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 up to 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 regions.

Answer 1

Hint: A semiconductor is a solid substance that has the value of conductivity just between the insulator and most of the metal, it is due to added impurities in the semiconductor material that the value of conductivity is like this.VI characteristics graph is a graph that gives us an idea about voltage and current relationship in a semiconductor.

Complete step-by-step solution:
In the graph below we see that when the graph reaches certain points, that is when the current is 100 mA approximately and the voltage 15 V approximately then it reaches the breakdown voltage and after that, there is a rapid change in VI characteristics. The same happens when it reaches barrier voltage after reaching the barrier voltage it suddenly gives a rapid change to the VI characteristics.

(i) The reverse current is almost independent of critical voltage because the current in a reverse-biased diode is due to the drifting of the minority charge carriers from one region to another through the junction. Hence a small amount of voltage is enough to carry on the sweeping of the minority charge carriers.
(ii) At critical voltage or breakdown voltage, there is an enormous breakdown of covalent bonds, resulting in a rapid increase in the number of charge carriers hence it shows a sudden hike in the current. Zener diode operates following the reverse bias condition in the breakdown regions. We know that critical voltage is the highest value of steady anode voltage that is possible theoretically, only at a fixed given steady, magnetic flux density.

Note: Minute details to be covered in the chapter, sometimes students confuse between reverse biased and forward biased. They also confuse the concept of electrons exchange. They should remember that the reverse current is independent of critical voltage.