University of Cambridge > Talks.cam > Hitachi Cambridge Seminar Series > Lighting the Future: the science behind understanding the efficiency and reducing the cost of GaN LEDs (Prof. Sir Colin J. Humphreys FRS, University of Cambridge)

Lighting the Future: the science behind understanding the efficiency and reducing the cost of GaN LEDs (Prof. Sir Colin J. Humphreys FRS, University of Cambridge)

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Solid-state lighting using GaN-based LEDs could reduce the global amount of electricity used for lighting by 50%. Lighting would then use 10% of all electricity instead of the current 20%. In the UK this would save £2 billion per annum in electricity costs, and save 10% of carbon emissions from our power stations. GaN LEDs are highly efficient: the internal quantum efficiency of blue LEDs is about 80%. A major puzzle has been why such InGaN/GaN quantum well LEDs are so efficient despite a high density of dislocations, which act as non-radiative recombination centres. Joint work by Cambridge and Manchester has shown that this is because the carriers are localised on a nm scale, which prevents them from diffusing to the dislocations. In fact the carriers are localised by two different mechanisms: the electrons are localised by monolayer variations in the InGaN quantum well width and the holes by InGaN random alloy fluctuations.

The main factor preventing the widespread use of LED lighting in our homes and offices is cost. The reason why GaN LEDs are relatively expensive (a 40 Watt equivalent replacement LED bulb costs about £15) is that they are grown on low-diameter sapphire or SiC substrates. The Cambridge GaN group has pioneered the growth of GaN LEDs on 6-inch Si substrates, which will substantially reduce the cost. The growth is difficult because of the large difference in thermal expansion coefficients (54%) of GaN and Si, and the large lattice mismatch (17%). This talk will describe how these difficulties have been overcome. A patent has been filed and two spin-off companies set up. Plessey acquired these in 2012 and is now manufacturing GaN LEDs on 6-inch Si at its factory in Plymouth, Devon. These are the world’s first commercially available LEDs on 6-inch Si (and the first LEDs to be manufactured in the UK).

This talk is part of the Hitachi Cambridge Seminar Series series.

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