Difference Between Zener Breakdown And Avalanche Breakdown

The Zener Breakdown and Avalanche Breakdown are two different mechanisms by which a PN junction breaks. Avalanche and Zener breakdown both occur in diode under reverse bias. The avalanche breakdown occurs because of the ionization of electrons and hole pairs whereas the zener breakdown occurs because of heavy doping.

What Is Zener Breakdown?

When a reverse voltage is applied to a zener diode, it causes a very intense electric field to appear across a narrow depletion region. Such an intense electric field is strong enough to pull some of the valence electrons into the conduction band by taking their covalent bond. These electrons then become free electrons which are available for conduction. A large number of such free electrons will constitute a large reverse current through the Zener diode and breakdown is to have occurred due to the zener effect.

The process in which the electrons are moving across the barrier from the valence band of the p-type material to the conduction band of the lightly filled n-type material is referred to as the Zener breakdown.

What Is Avalanche Breakdown?

The Avalanche breakdown is a phenomenon that can occur in both semiconductor and insulating materials and can be described as a process of increasing the free electrons or electric current in semiconductor and insulating material by applying the high voltage. When high voltage is applied electrons are pulled from their covalent bonds and then accelerated to high velocities. These electrons subsequently collide with other atoms. Each collision produces more electrons which further leads to more collisions henceforth the current in the semiconductor rapidly increases and the material can quickly be destroyed.

Below, get to understand more differences between Zener and Avalanche breakdown.

Key Differences

The Zener breakdown occurs when the heavy electric field is applied across the P-N junction whereas the Avalanche breakdown occurs because of the collision of the electrons inside the P–N junction.
Zener breakdown occurs in the junctions which are heavily doped and have narrow depletion widths (thin region) while avalanche breakdown occurs in the junctions which are lightly doped and have wide depletion widths (thick region).
Zener breakdown occurs due to rupture of covalent bonds by strong electric fields set up in depletion region by the reverse voltage whereas avalanche breakdown occurs at higher reverse voltages when thermally generated electrons get enough kinetic energy to produce more electrons by collision.
The breakdown voltage and temperature of Zener breakdown are inversely proportional to each other whereas the breakdown voltage and the temperature of avalanche breakdown are directly proportional to each other.
The temperature coefficient of the Zener is negative whereas the temperature coefficient of avalanche breakdown is positive.
The breakdown voltage of Zener decreases when the temperature increases whereas the breakdown voltage of the Zener decreases when the temperature increases.
The ionization in Zener breakdown is due to the strong intensity of the electric field whereas the ionization in avalanche breakdown is due to the influence of collision effect.
In Zener breakdown, the intensity of the electric field is strong enough whereas the intensity of the electric field is low.
In Zener breakdown, the concentration level of doping is high at the junction whereas the concentration of doping at the junction is at the minimum in avalanche breakdown.
After the Zener breakdown, the voltage is not affected whereas when avalanche breakdown occurs, the voltage tend to get affected (tend to vary).
Once Zener undergoes breakdown, as the reverse voltage is removed from the diode, the junction gets back to its normal position. On the other hand, once avalanche undergoes the breakdown, the junction gets destroyed completely and it cannot regain back its position.
The Zener breakdown V-I characteristics have a sharp curve whereas the avalanche breakdown characteristics do not have a sharp curve.
The Zener breakdown generates electrons whereas the avalanche generates pairs of electrons and holes because of the thermal effect.
The reverse potential of the Zener is low whereas the reverse potential of avalanche is high.

Also Read: Difference Between Intrinsic and Extrinsic Semiconductors

Zener Breakdown Vs. Avalanche Breakdown In Tabular Form

BASIS OF COMPARISON	ZENER BREAKDOWN	AVALANCHE BREAKDOWN
Occurrence	Occurs when the heavy electric field is applied across the P-N junction	Occurs because of the collision of the electrons inside the P–N junction.
Doping	Occurs in the junctions which are heavily doped and have narrow depletion widths (thin region).	Occurs in the junctions which are lightly doped and have wide depletion widths (thick region).
Condition	Occurs due to rupture of covalent bonds by strong electric fields set up in depletion region by the reverse voltage.	Occurs at higher reverse voltages when thermally generated electrons get enough kinetic energy to produce more electrons by collision.
Relation Between Voltage And Temperature	The breakdown voltage and temperature of Zener breakdown are inversely proportional to each other.	Breakdown voltage and the temperature of avalanche breakdown are directly proportional to each other.
Temperature Coefficient	The temperature coefficient of the Zener is negative.	The temperature coefficient of avalanche breakdown is positive.
Voltage Vs Temperature	The breakdown voltage of Zener decreases when the temperature increases.	The breakdown voltage of the Zener decreases when the temperature increases.
Ionization	The ionization in Zener breakdown is due to the strong intensity of the electric field.	The ionization in avalanche breakdown is due to the influence of collision effect.
Intensity Of Electric Field	In Zener breakdown, the intensity of the electric field is strong enough.	The intensity of the electric field is low.
Concentration Level Of Doping At The Junction	The concentration level of doping is high at the junction	The concentration of doping at the junction is at the minimum in avalanche breakdown.
At The End Of Breakdown	After the Zener breakdown, the voltage is not affected.	When avalanche breakdown occurs, the voltage tend to get affected (tend to vary).
After Breakdown	Once Zener undergoes breakdown, as the reverse voltage is removed from the diode, the junction gets back to its normal position.	Once avalanche undergoes the breakdown, the junction gets destroyed completely and it cannot regain back its position.
Breakdown Characteristics	The Zener breakdown V-I characteristics have a sharp curve.	The avalanche breakdown characteristics do not have a sharp curve.
Result Of Breakdown	The Zener breakdown generates electrons.	The avalanche generates pairs of electrons and holes because of the thermal effect.
Reverse Potential	The reverse potential of the Zener is low.	The reverse potential of avalanche is high.

Also Read: Difference Between P-type Semi Conductor And N-type Semiconductor