Patent ID: 8415690

Claim:
An epitaxial substrate for a semiconductor element, 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 first group-III nitride layer made of AlN and formed on said base substrate; a second group-III nitride layer made of Al p Ga 1-p N (0≦p<1) and formed on said first group-III nitride layer; a third group-III nitride layer expressed by a composition formula of Al q Ga 1-q N (0≦q≦1) and epitaxially formed on said second group-III nitride layer; and at least one fourth group-III nitride layer epitaxially formed on said third group-III nitride layer, 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 shaped into a three-dimensional concave-convex surface, said third group-III nitride layer is formed as a graded composition layer in which the proportion of existence of Al in a group-III element continuously decreases progressively from a first boundary portion at a boundary with said second group-III nitride layer toward a second boundary portion at a boundary with said fourth group-III nitride layer.