Epitaxial base substrate and epitaxial substrate

摘要

A III nitride buffer film including at least A1 element and having a screw-type dislocation density of 1×10 8 /cm 2 or below is formed on a base made of a sapphire single crystal, etc., to fabricate an epitaxial base substrate. Then, a III nitride underfilm is formed on the III nitride buffer film, to fabricate an epitaxial substrate.