majority carrier
/ muh-JOR-ih-tee KAIR-ee-er /
In a doped semiconductor, two kinds of moving charge coexist: free electrons and holes. Usually one kind vastly outnumbers the other, the way a packed stadium has far more home fans than visitors. The crowd that dominates — the carrier that does almost all the work of conducting current — is the majority carrier.
Which carrier is the majority is decided by doping. Add donors and you flood the crystal with free electrons, so electrons are the majority carrier and the material is n-type. Add acceptors and you fill it with holes, so holes are the majority and the material is p-type. The other, scarcer kind is called the minority carrier; it is always present in small numbers from ordinary thermal excitation, but contributes little to the bulk current.
The majority-versus-minority distinction matters because it explains why a piece of doped silicon conducts the way it does, and it becomes the whole story at a p-n junction, where majority carriers from each side meet and a few minority carriers do surprisingly important things. A common misconception is that minority carriers are negligible. In transistors and solar cells, the behavior of those scarce minority carriers can decide whether the device works at all.
In phosphorus-doped (n-type) silicon, electrons might outnumber holes by a billion to one. The electrons are the majority carriers that carry the current; the rare holes are the minority carriers, yet they are exactly what gets injected and tracked when this n-region forms part of a transistor.
Doping sets which carrier is the majority — electrons in n-type, holes in p-type.
Majority and minority refer to numbers, not to importance. Many devices are deliberately designed around the injection and lifetime of the minority carriers, precisely because those are the ones whose behavior you can most sensitively control.