Construct the circuit symbol of Zener diode.

Hint: Zener diode is a p-n junction diode that is designed to works under reverse bias. A Zener diode is a type of diode which is designed in such a way that it allows the current to flow backward when a set reverse voltage (Zener voltage) is reached.

Complete step-by-step answer:
The circuit symbol of Zener diode is :

Zener diodes operation depends on high doping of its p-n junction. The depletion region formed in the diode is very thin i.e.($ < 1\mu m$ ) and the electric field is consequently very high( i.e. about 500kV/m) even for a very small reverse bias voltage of about 5V allowing electrons to tunnel from the valence bond of p-type material to the conduction band of n-type material.

Additional information:
A diode is a two-terminal electric component made of a semiconductor, which conducts current only in one direction. It has low resistance in one direction and very high in the other thus allowing current to flow in only one direction.

Zener diodes have a wide application as a voltage regulator. When it is connected in parallel with a variable voltage source in such a way that it is reverse biased, a Zener diode conducts when the voltage reaches the diode's reverse breakdown voltage. From that breakdown voltage, the low impedance of the diode keeps the voltage across the diode at that value.
When the Zener diode is connected in forwarding bias then the diode acts as a normal diode.

Note:
For lightly doped diodes the breakdown is denoted as avalanche effect.
The breakdown voltage for Zener diode is higher i.e.(over 5.6 V) for devices.