Question

2. Light emitting diodes Technology companies combine the three elements indium, gallium and nitrogen in the correct ratio to make InGaN crystals. InGaN is found inside blue light emitting diodes (LEDs). The figure above shows a small sample of InGaN crystals. The crystals needed for red LEDs are produced by combining aluminum, gallium and arsenide. InGaN and AlGaAs are both semiconductors. In a semiconductor, there are many low- lying energy levels for electrons to occupy. There are also high-lying energy levels into which electrons can be injected from a battery. There is an energy gap between the high-lying energy levels and the low-lying energy levels. The size of this energy gap determines the color of light that is emitted by an LED.
(a) Estimate the size of the energy gap in InGaN. Give your answer in eV or joules.
(b) Estimate the size of the energy gap in AlGaAs. Give your answer in eV or joules.

Answer 1

(a) Size of energy gap in InGaN emitting blue light

(b) Size of energy gap in AlGaAs emitting red light