Method of manufacturing a GaN substrate, a manufacturing method of a group III nitride substrate, a manufacturing method and a semiconductor device substrate with an epitaxial layer

III-nitride substrate and a manufacturing method thereof capable of forming an epitaxially grown layer of good quality can be obtained. GaN substrate as a Group III nitride substrate (1) are those following either. Surface (3) the number of atoms in the acidic substance of Surface (3) the number of silicon atoms of Surface (3) the number of atoms in the acidic substance of