Q3. (a) Draw a schematic of a heterojunction LED and explain its operation. [6 marks] (b) The bandgap, Eg, of a ternary

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Q3.
(a) Draw a schematic of a heterojunction LED and explain its
operation. [6 marks]
(b) The bandgap, Eg, of a ternary AlxGa1-xAs alloys follows the
empirical expression, Eg(eV) = 1.5 + 1.3x + 0.3x2 What is the
composition of the alloy if the peak emission of an LED based on it
is at a wavelength of 810 nm. [8 marks]
(c) Calculate the critical angle when the emitted light from an
LED is incident at semiconductor-air interface knowing that the
refractive index of AlGaAs is 3.66. What will be the critical angle
if the LED is covered with epoxy that has refractive index of 1.4?
Calculate reflectance at normal incidence for both cases. [6
marks]