Semiconductors: Field-Effect Transistors

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Semiconductors: Field-Effect Transistors

Unlike the three-layer PNP and NPN transistors we've already studied, field-effect transistors (FETs) make use of the electric field that appears between semiconductor regions when external voltages are applied. In fact, that's how these devices get their general name: they use the effect of the electric field.

Junction FET: The junction FET uses a reverse-biased junction to create the controlling electric field.
Depletion Mode MOSFET: A second approach is to start with a conductive path and then use the electric field to deplete that path of current carriers.
Enhancement Mode MOSFET: The third option is to start with no conducting path, but use the electric field to attract current carriers and thus create a channel where it didn't exist before.