Explain why elemental semiconductors cannot be used to make visible LEDs.

Hint: The band gap in an elemental semiconductor has a value that allows it to detect light with a wavelength in the infrared (IR) range. The number of free electrons in an elementary semiconductor is relatively minimal, resulting in little conduction.

Complete answer:
LED stands for light emitting diode. The elemental semiconductors are those composed of a single species of atoms, such as silicon (Si), germanium (Ge).Compound semiconductors are semiconductors that are made from two or more elements like GaAs.

The band gap in an elemental conductor is such that the emissions are in the infrared region rather than in the visible region. The energy emitted by the combination of holes and electrons in basic semiconductors does not fall within the visible spectrum, so our eyes cannot see light emissions from the infrared region but from the visible region only, hence it is not visible.

LEDs are made up of compound semiconductors and not by the elemental conductor because the band gap in the elemental conductor has a value that can detect the light of a wavelength which lies in the infrared (IR) region. In elementary semiconductors numbers of free electrons are very small leading to negligible conduction. Thus, LEDs are made up of combined semiconductors.

Note: The energy released in the recombination of holes and electrons is the central concept of LEDs. All of the diodes have the ability to emit an electromagnetic spectrum. LEDs have a reduced band gap than incandescent bulbs, making them ideal for visible light emission.