Download Diapositiva 1

Light-Emitting Diodes (LED)
Lecturer: Mauro Mosca
(www.dieet.unipa.it/tfl)
A.A. 2015-16
University of Palermo –DEIM
LED: injection luminescence
p
EC - EV = hc/l
n
EC
EF
EF
EV
E r [eV]  EG 
p
n
V0
1,24
l [  m]
LED: radiative recombination
LED: radiative recombination
no equilibrium:
LED: radiative recombination
LED: radiative recombination
tramite eccitoni
LED: NON
radiative recombination
LED:
non-radiative recombination
deep-level
radiant process predominant
at low temperature
Auger
Emission linewidths
effective mass
density of states
N(E), Z(E)
Prof. D. Persano Adorno
Emission linewidths
Dn
= 1.8 kT/h
LED construction
minore
autoassorbimento
n+-p diode
Light extraction
total internal reflection
ENCAPSULATION
TECHNIQUE
n1sinq1 = n2sin(90°)
qc = arcsin(n2/n1)
most rays strike the surface at an angle less than the critical angle
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
Radiation pattern
?
Radiation pattern
(
)
Radiation pattern
0.5
Response time
two limitations
c
Ge in GaAs
signal distortion
Electrical properties
diffusion voltage (or built-in voltage, or potential barrier)
Electrical properties
Schokley
equation
Diffusion Voltage
e
e (V VD ) kT
e eV kT
e eV kT
 eVD kT 
NAND
e
ni2
Electrical properties
Eg
Electrical properties
Electrical properties
Light-current characteristic
LED drive circuit for d.c. operations
+
Vd
Vb  Vd
Rs 
id
LED drive circuit for a.c. operations
LED on/off modulation circuit
LED linear modulation circuit
Efficiency