There are several types of field effect transistors (FETs) that are classified based on their construction and operation: - JFETs operate using only one type of charge carrier and have either an n-channel or p-channel. The gate voltage controls the drain current. - MOSFETs also come in n-channel or p-channel varieties and include depletion mode and enhancement mode types. Depletion mode MOSFETs operate in depletion mode like JFETs when the gate-source voltage is less than or equal to 0 and in enhancement mode when it is greater than 0. Enhancement mode MOSFETs only allow drain current when the gate-source voltage exceeds the threshold voltage. -

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Field Effect Transistor (FET)
Mr.Nikunj Bhensdadiya
(lecturer - Electrical Dept.)
Kalyan Polytechnic - jamnagar

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What is FET?
FET is uni-polar device i.e.
operation depends on only one type
of charge carriers (h or e) . It is a
Voltage controlled Device (gate
voltage controls drain current)

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Current Controlled vs Voltage Controlled
Devices

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Types of Field Effect Transistors
(The Classification)
n-Channel JFET
p-Channel JFET
n-Channel
EMOSFET
p-Channel
EMOSFET
Enhancement
MOSFET
Depletion
MOSFET
n-Channel
DMOSFET
p-Channel
DMOSFET
FETFETFET » JFET
MOSFET (IGFET)
FET » JFET
MOSFET (IGFET)
FET
• classifiacation

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JFET Construction
There are two types of JFET’s: n-channel and p-channel.
The n-channel is more widely used.
There are three terminals: Drain (D) and Source (S) are connected to n-channel
Gate (G) is connected to the p-type material

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The nonconductive depletion region becomes thicker with increased reverse bias.
(Note: The two gate regions of each FET are connected to each other.)
N-Channel JFET Operation

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Gate
Drain
Source
SYMBOLS
n-channel JFET
Gate
Drain
Source
p-channel JFET

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p-Channel JFET
p-Channel JFET operates in a similar manner as the n-channel JFET except the voltage
polarities and current directions are reversed

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MOSFET
(Metal Oxide Semiconductor FET)

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MOSFET
There are two types of MOSFET’s:
• Depletion mode MOSFET (D-MOSFET)
• Operates in Depletion mode the same way as a JFET
when VGS ≤ 0
• Operates in Enhancement mode like E-MOSFET when
VGS > 0
• Enhancement Mode MOSFET (E-MOSFET)
• Operates in Enhancement mode
• IDSS = 0 until VGS > VT (threshold voltage)

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Depletion Mode MOSFET Construction
The Drain (D) and Source (S) leads connect to the to n-doped regions
These N-doped regions are connected via an n-channel
This n-channel is connected to the Gate (G) via a thin insulating layer of SiO2
The n-doped material lies on a p-doped substrate that may have an additional terminal
connection called SS

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D-MOSFET Symbols

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Enhancement Mode
MOSFET’s

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Enhancement Mode MOSFET Construction
The Drain (D) and Source (S) connect to the to n-doped regions
These n-doped regions are not connected via an n-channel without an external voltage
The Gate (G) connects to the p-doped substrate via a thin insulating layer of SiO2
The n-doped material lies on a p-doped substrate that may have an additional terminal
connection called SS

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E-MOSFET Symbols

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