To create an n-type extrinsic semiconductor from pure intrinsic silicon, which type of dopant impurity atoms must be added to the crystal lattice?
Answer and explanation
Correct answer: C. Pentavalent atoms such as phosphorus or arsenic
- Step 1: Silicon is a Group 14 element with 4 valence electrons forming covalent tetrahedral bonds.
- Step 2: When a Group 15 pentavalent impurity (such as phosphorus or arsenic) substitutes for a silicon atom, four of its valence electrons bond with neighboring silicon atoms.
- Step 3: The fifth valence electron is loosely bound with ionization energy and easily enters the conduction band at room temperature, donating free conduction electrons (n-type).
Answer
Pentavalent atoms such as phosphorus or arsenic.
Why not the others: Trivalent dopants create p-type semiconductors with majority holes; Monovalent atoms do not fit substitutionally into diamond cubic lattices; Tetravalent atoms do not introduce charge carriers.
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