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Asked in GSEB Board March 2020 · Doping and carrier concentration
Idea: the valency of the dopant decides which carrier ends up in the majority.
n-type means the majority carriers are electrons. To get them the dopant must be pentavalent: four of its five valence electrons complete the covalent bonds and the fifth is left loosely bound, free to conduct.
So the dopants are pentavalent, not trivalent, and that rules out the two choices that name trivalent atoms.
If electrons are the majority carriers then holes must be the minority carriers -- only the few that thermal breaking of bonds still produces.
So in n-type silicon holes are minority carriers and pentavalent atoms are the dopants.
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