Patent ID: 8890208

Claim:
A semiconductor device, comprising: an epitaxial substrate for a semiconductor device, comprising, a base substrate, a channel layer formed of a first group III nitride having a composition of In x1 Al y1 Ga z1 N (x1+y1+z1=1), and a barrier layer formed of a second group III nitride containing at least In and Al and having a composition of In x2 Al y2 Ga z2 N (x2+y2+z2=1); and a source electrode, a drain electrode and a gate electrode formed directly on said barrier layer of the epitaxial substrate for a semiconductor device, wherein: the barrier layer has a thickness of 5 nm or less; all of the source electrode, the drain electrode and the gate electrode consist of metal elements; the composition of said first group III nitride is in a range determined by x1=0 and 0≦y1≦0.3; and the composition of said second group III nitride is, in a ternary phase diagram with InN, AlN and GaN being vertices, in a range surrounded by straight lines respectively represented by the following expressions determined in accordance with the composition of said first group III nitride: x ⁢ ⁢ 2 = y ⁢ ⁢ 2 - ( 0.27 + 0.5 ⁢ y ⁢ ⁢ 1 ) 1.78 = - z ⁢ ⁢ 2 - ( 0.73 - 0.5 ⁢ y ⁢ ⁢ 1 ) 2.78 ; x ⁢ ⁢ 2 = y ⁢ ⁢ 2 - ( 0.4 + 0.6 ⁢ y ⁢ ⁢ 1 ) 1.78 = - z ⁢ ⁢ 2 - ( 0.6 - 0.6 ⁢ y ⁢ ⁢ 1 ) 2.78 ; z2=0.4; and z2=0.