Current through a reverse biased p-n junction, increases abruptly at

In a reverse biased p-n junction, the reverse current is initially very small and almost constant, known as the reverse saturation current.

When the applied reverse voltage is increased and reaches a critical value, a large number of covalent bonds break due to high electric field or collision of minority carriers, resulting in a sudden increase in the number of charge carriers.

This causes the reverse current to increase abruptly. This critical voltage is called the break-down voltage.

Answer: break-down voltage.