The Two-Dimensional Electron Gas Field Effect Transistor

TLDR: The role of field effect transistor (FET) is to act as a switch between source and drain this paper, where the gate current is purely a displacement current, and a very small input power can be amplified.

Abstract: A field effect transistor (FET) is a semiconductor device in which the current between two contacts — source and drain — is controlled by the voltage on a third contact — the gate. The role of such devices in electronic circuits is simple in principle. In logic circuits it functions as a switch — depending on the gate voltage the connection between source and drain is broken or closed — and in analogue circuits a small time-varying signal on the gate yields a time-varying current between source and drain, and since the gate current ideally is purely a displacement current, a very small input power can be amplified.