Chapter 6

Question 1

What’s an LED?

Answer 1

a pn junction made from a direct bandgap semiconductor (GaAs), electron-hole recombination emits a photon

Question 2

What is the emitted photon’s energy?

Answer 2

hv, equals Eg

Question 3

What is a requirement of equilibrium with no applied bias?

Answer 3

The fermi level is uniform throughout the device

Question 4

What is the potential energy barrier? What does it do?

Answer 4

eVo, prevents the diffusion of electrons from the n side to p side (for n type doped)

Question 5

What happens when a voltage is applied ot the pn junction?

Answer 5

The built in potential Vo is reduced to Vo-V

Question 6

What causes defects in LEDs?

Answer 6

If the epitaxial layers and substrate have different crystal lattice parameters

Question 7

What effect do defects have in LEDs?

Answer 7

They act as a recombination center

Question 8

What type of structure do LEDs use?

Answer 8

Double heterostructures: two different semiconductor materials with two different bandgaps