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13.White_LEDs - 1 Example of p pn heterostructure LED...

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Unformatted text preview: 1 Example of p+pn+ heterostructure LED Example E0 El 2 Next step in the design of LEDs Next LEDs We have chosen the bandgap (to get the desired colour), and we have chosen the structure (heterojunction diode) to get the confinement of the recombination. Now we have to make sure that the recombination is radiative, and not non-radiative. 3 Non-radiative recombination mechanisms RG-centre (SRH) for p-type material Auger 4 Radiative recombination lifetime What are the underlined terms? np-n0p0 5 White LEDs White LEDs Sections 3.2, 8.3, 8.4, 8.5, 8.6, 8.7, 8.8 of course text: 1. 2. 3. 4. 5. 6. Minority-carrier lifetime Radiative recombination efficiency Extraction efficiency Various efficiencies White-light LEDs Prospects for general-purpose lighting 6 Minority-carrier lifetime 7 Radiative efficiency 8 TIR How much power gets out for GaAs? Designs to improve extraction efficiency 9 (a) (b) (c) 10 Various efficiencies Wall-plug efficiency Present record is 56% Wall-plug efficiency is a radiometric measurement. Light perception is personal, so photometric measurements are usually used in specifying LEDS., and are based on a standard eye-sensitivity function. 11 Perception of light 12 Eye sensitivity function What is luminous efficacy? 13 Colour matching functions Cone stimulation Chromaticity coordinates 14 Chromaticity and LEDs Chromaticity LEDs 15 Additive LEDs Additive LEDs 16 Dichromatic LED Li et al.,JAP, 94, 2167, 2003 Not quite complementary, but broadening (35nm for blue and 50nm for green) give possibility of white light. 17 Blue/yellow phosphor LEDs Blue/yellow LEDs 18 High-brightness with phosphor dome 19 Colour rendering Illuminated by: (a) high-CRI source (b) low-CRI source 20 Luminous efficacy and efficiency Luminous flux aka luminous efficacy of the source! 21 LED Roadmap * * Our luminous efficiency 22 White-llight LEDs are here! ight LEDs 23 Osram announces 1000 lm LED http://www.physorg.com/news93198212.html 24 The shape of things to come ...
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