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Light-Emitting Diodes (LED) Lecturer: Mauro Mosca (www.dieet.unipa.it/tfl) University of Palermo –DEIM A.A. 2014-15

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p n ECEC EVEV EFEF EFEF p n V0V0 E C - E V = hc/ LED: injection luminescence

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LED: radiative recombination

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no equilibrium:

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LED: radiative recombination p-doped n-doped

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LED: radiative recombination tramite eccitoni

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LED: radiative recombination NON

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LED: non-radiative recombination deep-level Auger

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Emission linewidths density of states N(E), Z(E) effective mass Prof. D. Persano Adorno

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Emission linewidths

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LED construction n + -p diode minore autoassorbimento

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Light extraction total internal reflection c = arcsin(n 2 /n 1 ) n 1 sin 1 = n 2 sin(90°)

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Esercizio Si calcoli la frazione di luce trasmessa per radiazione isotropica F originata da un LED in GaAs. Si esegua lo stesso calcolo per un LED incapsulato in una resina epossidica avente indice pari a 1,5. Per il GaAs si consideri n = 3,6 Soluzione: F = 0.013 (1,3%) per GaAs/air F = 0.036 (3,6%) per GaAs/epoxy/air

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Radiation pattern

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) (

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0.5

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Response time two limitations Ge in GaAs signal distortion c

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Electrical properties diffusion voltage (or built-in voltage, or potential barrier)

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Electrical properties Schokley equation Diffusion Voltage

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Electrical properties EgEg

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Light-current characteristic

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LED drive circuit for d.c. operations + VdVd

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LED drive circuit for a.c. operations

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LED on/off modulation circuit

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LED linear modulation circuit

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Efficiency

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