- Avalanche breakdown occurs when a high reverse voltage causes electrons to gain enough energy to create additional electron-hole pairs, leading to a sudden surge in current.
- Zener breakdown happens at a lower voltage level and involves tunneling electrons across a narrow, highly-doped depletion region.
- Both breakdown mechanisms can be intentionally used in designing Zener diodes, which regulate voltage by providing a stable reference voltage.
What is Avalanche Breakdown?
John Sealy Townsend discovered the phenomenon of Avalanche breakdown between 1897 and 1901. This phenomenon is also known as Townsend discharge and involves the production of a flow of current through a semiconductor when a strong electric field is passed through it. The repeated production of free electrons as a result of this process causes extreme damage to the semiconductor device but, in turn, increases the current flow.
This breakdown is observed when a reverse voltage is applied to the diode. When the reverse voltage increases, the electric field also increases, leading to the entire process. This process occurs in the Zener diode with a breakdown voltage greater than 8 volts. With the increase in temperature, the breakdown voltage increases as well. Avalanche breakdown occurs in the diodes that are lightly doped p-n junction.
Avalanche breakdown has a positive temperature coefficient. The electric field formed around the depletion region is weak. Avalanche breakdown is not a reversible process. This happens because the p-n junction is permanently damaged. Sometimes, it can be reversed if a series resistor is placed in the diode.
What is Zener Breakdown?
Zener breakdown is named after Clarence Melvin Zener, who discovered it. This phenomenon takes place as a result of high doping concentrations. During the process, reverse bias is applied to a highly doped diode, and the junction narrows down due to increased doping. The electrons move from the valence band of p-type material to the n-type materials’ conduction band.
The phenomenon of Zener breakdown takes place in Zener diodes which have a Zener breakdown voltage of 5 to 8 volts. The extremely high electric field in the narrow depletion region causes the valence electrons to be pulled into conduction. The continuation of this process during the phenomenon causes an increase in the temperature, which decreases the breakdown voltage.
The temperature coefficient of Zener breakdown is negative. The phenomenon of Zener breakdown uses only semiconductors and not insulators. This phenomenon is reversible as opposed to Avalanche breakdown. It is possible because, in the p-n Zener breakdown, the p-n junction is not damaged and can be returned to its original place when the reverse bias voltage is reduced.
Difference Between Avalanche Breakdown and Zener Breakdown
- Avalanche breakdown occurs when an electric field is applied to a material. In contrast, Zener breakdown occurs when a reverse-biased p-n junction is exposed to a high enough electric field.
- Avalanche breakdown happens at lower voltages and higher current levels, whereas Zener breakdown needs a higher voltage to occur, resulting in a lower current level.
- Avalanche breakdown can cause the breakdown voltage to decrease, whereas Zener breakdown voltage remains relatively constant.
- Avalanche breakdown can occur in any material, whereas Zener is specific to semiconductors.
- Avalanche breakdown is used in applications such as protection diodes and voltage regulators, whereas Zener breakdown has its applications such as voltage references and voltage regulators.
Comparison Between Avalanche Breakdown and Zener Breakdown
|Parameters of Comparison||Avalanche Breakdown||Zener Breakdown|
|Mechanism||Electric field||Reverse-biased p-n junction|
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Piyush Yadav has spent the past 25 years working as a physicist in the local community. He is a physicist passionate about making science more accessible to our readers. He holds a BSc in Natural Sciences and Post Graduate Diploma in Environmental Science. You can read more about him on his bio page.