Explanation

(c) Under normal reverse voltage, a very little reverse current flows through a $p$-$n$ junction. However, if the reverse voltage attains a high value, the junction may breakdown with sudden rise in reverse current.
If reverse voltage is increased continuously, the kinetic energy of electrons (minority carriers) may become high enough to knock out electrons from the semiconductor atoms. At this stage breakdown of the junction occurs characterised by a sudden rise of reverse current and a sudden fall of the resistance of barrier region. This may destroy the junction permanently.