mesfet

A MESFET, or metal–semiconductor field-effect transistor, is a type of transistor in which the gate forms a Schottky contact with a semiconductor channel. The channel is typically an n-type layer of a compound semiconductor such as gallium arsenide (GaAs) or indium phosphide (InP), with source and drain regions forming Ohmic contacts. The metal gate controls the current between source and drain by modifying the width of the conducting channel through an electric field. Most MESFETs operate as depletion-mode devices, conducting with zero gate bias and turning off when a reverse bias is applied to the gate.

In operation, the Schottky gate draws only a small gate current, so the device is primarily voltage-controlled. Applying a reverse bias to the gate expands the depletion region under the gate and reduces the drain current. Some designs can be configured for enhancement-mode operation by altering channel doping, but depletion-mode GaAs MESFETs remain common. The high electron mobility of III-V materials enables favorable high-frequency performance, giving MESFETs strong transconductance at microwave frequencies.

MESFETs have been widely used in RF and microwave circuits, including amplifiers, mixers, and oscillators, with operationinto tens of gigahertz in many GaAs devices. Their fabrication is relatively simple compared with early MOSFETs since no gate oxide is required, and they benefit from the intrinsic material properties of III-V semiconductors. Limitations include gate leakage and, at high temperatures, reliability concerns, and typically lower breakdown voltages compared with silicon devices.

Most MESFETs are n-channel; p-channel variants are rare. The technology remains a foundational component in the family of GaAs FETs, and is closely related to heterostructure devices such as HEMTs, which use a two-dimensional electron gas to achieve even higher performance.