The second important type of transistors, next to the field-effect transistor, is the bipolar transistor. Its mode of operation is based on both charge carriers (thus bipolar), electrons and holes. Bipolar transistors are faster than field-effect transistors, however, they require more space and are therefore more expensive in mass production.
Bipolar transistors consist essentially of two mutually connected p-n junctions with the layer sequence n-p-n or p-n-p. The connections of the bipolar transistor are emitter (E), base (B) and collector (C). While emitter and collector have the same doping, the very thin base layer in-between is doped contrarily.
In this article an NPN transistor in standard buried collector (SBC) construction is described, the mode of operation of PNP transistors is analog (the signs of the applied voltages have just to be reversed).