Formation of Zener diode

The breakdown voltage of a diode depends on the amount of doping. In a heavily doped diode, the depletion layer is thin, so the breakdown of the junction occurs at a lower reverse bias voltage. On the other hand, a lightly doped diode has a higher breakdown voltage. When an ordinary crystal is properly doped so as to have a sharp breakdown voltage, it is known as Zener diode.

Voltage and Current Characteristics of Zener Diode

When the reverse bias voltage on a normal crystal diode is increased a point known as knee point is reached at a voltage known as breakdown voltage, when the reverse current increases sharply to a high value. The breakdown voltage is also known as Zener Voltage and the sharp increase in current is known as Zener Current.

During forward bias, Zener diode characteristics will remain same as that of a normal diode. When the applied voltage crosses the value of Zener Voltage, the Zener breakdown takes place. After breakdown, the flow of the current in the circuit tends to increase immediately.

Applications of Zener Diode

• Voltage Regulators. Zener diodes have the property of maintaining low voltages even though high voltages are applied and hence make nice voltage regulators.

• Ammeters

• Voltmeters

• Ohmmeters

Avalanche Breakdown

As the functionality of the basic diode is already known in reverse bias condition the diode gets affected as it is non-conducting. But still there is movement noticed due to minority carriers. The current generated because of the minority charge is referred to as reverse saturation current and this is responsible for the occurrence of avalanche breakdown.

In the case of the reverse bias, the width of the region will be more. This can affect the working condition of the diode. But in this condition, the minority charges get sufficient kinetic velocity so that it can overcome the barrier of the junction.

Due to this process, collisions in between occurs. These are responsible for the generation of free charges. As this process goes on further generation of carriers takes place resulting in the formation of a larger number of free carriers. This phenomenon is referred to as carrier multiplication. Hence the flow of reverse current is noticed. This leads to the condition in the diode breakdown referred to as avalanche breakdown. This can damage the junction completely.

Zener Breakdown

In the basic diode, a junction is formed due to the interaction of p-type and n-type. This has the depletion region at the junction. The width of this region is also the factor of the doping concentration. The doping at the junction can be done lightly or heavily. The width of the depletion and the doping levels are inversely related to each other. It means if the junction is heavily doped then the width will be minimum and vise-verse. If the considered junction is of high doping value then undergoes the phenomena of Zener breakdown.

If it has a minimum width of depletion region it suggests that it has the number of free charges present. These tend to cross the junction. Because it has the highest electric intensity of the field the rapid movement in the carriers is noticed. Hence it results in the formation of free carriers and the flow of reverse current can be seen. This eliminates the depletion region. This type of phenomena is known as Zener breakdown. In Zener breakdown, the depletion region will retain back once the reverse voltage has been removed.