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Interrelationships of electrical, optical, temperature characteristics and defect density in GaN-based light-emitting diodes

Title
Interrelationships of electrical, optical, temperature characteristics and defect density in GaN-based light-emitting diodes
Author
윤주선
Advisor(s)
심종인
Issue Date
2013-08
Publisher
한양대학교
Degree
Doctor
Abstract
This dissertation discusses correlations among temperature, current, voltage, carrier recombination mechanisms, defect density and electrode structure in GaInN/GaN multiple quantum well (MQW) blue light-emitting diode (LED). In the first part, how electrode structure and material parameters of LEDs influence to current, voltage, and temperature distribution are investigated. In order to study this, firstly, an LED is modeled as three-dimensional equivalent circuit which makes it available to solve current and voltage distribution. In this equivalent circuit, active layer is converted to diodes and metal, p-GaN and n-GaN layers are converted to resistors. Analyzed results with diode and resistance parameters experimentally extracted show identical results with surface light distribution and current vs. voltage characteristics practically measured. As heat generation rate can be calculated with current and voltage distribution already solved, three-dimensional temperature distribution in LED is obtained by means of solving thermal resistor network which is created by using heat generation rate as heat sources and by converting each material’s thermal conductivity as thermal resistor. In the analysis process, contact resistance among materials, air and heat sink are considered. Apparent temperature distribution on surface and in each epitaxial layer is also analyzed with method explained above. Result of apparent temperature distribution on surface extracted with the circuit model is in accord with experimentally measured results from Infrared camera. After that a new electrode structure is suggested, which increase light-extraction efficiency, and compared with other various electrode structure by means of the established analysis methodology. In the second part, correlations among defect density, temperature, carrier recombination mechanisms as a function of current and efficiency droop are investigated theoretically and experimentally. Relative defect density is extracted by image processing of dot emission in reverse bias. In order to investigate junction temperature vs. current, forward bias method is used in this study. Research of carrier recombination mechanisms vs. total injection current are conducted by combination of rate equation, optical power vs. current and internal quantum efficiency (IQE) charactreristics. The radiative and nonradiative current components are separated by using the information of the IQE vs. current, obtained from the temperature-dependent electroluminescence (TDEL) measurement, optical power vs. current and current vs. voltage characteristics. Analyzed results with experimental and analysis techniques above clarify that Auger recombination cannot be a dominant cause for efficiency droop. Also, it is deduced that the dominant nonradiative mechanisms of the GaN-based LEDs change from the competing mechanisms of Shockley-Read-Hall or tunneling recombination at low current density to the carrier overflow at high current density, inducing the IQE droop.
URI
https://repository.hanyang.ac.kr/handle/20.500.11754/133186http://hanyang.dcollection.net/common/orgView/200000422250
Appears in Collections:
GRADUATE SCHOOL[S](대학원) > ELECTRONIC COMMUNICATION ENGINEERING(전자통신공학과) > Theses (Ph.D.)
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