Fet

A field-effect transistor (FET) is a type of transistor in which the conductivity between two terminals, called the source and drain, is controlled by an electric field generated by a voltage applied to a third terminal, the gate. The gate draws very little current, so the gate voltage modulates the current flowing through the channel between source and drain rather than supplying carriers directly.

FETs are commonly categorized by their gate structure and channel type. The main families include junction FETs (JFETs), which use a reverse-biased p–n junction as the gate; metal-oxide-semiconductor FETs (MOSFETs), which have an insulated gate oxide; and MESFETs, which use a Schottky gate. A MOSFET is the dominant transistor in modern integrated circuits. FETs can carry either n-type or p-type channels, leading to n-channel or p-channel devices. They also differ in how they operate: enhancement-mode devices require a gate voltage to form a conductive channel, while depletion-mode devices have a channel present at zero gate voltage and can be turned off with an appropriate gate bias. Advanced variants such as FinFETs arrange the channel in a 3D fin structure to improve control in dense ICs.

Operation and characteristics of FETs center on high input impedance and the ability of the gate voltage to regulate the drain current. The relationship between gate-source voltage and drain current defines the device’s transconductance and threshold behavior, with MOSFETs commonly described by a threshold voltage. FETs are widely used as switches in digital logic and power electronics, and as amplifiers in analog circuits. MOSFETs, particularly in CMOS technology, dominate contemporary electronics, while JFETs remain valued for certain low-noise or high-speed applications.