Bipolar junction transistor

A bipolar junction transistor is a three-terminal semiconductor device with two p–n junctions. A small base current controls a larger current between its emitter and collector.

Emitter injection efficiency: The fraction of emitter-injected charge carriers that enter the base rather than returning to the emitter. It determines how effectively the emitter supplies carriers for collector current.
P–n junction: An interface between p-type and n-type semiconductor regions, with a depletion region and an electric field. Each transistor contains two such junctions whose bias controls carrier flow.
Common-base configuration: A transistor circuit configuration in which the base is shared by the input and output circuits. It provides current transfer with low input impedance and useful high-frequency behavior.
MOSFET: A field-effect transistor in which an insulated gate voltage controls current through a semiconductor channel. Unlike a BJT, it is controlled primarily by gate voltage rather than continuous base current.
John Bardeen: An American physicist who co-invented the point-contact transistor and later developed the theory of superconductivity. His transistor research at Bell Labs preceded the junction transistor.
Base transport factor: The fraction of carriers injected into a transistor base that cross it without recombining. A thin, lightly doped base lets most injected carriers reach the collector.
Semiconductor doping: The intentional addition of impurities to a semiconductor to change its carrier concentration and conductivity. Different doping levels in emitter, base, and collector shape transistor operation.
Common-collector configuration: A transistor circuit configuration in which the collector is shared by the input and output circuits. Also called an emitter follower, it buffers signals with high input impedance.
JFET: A field-effect transistor whose reverse-biased p–n junction controls current through a semiconductor channel. It controls channel current with an electric field rather than bipolar carrier injection.
Walter Brattain: An American physicist who co-invented the point-contact transistor with John Bardeen. His experimental work helped launch transistor technology before the BJT became dominant.

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