Patent ID: 8860084

Claim:
An epitaxial substrate for semiconductor device, comprising a base substrate; a channel layer made of a first group-III nitride having a composition of In x1 Al y1 Ga z1 N (x1+y1+z1=1) that contains at least Al and Ga; and a barrier layer made of a second group-III nitride having a composition of In x2 Al y2 Ga z2 N (x2+y2+z2=1) that contains at least In and Al, wherein the composition of said first group-III nitride is in a range determined by x1=0 and 0≦y1≦0.3, the composition of said second group-III nitride is, in a ternary phase diagram for InN, AlN, and GaN, in a range that is enclosed by straight lines represented by the following expressions and that is determined in accordance with the composition of said first group-III nitride, said barrier layer has a thickness of 3 nm or less, a low-crystallinity insulating layer is formed on said barrier layer, said low-crystallinity insulating layer being made of silicon nitride and having a thickness of 3 nm or less, x ⁢ ⁢ 2 = y ⁢ ⁢ 2 - ( 0.27 + 0.5 ⁢ yl ) 1.78 = - z ⁢ ⁢ 2 - ( 0.73 - 0.5 ⁢ yl ) 2.78 x ⁢ ⁢ 2 = y ⁢ ⁢ 2 - ( 0.4 + 0.6 ⁢ yl ) 1.78 = - z ⁢ ⁢ 2 - ( 0.6 - 0.6 ⁢ yl ) 2.78 z2=0.4 z2=0.