How does adding a tiny amount of another element (doping) turn silicon into a useful semiconductor?
Pure silicon has few free carriers.
Pure silicon has few free carriers. Doping it with a group-15 element (like phosphorus) adds an extra electron per atom, giving n-type silicon with mobile negative carriers; doping with a group-13 element (like boron) creates 'holes', giving p-type with positive carriers. Joining p- and n-type regions makes the p–n junction at the heart of every diode, transistor and solar cell — all built on this defect chemistry of solids.
Key point
Doping introduces extra electrons (n-type) or holes (p-type), controlling conductivity.
Common mistake
thinking pure silicon is already a good conductor.
Memory tip
add group-15 → n-type (electrons); add group-13 → p-type (holes).
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