Question

Why we cannot use Si and Ge in the fabrication of visible LEDs?

Answer 1

Silicon is NOT used in LEDs to obtain visible light emission, as it is an indirect band gap material with reference to visible light energy and very inefficient one at that.

Answer 2

Due to less energy gap in Si and Ge, they cannot be used in the fabrication of visible LEDs.

• The energy gap of Si and Ge is less than 1.8eV.
• If they are used, then they will only emit infrared rays which are not visible to us.
• A LED requires a direct bandgap semiconductor but Si and Ge are indirect bandgap semiconductors.
• There is a requirement of photons(to emit light) in LEDs that cannot be done by Si and Ge as the electrons and holes in them do not combine to form photons.
• Therefore, Si and Ge cannot be used in the fabrication of LEDs.