Solid State Electronic Devices, 7th Edition

6.2 The Junction Fet

In a junction FET (JFET) the voltage-variable depletion region width of a junction is used to control the effective cross-sectional area of a conducting channel. In the device of Fig. 6–3, the current I_D flows through an n-type channel between two p⁺ regions. A reverse bias between these p⁺ regions and the channel causes the depletion regions to intrude into the n material, and therefore the effective width of the channel can be restricted. Since the resistivity of the channel region is fixed by its doping, the channel resistance varies with changes in the effective cross-sectional area. By analogy, the variable depletion regions serve as the two doors of a gate, which open and close on the conducting channel.

In Fig. 6–3 ...