Field Effect Transistor

The term field effect transistor (FET) refers to a class of transistors in which current flows from a source to a drain via a channel whose resistance is controlled by applying a voltage to a gate. The FET is a unipolar device (the term unipolar denotes a device in which current results from the flow of charge carriers of only one polarity: electrons or holes). The name field effect suggests that the current flow is controlled by an electric field set up in the device by an externally applied voltage to the gate.

There are three types of FET such as Junction Field Effect Transistor, Metal Oxide Semiconductor  Field effect transistor and the Metal Semiconductor Field Effect Transistor. Let us know more about these three types of circuits:

JFET or Junction Field Effect Transistor:

JFET (Junction Field Effect Transistor), in which the junction gate (re­verse biased) controls the resistance of the channel by means of the width of the depletion layer. Currently these are fabricated in silicon as discrete devices or as monolithic integrated circuits.

MOS or MOSFET (Metal Oxide Semiconductor):

In the MOSFET (Metal Oxide Semiconductor Field Effect Transistor) or MOS, the gate is isolated from the channel by a thin silicon dioxide layer. These are also fabricated in silicon (as discrete devices or in monolithic integrated cir­cuits).

MESFET (Metal Semiconductor Field Effect Transistor):

MESFET (Metal Semiconductor Field Effect Transistor), where the gate electrode forms a Schottky barrier contact with a doped semiconduc­tor region. These transistors are usually fabricated in GaAs. Belonging to this family is the modulation-doped AlGaAs/GaAs transistor, also called HFET (Heterostructure FET) or TEGFET (Two-Dimensional Electron Gas Field Effect Transistor), or MODFET (Modulation Doped Field Effect Transistor), or HEMT (High Electron Mobility Transistor).

Questionnaire:

• What is field effect transistor?
• What are the types of field effect transistor? Explain.