Write the working principle of zener diode and LED diode

The working principle of zener diode:

Working principle of zener Diode: When a PN junction diode is reversed biased the depletion layer becomes wider. If this reverse biased voltage across the diode is increased continually, the depletion layer becomes more and more wide. At the same time there will be a constant reverse saturation current due to minority carriers. After certain reverse voltage across the junction, the minority carriers get sufficient kinetic energy due to the strong electric field. In the depletion layer the entire diode will become conductive. This type of breakdown of the depletion layer is known as avalanche breakdown but this breakdown is not quite sharp. Comparing with avalanche breakdown this breakdown is called zener breakdown.  The voltage at which this breakdown occurs is called zener voltage. Although the condition current through the diode can be of any value depending on the load connected with the diode. That is why zener diode is mainly used for controlling voltage in different circuits.

Working principle of LED:

(i) When light emitting diode in forward biased the electrons from the n-type material class the p-n junction and the recombine with holes in the p-type material.

(ii) These free electrons are in the conduction band at a higher energy state than the hole in the balance band.

(iii) When recombination takes place or electron hole pair generates the recombined electrons release energy.