junction field-effect transistor (JFET)
The Junction Field Effect Transistor (JFET) has an extremely simple structure and a high input resistance, which is lower than that of the MOSFET. This is also the reason why JFETs are only used to a limited extent in discrete circuits.
Junction FET s are available in two versions as p- channel and n-channel JFET. In the n-channel design, the current-carrying channel is n-doped silicon enclosed by the p-doped gate. In the JFET, the pn junction between the gate and n-channel is negatively biased, thereby controlling the current flow between the source and drain. In the p-channel design, the semiconductor materials are reversed accordingly. The p-doped silicon is used for the current carrying channel, the n-doped for the gate.
The current- voltage characteristics of JFETs are essentially the same as those of MOSFETs with the exception that the allowable source-gate voltage is 0 V. In the schematic, the two designs are indicated by the direction of the arrow to or from the gate.
In addition to silicon-based JFETs, silicon carbide( SiC) is increasingly being used as a semiconductor material, since the lower power dissipation means that power JFETs can be manufactured for power electronics.