Main Question or Discussion Point
Why there is sudden increase in the small reverse saturation current at the breakdown voltage in PN-junction Diode?
Although breakdown can cause irreversible damage to a junction, that's not the cause but a possible effect of the high current.The phenomenon is called "breakdown" because the junction is literally broken. A typical failure mechanism when the applied voltage gets too big is equivalent to an arc through the junction, resulting in localized crystal melting. This in turn puts a low resistance "short" in parallel with the junction, giving rise to large current flow.