Question:
a) Describe five advantages of LED lighting over conventional incandescent lighting.
b) State two impairments that reduces the radiant flux of a surface-emitting LED. Illustrate one way how any one of these impairments may be addressed?
c) Illustrate how white light can be generated using a blue Gallium Nitride (GaN) LED.
d) Find the composition of the quaternary alloy In1-xGaxAsyP1-y for making semiconductor LEDs operating at 1.27μm. The bandgap energy Eg of the quartenary alloy in eV is then given by the empirical relationship Eg = 1.35 - 0.72y + 0.12y2 where y=2.2x.
e) Given a particular Gallium Nitride (GaN) Edge-emitting LED drawing a current 50 mA when the voltage is 1.5 V and operating at 450 nm wavelength with light power of 5 µW coupled with a 9 µm single-mode fibre.
i) What is the colour of the light emitted from the LED?
ii) Calculate the overall efficiency of the LED.
iii) Calculate its internal quantum efficiency given that Tr = 50ns and Tnr = 70 ns.
iv) Hence, calculate the internal optical power generated by the LED.