Question

When a zener diode is operated forward biased then?

Answer 1

A diode is a two-terminal electrical component with low (preferably zero) resistance in one direction and high (ideally infinite) resistance in the other. It conducts current preferentially in one way (asymmetric conductance). A vacuum tube with two electrodes, a heated cathode and a plate, in which electrons can only flow in one direction, from cathode to plate, is known as a diode vacuum tube or thermionic diode.

Complete step by step answer:
When a particular set reverse voltage, known as the Zener voltage, is attained, a Zener diode reliably allows current to flow "backwards."
Zener diodes come in a wide range of Zener voltages, some of which are even tunable. The reverse conduction occurs in some Zener diodes with a sharp, highly doped p–n junction and a low Zener voltage, in which case electron quantum tunnelling across the small gap between p and n regions is known as the Zener effect, after Clarence Zener. Higher Zener voltage diodes feature a more progressive junction, and its operation mode also includes avalanche breakdown. Zener diodes have both forms of breakdown, with the Zener effect dominating at lower voltages and avalanche breakdown dominating at higher voltages.
When connected in forward bias, the Zener diode operates like a regular diode. With respect to the applied voltage, the current flowing through the diode is linear.

Note: Zener diodes are one of the main building blocks of electronic circuits and are widely utilised in electronic equipment of all kinds. They're used to create low-power stabilised supply rails from a larger voltage and give reference voltages for circuits, particularly stabilised power supplies. They're also employed to guard against overvoltage, particularly electrostatic discharge (ESD).