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CONNECTING THE COMPOUND SEMICONDUCTOR COMMUNITY


March 2013 Volume 19 Number 2


Editor Dr Richard Stevenson richardstevenson@angelbc.co.uk +44 (0)1291 629640


Contributing Editor Dr Rebecca Pool


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Until recently, it seemed that theorists were starting to narrow down some of the potential causes of droop. A few years back, some were arguing that it could be caused by Auger recombination, while others had ruled it out, and only more recently has it seemed that if an Auger-related processes is to blame, it must involve phonons and alloy disorder.


Now, however, the simplest form of Auger recombination is firmly back on the agenda, getting the blame for droop once again. This time it is a partnership between researchers at Technion-Israel Institute of Technology and the US Naval Research Laboratory that is making this claim. They argue that they have arrived at a different conclusion from their peers by calculating Auger rates in realistic active regions: Their model includes quantum wells, while those of others are based on bulk material (see page 65 for details).


If they are right, then one way to reduce droop in the wells is to make them thicker, because this reduces the carrier density. However, thicker wells have a major downside in conventional LEDs, because they lead to a separation of electrons and holes, due to the strong internal electric fields in these devices.


An alternative option put forward by the US-Israeli team is to introduce grading into the well. Calculations suggest that this can lead to a three-fold reduction in Auger recombination rates, and boost LED output by a fifth.


It will be interesting to see how the nitride community views this latest contribution to the debate on droop. As it drags on, it seems to me that many researchers are becoming increasingly entrenched in their own views, so I don’t think that claims for Auger recombination as the cause of droop will be universally popular. But I expect that they will be welcomed by some.


Dr Richard Stevenson Editor


March 2013 www.compoundsemiconductor.net 3 debbie.higham@angelbc.com jan.smoothy@angelbc.com mitch.gaynor@angelbc.com


The latter problem, which goes by the name of droop, looks at first sight as though it could be solved by a postgraduate student in a few months. But far, far more hours than that have been devoted to trying to get to the bottom of this mysterious malady, and as of yet, there is no consensus of opinion over its origin.


sharon.cowley@angelbc.com shehzad.munshi@angelbc.com robin.halder@angelbc.com Droop courts controversy again E: tbrun@brunmedia.com E: jjenkins@brunmedia.com


Some puzzles seem simple, but the deeper you delve into them, the further you are from a solution. That's the case with a selection of endgame positions in chess, various moral dilemmas, and uncovering an explanation for why an LED diminishes in efficiency as the current passed through it is cranked up.


jackie.cannon@angelbc.com


editorial view


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