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): n-type semiconductor is not negatively charged.
Reason (R): Neutral pentavalent impurity atom doped in intrinsic semiconductor (neutral) donates its fifth unpaired electron to the crystal lattice and becomes a positive donor.

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

Hint:

Doping a semiconductor increases its conductivity but doesn't make it charged overall. The number of positive and negative charges remains balanced.

Answer 1

The Correct Option is A

In an n-type semiconductor, a pentavalent atom (like phosphorus or arsenic) is doped into a pure semiconductor (like silicon).
- The pentavalent atom forms covalent bonds using four of its electrons.
- The fifth electron becomes a free charge carrier, contributing to conduction.
- The impurity atom, after donating this extra electron, becomes a positively charged donor ion.
Even though there are extra electrons for conduction, the overall crystal remains electrically neutral because the donor atom itself is neutral before doping and just redistributes charges.
Thus: - The assertion is true: n-type semiconductors are not negatively charged.
- The reason is also true: the pentavalent atom becomes a positive donor after donating its fifth electron.
- The reason correctly explains the assertion.
Final answer: Option (A)