MESFET

The metal oxide semiconductor field effect transistor (English metal semiconductor field effect transistor, MESFET ) belongs to the group of the junction field- effect transistors ( JFET). In construction it is similar to an n- channel JFET, but takes the place of the gates of a p-doped gate metal. This a rectifying metal -semiconductor junction is formed instead of a pn junction ( Schottky junction ) from, because of the gate metal touches on directly the semiconductor material.

Due to the very similar construction and operation of the MESFET has almost the same characteristics of an n -channel JFET:

• Like all JFETs are MESFETs usually self- conducting ( engl. normally- on), that is, at a control voltage of a drain current flows.
• Control is provided by a negative control voltage through it widens the space charge region of the Schottky junction, resulting in the threshold voltage to the conductive channel, the MESFET is now blocked. In silicon MESFETs that would be about 0.3 V. GaAs However, if used as the semiconductor material, the potential voltage is about 0.7 V.

Advantage of the MESFET is that through the adjacent Schottky junction, the charge carrier mobility in the channel is approximately twice as large as the MOSFET. This larger currents with the same dimensions, and higher operating frequencies are possible. In addition, a self-locking (English normally- off), in contrast to variant JFET be constructed, in which the gate is embedded in the substrate.

Apply MESFETs (especially GaAs MESFETs ) as microwave transistors in high-frequency amplifiers. They are also used in very fast logic circuits ( gigabit logic).