Why and how do breakdowns happen in reverse bias diodes ?

Breakdowns in reverse bias diodes occur primarily due to the application of a voltage that exceeds the diode’s breakdown voltage rating. When a diode is reverse biased, meaning the voltage across it is applied in the opposite direction to its intended forward operation, a sufficiently high reverse voltage can cause the diode to conduct heavily. This situation leads to breakdown, where the diode conducts a large current uncontrollably, potentially damaging it permanently if the current exceeds its maximum ratings.

The occurrence of breakdown in reverse bias is fundamentally due to the electric field across the depletion region within the diode. In reverse bias, this electric field can become strong enough to cause electrons and holes in the depletion region to accelerate, leading to collision and subsequent generation of electron-hole pairs. This phenomenon creates a sudden increase in current through the diode, known as breakdown current, which can lead to overheating and eventual failure if not controlled.

Several factors contribute to the breakdown of a diode, including the material properties of the semiconductor from which it is made, the physical dimensions of the diode structure, and the amount of reverse voltage applied. Different types of diodes have varying breakdown mechanisms and characteristics, such as Zener diodes designed to operate in reverse breakdown to regulate voltage, while others like standard rectifier diodes are typically not intended to operate in breakdown mode.

The breakdown voltage of a reverse biased diode refers to the specific voltage at which the diode begins to conduct heavily in reverse bias, leading to breakdown. This voltage is a critical parameter specified by the manufacturer and indicates the maximum reverse voltage that the diode can withstand without entering breakdown. Exceeding this voltage can result in irreversible damage to the diode due to excessive current flow and heat generation.

When a diode is subjected to reverse bias, it normally blocks current flow, allowing only a small leakage current to pass through. However, as the reverse voltage increases towards the diode’s breakdown voltage, the electric field in the depletion region grows stronger. At the breakdown voltage, the depletion region breaks down and current suddenly increases, causing the diode to conduct heavily in reverse direction. This behavior is characteristic of Zener diodes used in voltage regulation or avalanche diodes used in protection circuits, where controlled breakdown is utilized for specific applications.

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