Question

An $n$-type semiconductor is formed

• A. when germanium crystal is doped with an impurity containing 3 valence electrons
• B. when germanium crystal is doped with an impurity containing 5 valence electrons
• C. from pure germanium
• D. from pure silicon

Answer 1

Answer: (B)

Pentavalent impurity atoms ie, atoms having $5$ valence electrons such as antimony $(Sb)$ or arsenic $(As)$, when added to a pure semiconductor, produce excess of free electrons ie, donor electrons to the semiconductor. For this reason, pentavalent impurity atoms are called donor impurity atom. The semiconductor so produced is called n-type extrinsic semiconductor.