Field-Effect Transistor (FET) Definition/Meaning:
A semiconductor device having three terminals:
source, gate, and drain. Current flow in a narrow conduction channel between
drain and source is controlled by the voltage applied between gate and source,
which can deplete the conduction channel of charge carriers. If the source and
drain regions are composed of n-type semiconductor the conduction channel is
n-type; these devices are known as n-channel devices. Devices with p-type source, drain, and
channel are called p-channel devices.
In the junction FET the channel is a composite part of the structure. In the
MOS-FET the gate is insulated from the
source and drain regions and the channel forms when the gate voltage is applied.
Unlike the bipolar transistor both types of FET require virtually no input
current to the gate except a pulse to charge or discharge the output
capacitance. Junction FETs have relatively slow switching speeds compared with
MOSFETs and bipolar transistors, and are therefore not used in logic circuits.