FET Transistor: Types of Field-Effect Transistors and Their Working

FET transistors (Field-Effect Transistors) control the form of the charge carrier and therefore its conductivity in a semiconductor using an electric field. Since the FET transistor also undergoes a single carrier type operation, they are also known as unipolar transistors. The density of charge carriers affects the conductivity.

Key Terms: FET Transistor, Semiconductor, Conductivity, Charge, Transistor, Voltage, Unipolar transistors, Electric field, Impedence

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What is a FET Transistor?

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FET transistors control the conductivity of the charge carrier in a semiconductor. The conductivity of the charge carriers is controlled through the electric field. The terminal of a field-effect transistor has an applied voltage through which conductivity is regulated.

FET Transistor

• All FET forms have high input impedance.
• The input current adjusts the conductivity of a non-FET transistor and therefore is low in input impedance.  
• The terminals of a field effect transistor apply a voltage through which the conductivity is regulated.
• The voltage applied to the gate produces an electric field causing attraction and repulsion to the charges carried between the two terminals.
• The conductivity is also affected by the density of the charge carriers.

The video below explains this:

Transistor Detailed Video Explanation:

Also Read: 

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Types of FET Transistors

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There are two types of Field Effect Transistors. These are:

1. Metal oxide semiconductor Field-Effect Transistor (MOSFET)

Metal oxide semiconductor Field Effect Transistors are mainly used to amplify voltages in circuits. It consists of three terminals: Gate, Source, and Drain. Based on their operation modes, the two classes of MOSFETs are –

• Depletion mode – MOSFET operates owing to the channel that is already present.
• Enhancement mode – Gate Voltage induces channel.

There are three operating regions of MOSFET: cut-off region, saturation region, and ohmic region. MOSFETs are bidirectional. P-type and n-type are the two types of MOSFET depletion models..

2. Junction Field-effect Transistor (JFET

Junction Field effect Transistor consists of two configurations: the N-Channel JFET and the P-Channel JFET. The two types of JFETs are classified on the basis of the current flow. Such transistors are used to amplify weak signals. JFETs are unidirectional.

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Terminals of FET Transistors 

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The FET transistors have three terminals: Source, Drain, and Gate.

• Source: The first terminal is the source. The current that enters through the source is denoted by I_S.
• Drain: The current that leaves through the drain is denoted by I_D. There is a presence of voltage between drain and source which is denoted by V_DS.
• Gate: Gate controls and modulates the conductivity of the channels. It is denoted by G. By applying a voltage at the gate, the current that leaves through the drain can be controlled.

The FETs in which current is essentially taken by majority carriers are called majority charge carrier devices. The FETs in which current is essentially taken by minority carriers are called minority charge carrier devices.

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Working of Field Effect Transistor

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FET transistors are also called unipolar transistors as their operations are single-carrier type. The current flowing through the FET transistor is controlled by using the voltage applied. Conductivity is affected by the density of the carrier charge. The three major components of a FET transistor are Source, Gate, and Drain.

• The first terminal is the source, through which most carriers enter the bar.
• The Drain is the second terminal through which the majority of carriers lead the bar.
• The Gate has two terminals that are internally connected with each other. 
• The flow of electrons in the device is from the source to drain through active channels.
• The channel between the gate and source terminal has potential and its function is conductivity.
• The terminal conductors and semiconductors are connected to each other through ohmic contacts.

Working of FET Transistor

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Difference between JFET and MOSFET

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The difference between JFET and MOSFET are as given below – 

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Things to Remember

• The full form of FET transistors is the Field-effect transistor. 
• FET transistors control the conductivity of the charge carrier in a semiconductor. They do so through an electric field. 
• FET Transistors have high input impedance and are also known as unipolar transistors.
• There are two types of FET transistors: Metal oxide semiconductor Field Effect Transistor (MOSFET) and Junction Field-effect Transistor (JFET).
• The FET transistors have three terminals: source, drain, and gate. The first terminal is the source. The current that leaves through the drain is denoted by ID. Gate (G) controls and modulates the conductivity of the channels.

Also Read: 

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