Question

The diode that is specially designed to work in reverse breakdown voltage is ?

Answer 1

Hint: A diode is a device that only allows unidirectional flow of current if operated within a rated specified voltage level. A diode blocks current only in the reverse direction, while the reverse voltage is within a limited range otherwise reverse barrier breaks and the voltage at which this breakdown occurs is called the reverse breakdown voltage.

Complete answer:
At some voltage higher than the reverse breakdown voltage the current starts flowing in reverse biased mode also. This is why it is said that in reverse biased mode, practically a diode has very high resistance but not infinite.At those higher voltages (higher than reverse breakdown) the minority carriers of the depletion region of a PN junction diode get sufficient kinetic energy due to the strong electric field.

With this kinetic energy they collide with stationary ions of the depletion layer and knock out more free electrons, this process happens continuously and after some time, the entire diode will become conductive. This type of breakdown of the depletion layer is known as avalanche breakdown but it is not quite sharp.

There is another type of breakdown in the depletion layer which is sharper compared to avalanche breakdown, called Zener breakdown.When a PN junction diode is highly doped, the concentration of impurity atoms will be high in the crystal. This higher concentration of impurity atoms increases the concentration of ions in the depletion layer hence for the same applied reverse-biased voltage, the width of the depletion layer becomes thinner than in the case of a normally doped diode.

If the reverse voltage is continued to increase, after a certain applied voltage, the electrons from the covalent bonds within the depletion region come out and make the depletion region conductive. This breakdown is called Zener breakdown. The voltage at which this breakdown occurs is called Zener voltage.

So the diode that is specially designed to work in reverse breakdown voltage by high doping of impurity is the Zener diode.

Note: The voltage across a Zener diode remains fixed irrespective of the source voltage. That is why we use a Zener diode mainly for controlling voltage in different circuits. Hence the applications include voltage regulation, as reference elements, surge suppressors, in switching applications and clipper circuits.