Freestanding substrate (21] for epitaxial
crystal growth, wherein the freestanding substrate (21] comprises a
crystal of a Group 13
nitride selected from
gallium nitride, aluminum
nitride,
indium nitride, or a
solid solution thereof; wherein the freestanding substrate (21) comprises a
nitrogen polar surface (21a) and a group 13 element polar surface (21b); wherein the
nitrogen polar surface (21a) is curved into a convex shape; wherein the
nitrogen polar surface (21a) comprises an outer
peripheral part (22) with a chamfer part (21c); and wherein an absolute value of a
radius of curvature of the fault of the element-of-group 13 polar surface (21b) is smaller than an absolute value of a
radius of curvature of the fault of the nitrogen polar surface (21a).