Field effect transistor having recessed gate in compositional graded layer

摘要

A GaN heterojunction FET has an AlxGa1-xN first graded layer and an AlyGa1-yN second graded layer, which are formed sequentially on a channel layer. The Al mole fraction x of the first graded layer decreases linearly from, for example, 0.2 at an interface of the first graded layer with the channel layer to 0.1 at an interface thereof with the second graded layer. The Al mole fraction y of the second graded layer increases from, for example, 0.1 at an interface of the second graded layer with the first graded layer to 0.35 at a surface located on the opposite side from the first graded layer. Because the intrinsic polarization of AlGaN depends on the Al mole fraction, fixed negative charge is generated in the AlxGa1-xN first graded layer, and fixed positive charge is generated in the AlyGa1-yN second graded layer.