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

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

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

3 LED: radiative recombination

4 no equilibrium:

5 LED: radiative recombination p-doped n-doped

6 LED: radiative recombination tramite eccitoni

7 LED: radiative recombination NON

8 LED: non-radiative recombination deep-level Auger

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

10 Emission linewidths

11 LED construction n + -p diode minore autoassorbimento

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

13 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 = (1,3%) per GaAs/air F = (3,6%) per GaAs/epoxy/air

14 Radiation pattern

15 ) (

16 0.5

17 Response time two limitations Ge in GaAs signal distortion c

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

19 Electrical properties Schokley equation Diffusion Voltage

20 Electrical properties EgEg

21

22

23 Light-current characteristic

24 LED drive circuit for d.c. operations + VdVd

25 LED drive circuit for a.c. operations

26 LED on/off modulation circuit

27 LED linear modulation circuit

28 Efficiency


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