Question

In a semiconductor diode, the barrier potential offers opposition to only
(A) Majority carriers in both regions
(B) Minority carriers in both regions
(C) Free electrons in the n-region
(D) Holes in the p-region

Answer 1

Hint: To answer this question, we need to figure out the polarity of the barrier potential. From that, we can predict the direction of the electric field of the barrier potential. The direction of the electric field will give us the final answer.

Complete step by step answer:
The barrier potential is the potential difference across the depletion layer between the p and the n regions of a semiconductor. It is known as the barrier potential since it opposes the flow of the charge carriers on either side of the semiconductor.
Now, a semiconductor is formed by two regions, namely the p-region and the n-region, which are adjacent to each other. The p-region is the p-type semiconductor, in which the holes are the majority charge carriers, and the electrons are the minority charge carriers. Similarly, the n-region is the n-type semiconductor, in which the electrons are the majority charge carriers, and the electrons are the majority charge carriers. So the electrons from the n-region move into the p-region, and the holes from the p-region move into the n-region. Therefore, the p-region occupies a negative charge and the n-region occupies a positive charge. The potential difference generated across both the regions is called the barrier potential.
The electric field of the barrier potential flows from the n-region to the p-region. So the holes in the p-region which try to enter the n-region are opposed by this electric field. Also, the electrons are opposed by the electric field from entering the p-region. Since the holes and electrons are the majority carriers in the p and the n regions respectively, we can say that the barrier potential offers opposition to the majority carriers in both regions.
Hence, the correct answer is option A.

Note:
It is this barrier potential which keeps the holes in the p-region from entering the n-region, and also the electrons in the n-region from entering the p-region. The biasing done on a semiconductor is termed as forward or reversed with reference to the barrier potential. The external voltage which has the same polarity as that of the barrier potential is termed as reverse bias; while in the opposite case we call the external bias as forward bias.