Patent ID: 8198652

Claim:
A field effect transistor comprising: a channel layer composed of In y Ga 1-y N (0≦y≦1); a carrier supply layer composed of Al x Ga 1-x N (0≦x≦1), said carrier supply layer being provided over said channel layer and including at least one p-type layer; and a source electrode, a drain electrode and a gate electrode which are disposed facing said channel layer through said p-type layer, and provided over said carrier supply layer, wherein the following relational expression is satisfied: 5.6×10 11 x<N A ×η×t [cm −2 ]<5.6×10 13 x, [Mathematical Formula 1] where x denotes an Al compositional ratio of said carrier supply layer, t denotes a thickness of said p-type layer, N A denotes an impurity concentration of said p-type layer, and η denotes an activation ratio of said p-type layer.