Patent ID: 8853735

Claim:
An epitaxial substrate for semiconductor device, comprising: a base substrate; a channel layer formed of a first group III nitride containing at least Ga and 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), wherein the composition of said first group III nitride falls within a range determined by x1=0 and 0≦y1≦0.3, the composition of said second group III nitride falls, in a ternary phase diagram with InN, AlN and GaN being vertices, within a first composition range surrounded by straight lines respectively represented by expressions below determined in accordance with the composition of said first group III nitride: x ⁢ ⁢ 2 = y ⁢ ⁢ 2 - y ⁢ ⁢ 1 4.56 = - z ⁢ ⁢ 2 - ( 1 - y ⁢ ⁢ 1 ) 5.56 ; z2=0; and x2=0, said barrier layer has tensile strains in an in-plane direction, and pits are formed on a surface of said barrier layer at a surface density of 5×10 7 /cm 2 or more and 1×10 9 /cm 2 or less.