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
Correct Answer: B
Solution :
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.
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