Explain avalanche breakdown in a diode and Zener breakdown in a Zener diode.
In p-n junctions, there are two primary types of breakdown: avalanche breakdown and Zener breakdown. Avalanche breakdown results from the rapid collisions of electrons with other atoms, while Zener breakdown occurs due to a strong electric field. Zener breakdown can be seen as a controlled form of avalanche breakdown in a specially modified p-n junction.
Structure of a P-N Junction Diode
To begin, let’s examine the structure of a p-n junction diode. The p-type semiconductor is typically doped with boron, which creates electron deficiencies, while the n-type semiconductor is doped with elements like arsenic or phosphorus, which contribute excess electrons. When one part of an intrinsic semiconductor is doped to form p-type material and another part is doped to create n-type material, this configuration is known as a p-n junction diode. This diode can respond to reverse bias in two main ways:
1. Avalanche Breakdown
2. Zener Breakdown
Avalanche Breakdown
Avalanche breakdown occurs under the influence of a strong electric field. In reverse bias conditions, electrons gain significant kinetic energy. These energized electrons can break additional covalent bonds, generating more hole-electron pairs. As these pairs move through the depletion region, they lead to a substantial reverse-biased current. The bond breaking process is irreversible, resulting in permanent damage to the p-n junction following an avalanche breakdown.
Zener Breakdown
Zener breakdown is a controlled method for inducing breakdown in p-n junctions. To achieve this, the p-n junction must be heavily doped, allowing electrons in the p-type region’s valence band to easily jump to the conduction band of the n-type region. This breakdown is temporary and occurs due to the intense electric field, and since it does not trigger a chain reaction, its effects are brief.
Refer to the accompanying I-V diagram to better understand the two types of breakdowns.
Note: As shown in the earlier diagram, Zener breakdown occurs at a much lower voltage compared to avalanche breakdown. This characteristic makes Zener diodes useful as circuit breakers; when the voltage exceeds a certain limit, they provide a low-resistance path for current flow. Additionally, Zener diodes can also function as voltage regulators.