A MESFET (Metal Semiconductor Field Effect Transistor) belongs to the group of MOSFETs. Its structure is similar to that of a junction field effect transistor( JFET). The difference between the two is that the MESFET uses a Schottky junction with a low-capacitance metal electrode instead of a pn junction.
MESFETs are made of compound semiconductors such as gallium arsenide( GaAs), indium phosphide ( InP) or silicon carbide( SiC), have a high charge carrier mobility due to the metal- semiconductor junction and are characterized by particularly short switching times. However, they are also more expensive than MOSFETs or Junction Field-Effect Transistors (JFET). They can be used in the microwave range up to about 50 GHz in Monolithic Microwave Integrated Circuits( MMIC), High Power Amplifiers( HPA) of satellite transmission systemsor in radar systems.
The MESFET differs in construction from normal field effect transistors( FET) in that there is no insulator below the gate. The MESFET is self-conducting and is controlled by a control voltage. At a control voltage of 0 V, a drain current flows. With a negative control voltage, the space charge zone widens and thus interrupts the current flow to the drain.