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SUMMARY:Lighting the Future: the science behind understanding the efficien
 cy and reducing the cost of GaN LEDs (Prof. Sir Colin J. Humphreys FRS\, U
 niversity of Cambridge) - Prof. Sir Colin J. Humphreys FRS\, Department of
  Materials Science &amp\; Metallurgy\, University of Cambridge
DTSTART:20140115T150000Z
DTEND:20140115T160000Z
UID:TALK50841@talks.cam.ac.uk
CONTACT:Dr. Jonathan D. Mar
DESCRIPTION:Solid-state lighting using GaN-based LEDs could reduce the glo
 bal amount of electricity used for lighting by 50%. Lighting would then us
 e 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 e
 missions from our power stations. GaN LEDs are highly efficient: the inter
 nal 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 densi
 ty of dislocations\, which act as non-radiative recombination centres. Joi
 nt work by Cambridge and Manchester has shown that this is because the car
 riers are localised on a nm scale\, which prevents them from diffusing to 
 the dislocations. In fact the carriers are localised by two different mech
 anisms: the electrons are localised by monolayer variations in the InGaN q
 uantum well width and the holes by InGaN random alloy fluctuations.\n\nThe
  main factor preventing the widespread use of LED lighting in our homes an
 d 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 gr
 own on low-diameter sapphire or SiC substrates. The Cambridge GaN group ha
 s pioneered the growth of GaN LEDs on 6-inch Si substrates\, which will su
 bstantially 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 difficult
 ies 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 f
 irst commercially available LEDs on 6-inch Si (and the first LEDs to be ma
 nufactured in the UK).
LOCATION:Small Lecture Theatre\, Bragg Building\, Cavendish Laboratory (Ph
 ysics Department)
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