MCQ
A semiconductor is doped with a donor impurity:
- AThe hole concentration increases.
- BThe hole concentration decreases.
- ✓The electron concentration increases.
- DThe electron concentration decreases.
✓
Answer
Correct option: C.
The electron concentration increases.
When a semiconductor is doped with a donor type such as arsenic or phosphorous, which has five valence electrons, the donor atom replaces the $Si$ or $Ge$ atom. As a result, four out of the five electrons of the donor atom form a covalent bond by sharing an electron with four atoms of silicon. However, the fifth electron is free to move. Also, due to the breaking up of covalent bonds at room temperature, equal number of electrons and holes are produced. Thus, the total number of holes in the $n-$type semiconductor is less compared to the number of free electrons.
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