Question

How is a Zener diode fabricated? What causes the setting up of high electric field even for small reverse bias voltage across the diode?
Describe, with the help of a circuit diagram, the working of Zener diode as a voltage regulator.

Answer 1

Fabrication:

1. Heavily doped p and n junction are to be used for fabricating zener diode.
2. The breakdown voltage of the material should be considered to avoid the destruction of the device.
   Zener diodes have breakdown voltages ranging from 3-200 Volts.
3. The zener diodes are fabricated with precise breakdown voltages, by controlling the doping level during manufacturing.

The zener or breakdown voltage depends on the concentration of doping. The n and p regions of zener diode are heavily doped. The depletion layer of heavily doped p-n junction diode is very thin. Since electron field $ϵ=-\frac{dV}{dr}$ across the junction would be very high even for small voltage. this electron field is called ionizing field.
Zener Diode as a Voltage Regulator:

The circuit diagram using zener diode as a voltage stabilizer is as shown:
The zener diode is connected across the fluctuating voltage source through a dropping resistor of resistance $R_S$. The constant voltage supply is obtained across positive Load resistance $R_L$. When the input voltage increases, resistance of zener diode decreases and hence current through the diode increases to high value.
As a result, a large voltage drop occurs across the dropping resistance $R_S$. Hence, the output voltage across $R_L$ is maintained to the desired value. When the input voltage decreases, the current through the diode also decreases. So now small voltage drop takes place across the resistance $R_S$ and the output voltage across $R_L$ is maintained at a desired constant value.
Thus, we get a constant voltage in spite of fluctuating input voltage. Hence, zener diode acts as a voltage regulator.