Why does breakdown occur in reverse bias ?

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Solution

Breakdown Voltage
Breakdown voltage of a diode is the reverse-bias voltage at which current increases suddenly across it.
If reverse bias is increased, the current through PN junction will also increase resulting in formation of a voltage called breakdown voltage.
The V-I characteristic graph of a reverse biased diode is shown in the figure, in the figure we can see that after breakdown voltage, the current is increasing rapidly towards the negative side.
Since, the line is becoming a straight line, this results in a practically constant voltage equal to breakdown voltage across the diode.
When a PN junction diode is reverse biased, a small current flows through it. It consists of the movement of minority carriers across the diode.
This current produced by the flow of minority carriers is called saturation current.

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