LEDs

Question 1

What is the principal process of photon interaction for LEDs

Answer 1

Spontaneous emission

E_g = hν = h(c/λ)

The energy wavelength relationship is characterized by the above.

where E_g is the bandgap energy(E_c – E_v)

Question 2

What is intrinsic transition?

Answer 2

Direct promotion of an electron from the ground state to the excited state.

Occurs if If hν >> E_g

Any excess energy is dissipated as heat

Also known as band-band transition

Question 3

What is extrinsic transition?

Answer 3

Absorption to an intermediate energy level
(below E_C) this is known as trapped assisted recombination

Occurs when When hν < E_g

Question 4

What types of recombination are there?

Answer 4

Electron-hole recombination:

where the electron and hole recombine when the electron falls from the conduction band.

Trapped Assisted Recombination:

where the electron and hole recombine when the electron falls from an intermediary band between the valence and conduction band.

Auger Recombination:

where the excess energy from the electron-hole recombination is transferred to electrons or holes that are subsequently excited to higher energy states within the same band instead of giving off photons (the radiative process).

Nonradiative Process.

Question 5

Give the equation for absorption rate in LEDs

Answer 5

• Assumed under thermal equilibrium (black body radiation)
• Absorption rate = spontaneous emission rate + stimulated emission rate

B₁₂ N₁ Φ(ν) = A₂₁ N₂ + B₂₁ N₂ Φ(ν)

• A21 = Spontaneous emission
• B21 = Stimulated emission
• B12 = Absorption
• Φ(ν) = Optical field density [Js/m3 or J/m3 Hz]
• N₁ = Electron concentration at E1 (EV)
• n₂ = Electron concentration at E2 (EC)