Question

Two statements are given, one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer from the codes (A), (B), (C), and (D) as given below.
Assertion (A): The impurities in p-type Si are not pentavalent atoms.
Reason (R): The hole density in the valence band in a p-type semiconductor is almost equal to the acceptor density.

• A. Both Assertion (A) and Reason (R) are true, and Reason (R) is the correct explanation of Assertion (A).
• B. Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).
• C. Assertion (A) is true, but Reason (R) is false.
• D. Both Assertion (A) and Reason (R) are false.

Hint:

In semiconductors, p-type doping involves adding trivalent elements (like boron), while n-type doping involves pentavalent elements (like phosphorus). The hole density in p-type semiconductors is nearly equal to the acceptor density.

Answer 1

The Correct Option is B

- Assertion (A): In p
-type semiconductors, the majority charge carriers are holes, which are created by doping with trivalent elements (such as boron), not pentavalent elements. Pentavalent elements (like phosphorus) are used in n
-type semiconductors to provide extra electrons. Therefore, the assertion that impurities in p
-type Si are not pentavalent atoms is true.
- Reason (R): In p
-type semiconductors, the acceptor atoms (such as boron) create holes in the valence band. The number of holes generated is approximately equal to the number of acceptor atoms, leading to the conclusion that the hole density is almost equal to the acceptor density. Hence, Reason (R) is also true. However, Reason (R) does not explain Assertion (A) directly because the hole density in p
-type semiconductors being equal to the acceptor density is not related to whether the dopant is pentavalent or trivalent. The assertion is about the type of dopant (trivalent for p
-type), while the reason is a property of the hole density in p
-type materials. Thus, the correct answer is option (B): Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of Assertion (A).