MESFETs

MESFET stands for metal–semiconductor field-effect transistor. It is a type of field-effect transistor that uses a Schottky metal–semiconductor gate rather than a metal-oxide gate. The channel is formed in a doped semiconductor, typically a III–V material such as GaAs or InP, with ohmic source and drain contacts and a gate metal that forms a Schottky barrier to the channel. The gate voltage modulates the width of the depletion region under the gate, thereby controlling the drain current.

Most MESFETs are depletion-mode devices, meaning a conductive channel exists at zero gate bias. Applying a reverse or negative gate voltage reduces the channel conductivity and can pinch it off. There are also enhancement-mode variants that require a positive gate bias to induce a conducting channel, but these are less common. The device is valued for its relatively simple Schottky-gate structure and high-frequency potential.

High-frequency performance is a defining characteristic of MESFETs. III–V materials offer high electron mobility, enabling high transconductance and operation into the microwave region. This has made MESFETs widely used in RF amplifiers, microwave front ends, and MMICs, especially in aerospace and telecommunications. However, gate leakage under forward bias, thermal sensitivity, and limited integration with silicon-based digital circuits are practical considerations. In many high-frequency applications, MESFETs have been partially supplanted by HEMTs, which use heterojunctions to form a higher-mobility two-dimensional electron gas.

Overall, MESFETs remain a foundational technology for certain high-speed and microwave applications, particularly where III–V materials and Schottky-gate operation are advantageous.