The Bipolar Junction Transistor (BJT) is a type of semiconductor device that functions as a bipolar diode.
A BJT has three terminals: the emitter, the base, and the collector. The base-emitter junction acts as a forward-biased diode when the transistor is conducting current.
Here's why the BJT is considered bipolar:
- Bipolar refers to the use of both electrons and holes as charge carriers in the device.
- Electrons are the majority carriers in the emitter and collector regions.
- Holes are the majority carriers in the base region.
The base-emitter junction acts as a diode because it allows current to flow in one direction but not the other. When the base-emitter junction is forward-biased, electrons from the emitter flow into the base, and holes from the base flow into the emitter. This flow of charge carriers constitutes the diode current.
However, the BJT is more than just a diode. It also has a collector-base junction which acts as a reverse-biased diode. This junction is typically kept reverse-biased to prevent current flow.
The BJT is a versatile device that can be used as an amplifier, a switch, or a logic gate. It is widely used in electronic circuits, including amplifiers, oscillators, and digital circuits.
