Optical cavity effects have a significant influence on the extraction efficiency of InGaN/GaN quantum-well-heterostructure flip-chip light-emitting diodes (FCLEDs). Light emitted from the quantum well (QW) self-interferes due to reflection from a closely placed reflective metallic mirror. These interference patterns couple into the escape cone and cause significant changes in the extraction efficiency as the distance between the QW and the metallic mirror varies. In addition, the radiative lifetime of the QW also changes as a function of the distance between the QW and the mirror surface. Experimental results from packaged FCLEDs, supported by optical modeling, show that a QW placed at a neighboring position corresponding to a minimum in overall light extraction. Furthermore, the optical model and experimental data are used to estimate the absolute internal quantum efficiency.
Green phosphor-converted LEDs using a blue pump InGaN diodes have advantages over the direct green InGaN LED with regards to color stability with drive and/or temperature. Added manufacturing steps are outweighed by higher color yield, as a range of pump colors can be used without changing the final chromaticity. The conversion losses can be smaller than the decrease in wall-plug efficiency from blue towards green, which has been reported by many sources. A distinct disadvantage of the concept is due to only one color and phosphor proven - SrGa2S4:Eu2+ and 535 nm peak wavelength.
Jonathan Wierer, Jerome Bhat, Chien-Hua Chen, G. Christenson, Lou Cook, M. Craford, Nathan Gardner, Werner Goetz, R. Scott Kern, Reena Khare, A. Kim, Michael Krames, Mike Ludowise, Richard Mann, Paul Martin, Mira Misra, J. O'Shea, Yu-Chen Shen, Frank Steranka, Steve Stockman, Sudhir Subramanya, S. Rudaz, Dan Steigerwald, Jingxi Yu
High-power light-emitting diodes (LEDs) in both the AlInGaP (red to amber) and the AlGaInN (blue-green) material systems are now commercially available. These high-power LEDs enable applications wherein high flux is necessary, opening up new markets that previously required a large number of conventional LEDs. Data are presented on high-power AlGaInN LEDs utilizing flip-chip device structures. The high-power flip-chip LED is contained in a package that provides high current and temperature operation, high reliability, and optimized radiation patterns. These LEDs produce record powers of 350 mW (1A dc, 300 K) with low (<4V) forward voltages. The performance of these LEDs is demonstrated in terms of output power, efficiency, and electrical characteristics.
We present the development of high-quality InxGa1-xP graded buffers on GaP substrates (InxGa1-xP/GaP) for use in epitaxial transparent-substrate light-emitting diodes. The evolution of microstructure and dislocation dynamics of these materials has been explored as a function of growth conditions. The primarily limiting factor in obtaining high-quality InxGa1-xP/GaP is a new defect microstructure that we call branch defects. Branch defects pin dislocations and result in dislocation pileups that cause an escalation in threading dislocation density with continued grading.
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