The
field-effect transistor (
FET) is a transistor that uses an
electric field to control the shape and hence the electrical
conductivity of a
channel of one type of charge carrier in a
semiconductor material. FETs are also known as
unipolar transistors as they involve single-carrier-type operation. The FET has several forms, but all have high input
impedance. While the conductivity of a non-FET transistor is regulated by the input current (the emitter to base current) and so has a low input impedance, a FET's conductivity is regulated by a voltage applied to a terminal (the gate) which is insulated from the device. The applied
gate voltage imposes an electric field into the device, which in turn attracts or repels charge carriers to or from the region between a source terminal and a drain terminal. The density of charge carriers in turn influences the conductivity between the source and drain.
