Journal
IEEE TRANSACTIONS ON ELECTRON DEVICES
Volume 57, Issue 1, Pages 79-87Publisher
IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC
DOI: 10.1109/TED.2009.2035538
Keywords
Droop; GaN; InGaN; internal quantum efficiency (IQE); LED-chip technology; LED degradation; LED package technology; light-emitting diode (LED); nitride
Funding
- German Federal Ministry of Education and Research (BMBF) [13N9400]
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In this paper, we report on the latest advancements in improving AlGaInN-based visible-light-emitting-diode (LED) efficiency in epitaxy, chip, and package designs. We investigate the fundamental origin of the typical high current droop of efficiency observed in such LEDs. We show that this effect is most likely not caused by incomplete carrier injection or carrier escape but that it is rather a fundamental material property of InGaN/GaN-heterostructure-based light emitters. The droop can be reduced in improved epitaxial LED active-layer designs. We show how this can be achieved by lowering InGaN volume carrier density in multiple quantum wells (MQWs) and thick InGaN layers. Improved epitaxial MQW structures are then combined with a new advanced chip concept. It is optimized for high efficiency at high current operation and arbitrary scalability and can be manufactured at low cost. This is accomplished by improving light-extraction efficiency, homogenizing the emission pattern, reducing forward voltage, and lowering thermal resistance. The improved high current efficiency can be fully exploited by mounting the chip in the highly versatile new OSLON SSL package. It features very stable package materials, a small footprint, and an electrically isolated design decoupling electrical and thermal contacts.
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