The Zener diode is a PN junction diode that was specially developed for operation in the blocking mode. In the forward bias mode, it acts as a normal diode. It has a certain voltage, known as the breakdown voltage, at which the diode breaks down while being reverse biased. With normal diodes, the diode damages at the breakdown voltage.
The basic principle of the Zener diode is the Zener failure. If a diode is heavily doped, its depletion region is narrow. If a high reverse voltage is applied to the connection point, a very strong electric field is present at the connection point. And the generation of electron hole pairs takes place. Thus strong current flows. This is known as zener mining.
Zener diodes are often used as voltage references and as shunt regulators to regulate the voltage on small circuits.
