Question: An n-type semiconducting Si is obtained by doping intrinsic Si with :
Step 1 (Governing Principle & Definition): [0.5 Mark]
An n-type semiconductor is formed when intrinsic Silicon (a Group 14 element) is doped with a pentavalent impurity (Group 15 element). These impurities have $5$ valence electrons. Four electrons form covalent bonds with neighboring Si atoms, while the fifth electron remains loosely bound, acting as a free charge carrier (donor electron).
Step 2 (Analysis of Options): [0.25 Mark]
- (A) Al (Aluminum): Group 13 (Trivalent) $\rightarrow$ p-type
- (B) B (Boron): Group 13 (Trivalent) $\rightarrow$ p-type
- (C) P (Phosphorus): Group 15 (Pentavalent) $\rightarrow$ n-type
- (D) In (Indium): Group 13 (Trivalent) $\rightarrow$ p-type
Step 3 (Final Concluded Answer): [0.25 Mark]
Since Phosphorus ($P$) is a pentavalent atom, it provides an extra electron to the conduction band of Silicon. Therefore, the correct option is (C) P.
💡 EL10 Concept Insight: Think of it like adding an extra player to a team; because Phosphorus has one "extra" electron that doesn't have a partner to bond with, that electron is free to roam around and carry electricity, making the material "n-type" (negative-type).