Group III nitride crystal substrate, epilayer-containing group III nitride crystal substrate, semiconductor device and method of manufacturing the same

A group III nitride crystal substrate, wherein,

• a plane spacing of arbitrary specific parallel crystal lattice planes of said crystal substrate being obtained from X-ray diffraction measurement performed with variation of X-ray penetration depth from a main surface of said crystal substrate while X-ray diffraction conditions of said specific parallel crystal lattice planes of said crystal substrate are satisfied,
• a uniform distortion at a surface layer of said crystal substrate represented by a value of |d1−d2|/d2 obtained from a plane spacing d1 at said X-ray penetration depth of 0.3 μm and a plane spacing d2 at said X-ray penetration depth of 5 μm is equal to or lower than 1.9×10−3, and
• said main surface has a plane orientation inclined in a <10-10> direction at an angle equal to or greater than 10° and equal to or smaller than 80° with respect to one of (0001) and (000-1) planes of said crystal substrate.