Difference Between Zener and Avalanche Breakdown for JEE Main 2024

To explain Zener breakdown and Avalanche Breakdown: In the realm of semiconductor devices, breakdown phenomena are of significant interest due to their impact on device performance and functionality. Two commonly encountered breakdown mechanisms in diodes are Zener breakdown and avalanche breakdown. Understanding the differences between these two phenomena is crucial in selecting appropriate diodes for specific applications and designing circuits that require precise voltage regulation or protection against excessive voltage.

Zener breakdown occurs when a diode is reverse-biased, and the electric field across the depletion region reaches a critical value. This leads to a sudden increase in current, while the diode maintains a nearly constant voltage. Zener breakdown is named after Clarence Zener, an American physicist who first described this effect. It is utilized in Zener diodes, which are specifically designed to exhibit the controlled breakdown characteristic.

In contrast, avalanche breakdown occurs under high reverse-bias conditions when the electric field across the depletion region is strong enough to cause electron-hole pairs to be generated through collision processes. This results in an avalanche-like multiplication of charge carriers, leading to a rapid increase in current. Avalanche breakdown is typically observed in diodes with lightly doped regions or high doping concentrations.

This article delves into the nuances of Zener breakdown and avalanche breakdown, exploring their distinct characteristics of zener breakdown and avalanche breakdown, mechanisms, and applications. By understanding the differences between these breakdown phenomena, engineers and designers can make informed decisions regarding the selection and implementation of diodes in various electronic circuits.

What is Zener and Avalanche Breakdown? 

Zener Breakdown:

Zener breakdown is a phenomenon that occurs in a diode when it is reverse-biased and the electric field across the depletion region becomes strong enough to cause a significant flow of current. It is named after the American physicist Clarence Zener, who first described this effect.

Under normal reverse-biased conditions, a diode allows only a small leakage current to pass through it. However, as the reverse voltage across the diode increases, the electric field within the depletion region also increases. When the electric field reaches a critical value, known as the breakdown voltage or Zener voltage (Vz), the diode experiences a sudden and dramatic increase in current flow.

During Zener breakdown, the diode operates in the reverse breakdown region, characterized by a highly non-linear current-voltage relationship. Unlike the forward conduction mode of a diode, where the current increases rapidly with voltage, Zener breakdown allows the diode to maintain a nearly constant voltage across its terminals while a large current flows through it.

Zener breakdown can occur in specially designed diodes known as Zener diodes, which are optimized to exhibit this effect. Zener diodes are heavily doped, allowing them to sustain the high electric fields required for Zener breakdown to occur.

Zener breakdown is a useful phenomenon and finds applications in voltage regulation circuits, surge protection devices, and voltage reference circuits. By exploiting the controlled breakdown characteristics of Zener diodes, precise voltage regulation and protection against excessive voltage can be achieved.

It is important to note that Zener breakdown is distinct from avalanche breakdown, which is another type of breakdown that can occur in diodes under high reverse bias. While both phenomena involve the sudden increase in current, Zener breakdown is characterized by a lower breakdown voltage and occurs due to a different mechanism involving quantum tunneling and carrier multiplication.

Avalanche Breakdown:

Avalanche breakdown is a phenomenon that occurs in a diode when it is reverse-biased and the electric field across the depletion region causes the generation of charge carriers through collision processes. It is named "avalanche" because it involves an avalanche-like multiplication of charge carriers.

When a diode is reverse-biased, the electric field within the depletion region increases. If the electric field is strong enough, it can impart sufficient energy to valence electrons, enabling them to break free from their atomic bonds through collision with other atoms. These liberated electrons, called impact ionization electrons, can collide with other atoms and generate additional electron-hole pairs through the process of impact ionization.

As more charge carriers are generated, the current in the diode increases exponentially. This phenomenon is known as avalanche breakdown. Avalanche breakdown occurs in diodes with lightly doped regions or high doping concentrations, as these conditions facilitate the multiplication of charge carriers.

Unlike Zener breakdown, where the diode maintains a nearly constant voltage during breakdown, avalanche breakdown exhibits a voltage-dependent breakdown region. The current increases rapidly with voltage, and the breakdown voltage is generally higher than that of Zener breakdown.

Avalanche breakdown is utilized in certain applications, such as in avalanche diodes or in photomultiplier tubes, where the generation of a large number of charge carriers is desired for amplification or detection purposes. However, in most cases, avalanche breakdown is an undesirable effect that needs to be carefully managed to prevent damage to electronic devices.

It is important to note that avalanche breakdown is distinct from Zener breakdown, which occurs at lower breakdown voltages and involves a different mechanism primarily driven by quantum tunneling and carrier multiplication.

Zener Breakdown and Avalanche Breakdown Difference

The above table describes some characteristics of Zener and Avalanche Breakdown.

Summary

Zener breakdown and avalanche breakdown are two types of breakdown phenomena observed in diodes. Zener breakdown occurs in heavily doped diodes designed for controlled breakdown, while avalanche breakdown is observed in diodes with lightly doped regions or high doping concentrations. Zener breakdown maintains a nearly constant voltage while experiencing a sudden increase in current and is utilized in Zener diodes for voltage regulation and protection. Avalanche breakdown, on the other hand, exhibits an exponential increase in current with increasing voltage and is used in applications requiring signal amplification or detection. Understanding these breakdown phenomena is crucial for selecting appropriate diodes and optimizing electronic device performance.