Physics - Semiconductors Question with Solution | TestHub

A Light Emitting Diode (LED) is a heavily doped p-n junction diode that operates in forward bias.

When the diode is forward biased, electrons from the n-region and holes from the p-region cross the junction and recombine with each other.

During this recombination process, the energy difference between the conduction band and the valence band is released in the form of photons.

If the semiconductor material has a band gap in the range of $1.8\text{ eV}$ to $3.0\text{ eV}$, the emitted photons fall in the visible light spectrum.

Thus, an LED emits visible light when holes and electrons recombine.

Answer: holes and electrons recombine.