Zener Diode is a special purpose silicon PN junction diode which differs from other diodes in the sense that it operates in the reverse biased mode.
Zener diode is also known as a voltage regulator or voltage reference or breakdown diode.
Fig. : Symbol of Zener Diode
Fig. : V.I. characteristic of Zener Diode
Fig. : Practical zener diode equivalent circuit
The two layers of impurity ions in depletion region act as plates of capacitor. This depletion layer capacitance is also known as junction capacitance.
CT = Junction capacitance
K = constant
VB = Barrier voltage (0.6 for Si and 0.2 for GE)
Vr = Reverse Voltage
n = constant (depends upon the nature of junction)