Page 146 - Photonics Essentials an introduction with experiments

Light-Emitting Diodes

140 Photonic Devices

runs a spectrum on a sample diode, which is shown in the figure
below.

0.10

0.08 Drive current = 20 mA

Optical power (mW) 0.06

0.04

0.02

0
400 450 500 550 600 650
Wavelength, (nm)

a) What is the energy width at half-maximum?
b) What is the quantum efficiency at the wavelength of maxi-
mum output?
c) Do you accept the shipment?
6.4 Perform an engineering estimate for the profitability of LED-
based traffic lights in your city. Try to improve on the estimate
procedure given in the text. For example, you may be able to
learn the maintenance cost per light from your city engineer’s of-
fice. The savings will depend on the price the city pays for elec-
tricity, etc. Compare your conclusions to those given in Example
6.3.
6.5 Referring to Eq. 6.40,
a) Show that the bandwidth is given by: f = 3 /2 è .
b) Derive corresponding expressions for the dependence of the
bandwidth on the recombination coefficient for the high-injec-
tion and the low-injection cases.

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