In V-I characteristics of a p-n junction diode, why is the current under reverse bias almost independent of the applied potential upto a critical voltage?

In V-I characteristics of a p-n junction diode, why is the current under reverse bias almost independence of the applied potential upto a critical voltage?

In V - I characteristics of p-n junction in reverse biasing results in

When a p-n junction diode is reverse biased

A p-n junction diode is reverse biased. Then

Draw V-I characterictics of a p-n junction diode. Why does the reverse current show a sudden increase at the critical voltage? Name any semiconductor device which operates under the reverse bias in the breakdown region.

No bias is applied to a P-N junction, then the current-