Patent ID: 8680580

Claim:
A field effect transistor, comprising: a channel layer comprising gallium nitride (GaN) or indium gallium nitride (InGaN); a first electron-supplying layer, disposed over said channel layer and comprising InxAl y Ga 1-x-y N (0≦x<1, 0<y<1, 0<x+y<1); a first layer, disposed over said first electron-supplying layer and comprising indium aluminum nitride (InAlN); a second electron-supplying layer, provided over said first layer and comprising In a Al b Ga 1-a-b N (0≦a<1, 0<b<1, 0<a+b<1); a source electrode and a drain electrode, provided over said second electron-supplying layer and disposed separately from each other; and a gate electrode provided between said source electrode and said drain electrode, wherein a first recess is provided in said second electron-supplying layer and said first layer, said first recess extending through thereof and comprising a bottom surface including a section of said first electron-supplying layer, wherein said gate electrode covers the bottom surface of said first recess and is buried in said first recess, wherein said second electron-supplying layer is provided so as to overlap with regions of an interface between said first electron-supplying layer and said channel layer except a region thereof under the bottom surface of said first recess covered by said gate electrode, in a plan view from a side of each of the surfaces of said layers, wherein said first electron-supplying layer and said second electron-supplying layer comprise aluminum gallium nitride (AlGaN), wherein a content ratio of aluminum (Al) in said second electron-supplying layer is equal to or higher than a content ratio of Al in said first electron-supplying layer, and wherein said first layer comprising indium aluminum nitride has a thickness of within a range of from 0.5 nm to 5 nm, wherein the first layer is in contact with the first electron-supplying layer, and wherein an Al content ratio in the first electron-supplying layer is equal to or lower than 30%, and an Al content ratio of said first layer is equal to or higher than 80%.