Heterojunction field effect transistor

Abstract

A heterojunction field effect transistor according to the invention, comprises: first, second and third semiconductor layers which are sequentially stacked on each other; a first heterojunction formed between said first and second semiconductor layers; a second heterojunction formed between the second and third semiconductor layers; first and second two-dimensional electron gas layers formed in portions of the second semiconductor layer adjacent respectively to the first and second heterojunctions; and a gate electrode, a source electrode and a drain electrode formed on either of the first and third semidconductor layers, wherein the first two-dimensional electron gas layer extends from a portion corresponding to the gate electrode to the drain electrode and has one end virtually connected to the drain electrode, the second two-dimensional electron gas layer extends from a portion corresponding to the gate electrode to the source electrode and has one end virtually connected to the source electrode, and the number of electrons migrating between the first and second two-dimensional electron gas layers is modulated, in the portion of the second semiconductor layer corresponding to the gate electrode, by a voltage to be applied to the gate electrode, thereby controlling a current flowing between the source electrode and the drain electrode. With this structure, an effective gate length is defined by the thickness of the second semiconductor layer. Therefore, when the thickness of the second semiconductor layer is precisely controlled, a gate length can easily be shortened, and a current density can be increased when compared with a conventional device.