Integrated Circuits

As the gate varies between more and less positive, the depth of the p channel alters accordingly, in turn altering the current between source and drain. In this way it can be used as an amplifier or a switch. Unlike the BJT, the FET uses only one carrier, in this case the holes (but if it were an n type device it would be electrons) and so it is a unipolar device. It can also be considered to be voltage, rather than current controlled.