Draw V-I characteristics of p-n junction diode. Answer the following questions giving reasons:
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.

Explanation

Either (i) when the reverse bias potential is fairly high the high velocity attained by the minority carriers becomes sufficient to break the crystal bonds and to produce a large number of electron-hole pairs. For this increase in the number of charge carriers (avalanche breakdown) the reverse current shows a sudden increase.
Or (ii) when the dopings of the p-n junction are sufficiently high even a comparatively small reverse potential can produce a high electric field across the junction . As a result a large number of charge carriers becomes free (Zener breakdown ). So the reverse current shows a sudden increase. The semiconductor device used in this case is called a Zener diode.