Question

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

(i) Why is the current under reverse bias almost independent of the applied potential upto a critical voltage? 

(ii) 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.

Answer 1

(i) In the reverse biasing, the current of order of m A is due to movement/drifting of minority charge carriers from one region to another through the junction. 

A small applied voltage is sufficient to sweep the minority charge carriers through the junction. So reverse current is almost independent of critical voltage.

(ii) At critical voltage (or breakdown voltage), a large number of covalent bonds break, resulting in the increase of large number of charge carriers. Hence current increases at critical voltage. Semiconductor device that is used in reverse biasing is zener diode.