Question

Addition of arsenic to germanium makes the latter:

• A. metallic conductor
• B. intrinsic semiconductor
• C. mixed conductor
• D. extrinsic semiconductor

Hint:

Pentavalent impurity (Group 15) → n-type. Trivalent impurity (Group 13) → p-type.

Answer 1

The Correct Option is D

Concept: Doping pure intrinsic semiconductor with impurities gives extrinsic semiconductor.

Step 1: Nature of dopant. Arsenic (As) is Group 15 — pentavalent impurity (5 valence electrons).

Step 2: Effect on germanium. Ge has 4 valence electrons. As forms 4 bonds, leaving one extra free electron → n-type semiconductor.

Step 3: Conclusion. Doping changes intrinsic → extrinsic semiconductor (n-type).