Introduction
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 are 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 areas are listed below. Sometimes this can also be asked to differentiate between Zener breakdown and avalanche breakdown mechanism, one should not get confused while answering.
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 if we increase them. Potential again then an increase in the current can be seen.
Break Down Mechanism
When the reverse bias on a p-n junction is raised, the connection breaks down and the reverse current climbs quickly to a magnitude limited only by the external resistance connected in series. The breakdown voltage is the particular value of the reverse bias voltage (vz). After the breakdown, boost the reverse current by a very little amount. The breakdown voltage is determined by the thickness of the depletion layer. The doping level determines the breadth of the depletion layer. We have attempted to explain the idea of Zener Breakdown and Avalanche Breakdown Mechanism as Basic Electronics Notes in depth with the aid of this post.
In a Zener diode, what form of breakdown occurs?
Breakdown of an avalanche happens in a Zener Diode.
Avalanche breakdown occurs in Zener diodes. Avalanche breakdown happens in a Zener diode when the Vz is larger than 8 volts because electrons and holes are isolated.
FAQs on Difference Between Zener Breakdown and Avalanche Breakdown
1. What is the fundamental difference between Zener breakdown and Avalanche breakdown for the JEE Advanced 2026 exam?
The fundamental difference lies in their operating mechanisms and the required doping levels of the p-n junction. Zener breakdown is a quantum tunnelling phenomenon that occurs in heavily doped diodes under a strong electric field. In contrast, Avalanche breakdown is due to carrier multiplication through collisions in lightly doped diodes subjected to a high reverse voltage.
2. What is the detailed mechanism of Zener breakdown in a semiconductor diode?
Zener breakdown occurs in a heavily doped p-n junction, which results in a very thin depletion region (typically less than 10 nm). When a reverse bias voltage is applied, it creates an extremely strong electric field (around 3 x 107 V/m) across this narrow region. This intense field is sufficient to directly pull electrons from the valence band of the p-side atoms into the conduction band of the n-side, a process known as quantum tunnelling. This generates a large number of free charge carriers, leading to a sharp increase in reverse current.
3. How does Avalanche breakdown occur, and what is meant by 'carrier multiplication'?
Avalanche breakdown occurs in lightly or moderately doped p-n junctions, which have a wider depletion region. Under a high reverse bias, minority charge carriers (electrons or holes) gain significant kinetic energy while crossing this region. These high-energy carriers collide with atoms in the crystal lattice, imparting enough energy to break covalent bonds and generate new electron-hole pairs. These newly created carriers are also accelerated and cause further collisions, creating even more carriers. This cumulative process, known as carrier multiplication or the avalanche effect, results in a large reverse current.
4. Why does Zener breakdown dominate in heavily doped diodes while Avalanche breakdown is characteristic of lightly doped ones?
This is a critical concept for JEE Advanced. The doping concentration directly determines the width of the depletion region.
- In heavily doped diodes, the depletion region is extremely narrow. This allows a strong electric field to be established at a relatively low voltage, making quantum tunnelling (Zener effect) the dominant breakdown mechanism.
- In lightly doped diodes, the depletion region is wide. The electric field is not strong enough for tunnelling. Instead, charge carriers have a longer path to accelerate and gain enough kinetic energy to initiate carrier multiplication through collisions (Avalanche effect).
5. How does temperature affect the breakdown voltage in Zener and Avalanche mechanisms?
The temperature coefficients for the two mechanisms are opposite, which is a key distinguishing feature:
- Zener Breakdown: It has a negative temperature coefficient. As temperature increases, the bandgap of the semiconductor decreases slightly, making it easier for valence electrons to tunnel into the conduction band. Therefore, the Zener breakdown voltage (Vz) decreases as temperature rises.
- Avalanche Breakdown: It has a positive temperature coefficient. As temperature increases, lattice vibrations (phonons) become more frequent. This increases the probability of collisions, reducing the mean free path of charge carriers. A higher electric field (and thus higher voltage) is required for the carriers to gain enough kinetic energy between collisions to cause ionisation. Therefore, the Avalanche breakdown voltage increases with temperature.
6. From a physics perspective, is Zener breakdown a form of quantum tunnelling?
Yes, absolutely. Zener breakdown is a direct consequence of a quantum mechanical phenomenon called band-to-band tunnelling. Classically, an electron in the valence band does not have enough energy to overcome the forbidden energy gap and enter the conduction band. However, in the presence of a very strong electric field across a very narrow depletion region, the energy bands bend steeply. This creates a scenario where there is a finite, non-zero probability for an electron to 'tunnel' through the potential barrier of the forbidden gap, a purely quantum effect.
7. Are Zener and Avalanche breakdown processes reversible, or do they damage the diode?
Both breakdown mechanisms are reversible and non-destructive, provided the current is limited by an external series resistor. The breakdown phenomenon itself does not damage the p-n junction. However, if the reverse current is not controlled, the excessive power dissipation (P = Vz * I) will lead to overheating and can permanently destroy the diode. Zener diodes are specifically designed to operate repeatedly in their breakdown region.
8. What are the primary applications of diodes based on Zener and Avalanche breakdown?
The primary application for diodes operating on both principles is voltage regulation.
- Zener Diodes: These are widely used as voltage regulators, voltage references, and in surge protection circuits to clamp voltage at a specific level. Their sharp breakdown characteristic at a well-defined voltage (Vz) makes them ideal for these roles.
- Avalanche Diodes: While also used for voltage regulation (especially at higher voltages), they are specifically utilised in photodetectors (Avalanche Photodiodes or APDs) where the carrier multiplication effect is used to achieve internal signal gain, enabling the detection of very low light levels. They are also crucial in transient voltage suppression (TVS) devices.
