JFETs (Junction Field Effect Transistors) are four-terminal devices in which the current between two electrodes is controlled by the action of an electric field across a reverse-biased PN junction. Their terminals are referred to as Gate, Drain, Source, and Body, where the body connects to the source. The integrated semiconductor materials in JFETs are positively and negatively doped and configured to form channels for efficient device operation. They are used as electronically controlled switches, amplifiers, and voltage-controlled resistors.
Doping of semiconductors:
Doping is the electrical property alteration process of intrinsic semiconductors by adding foreign impurities. The intrinsic semiconductors become P-Type semiconductors by doping with trivalent atoms used to dope silicon. On the other hand, pentavalent atoms designed to dope silicone convert an intrinsic semiconductor into an N-Type semiconductor.
Types of JFETs:
A JFET is mainly classified into two types, N-Channel and P-Channel JFET construction.
- N-Channel JFET Construction
The N-Channel illustrated that the majority of charge carriers are electrons. The N-type semiconductor (used as a base) is doped with a P-Type semiconductor on both sides to construct the N-Channel. These two P-zones are electrically connected to the gate with ohmic contacts. The other two terminals are at the opposite ends of the drain and source.
- P-Channel JFET Construction
The name P channel denotes the holes as the major charge carriers. The P-type semiconductor (used as a base) is doped with an N-Type semiconductor on both sides to construct the P-Channel. These two N-zones are electrically connected to the gate with ohmic contacts. The other two terminals are at the opposite ends of the drain and source.
Typical benefits and specifications:
These semiconductor devices offer various benefits with excellent attributes, such as:
- They offer a considerably high degree of isolation between the input and the output
- They feature a high input impedance
- They generate less noise.
- They are voltage-controlled devices.
How does a JFET differ from a BJT (Bipolar Junction Transistor)?
They feature a fundamental difference in their charge carrier flow kinetics. The JFET offers a majority charge carrier flow only, whereas the BJT features majority as well as minority charge carrier flow.
Applications of JFETs:
JFET transistors are found in a vast array of electronic and communication applications. They act as electronically controlled switches to regulate the power supply to a load. They are also used as:
- Amplifiers
- Buffers
- Phase shift oscillators
- Voltage variable resistors, and
- Choppers.
