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PHOTOS Photo: speakers

Department of Materials at University of California Santa Barbara


Claude Weisbuch is a “Directeur de Recherche” (emeritus) at the Centre National de la Recherche Scientifique (CNRS), Ecole Polytechnique, and a distinguished professor in the materials department of University of California at Santa Barbara, he has been at Bell Laboratories (1979‐1981), then at Saint Gobain and Thomson CSF (now Thales).
He was “directeur scientifique” (chief scientist) of Délégation Générale pour l’Armement (procurement), ministry of defense, France, from 1992 to 1998. He founded in 2002 a high tech company, Genewave, Paris, devoted to fluorescence based molecular diagnostics systems. He Has authored or co-authored more than 200 papers and 35 patents.


Session: White LEDs : New researches, new results
Wednesday October, 15: 09:00

The efficiency challenge of nitride LEDs at High current : the Auger effect

High efficiency lighting will enable to tap a huge reservoir of energy, but LEDs need to reach efficiencies higher than the dominant fluorescents lamps, to have a lower cost of ownership. To achieve this, LEDs have to perform at the physical limits of electricity-to-light conversion efficiency, requiring mastering of the intrinsic electrical and optical properties of the materials. Today’s LEDs operate in the blue range with both 90%+ internal quantum efficiency (IQE) and light extraction efficiency (LEEs). However, the 90%+ performance of IQE is only obtained in the blue/violet spectral range at low carrier injection. The required operation at high current densities, a prerequisite to lower lamp costs, leads to nonlinear phenomena, which diminish the IQE, the droop. A recent measurement of hot electron generation in LEDs points to Auger non-radiative recombination as the main cause of droop. The “green gap” of IQE in the green-yellow spectral range also presents major hurdles. I will introduce some paths to solve droop and/or green gap: designing better LED structures leading to diminished carrier densities at high current injection, avoiding c-plane limitations by new substrates (semipolar and non polar GaN), using new concepts of active materials (quantum wires, QWRs, quantum dots, QDs), relying on lasers as alternatives to LEDs, switching to large Si substrates, …