A5100617952- GaN-based semiconductor devices and materials
- ZnO doping and properties
- Metal and Thin Film Mechanics
- Semiconductor Quantum Structures and Devices
- Ga2O3 and related materials
- Semiconductor materials and devices
- High-Voltage Power Transmission Systems
- Power System Optimization and Stability
- Photocathodes and Microchannel Plates
- HVDC Systems and Fault Protection
- Smart Grid and Power Systems
- Power Systems and Renewable Energy
- Plasma Diagnostics and Applications
- Advanced Battery Technologies Research
- Optical Coatings and Gratings
- Multilevel Inverters and Converters
- Power Systems Fault Detection
- Microgrid Control and Optimization
- Magnetic Properties and Applications
- Machine Fault Diagnosis Techniques
- Wind Turbine Control Systems
- Thin-Film Transistor Technologies
- Industrial and Mining Safety
- Turbomachinery Performance and Optimization
- Energy and Environmental Systems
Samsung (South Korea)
2003-2025
Korea Electrotechnology Research Institute
2007-2019
Korea Economic Research Institute
2005
Gwangju Institute of Science and Technology
1999-2004
Materials Science & Engineering
2001
The effect of an electron blocking layer (EBL) on the efficiency droop in InGaN/GaN multiple quantum well light-emitting diodes (LEDs) is investigated. At low current density, LEDs with a p-AlGaN EBL show higher external (EQE) than without EBL. However, EQE as injection density increased. improved at high attributed to increased hole efficiency.
The characteristics of the GaN/InGaN multiquantum-well light-emitting diode (LED) have been examined from view point uniform current spreading. By means simple modeling, it was found that density and length lateral path through transparent layer represent dominant parameters in determining In this regard, we studied effect on reliability LED. We were able to significantly improve electrical, optical, LED terms reducing layer.
The effects of indium segregation and hydrogen on the optical structural properties InGaN/GaN multiple quantum wells, grown by metalorganic chemical vapor deposition were investigated. Photoluminescence high-resolution transmission electron microscopy analysis showed that two types indium-rich regions can be formed in InGaN well layers. Self-assembled dot-like found layer at a normal growth temperature. These behaved as luminescent centers, showing maximum content center region. However,...
The fabrication and characterization of an InGaN/GaN multiple-quantum well (MQW) light-emitting diode (LED) with a SiO2 current blocking layer inserted beneath the p-pad electrode is described. light-output power external quantum efficiency for MQW LED chip were significantly increased compared to those conventional chip. increase in can be attributed injection additional into by reduction parasitic optical absorption electrode.
We demonstrate a high efficiency and an improvement of the electrical properties in InGaN/GaN multiple quantum well light-emitting diodes (LEDs) using intentionally formed V-shaped pits. Efficiency droop behaviors are measured LEDs with pits act like low dislocation density. The reverse voltage at −10 μA shows −120 V, which is comparable to p-i-n rectifiers grown on free-standing GaN, leakage current decreased indicating passivation dislocation. A calculated diode ideality factor that...
The temperature dependence of the photoluminescence (PL) InGaN films, grown by metalorganic chemical vapor deposition, has been investigated. A strained thin film which contains composition-fluctuated regions shows so-called S-shaped dominant PL peak energy. However, an thick quantum dot-like In-rich a sigmoidal energy, as result transfer carriers from band-edge related luminescent centers to regions. It is also found that activation energy for thermal quenching intensity in larger than
The enhancement of phase separation in the InGaN layer grown on a GaN with rough surface was investigated for formation self-assembled In-rich quantum dots (QDs) layer. Transmission electron microscopy images showed that QDs size 2–5 nm were formed even an low indium content, and thickness less than critical thickness. room-temperature photoluminescence (PL) spectrum this emission peaks corresponding to QDs. temperature-dependent PL spectra dominant peak shifts lower energy side, indicating...
This paper presents a practical approach for supplementary control of high voltage direct current (HVDC) system to damp subsynchronous oscillation (SSO) involving HVDC converters and turbine-generator shaft systems. A novel eigenvalue analysis (NEA) program, modeling consider steady-state dynamic conditions in combined ac/dc system, an appropriate scheme have been utilized. The design method proposed facilitates the damping controller (SODC) provide positive torque dominant torsional mode...
This paper proposes a new simplified model of doubly fed induction generator (DFIG) that is integrated with rotor-side converter for studies large-scale transient stability. accurately considers the rotor field dynamics an to yield simulation results are more accurate in terms voltage stability, as well angle The purpose this provide simple but effective DFIG study and examine important aspects slip power. electric/turbine control system was tested against six-machine 23-bus system,...
We investigated the effect of barrier thickness on interfacial and optical properties InGaN/GaN multiple quantum wells (MQWs) grown in a low-pressure metalorganic chemical vapor deposition system. The GaN MQWs was found to play key role determine structural characteristics MQWs. As layer increased, abruptness interface between InGaN layers deteriorated, probably due generation defects induced by strain accumulation Accordingly, intensity line-width photoluminescence taken from were reduced...
Etch-induced damage in GaN/InGaN multi-quantum well light-emitting diodes (LEDs) caused by a Cl2-base plasma and its recovery means of N2-plasma annealing process n-GaN is described. The photoluminescence intensity etched n-type GaN was decreased several orders magnitude due to etch-induced damage, giving rise an increase the leakage current LED current–voltage curves. However, treatment LEDs with N2 along rapid thermal led enhancement I–V characteristics suppression current....
The effects of an alcohol-based (NH4)2S solution [t-C4H9OH+(NH4)2S] treatment on Pt Ohmic contacts to p-type GaN are presented. specific contact resistance decreased by three orders magnitude from 2.56×10−2 4.71×10−5 Ω cm2 as a result surface using compared that the untreated sample. O 1s and 4f core-level peaks in x-ray photoemission spectra showed was effective removing oxide layer. Compared sample, (NH4)2S-treated sample Ga 2p peak which shifted toward valence-band edge 0.25 eV,...
Feasibility of an oxidized Ni/Au p contact on some aspects device applications for a GaN/InGaN multiple quantum well light-emitting diode (LED) was investigated. For the oxidation contact, furnace annealing completely fabricated LED performed at 600 °C 5 min in O2 ambient. case with system, I–V measurements showed reduction series resistance by 17.2%. In addition, optical output power increased factor 2. However, significant degradation reliability characteristics observed, which might...
The fabrication and characterization of an InGaN/GaN multiple quantum well light-emitting diode (LED) with a highly transparent Pt thin film as current spreading layer are described. room temperature electroluminescence exhibits strong emission at 453 nm. Pt-contacted LEDs show good electrical properties high light-output efficiency compared to Ni/Au-contacted ones. light transmittance the specific contact resistance thickness 8 nm on p-GaN was determined be 85% 450 9.12×10−3 Ω cm2,...
We report that NH3 ambient thermal annealing is a promising method for recovering the dry- etch-induced damage on Mg-doped GaN surfaces. The surface electrical properties of dry-etched can be fully recovered by using as an gas at temperatures above 900 °C. complete recovery sheet hole concentration in attributed to reduction excess nitrogen vacancies damaged region reactive atoms supplied during annealing.
The proposed algorithm is based on the discrete Fourier transform (DFT) and a software-based synchronous sampling technique that locked to power system frequency using reconfigurable field-programmable gate arrays (FPGAs). main purposes of this paper are provide new method recording high-resolution rotor angle machine practical for deriving more accurate d-q-axis parameters. An FPGA used in realizing rotor-angle transducer it simultaneously detects generator terminal voltage. DFT combined...
We investigate the effect of internal electric field in InGaN well layer InGaN/GaN multiple quantum light-emitting diodes (LEDs) on efficiency droop behavior. The simulation results show that layers Ga-polar LEDs is same as direction external by forward bias voltage, resulting a strong droop. However, N-polar drastically improved due to an increase and carrier injection weakening with increasing voltage decrease electron overflow.
Frequency drops and the high ambient temperature cause a decrease in airflow an increase exhaust gas of turbine (GT). These two conditions significantly reduce maximum continuous power output GTs. Correct modeling these under heavily loaded conditions, such as hot summer, is very important. Otherwise, simulated GT may be higher than real one estimation frequency responsive reserve spinning gravely erroneous. This paper describes simulation heavy-duty operating control to study its impact on...
The effects of the growth interruption and introduction H2 during time on optical structural properties InGaN/GaN multiquantum wells (MQWs), grown by metalorganic chemical vapor deposition, were investigated. When was interrupted formation interfaces in MQWs, intensity photoluminescence (PL) greatly increased InN-rich regions near surface InGaN well layer suppressed. As increased, however, PL decreased average In composition MQWs decreased. introduced interruption, significantly enhanced...
We report on the activation of Mg acceptors in Mg-doped GaN films, grown by metalorganic chemical vapor deposition, via use a pulsed KrF (248 nm) excimer laser irradiation. The as-grown : Mg, which was irradiated at energy density 590 mJ/cm2 N2 ambient showed hole concentration 4.42 × 1017 cm—3. Furthermore activated conventional rapid thermal annealing, increased from 4.3 to 9.42 cm—3 as result subsequent These results suggest that irradiation can dramatically enhance p-type conductivity...