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Difference Between Zener Breakdown and Avalanche Breakdown

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We know that a PN-junction diode can be operated in both forward biased and reverse biased conditions. The type of diode that particularly works in the reverse biased condition is a Zener diode. Both Zener breakdown and avalanche breakdown occurs in reverse biased condition. The major difference between Zener breakdown and avalanche breakdown is the nature of operations.

In the forward biased condition, we notice that the flow of the current of flow charge carriers can be seen if the applied voltage is more than the threshold voltage (which is also known as the barrier potential). Whereas in the reverse biased condition, the major flow of current is due to the minority charge carriers, this saturation current will not change up to a certain voltage, after a certain limit of voltage we notice the flow of current in the reverse direction and that region is known as breakdown region and this applied potential is called as the Breakdown potential. This effect is known as the avalanche effect.


Zener Breakdown Vs Avalanche Breakdown:

Before we start with the Zener breakdown vs avalanche breakdown, let us understand the meaning of avalanche breakdown and the Zener breakdown individually. 


What is Avalanche Breakdown?

We know that the current reverse biased condition is mainly due to the minority charge carriers. On increasing the applied voltage the width of the depletion region will also increase resulting in increased immobile charged carriers in the depletion region. Due to the increased immobile charge carriers, a strong electric field will be developed in the depletion region and hence, the minority charge carriers present in the depletion region will get accelerated and they can tunnel through the depletion region. 

When the applied voltage reaches the breakdown region or the breakdown potential the accelerated charge carriers will collide with the atoms present and gain enough kinetic energy such that it will eliminate the valence electrons. After the collision two free electrons are generated. These two free electrons that generated can further collide with other atoms resulting in four free electrons, this collision continues and hence there will be a drastic increase in charge carriers in the depletion region. Due to these increased charge carriers, we will see a sudden jump in the reverse saturation current. 

This effect is known as the Avalanche effect and the voltage after which the avalanche effect is noticed is known as the breakdown voltage. The avalanche breakdown effect is a result of impact ionization. 


What is Zener Breakdown?

For normal diodes, this region of operation must be avoided to save the equipment from damage. There are some special kinds of diodes designed specifically to operate in this region, for example, the Zener diode. Zener diode is a special type of PN-junction diode that operates in the reverse biased condition. But in the Zener diode, the breakdown operation is different from that of the avalanche breakdown, this breakdown is known as the Zener breakdown.

Unlike in the regular PN-junction diodes the P and n region of the Zener diodes are heavily doped, in other words, the number of impurity atoms in the Zener diode will be more in comparison with the regular PN-junction diode. Due to the presence of large impurity charge carriers, there will be a large number of free charge carriers. As a result of heavy doping, the width of the depletion region will be narrow and hence a very strong electric field will be generated. Due to the strong electric field, many free electrons are generated and they can tunnel through the depletion region easily resulting in the reverse saturation current.

This effect is known as the Zener breakdown effect and the potential at which we witness this effect is known as the Zener breakdown voltage. This is the basic difference between Zener breakdown and avalanche breakdown and one can now easily list out the Zener breakdown vs avalanche breakdown.


Difference Between Avalanche and Zener Breakdown:

Now let us start with the difference between Zener breakdown and avalanche breakdown. Few Zener breakdown and avalanche breakdown differences are as listed below. Sometimes this can also be asked to differentiate between Zener breakdown and avalanche breakdown mechanism, one should not get confused while answering. 

Sl. No.

Avalanche Breakdown

Zener Breakdown

1.

What is avalanche breakdown?

It occurs in the regular PN-junction diode as a result of the collision of charge carriers with the crystal ions. 

What is Zener breakdown?

It occurs due to the direct rupture of the covalent bond due to a strong electric field across the junction or at the depletion region.

2.

It can be noticed in the lightly doped PN-junction diodes.

It is noticed in heavily doped PN-junction diodes.

3.

The width of the depletion region will be comparatively wide and it requires more potential to make accelerated charge carriers tunnel through.

The width of the depletion region will be narrow and the accelerated charge carriers can easily tunnel through.

4.

The avalanche breakdown for the Si PN-junction diode is 6V.

The Zener breakdown for the Si PN-junction diode is less than 6V.

5.

The temperature coefficient is positive. The breakdown voltage increases as the junction temperature increases.

The temperature coefficient is negative. The breakdown voltage decreases as the junction temperature increases.

6.

The VI characteristic curve is not as sharp as the Zener breakdown in the breakdown region.

The VI characteristic curve is sharp in the breakdown region.


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These are important avalanche breakdown and Zener breakdown differences. We can understand what is Zener breakdown and avalanche breakdown with the help of avalanche vs Zener breakdown as listed above.


Did You Know

Avalanche breakdown is a non-destructive and 2 reversible process, which means if we decrease the voltage down. The current eventually decreases and crossing two certain points may cause a breakdown but if we increase them. Potential again then an increase in the current can be seen.

FAQ (Frequently Asked Questions)

1. What is Meant By Zener Breakdown?

Ans: It is an effect where the reverse saturation current is suddenly increased. It occurs due to the direct rupture of the covalent bond due to a strong electric field across the junction or at the depletion region.

2. Difference Between Zener and Avalanche or Avalanche and Zener Breakdown Difference?

Ans: Zener breakdown and avalanche breakdown occurs in reverse biased condition. The major difference between Zener breakdown and avalanche breakdown is the nature of operations. Another major difference is the doping, the avalanche effect occurs in lightly doped PN-junction diodes, whereas the Zener breakdown occurs in heavily doped diodes.