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Schematic representation of recombination in a nitride semiconductor
Presented Tuesday, March 16, 2010
Chris G. Van de Walle
University of California, Santa Barbara
Santa Barbara, CA 93106
Computational scientists at the University of California, Santa Barbara (UCSB), have provided compelling evidence that Auger recombination contributes strongly to "droop", the decline in external quantum efficiency observed at higher drive currents in nitride LEDs. The researchers demonstrate, by means of rigorous quantum-mechanical calculations in which individual loss processes can explicitly be isolated, that Auger recombination is a serious loss mechanism in wurtzite InGaN.
Auger recombination had previously been proposed as a loss mechanism based on experiments; however, experimentally it is very difficult to discriminate between different nonradiative processes, and the role of Auger losses had remained controversial. The Auger process is a nonradiative process, in which an electron recombines with a hole, but instead of emitting a photon, the process results in the excitation of another carrier to a higher-energy state. The researchers have also investigated other loss mechanisms, including free-carrier absorption. As in the case of the Auger recombination calculations, this is the first time that phonon-assisted indirect absorption processes have been explicitly evaluated from first principles, for any material.
The results show that free-carrier absorption is not an important mechanism in the case of LEDs, but it can account for the previously puzzling losses observed in nitride-based lasers. With these mechanisms now identified and quantified future developments can focus on removing or reducing these losses.
"Auger recombination rates in nitrides from first principles", K. T. Delaney, P. Rinke, and C. G. Van de Walle, Appl. Phys. Lett. 94, 191109 (2009).
Reporters may freely use this image as long as they include the following credit: "Image courtesy of K. T. Delaney, P. Rinke, and C. G. Van de Walle/UC Santa Barbara".
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