Method of manufacturing epitaxial substrate and epitaxial substrate

A method of manufacturing an epitaxial substrate including a single-crystal Si substrate and a group-III nitride epitaxial layer on the single-crystal Si substrate, the method comprising:

• a correlation acquisition step in which a single-crystal Si substrate with a thickness equal to or greater than 1,500 μm is used, resistivity of the single-crystal Si substrate and a ratio “a” between a thickness of the single-crystal Si substrate and a thickness of the group-III nitride epitaxial layer (the thickness of the single-crystal Si substrate/the thickness of the group-III nitride epitaxial layer) are set as parameters, an epitaxial growth of the group-III nitride epitaxial layer on the single-crystal Si substrate and measurement about a warp of the obtained epitaxial substrate are performed while the parameters are changed, and a correlation between the ratio “a” and the warp of the epitaxial substrate is obtained for each value of the resistivity of the single-crystal Si substrate;
• a manufacturing parameter determination step of determining the resistivity of the single-crystal Si substrate and the ratio “a”, with which an absolute value of the warp of the epitaxial substrate becomes equal to or smaller than 50 μm based on the correlation;
• and
• an epitaxial substrate manufacturing step of epitaxially growing the group-III nitride epitaxial layer on the single-crystal Si substrate by using the determined manufacturing parameters.