Question

Identify the mismatched pair from the following
A. Zener diode: voltage regulator
B. germanium doped with phosphorus: n-type semiconductor
C. Semiconductor: bandgap > 3eV
D. p-n junction diode: rectifier
E. Silicon diode doped with aluminium: p-type semiconductor

Answer 1

Hint: As a very first step, one could read the question well along with the given options. Since this is a theory based question, you may recall all the important points from this concept accordingly. Also, mention how these are related to each other as a justification.

Complete step by step solution:
In the question we are given five options in which they have mentioned pairs that are related to semiconductor devices. We are supposed to find the mismatched pair among them.
Let us approach each of these pairs one by one.
For option A;
It is a well known fact that when Zener diodes are operated in the breakdown region, voltage across this Zener diode always remains constant even if we are changing the current by a huge amount. So, we could say that the Zener diodes are voltage regulators and hence they are correctly matched.
For option B;
Phosphorus being a pentavalent element, brings in free valence electrons into germanium on being doped in it and hence forming n-type semiconductors and hence they are correctly matched.
For option C;
For semiconductors, the band gap is found to be less than 3eV and hence this option is a mismatch.
For option D,
You may recall learning about half wave and full wave rectifiers which are made using p-n junction diodes. Hence, this is correctly matched.
For option E,
Aluminium being a trivalent impurity forms holes and thereby making it p-type semiconductor. Hence, we found that the option C is the only mismatch.

Note: In questions like this, there are chances for multiple options being a mismatch. Hence, one should check for each option being a mismatch or not. Now, from this question you may have understood how theory based questions can come for competitive exams. So make sure you cover the concepts well.