Patent ID: 8853829

Claim:
An epitaxial substrate for a semiconductor device, in which a group of group-III nitride layers are formed on a base substrate made of (111)-oriented single crystal silicon such that a (0001) crystal plane of said group of group-III nitride layers is substantially in parallel with a substrate surface of said base substrate, said epitaxial substrate comprising: a base layer group formed on said base substrate, said base layer group including a plurality of base layers being repeatedly laminated, each of said plurality of base layers including a first group-III nitride layer made of AlN and a second group-III nitride layer made of Al yy Ga zz N (yy+zz=1, 0≦yy<1, 0<zz≦1), said second group-III nitride layer being formed on said first group-III nitride layer; and at least one third group-III nitride layer that is epitaxially formed on said base layer group, wherein said first group-III nitride layer is a layer with many crystal defects configured of at least one kind from a columnar or granular crystal or domain, an interface between said first group-III nitride layer and said second group-III nitride layer is a three-dimensional concavo-convex surface, when, among said plurality of base layers, the base layer formed immediately above said base substrate is defined as a first base layer and the base layer other than said first base layer is defined as a second base layer, said first group-III nitride layer included in said second base layer has a thickness of 50 nm or more and 100 nm or less and said second group-III nitride layer included in said second base layer is made of Al yy Ga zz N (yy+zz=1, 0≦yy≦0.2, 0.8≦zz≦1).