Electrical engineering - Mesfet stands for metal semi-conductor field effect transistor. Mesfets are constructed in compound semiconductor technologies lacking high quality surface passivation.

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Electrical Engineering

The circuit symbol of a Mesfet

The circuit symbol of a Mesfet is

The construction of the MESFET from semiconductor materials

Mesfet stands for metal semi-conductor field effect transistor. Mesfets are constructed in compound semiconductor technologies lacking high quality surface passivation.

Metal semiconductor field effect transistors have been mainly developed for high frequency applications as the majority carriers carry currents.

The Mesfet mainly consists of a conducting channel between a source and drain contact region. The carrier flow within the Mesfet is controlled by a Schottky metal gate (Schottky is a potential barrier formed at a metal-semiconductor junction). The channel is mainly controlled by varying the depletion layer width underneath the metal contact which modulates the thickness of the conducting channel and thereby the current.

The main advantage of Mesfets structure is that it has a high mobility of the carriers in the channel. The high mobility leads to a high current, transconductance and transit frequency of the device.

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The main disadvantage of Mesfet structure is the presence of a Schottky metal gate. The Schottky metal gate limits the voltage on the gate to turn on the voltage of the Schottky diode. The turn on voltage is usually 0.7V for Schottky diodes. Therefore the threshold voltage must be lower than the turn on voltage (0.7V)

There are two main structures that are used for Mesfets;

There are two main structures, Non-Self aligned source and drain and Self aligned source and drain.

Below I have shown Non-Self aligned source and drain structure;

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