlinear model. The results simulated from the newly developed NWFET model reproduce considerably well the reported experimental results.