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 pure semiconductor (such as silicon) is doped with a pentavalent atom (e.g., phosphorus or arsenic).

• The pentavalent atom utilizes four of its electrons to form covalent bonds.
• The fifth electron is released as a free charge carrier, facilitating conduction.
• Following the donation of this extra electron, the impurity atom transforms into a positively charged donor ion.

Despite the presence of surplus electrons available for conduction, the crystal lattice maintains electrical neutrality. This is because the donor atom is electrically neutral prior to doping and simply redistributes charges within the structure. Therefore:

• The statement is accurate: n-type semiconductors do not possess a net negative charge.
• The explanation is also accurate: the pentavalent atom becomes a positive donor ion after relinquishing its fifth electron.
• The explanation correctly justifies the statement.

Final answer: Option (A)