Chapter 5. Field effect transistors

Field effect transistors (FET’s) are unipolar semiconductor devices, i.e. flowing current is a drift of one-polarity charge carriers which move into the longitudinal electric field through the controlled p-type or n-type channel. The current, flowing through the device, is controlled by crossed field (not by a current as in BT). The name “field effect transistor” has come from there. The principle of FET operation is based on changes of channel conduction. It gives a possibility to realize the relay rule and to control the power which is transmitted from a source to a load.

There are two ways to control channel resistance. The first one is to change the conductivity of a material. The second is to change the cross section of a channel. FET’s, with reference to that, are divided into FET’s with insulated gate and FET’s with controlled p-n-junction.