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Lighting is essential to modern society but it accounts for nearly 20 % of the electrical energy usage. Thus efforts to increase the conversion efficiencies of light sources are attracting more and more attention. Potential high efficiency light sources are fluorescent lamps or light-emitting diodes (LEDs). Modern LEDs show internal quantum efficiencies of virtually 100 %. However, in the case of standard LEDs most of this light is trapped inside the device because of total internal reflection at the interface semiconductor-air. Several methods have been developed in order to increase the extraction efficiency. This can be done either by optimizing the device geometry in order to increase the escape cone or by incorporating a resonant structure in order to force the internal emission into the existing escape cone. The latter approach is called microcavity LED (MCLED) or resonant cavity LED (RCLED) and is presented in detail in this work. Novel concepts to further increase the external quantum efficiency are discussed and experimental results are presented.
About the author
Reto Joray, Dr. sc. techn. ETH: Ph. D. in Physics from the SwissFederal Institute of Technology, EPFL Lausanne, Switzerland. M.Sc. in Materials Science from the Swiss Federal Institute ofTechnology, ETH Zürich, Switzerland.
