Aluminum nitride plate

An aluminum nitride plate, wherein

• the aluminum nitride plate satisfies-both all three of following relations (1), (2) and (3),
• c1>97.5% (1):
• c2>97% (2):
• c2/c1<0.995 (3):
• where c1 is a c-plane degree of orientation that is defined as a ratio of a diffraction intensity of (002) plane to a sum of the diffraction intensity of (002) plane and a diffraction intensity of (100) plane when a surface layer of the aluminum nitride plate is subjected to an X-ray diffraction measurement along a thickness direction of the surface layer, and
• c2 is a c-plane degree of orientation that is defined as a ratio of the diffraction intensity of (002) plane to the sum of the diffraction intensity of (002) plane and the diffraction intensity of (100) plane when a portion other than the surface layer of the aluminum nitride plate is subjected to the X-ray diffraction measurement along a thickness direction of the portion, and
• a difference in nitrogen content between the surface layer and the portion other than the surface layer is less than 0.15 percent in weight ratio,
• wherein the surface layer is a portion included in a layer located at one end of the aluminum nitride plate out of 10 layers obtained by splitting the aluminum nitride plate into 10 along its thickness direction, and the portion is exposed at a surface of the aluminum nitride plate on the one end.