n-type semiconductors
Mix a tiny amount of phosphorus (P) into silicon — about one phosphorus atom in a million silicon atoms. This is doping.
Phosphorus is in group V, with five outer electrons. It bonds with four silicon atoms using four of them; the fifth takes part in no bond and is free to move through the crystal.
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n-type semiconductor
Doping adds negative electrons as carriers, so this silicon is a negative-type (n-type) semiconductor. A semiconductor whose carriers are increased by doping with another element is an extrinsic semiconductor. Arsenic (As) and antimony (Sb), also in group V, make n-type material too. Group V elements donate free electrons, so they are donor atoms.