Semiconductor Electronics Materials Devices And Simple Circuits

Step 1: Concept
Doping a semiconductor with impurities of different valency changes its conductivity type.
Step 2: Analysis
Germanium (Group 14) has 4 valence electrons. A pentavalent impurity (Group 15) has 5 valence electrons.
Step 3: Conclusion
When doped, four electrons form bonds, while the fifth electron remains free. This excess of electrons leads to the formation of an n-type semiconductor.
Final Answer: (B)